[EE] Eliminating external noise through PS

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[EE] Eliminating external noise through PS

Neil
Hi,

I'm working on a device that takes 120VAC, converts to 5VDC with a
PCB-mounted power supply, then further reduces that to 3.3VDC with a
linear regulator.
A 3.3V microcontroller switches a relay to power a 120VAC pump.
Overview...
http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg

All has been great until we switched to a specific pump, which happens
to generate a LOT of conducted noise, which passes through the 5V PS,
and the 3.3V regulator, and causing the microcontroller to crash.
I did a bunch of tested and found that the noise is being conducted
through the wires back to the board through the PS, through the linear
regulator, and this is the 3.3V line...
http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg

I was over at someone else's place so did not have a lot of parts with
me, but...
Adding a bunch more 0.1uf bypass capacitors all over the board did not help.

Changing the power supply from an IRM-10-5 (industrial spec, 200mV
ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
of the crashing... but the ripple itself wasn't causing crashing.

Adding (non-specific size) ferrites to the pump wires, and 120VAC input
wires did not help.
I then tried to create a crude/uncalculated LC filter (which whatever
components I had on hand (33uh inductor and 1000uf capacitor, should be
low ESR), then a Pi filter (added 680 uF capacitor), and those barely
made a dent.
Eventually I added another 0.1uf capacitor to the output side of the pi
filter and that helped enough to prevent the microcontroller crashing.
But there is still a lot of noise on the 3.3V line...
http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg

FWIW, this is where it ended up...
http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg

The noise is in the 7Mhz to 30Mhz range (prob even higher).
I feel like smaller, low-ESR ceramic caps should help, but I doubt it
will take out most of the noise.
What is the right type of filter to eliminate this noise?

Cheers,
-Neil.

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Re: [EE] Eliminating external noise through PS

Roy Hopkins
Run the micro on batteries?
Take the micro further away from the motor power, power it from a different
phase?
Schottkyy Diodes on 5v to + and - to limit voltage swings to 5v +/- 0.2
volts.
Harmonic filter?


Roy Hopkins
ZL1RJH




On Wed, 9 Dec 2020 at 07:05, Neil <[hidden email]> wrote:

> Hi,
>
> I'm working on a device that takes 120VAC, converts to 5VDC with a
> PCB-mounted power supply, then further reduces that to 3.3VDC with a
> linear regulator.
> A 3.3V microcontroller switches a relay to power a 120VAC pump.
> Overview...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
>
> All has been great until we switched to a specific pump, which happens
> to generate a LOT of conducted noise, which passes through the 5V PS,
> and the 3.3V regulator, and causing the microcontroller to crash.
> I did a bunch of tested and found that the noise is being conducted
> through the wires back to the board through the PS, through the linear
> regulator, and this is the 3.3V line...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
>
> I was over at someone else's place so did not have a lot of parts with
> me, but...
> Adding a bunch more 0.1uf bypass capacitors all over the board did not
> help.
>
> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
> of the crashing... but the ripple itself wasn't causing crashing.
>
> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
> wires did not help.
> I then tried to create a crude/uncalculated LC filter (which whatever
> components I had on hand (33uh inductor and 1000uf capacitor, should be
> low ESR), then a Pi filter (added 680 uF capacitor), and those barely
> made a dent.
> Eventually I added another 0.1uf capacitor to the output side of the pi
> filter and that helped enough to prevent the microcontroller crashing.
> But there is still a lot of noise on the 3.3V line...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
>
> FWIW, this is where it ended up...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
>
> The noise is in the 7Mhz to 30Mhz range (prob even higher).
> I feel like smaller, low-ESR ceramic caps should help, but I doubt it
> will take out most of the noise.
> What is the right type of filter to eliminate this noise?
>
> Cheers,
> -Neil.
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
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Re: [EE] Eliminating external noise through PS

Manu Abraham-2
In reply to this post by Neil
I guess you need a common mode filter at the PSU 120V in might help.

Other than that:
Are you using a flyback PSU ?
If so, do you have a High voltage capacitor (the one between the
primary and secondary, for the noise return path) ?

On Tue, Dec 8, 2020 at 11:35 PM Neil <[hidden email]> wrote:

>
> Hi,
>
> I'm working on a device that takes 120VAC, converts to 5VDC with a
> PCB-mounted power supply, then further reduces that to 3.3VDC with a
> linear regulator.
> A 3.3V microcontroller switches a relay to power a 120VAC pump.
> Overview...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
>
> All has been great until we switched to a specific pump, which happens
> to generate a LOT of conducted noise, which passes through the 5V PS,
> and the 3.3V regulator, and causing the microcontroller to crash.
> I did a bunch of tested and found that the noise is being conducted
> through the wires back to the board through the PS, through the linear
> regulator, and this is the 3.3V line...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
>
> I was over at someone else's place so did not have a lot of parts with
> me, but...
> Adding a bunch more 0.1uf bypass capacitors all over the board did not help.
>
> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
> of the crashing... but the ripple itself wasn't causing crashing.
>
> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
> wires did not help.
> I then tried to create a crude/uncalculated LC filter (which whatever
> components I had on hand (33uh inductor and 1000uf capacitor, should be
> low ESR), then a Pi filter (added 680 uF capacitor), and those barely
> made a dent.
> Eventually I added another 0.1uf capacitor to the output side of the pi
> filter and that helped enough to prevent the microcontroller crashing.
> But there is still a lot of noise on the 3.3V line...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
>
> FWIW, this is where it ended up...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
>
> The noise is in the 7Mhz to 30Mhz range (prob even higher).
> I feel like smaller, low-ESR ceramic caps should help, but I doubt it
> will take out most of the noise.
> What is the right type of filter to eliminate this noise?
>
> Cheers,
> -Neil.
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
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Re: [EE] Eliminating external noise through PS

Neil
In reply to this post by Roy Hopkins
Roy,

Battery... ugh.  Outdoor application that's drawing over an amp currently.

