[EE] Current Sense Project

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[EE] Current Sense Project

Josh Koffman
Hi all,

I'm thinking about throwing together a quick monitor for my block
heater. I'd like to know when I forget to plug the car in (because
let's be honest, it's going to happen...). I've got a small current
transformer on the way (5A/5mA). I'd like to trigger a relay that
lights up a 120V indicator light when the block heater is plugged in
and powered.

My "current" thought is to run the transformer to an ADC on a micro
and use it to trigger a relay. Am I missing an easier solution? Could
I run the output of the current transformer to an opto that triggers
the relay? I would lose the "tweakability" of levels though.

Open to suggestions!

Thanks,

Josh
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Re: [EE] Current Sense Project

Clint Jay
Why not just put a pair of LEDs with appropriate dropper resistor across
the power?

On Thu, 26 Nov 2020, 17:34 Josh Koffman, <[hidden email]> wrote:

> Hi all,
>
> I'm thinking about throwing together a quick monitor for my block
> heater. I'd like to know when I forget to plug the car in (because
> let's be honest, it's going to happen...). I've got a small current
> transformer on the way (5A/5mA). I'd like to trigger a relay that
> lights up a 120V indicator light when the block heater is plugged in
> and powered.
>
> My "current" thought is to run the transformer to an ADC on a micro
> and use it to trigger a relay. Am I missing an easier solution? Could
> I run the output of the current transformer to an opto that triggers
> the relay? I would lose the "tweakability" of levels though.
>
> Open to suggestions!
>
> Thanks,
>
> Josh
> --
> A common mistake that people make when trying to design something
> completely foolproof is to underestimate the ingenuity of complete
> fools.
>         -Douglas Adams
> --
> 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] Current Sense Project

Manu Abraham-2
In reply to this post by Josh Koffman
On Thu, Nov 26, 2020 at 11:04 PM Josh Koffman <[hidden email]> wrote:

>
> Hi all,
>
> I'm thinking about throwing together a quick monitor for my block
> heater. I'd like to know when I forget to plug the car in (because
> let's be honest, it's going to happen...). I've got a small current
> transformer on the way (5A/5mA). I'd like to trigger a relay that
> lights up a 120V indicator light when the block heater is plugged in
> and powered.
>
> My "current" thought is to run the transformer to an ADC on a micro
> and use it to trigger a relay. Am I missing an easier solution? Could
> I run the output of the current transformer to an opto that triggers
> the relay? I would lose the "tweakability" of levels though.

Option #1
Use a transistor and a pot to set the trip point.

Option #2.
Use a zener to set trip point, maybe a TL431 even

Option #3
Use an opamp as a comparator, or maybe even a 555 timer

Option #4
use a microcontroller with a builtin ADC

Option #5
use a microcontroller with a builtin comparator

Could be a lot more options, though.


Cheers
Manu
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Re: [EE] Current Sense Project

James Cameron-2
In reply to this post by Josh Koffman
Sounds good.

For one-offs, my habit is to optimise my time rather than components.

I'd steal power from the heater supply, wired to a 5V SMPS if stolen
at AC line voltage, or some other converter if stolen from a low
voltage, and run an esp8266 or esp32 module with an optional ds18b20.

On my main server I'd script something that would ping the node at 8pm
and report if it was missing.  Or it could be an esp8266 at bedside.

Another way is to store the block heater power supply next to your
bed.  Repeated inconvenience of forgetting gradually reinforces
remembering.

--

Amazing the problems you wintering folks have to put up with!  Our
first for the season extreme heatwave forecast this weekend,

http://www.bom.gov.au/australia/heatwave/

... where "extreme" means failure of infrastructure; liquid roads,
flat tyres, engines overheating, transmission line protection trips,
babies kept indoors, dead pets, rains of dead birds,

... it is time to put the candles and medications in the fridge, not
leave the butter out, and watch the kangaroos shelter under trees.

... still pondering best way to put aluminium foil on windows.

--
James Cameron
http://quozl.netrek.org/
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Re: [EE] Current Sense Project

Dwayne Reid
In reply to this post by Josh Koffman
Hi there, Josh.