In the given enclosure, the micro is on the other corner (quadrant) of
the board from the 120VAC.  Some things have changed, so I am able to
push it a bit further on the next revision but not much. Layout here...
http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-05.jpg
The lower left is 4 relays, fuses, and screw terminal blocks.

Not sure what you mean by Schotty diodes on 5V to + & -, as it's the
power rails that are going above spec.
I was thinking 5.1V zener on the 5V line, but the PS seems to have a
built in zener at the output.  And not sure how a zener without a series
resistor would handle the power.

Will look into a harmonic filter.

Thanks,
-Neil.



On 12/8/2020 1:18 PM, roy hopkins wrote:

> Run the micro on batteries?
> Take the micro further away from the motor power, power it from a different
> phase?
> Schottkyy Diodes on 5v to + and - to limit voltage swings to 5v +/- 0.2
> volts.
> Harmonic filter?
>
>
> Roy Hopkins
> ZL1RJH
>
>
>
>
> On Wed, 9 Dec 2020 at 07:05, Neil <[hidden email]> wrote:
>
>> Hi,
>>
>> I'm working on a device that takes 120VAC, converts to 5VDC with a
>> PCB-mounted power supply, then further reduces that to 3.3VDC with a
>> linear regulator.
>> A 3.3V microcontroller switches a relay to power a 120VAC pump.
>> Overview...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
>>
>> All has been great until we switched to a specific pump, which happens
>> to generate a LOT of conducted noise, which passes through the 5V PS,
>> and the 3.3V regulator, and causing the microcontroller to crash.
>> I did a bunch of tested and found that the noise is being conducted
>> through the wires back to the board through the PS, through the linear
>> regulator, and this is the 3.3V line...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
>>
>> I was over at someone else's place so did not have a lot of parts with
>> me, but...
>> Adding a bunch more 0.1uf bypass capacitors all over the board did not
>> help.
>>
>> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
>> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
>> of the crashing... but the ripple itself wasn't causing crashing.
>>
>> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
>> wires did not help.
>> I then tried to create a crude/uncalculated LC filter (which whatever
>> components I had on hand (33uh inductor and 1000uf capacitor, should be
>> low ESR), then a Pi filter (added 680 uF capacitor), and those barely
>> made a dent.
>> Eventually I added another 0.1uf capacitor to the output side of the pi
>> filter and that helped enough to prevent the microcontroller crashing.
>> But there is still a lot of noise on the 3.3V line...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
>>
>> FWIW, this is where it ended up...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
>>
>> The noise is in the 7Mhz to 30Mhz range (prob even higher).
>> I feel like smaller, low-ESR ceramic caps should help, but I doubt it
>> will take out most of the noise.
>> What is the right type of filter to eliminate this noise?
>>
>> Cheers,
>> -Neil.
>>
>> --
>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>> View/change your membership options at
>> http://mailman.mit.edu/mailman/listinfo/piclist
>>

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Re: [EE] Eliminating external noise through PS

David Van Horn
"And not sure how a zener without a series
resistor would handle the power."

Poorly...  🙂

An output crowbar is not unusual, Vout > Vthreshold, then turn on an SCR and draw a ton of current till the fuse pops.
Theoretically protecting attached equipment.

________________________________
From: [hidden email] <[hidden email]> on behalf of Neil <[hidden email]>
Sent: Tuesday, December 8, 2020 12:13 PM
To: Microcontroller discussion list - Public. <[hidden email]>
Subject: Re: [EE] Eliminating external noise through PS

Roy,

Battery... ugh.  Outdoor application that's drawing over an amp currently.

In the given enclosure, the micro is on the other corner (quadrant) of
the board from the 120VAC.  Some things have changed, so I am able to
push it a bit further on the next revision but not much. Layout here...
http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-05.jpg
The lower left is 4 relays, fuses, and screw terminal blocks.

Not sure what you mean by Schotty diodes on 5V to + & -, as it's the
power rails that are going above spec.
I was thinking 5.1V zener on the 5V line, but the PS seems to have a
built in zener at the output.  And not sure how a zener without a series
resistor would handle the power.

Will look into a harmonic filter.

Thanks,
-Neil.



On 12/8/2020 1:18 PM, roy hopkins wrote:

> Run the micro on batteries?
> Take the micro further away from the motor power, power it from a different
> phase?
> Schottkyy Diodes on 5v to + and - to limit voltage swings to 5v +/- 0.2
> volts.
> Harmonic filter?
>
>
> Roy Hopkins
> ZL1RJH
>
>
>
>
> On Wed, 9 Dec 2020 at 07:05, Neil <[hidden email]> wrote:
>
>> Hi,
>>
>> I'm working on a device that takes 120VAC, converts to 5VDC with a
>> PCB-mounted power supply, then further reduces that to 3.3VDC with a
>> linear regulator.
>> A 3.3V microcontroller switches a relay to power a 120VAC pump.
>> Overview...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
>>
>> All has been great until we switched to a specific pump, which happens
>> to generate a LOT of conducted noise, which passes through the 5V PS,
>> and the 3.3V regulator, and causing the microcontroller to crash.
>> I did a bunch of tested and found that the noise is being conducted
>> through the wires back to the board through the PS, through the linear
>> regulator, and this is the 3.3V line...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
>>
>> I was over at someone else's place so did not have a lot of parts with
>> me, but...
>> Adding a bunch more 0.1uf bypass capacitors all over the board did not
>> help.
>>
>> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
>> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
>> of the crashing... but the ripple itself wasn't causing crashing.
>>
>> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
>> wires did not help.
>> I then tried to create a crude/uncalculated LC filter (which whatever
>> components I had on hand (33uh inductor and 1000uf capacitor, should be
>> low ESR), then a Pi filter (added 680 uF capacitor), and those barely
>> made a dent.
>> Eventually I added another 0.1uf capacitor to the output side of the pi
>> filter and that helped enough to prevent the microcontroller crashing.
>> But there is still a lot of noise on the 3.3V line...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
>>
>> FWIW, this is where it ended up...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
>>
>> The noise is in the 7Mhz to 30Mhz range (prob even higher).
>> I feel like smaller, low-ESR ceramic caps should help, but I doubt it
>> will take out most of the noise.
>> What is the right type of filter to eliminate this noise?
>>
>> Cheers,
>> -Neil.
>>
>> --
>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>> View/change your membership options at
>> http://mailman.mit.edu/mailman/listinfo/piclist
>>

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Re: [EE] Eliminating external noise through PS

Neil
In reply to this post by Manu Abraham-2
Looking at how common mode chokes work.  Was not aware of these.

This is the power supply I'm using (not sure if it's a flyback), and I
do not have any other caps...
https://www.meanwell.com/Upload/PDF/MPM-10/MPM-10-SPEC.PDF

Cheers,
-Neil.



On 12/8/2020 1:19 PM, Manu Abraham wrote:

> I guess you need a common mode filter at the PSU 120V in might help.
>
> Other than that:
> Are you using a flyback PSU ?
> If so, do you have a High voltage capacitor (the one between the
> primary and secondary, for the noise return path) ?
>
> On Tue, Dec 8, 2020 at 11:35 PM Neil <[hidden email]> wrote:
>> Hi,
>>
>> I'm working on a device that takes 120VAC, converts to 5VDC with a
>> PCB-mounted power supply, then further reduces that to 3.3VDC with a
>> linear regulator.
>> A 3.3V microcontroller switches a relay to power a 120VAC pump.
>> Overview...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
>>
>> All has been great until we switched to a specific pump, which happens
>> to generate a LOT of conducted noise, which passes through the 5V PS,
>> and the 3.3V regulator, and causing the microcontroller to crash.
>> I did a bunch of tested and found that the noise is being conducted
>> through the wires back to the board through the PS, through the linear
>> regulator, and this is the 3.3V line...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
>>
>> I was over at someone else's place so did not have a lot of parts with
>> me, but...
>> Adding a bunch more 0.1uf bypass capacitors all over the board did not help.
>>
>> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
>> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
>> of the crashing... but the ripple itself wasn't causing crashing.
>>
>> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
>> wires did not help.
>> I then tried to create a crude/uncalculated LC filter (which whatever
>> components I had on hand (33uh inductor and 1000uf capacitor, should be
>> low ESR), then a Pi filter (added 680 uF capacitor), and those barely
>> made a dent.
>> Eventually I added another 0.1uf capacitor to the output side of the pi
>> filter and that helped enough to prevent the microcontroller crashing.
>> But there is still a lot of noise on the 3.3V line...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
>>
>> FWIW, this is where it ended up...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
>>
>> The noise is in the 7Mhz to 30Mhz range (prob even higher).
>> I feel like smaller, low-ESR ceramic caps should help, but I doubt it
>> will take out most of the noise.
>> What is the right type of filter to eliminate this noise?
>>
>> Cheers,
>> -Neil.
>>
>> --
>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>> View/change your membership options at
>> http://mailman.mit.edu/mailman/listinfo/piclist

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Re: [EE] Eliminating external noise through PS

Neil
In reply to this post by David Van Horn
Oh good thought... I know of crowbars, but never used one.  Don't want
to pop fuses regularly, but thinking that since the spikes seem to be
very fast, any protection circuit shouldn't have to handle too much energy.

Cheers,
-Neil




On 12/8/2020 2:26 PM, David Van Horn wrote:

> "And not sure how a zener without a series
> resistor would handle the power."
>
> Poorly...  🙂
>
> An output crowbar is not unusual, Vout > Vthreshold, then turn on an SCR and draw a ton of current till the fuse pops.
> Theoretically protecting attached equipment.
>
> ________________________________
> From: [hidden email] <[hidden email]> on behalf of Neil <[hidden email]>
> Sent: Tuesday, December 8, 2020 12:13 PM
> To: Microcontroller discussion list - Public. <[hidden email]>
> Subject: Re: [EE] Eliminating external noise through PS
>
> Roy,
>
> Battery... ugh.  Outdoor application that's drawing over an amp currently.
>
> In the given enclosure, the micro is on the other corner (quadrant) of
> the board from the 120VAC.  Some things have changed, so I am able to
> push it a bit further on the next revision but not much. Layout here...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-05.jpg
> The lower left is 4 relays, fuses, and screw terminal blocks.
>
> Not sure what you mean by Schotty diodes on 5V to + & -, as it's the
> power rails that are going above spec.
> I was thinking 5.1V zener on the 5V line, but the PS seems to have a
> built in zener at the output.  And not sure how a zener without a series
> resistor would handle the power.
>
> Will look into a harmonic filter.
>
> Thanks,
> -Neil.
>
>
>
> On 12/8/2020 1:18 PM, roy hopkins wrote:
>> Run the micro on batteries?
>> Take the micro further away from the motor power, power it from a different
>> phase?
>> Schottkyy Diodes on 5v to + and - to limit voltage swings to 5v +/- 0.2
>> volts.
>> Harmonic filter?
>>
>>
>> Roy Hopkins
>> ZL1RJH
>>
>>
>>
>>
>> On Wed, 9 Dec 2020 at 07:05, Neil <[hidden email]> wrote:
>>
>>> Hi,
>>>
>>> I'm working on a device that takes 120VAC, converts to 5VDC with a
>>> PCB-mounted power supply, then further reduces that to 3.3VDC with a
>>> linear regulator.
>>> A 3.3V microcontroller switches a relay to power a 120VAC pump.
>>> Overview...
>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
>>>
>>> All has been great until we switched to a specific pump, which happens
>>> to generate a LOT of conducted noise, which passes through the 5V PS,
>>> and the 3.3V regulator, and causing the microcontroller to crash.
>>> I did a bunch of tested and found that the noise is being conducted
>>> through the wires back to the board through the PS, through the linear
>>> regulator, and this is the 3.3V line...
>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
>>>
>>> I was over at someone else's place so did not have a lot of parts with
>>> me, but...
>>> Adding a bunch more 0.1uf bypass capacitors all over the board did not
>>> help.
>>>
>>> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
>>> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
>>> of the crashing... but the ripple itself wasn't causing crashing.
>>>
>>> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
>>> wires did not help.
>>> I then tried to create a crude/uncalculated LC filter (which whatever
>>> components I had on hand (33uh inductor and 1000uf capacitor, should be
>>> low ESR), then a Pi filter (added 680 uF capacitor), and those barely
>>> made a dent.
>>> Eventually I added another 0.1uf capacitor to the output side of the pi
>>> filter and that helped enough to prevent the microcontroller crashing.
>>> But there is still a lot of noise on the 3.3V line...
>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
>>>
>>> FWIW, this is where it ended up...
>>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
>>>
>>> The noise is in the 7Mhz to 30Mhz range (prob even higher).
>>> I feel like smaller, low-ESR ceramic caps should help, but I doubt it
>>> will take out most of the noise.
>>> What is the right type of filter to eliminate this noise?
>>>
>>> Cheers,
>>> -Neil.
>>>
>>> --
>>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>>> View/change your membership options at
>>> http://mailman.mit.edu/mailman/listinfo/piclist
>>>
> --
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Re: [EE] Eliminating external noise through PS