I would connect the secondary of the CT to the input of a bridge
rectifier.  The output of the bridge rectifier drives the LED(s)
directly.  Usually, no resistors needed.

5mA is way tons of current for modern Green LEDs.

dwayne


At 10:32 AM 11/26/2020, Josh Koffman wrote:

>Hi all,
>
>I'm thinking about throwing together a quick monitor for my block
>heater. I'd like to know when I forget to plug the car in (because
>let's be honest, it's going to happen...). I've got a small current
>transformer on the way (5A/5mA). I'd like to trigger a relay that
>lights up a 120V indicator light when the block heater is plugged in
>and powered.
>
>My "current" thought is to run the transformer to an ADC on a micro
>and use it to trigger a relay. Am I missing an easier solution? Could
>I run the output of the current transformer to an opto that triggers
>the relay? I would lose the "tweakability" of levels though.
>
>Open to suggestions!
>
>Thanks,
>
>Josh


--
Dwayne Reid   <[hidden email]>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
780-489-3199 voice   780-487-6397 fax   888-489-3199 Toll Free
www.trinity-electronics.com
Custom Electronics Design and Manufacturing

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Re: [EE] Current Sense Project

RussellMc
In reply to this post by James Cameron-2
Extreme ... :

We skirted the edge of the outback on a 500 mile in one day drive (memory
says, may be wrong) starting at Emerald and heading south.
Somewhere along the way we came on a Holden with a car trailer, with
another Holden on the trailer. The latter had no wheels. We stopped, as one
does. He was immensely grateful. He'd used up all the wheels on the spare
car as he'd blown out tyres as he drove. He'd had a parrot, but it had
died  in the heat. He and his dog were still alive but not very happy. We
dropped them off somewhere further south.
That was probably early to mid December (we were on the Eyre Peninsula at
Christmas).

No Aircon in our old Falcon.
We opened the large front air flap and suspended ice cubes on the blast. It
worked albeit sensorially interesting - drops of iced water in a furnace
breeze.

Those were the days :-)
1977?


The

On Fri, 27 Nov 2020, 10:34 James Cameron, <[hidden email]> wrote:

> Sounds good.
>
> For one-offs, my habit is to optimise my time rather than components.
>
> I'd steal power from the heater supply, wired to a 5V SMPS if stolen
> at AC line voltage, or some other converter if stolen from a low
> voltage, and run an esp8266 or esp32 module with an optional ds18b20.
>
> On my main server I'd script something that would ping the node at 8pm
> and report if it was missing.  Or it could be an esp8266 at bedside.
>
> Another way is to store the block heater power supply next to your
> bed.  Repeated inconvenience of forgetting gradually reinforces
> remembering.
>
> --
>
> Amazing the problems you wintering folks have to put up with!  Our
> first for the season extreme heatwave forecast this weekend,
>
> http://www.bom.gov.au/australia/heatwave/
>
> ... where "extreme" means failure of infrastructure; liquid roads,
> flat tyres, engines overheating, transmission line protection trips,
> babies kept indoors, dead pets, rains of dead birds,
>
> ... it is time to put the candles and medications in the fridge, not
> leave the butter out, and watch the kangaroos shelter under trees.
>
> ... still pondering best way to put aluminium foil on windows.
>
> --
> James Cameron
> http://quozl.netrek.org/
> --
> 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] Current Sense Project

James Cameron-2
Russell wrote:
> He'd used up all the wheels on the spare
> car as he'd blown out tyres as he drove. [...]

Indeed; tyre maximum speed rating is based on thermal limits; if the
heat from flexing of the steel and rubber can't be released quickly
enough, the tyre separates from the wheel.

Reminds me a few years ago we stopped to rescue a 20-something
military male with two rear wheels blown at once, and no spares.  On a
120 km (75 mile) sealed highway with 110 kph (70 mph) speed limit,
just after a long sweeping bend.

He said the ride got really rough really quick, he was thrown forward
into seat belt, then he saw his tyres departing from the road in front
of him.

We got him radio coverage for long enough to call for road service.

He was driving from Adelaide to Brisbane, via Broken Hill, without any
stops planned.  2038km (1274 miles).

--
James Cameron
http://quozl.netrek.org/
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