David Van Horn
In reply to this post by Neil
Basically incoming and outgoing current pass through the core in opposite directions, so the core has very high impedance to HF energy, and almost no effect down at line frequency.  The energy from one side cancels out the other side.

________________________________
From: [hidden email] <[hidden email]> on behalf of Neil <[hidden email]>
Sent: Tuesday, December 8, 2020 12:41 PM
To: [hidden email] <[hidden email]>
Subject: Re: [EE] Eliminating external noise through PS

Looking at how common mode chokes work.  Was not aware of these.

This is the power supply I'm using (not sure if it's a flyback), and I
do not have any other caps...
https://www.meanwell.com/Upload/PDF/MPM-10/MPM-10-SPEC.PDF

Cheers,
-Neil.



On 12/8/2020 1:19 PM, Manu Abraham wrote:

> I guess you need a common mode filter at the PSU 120V in might help.
>
> Other than that:
> Are you using a flyback PSU ?
> If so, do you have a High voltage capacitor (the one between the
> primary and secondary, for the noise return path) ?
>
> On Tue, Dec 8, 2020 at 11:35 PM Neil <[hidden email]> wrote:
>> Hi,
>>
>> I'm working on a device that takes 120VAC, converts to 5VDC with a
>> PCB-mounted power supply, then further reduces that to 3.3VDC with a
>> linear regulator.
>> A 3.3V microcontroller switches a relay to power a 120VAC pump.
>> Overview...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
>>
>> All has been great until we switched to a specific pump, which happens
>> to generate a LOT of conducted noise, which passes through the 5V PS,
>> and the 3.3V regulator, and causing the microcontroller to crash.
>> I did a bunch of tested and found that the noise is being conducted
>> through the wires back to the board through the PS, through the linear
>> regulator, and this is the 3.3V line...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
>>
>> I was over at someone else's place so did not have a lot of parts with
>> me, but...
>> Adding a bunch more 0.1uf bypass capacitors all over the board did not help.
>>
>> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
>> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
>> of the crashing... but the ripple itself wasn't causing crashing.
>>
>> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
>> wires did not help.
>> I then tried to create a crude/uncalculated LC filter (which whatever
>> components I had on hand (33uh inductor and 1000uf capacitor, should be
>> low ESR), then a Pi filter (added 680 uF capacitor), and those barely
>> made a dent.
>> Eventually I added another 0.1uf capacitor to the output side of the pi
>> filter and that helped enough to prevent the microcontroller crashing.
>> But there is still a lot of noise on the 3.3V line...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
>>
>> FWIW, this is where it ended up...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
>>
>> The noise is in the 7Mhz to 30Mhz range (prob even higher).
>> I feel like smaller, low-ESR ceramic caps should help, but I doubt it
>> will take out most of the noise.
>> What is the right type of filter to eliminate this noise?
>>
>> Cheers,
>> -Neil.
>>
>> --
>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>> View/change your membership options at
>> http://mailman.mit.edu/mailman/listinfo/piclist

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Re: [EE] Eliminating external noise through PS

Manu Abraham-2
In reply to this post by Neil
Hi Neil,

I had similar problems, when I was running a DSP->Gate Driver->BLDC Motor
powered from a Flyback SMPS.

https://e2e.ti.com/support/tools/sim-hw-system-design/f/234/p/819727/3034699#3034699

The DSP would RESET in between. Initially I was able to filter out the noise
with a Common Mode Filter for the DSP stage.
You can see the DIY common mode filter, wound on a toroid in here

https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/234/20190713_5F00_162901.jpg

Eventually, the problem was figured out that the BLDC motor was
generating the spikes,
which was getting looped in everywhere, DSP, Gate drivers, all places.

The pulses were from the BLDC motor, which I was able to clamp with diodes,
but still there was some mains noise.

Changing the Y capacitor between the Primary and Secondaries did help
for that specific problem.

SMPS's are a pain, if they are not designed correctly. If you are
driving large loads,
then the pain is also larger.

Chinese SMPS's dont even mention. Likely they have no filters!

Best Regards,
Manu


On Wed, Dec 9, 2020 at 1:13 AM Neil <[hidden email]> wrote:

>
> Looking at how common mode chokes work.  Was not aware of these.
>
> This is the power supply I'm using (not sure if it's a flyback), and I
> do not have any other caps...
> https://www.meanwell.com/Upload/PDF/MPM-10/MPM-10-SPEC.PDF
>
> Cheers,
> -Neil.
>
>
>
> On 12/8/2020 1:19 PM, Manu Abraham wrote:
> > I guess you need a common mode filter at the PSU 120V in might help.
> >
> > Other than that:
> > Are you using a flyback PSU ?
> > If so, do you have a High voltage capacitor (the one between the
> > primary and secondary, for the noise return path) ?
> >
> > On Tue, Dec 8, 2020 at 11:35 PM Neil <[hidden email]> wrote:
> >> Hi,
> >>
> >> I'm working on a device that takes 120VAC, converts to 5VDC with a
> >> PCB-mounted power supply, then further reduces that to 3.3VDC with a
> >> linear regulator.
> >> A 3.3V microcontroller switches a relay to power a 120VAC pump.
> >> Overview...
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
> >>
> >> All has been great until we switched to a specific pump, which happens
> >> to generate a LOT of conducted noise, which passes through the 5V PS,
> >> and the 3.3V regulator, and causing the microcontroller to crash.
> >> I did a bunch of tested and found that the noise is being conducted
> >> through the wires back to the board through the PS, through the linear
> >> regulator, and this is the 3.3V line...
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
> >>
> >> I was over at someone else's place so did not have a lot of parts with
> >> me, but...
> >> Adding a bunch more 0.1uf bypass capacitors all over the board did not help.
> >>
> >> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
> >> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
> >> of the crashing... but the ripple itself wasn't causing crashing.
> >>
> >> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
> >> wires did not help.
> >> I then tried to create a crude/uncalculated LC filter (which whatever
> >> components I had on hand (33uh inductor and 1000uf capacitor, should be
> >> low ESR), then a Pi filter (added 680 uF capacitor), and those barely
> >> made a dent.
> >> Eventually I added another 0.1uf capacitor to the output side of the pi
> >> filter and that helped enough to prevent the microcontroller crashing.
> >> But there is still a lot of noise on the 3.3V line...
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
> >>
> >> FWIW, this is where it ended up...
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
> >>
> >> The noise is in the 7Mhz to 30Mhz range (prob even higher).
> >> I feel like smaller, low-ESR ceramic caps should help, but I doubt it
> >> will take out most of the noise.
> >> What is the right type of filter to eliminate this noise?
> >>
> >> Cheers,
> >> -Neil.
> >>
> >> --
> >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> >> View/change your membership options at
> >> http://mailman.mit.edu/mailman/listinfo/piclist
>
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Re: [EE] Eliminating external noise through PS

Manu Abraham-2
In reply to this post by Neil
On Wed, Dec 9, 2020 at 1:13 AM Neil <[hidden email]> wrote:
>
> Looking at how common mode chokes work.  Was not aware of these.
>

This one's a good document on the topic.

https://www.murata.com/~/media/webrenewal/products/emc/emifil/knowhow/26to30.ashx


Best Regards,
Manu
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Re: [EE] Eliminating external noise through PS

James Cameron-2
In reply to this post by Neil
The AC path is adjacent and parallel to the 3.3V bus; the motor
current will be coupled into that bus to some extent.

I would carry the 5V closer to the microcontroller and add another
linear 3.3V regulator there.  That way everything else that happens on
the 3.3V bus won't intrude so easily.

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Re: [EE] Eliminating external noise through PS

David Van Horn
Taking steps to decouple them magnetically would be a good idea.
Twist the AC pairs if you can, run a ground track between those and the low voltage stuff..

________________________________
From: [hidden email] <[hidden email]> on behalf of James Cameron <[hidden email]>
Sent: Tuesday, December 8, 2020 1:49 PM
To: Microcontroller discussion list - Public. <[hidden email]>
Subject: Re: [EE] Eliminating external noise through PS

The AC path is adjacent and parallel to the 3.3V bus; the motor
current will be coupled into that bus to some extent.

I would carry the 5V closer to the microcontroller and add another
linear 3.3V regulator there.  That way everything else that happens on
the 3.3V bus won't intrude so easily.

--
James Cameron
http://quozl.netrek.org/
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Re: [EE] Eliminating external noise through PS

Brent Brown-2
In reply to this post by Neil
Hi Neil,

Just to throw another thought or two into the mix...

You say noise is being conducted through wires, though what if the relay coils are
picking up magnetic signal from the AC load and coupling it back to the 5V line?
Shouldn't be difficult to separate and filter there.

Micro crashing (erratic execution) or just resetting? Some micros have flags for
reset cause e.g. if reset caused by brownout detector that would confirm suspicions
about noise on the supply being the primary issue.

Less likely... noise on I/O lines might not be being handled properly by code (for
example, generating too many interrupts too quickly and corrupting the stack).

Brent

On 8 Dec 2020 at 13:03, Neil wrote:

> Hi,
>
> I'm working on a device that takes 120VAC, converts to 5VDC with a
> PCB-mounted power supply, then further reduces that to 3.3VDC with a
> linear regulator.
> A 3.3V microcontroller switches a relay to power a 120VAC pump.
> Overview...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
>
> All has been great until we switched to a specific pump, which happens
> to generate a LOT of conducted noise, which passes through the 5V PS,
> and the 3.3V regulator, and causing the microcontroller to crash.
> I did a bunch of tested and found that the noise is being conducted
> through the wires back to the board through the PS, through the linear
> regulator, and this is the 3.3V line...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
>
> I was over at someone else's place so did not have a lot of parts with
> me, but...
> Adding a bunch more 0.1uf bypass capacitors all over the board did not help.
>
> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
> of the crashing... but the ripple itself wasn't causing crashing.
>
> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
> wires did not help.
> I then tried to create a crude/uncalculated LC filter (which whatever
> components I had on hand (33uh inductor and 1000uf capacitor, should be
> low ESR), then a Pi filter (added 680 uF capacitor), and those barely
> made a dent.
> Eventually I added another 0.1uf capacitor to the output side of the pi
> filter and that helped enough to prevent the microcontroller crashing.
> But there is still a lot of noise on the 3.3V line...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
>
> FWIW, this is where it ended up...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
>
> The noise is in the 7Mhz to 30Mhz range (prob even higher).
> I feel like smaller, low-ESR ceramic caps should help, but I doubt it
> will take out most of the noise.
> What is the right type of filter to eliminate this noise?
>
> Cheers,
> -Neil.
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist


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Re: [EE] Eliminating external noise through PS

Roy Hopkins
In reply to this post by Neil
[image: image.png]
Roy Hopkins
ZL1RJH




On Wed, 9 Dec 2020 at 08:15, Neil <[hidden email]> wrote:

> Roy,
>
> Battery... ugh.  Outdoor application that's drawing over an amp currently.
>
> In the given enclosure, the micro is on the other corner (quadrant) of
> the board from the 120VAC.  Some things have changed, so I am able to
> push it a bit further on the next revision but not much. Layout here...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-05.jpg
> The lower left is 4 relays, fuses, and screw terminal blocks.
>
> Not sure what you mean by Schotty diodes on 5V to + & -, as it's the
> power rails that are going above spec.
> I was thinking 5.1V zener on the 5V line, but the PS seems to have a
> built in zener at the output.  And not sure how a zener without a series
> resistor would handle the power.
>
> Will look into a harmonic filter.
>
> Thanks,
> -Neil.
>
>
>
> On 12/8/2020 1:18 PM, roy hopkins wrote:
> > Run the micro on batteries?
> > Take the micro further away from the motor power, power it from a
> different
> > phase?
> > Schottkyy Diodes on 5v to + and - to limit voltage swings to 5v +/- 0.2
> > volts.
> > Harmonic filter?
> >
> >
> > Roy Hopkins
> > ZL1RJH
> >
> >
> >
> >
> > On Wed, 9 Dec 2020 at 07:05, Neil <[hidden email]> wrote:
> >
> >> Hi,
> >>
> >> I'm working on a device that takes 120VAC, converts to 5VDC with a
> >> PCB-mounted power supply, then further reduces that to 3.3VDC with a
> >> linear regulator.
> >> A 3.3V microcontroller switches a relay to power a 120VAC pump.
> >> Overview...
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
> >>
> >> All has been great until we switched to a specific pump, which happens
> >> to generate a LOT of conducted noise, which passes through the 5V PS,
> >> and the 3.3V regulator, and causing the microcontroller to crash.
> >> I did a bunch of tested and found that the noise is being conducted
> >> through the wires back to the board through the PS, through the linear
> >> regulator, and this is the 3.3V line...
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
> >>
> >> I was over at someone else's place so did not have a lot of parts with
> >> me, but...
> >> Adding a bunch more 0.1uf bypass capacitors all over the board did not
> >> help.
> >>
> >> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
> >> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
> >> of the crashing... but the ripple itself wasn't causing crashing.
> >>
> >> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
> >> wires did not help.
> >> I then tried to create a crude/uncalculated LC filter (which whatever
> >> components I had on hand (33uh inductor and 1000uf capacitor, should be
> >> low ESR), then a Pi filter (added 680 uF capacitor), and those barely
> >> made a dent.
> >> Eventually I added another 0.1uf capacitor to the output side of the pi
> >> filter and that helped enough to prevent the microcontroller crashing.
> >> But there is still a lot of noise on the 3.3V line...
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
> >>
> >> FWIW, this is where it ended up...
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
> >>
> >> The noise is in the 7Mhz to 30Mhz range (prob even higher).
> >> I feel like smaller, low-ESR ceramic caps should help, but I doubt it
> >> will take out most of the noise.
> >> What is the right type of filter to eliminate this noise?
> >>
> >> Cheers,
> >> -Neil.
> >>
> >> --
> >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> >> View/change your membership options at
> >> http://mailman.mit.edu/mailman/listinfo/piclist
> >>
>
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Re: [EE] Eliminating external noise through PS

Ryan O'Connor
In reply to this post by Neil
Are you able to switch back to the old pump and take the same noise
measurements? I find it hard to believe that such strong filtering would
not virtually eliminate noise at that frequency...

On Wed, 9 Dec 2020 at 07:05, Neil <[hidden email]> wrote:

> Hi,
>
> I'm working on a device that takes 120VAC, converts to 5VDC with a
> PCB-mounted power supply, then further reduces that to 3.3VDC with a
> linear regulator.
> A 3.3V microcontroller switches a relay to power a 120VAC pump.
> Overview...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
>
> All has been great until we switched to a specific pump, which happens
> to generate a LOT of conducted noise, which passes through the 5V PS,
> and the 3.3V regulator, and causing the microcontroller to crash.
> I did a bunch of tested and found that the noise is being conducted
> through the wires back to the board through the PS, through the linear
> regulator, and this is the 3.3V line...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
>
> I was over at someone else's place so did not have a lot of parts with
> me, but...
> Adding a bunch more 0.1uf bypass capacitors all over the board did not
> help.
>
> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
> of the crashing... but the ripple itself wasn't causing crashing.
>
> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
> wires did not help.
> I then tried to create a crude/uncalculated LC filter (which whatever
> components I had on hand (33uh inductor and 1000uf capacitor, should be
> low ESR), then a Pi filter (added 680 uF capacitor), and those barely
> made a dent.
> Eventually I added another 0.1uf capacitor to the output side of the pi
> filter and that helped enough to prevent the microcontroller crashing.
> But there is still a lot of noise on the 3.3V line...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
>
> FWIW, this is where it ended up...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
>
> The noise is in the 7Mhz to 30Mhz range (prob even higher).
> I feel like smaller, low-ESR ceramic caps should help, but I doubt it
> will take out most of the noise.
> What is the right type of filter to eliminate this noise?
>
> Cheers,
> -Neil.
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
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Re: [EE] Eliminating external noise through PS

RussellMc
In reply to this post by Neil
On Wed, 9 Dec 2020 at 07:05, Neil <[hidden email]> wrote:

> Hi,
>
> I'm working on a device that takes 120VAC, converts to 5VDC with a
> PCB-mounted power supply, then further reduces that to 3.3VDC with a
> linear regulator.
> A 3.3V microcontroller switches a relay to power a 120VAC pump.
> Overview...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg


How are the grounds distributed between the various items?
Ideally you want a star with no loops that would allow alternative ground
paths between any two modules.
In your diagram it's not possible to determine how the ground runs run.


       Russell
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Re: [EE] Eliminating external noise through PS

Manu Abraham-2
In reply to this post by Ryan O'Connor
On Wed, Dec 9, 2020 at 3:09 PM Ryan O'Connor <[hidden email]> wrote:
>
> Are you able to switch back to the old pump and take the same noise
> measurements? I find it hard to believe that such strong filtering would
> not virtually eliminate noise at that frequency...

Unless .. The noise is Common Mode .., in all likelihood.

Best Regards,
Manu
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RE: [EE] Eliminating external noise through PS

FTL
In reply to this post by Neil
This is almost too obvious, but in the schematic I do not see a flyback
diode across the relay to suppress the back EMF when the relay is turned
off. The lack of diode would cause a serious spike in the 5V supply when the
relay is turned off.

Is the transistor being turned on hard enough to keep the relay on properly.
If it is not fully on with no flyback diode, maybe it is occasionally
releasing and causing big noise on the 5V bus.

> -----Original Message-----
> From: [hidden email] <[hidden email]> On Behalf Of Neil
> Sent: December 8, 2020 11:04 AM
> To: Microcontroller discussion list - Public. <[hidden email]>
> Subject: [EE] Eliminating external noise through PS
>
> Hi,
>
> I'm working on a device that takes 120VAC, converts to 5VDC with a PCB-
> mounted power supply, then further reduces that to 3.3VDC with a linear
> regulator.
> A 3.3V microcontroller switches a relay to power a 120VAC pump.
> Overview...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
>
> All has been great until we switched to a specific pump, which happens to
> generate a LOT of conducted noise, which passes through the 5V PS, and the
> 3.3V regulator, and causing the microcontroller to crash.
> I did a bunch of tested and found that the noise is being conducted
through
> the wires back to the board through the PS, through the linear regulator,
and
> this is the 3.3V line...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
>
> I was over at someone else's place so did not have a lot of parts with me,
> but...
> Adding a bunch more 0.1uf bypass capacitors all over the board did not
help.
>
> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
of
> the crashing... but the ripple itself wasn't causing crashing.
>
> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
wires
> did not help.
> I then tried to create a crude/uncalculated LC filter (which whatever
> components I had on hand (33uh inductor and 1000uf capacitor, should be
> low ESR), then a Pi filter (added 680 uF capacitor), and those barely made
a
> dent.
> Eventually I added another 0.1uf capacitor to the output side of the pi
filter

> and that helped enough to prevent the microcontroller crashing.
> But there is still a lot of noise on the 3.3V line...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
>
> FWIW, this is where it ended up...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
>
> The noise is in the 7Mhz to 30Mhz range (prob even higher).
> I feel like smaller, low-ESR ceramic caps should help, but I doubt it will
take

> out most of the noise.
> What is the right type of filter to eliminate this noise?
>
> Cheers,
> -Neil.
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist

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Re: [EE] Eliminating external noise through PS

Neil
Sorry, disappeared for a couple days, but some quick answers to
everything for now, and my next steps:

- Yes I have flyback diodes.   Highlighted with yellow here,  just above
the relays...
http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-06.jpg
- James & Russell, in that diagram also, I labeled the paths for power.  
The 5V to the relays is pretty much dedicated and 5V is on the top
layer, and (dedicated) ground for the relays on the bottom layer.  But
yes, it's right up against the AC section, but as many components have
been removed now, I will push that far away.
- The 3.3V regulator has been getting a bit warmer than I like, so I
have been planning to use a buck converter instead.  But maybe I should
run two 3.3V regulators instead?  I would think that the buck converter
would be pass less of the noise through.
- I ran over there quickly to pick up stuff and tried a crude
(uncalculated) common-mode choke I made up from stuff I could find. Did
not make in dent in the noise coming through.
See here...
http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-07.jpg
- I feel like Brent may be correct, that the noise may be coming from
the relay side.  The processor (ESP32) is resetting.  I know it's not a
firmware issue as it had zero crashes with the previous pump.


Adding some info:
The previous pump was a huge AC pump.  This new pump is actually DC, but
there's a bridge rectifier on the wires.  So I'm now convinced that the
noise is coming from brushes.
I brought the pump with me, and I have a new blank board.  My plan is to
reproduce just enough of the circuit to see the noise, and I can cut and
re-route traces (the 5V & ground to the relays) to see if helps.
I will also add a ceramic capacitor to the pump wires (right at the
pump), and hope that helps.  Plus twist the wires.

I'll be back with some results.

Cheers,
-Neil.



On 12/10/2020 7:28 PM, FTL wrote:

> This is almost too obvious, but in the schematic I do not see a flyback
> diode across the relay to suppress the back EMF when the relay is turned
> off. The lack of diode would cause a serious spike in the 5V supply when the
> relay is turned off.
>
> Is the transistor being turned on hard enough to keep the relay on properly.
> If it is not fully on with no flyback diode, maybe it is occasionally
> releasing and causing big noise on the 5V bus.
>
>> -----Original Message-----
>> From: [hidden email] <[hidden email]> On Behalf Of Neil
>> Sent: December 8, 2020 11:04 AM
>> To: Microcontroller discussion list - Public. <[hidden email]>
>> Subject: [EE] Eliminating external noise through PS
>>
>> Hi,
>>
>> I'm working on a device that takes 120VAC, converts to 5VDC with a PCB-
>> mounted power supply, then further reduces that to 3.3VDC with a linear
>> regulator.
>> A 3.3V microcontroller switches a relay to power a 120VAC pump.
>> Overview...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
>>
>> All has been great until we switched to a specific pump, which happens to
>> generate a LOT of conducted noise, which passes through the 5V PS, and the
>> 3.3V regulator, and causing the microcontroller to crash.
>> I did a bunch of tested and found that the noise is being conducted
> through
>> the wires back to the board through the PS, through the linear regulator,
> and
>> this is the 3.3V line...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
>>
>> I was over at someone else's place so did not have a lot of parts with me,
>> but...
>> Adding a bunch more 0.1uf bypass capacitors all over the board did not
> help.
>> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
>> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
> of
>> the crashing... but the ripple itself wasn't causing crashing.
>>
>> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
> wires
>> did not help.
>> I then tried to create a crude/uncalculated LC filter (which whatever
>> components I had on hand (33uh inductor and 1000uf capacitor, should be
>> low ESR), then a Pi filter (added 680 uF capacitor), and those barely made
> a
>> dent.
>> Eventually I added another 0.1uf capacitor to the output side of the pi
> filter
>> and that helped enough to prevent the microcontroller crashing.
>> But there is still a lot of noise on the 3.3V line...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
>>
>> FWIW, this is where it ended up...
>> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
>>
>> The noise is in the 7Mhz to 30Mhz range (prob even higher).
>> I feel like smaller, low-ESR ceramic caps should help, but I doubt it will
> take
>> out most of the noise.
>> What is the right type of filter to eliminate this noise?
>>
>> Cheers,
>> -Neil.
>>
>> --
>> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
>> View/change your membership options at
>> http://mailman.mit.edu/mailman/listinfo/piclist

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Re: [EE] Eliminating external noise through PS

Jason White-20
Hi Neil,

This may be a silly question: are you sure that some of these voltage
spikes that you've captured on the scope are not artifacts of your
measurement setup? The loop formed by the ground wire/clip on a scope probe
makes a very effective antenna. Maybe your power rail is cleaner than you
think - in which case the true problem might be elsewhere.

-Jason White

On Fri, Dec 11, 2020 at 3:11 PM Neil <[hidden email]> wrote:

> Sorry, disappeared for a couple days, but some quick answers to
> everything for now, and my next steps:
>
> - Yes I have flyback diodes.   Highlighted with yellow here,  just above
> the relays...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-06.jpg
> - James & Russell, in that diagram also, I labeled the paths for power.
> The 5V to the relays is pretty much dedicated and 5V is on the top
> layer, and (dedicated) ground for the relays on the bottom layer.  But
> yes, it's right up against the AC section, but as many components have
> been removed now, I will push that far away.
> - The 3.3V regulator has been getting a bit warmer than I like, so I
> have been planning to use a buck converter instead.  But maybe I should
> run two 3.3V regulators instead?  I would think that the buck converter
> would be pass less of the noise through.
> - I ran over there quickly to pick up stuff and tried a crude
> (uncalculated) common-mode choke I made up from stuff I could find. Did
> not make in dent in the noise coming through.
> See here...
> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-07.jpg
> - I feel like Brent may be correct, that the noise may be coming from
> the relay side.  The processor (ESP32) is resetting.  I know it's not a
> firmware issue as it had zero crashes with the previous pump.
>
>
> Adding some info:
> The previous pump was a huge AC pump.  This new pump is actually DC, but
> there's a bridge rectifier on the wires.  So I'm now convinced that the
> noise is coming from brushes.
> I brought the pump with me, and I have a new blank board.  My plan is to
> reproduce just enough of the circuit to see the noise, and I can cut and
> re-route traces (the 5V & ground to the relays) to see if helps.
> I will also add a ceramic capacitor to the pump wires (right at the
> pump), and hope that helps.  Plus twist the wires.
>
> I'll be back with some results.
>
> Cheers,
> -Neil.
>
>
>
> On 12/10/2020 7:28 PM, FTL wrote:
> > This is almost too obvious, but in the schematic I do not see a flyback
> > diode across the relay to suppress the back EMF when the relay is turned
> > off. The lack of diode would cause a serious spike in the 5V supply when
> the
> > relay is turned off.
> >
> > Is the transistor being turned on hard enough to keep the relay on
> properly.
> > If it is not fully on with no flyback diode, maybe it is occasionally
> > releasing and causing big noise on the 5V bus.
> >
> >> -----Original Message-----
> >> From: [hidden email] <[hidden email]> On Behalf Of
> Neil
> >> Sent: December 8, 2020 11:04 AM
> >> To: Microcontroller discussion list - Public. <[hidden email]>
> >> Subject: [EE] Eliminating external noise through PS
> >>
> >> Hi,
> >>
> >> I'm working on a device that takes 120VAC, converts to 5VDC with a PCB-
> >> mounted power supply, then further reduces that to 3.3VDC with a linear
> >> regulator.
> >> A 3.3V microcontroller switches a relay to power a 120VAC pump.
> >> Overview...
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-00.jpg
> >>
> >> All has been great until we switched to a specific pump, which happens
> to
> >> generate a LOT of conducted noise, which passes through the 5V PS, and
> the
> >> 3.3V regulator, and causing the microcontroller to crash.
> >> I did a bunch of tested and found that the noise is being conducted
> > through
> >> the wires back to the board through the PS, through the linear
> regulator,
> > and
> >> this is the 3.3V line...
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-01.jpg
> >>
> >> I was over at someone else's place so did not have a lot of parts with
> me,
> >> but...
> >> Adding a bunch more 0.1uf bypass capacitors all over the board did not
> > help.
> >> Changing the power supply from an IRM-10-5 (industrial spec, 200mV
> >> ripple) to MPM-10-5 (medical spec, 100mV ripple), helped reduce the rate
> > of
> >> the crashing... but the ripple itself wasn't causing crashing.
> >>
> >> Adding (non-specific size) ferrites to the pump wires, and 120VAC input
> > wires
> >> did not help.
> >> I then tried to create a crude/uncalculated LC filter (which whatever
> >> components I had on hand (33uh inductor and 1000uf capacitor, should be
> >> low ESR), then a Pi filter (added 680 uF capacitor), and those barely
> made
> > a
> >> dent.
> >> Eventually I added another 0.1uf capacitor to the output side of the pi
> > filter
> >> and that helped enough to prevent the microcontroller crashing.
> >> But there is still a lot of noise on the 3.3V line...
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-02.jpg
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-03.jpg
> >>
> >> FWIW, this is where it ended up...
> >> http://orlandorobotbuilders.com/stuff/SMNoise/20201207-SMN-04.jpg
> >>
> >> The noise is in the 7Mhz to 30Mhz range (prob even higher).
> >> I feel like smaller, low-ESR ceramic caps should help, but I doubt it
> will
> > take
> >> out most of the noise.
> >> What is the right type of filter to eliminate this noise?
> >>
> >> Cheers,
> >> -Neil.
> >>
> >> --
> >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> >> View/change your membership options at
> >> http://mailman.mit.edu/mailman/listinfo/piclist
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>


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