[EE] Microwave Oven Transformers

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[EE] Microwave Oven Transformers

Bob Blick-5
I am in need of a large DC choke and thinking about making one from a microwave oven transformer. It appears that the E's and I's of the core are not interleaved so all I need to do is cut the weld holding the core together and it should fall apart. Hopefully in just two pieces. Then I can strip out the windings, put my own winding on, and, most importantly, sandwich a spacer so I have a gap (I said this was a DC choke).

Anyone here ever play with microwave oven transformers at this level and learned any hard lessons?

Thanks, Bob
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Re: [EE] Microwave Oven Transformers

Denny Esterline-2
Personally, no. But the internet is full of people that have taken out the
secondary windings and wound on 2-3 turns of heavy wire to produce a spot
welder.
Google around a bit on DIY spot welder and I'm sure you find lots of people
hacking up these transformers in interesting ways. Probably something
relevant to be learned there.


-Denny

On Mon, Jul 13, 2020 at 9:23 AM Bob Blick <[hidden email]> wrote:

> I am in need of a large DC choke and thinking about making one from a
> microwave oven transformer. It appears that the E's and I's of the core are
> not interleaved so all I need to do is cut the weld holding the core
> together and it should fall apart. Hopefully in just two pieces. Then I can
> strip out the windings, put my own winding on, and, most importantly,
> sandwich a spacer so I have a gap (I said this was a DC choke).
>
> Anyone here ever play with microwave oven transformers at this level and
> learned any hard lessons?
>
> Thanks, Bob
> --
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Re: [EE] Microwave Oven Transformers

Alan Pearce
I would have thought that a DC choke would not want the E and I
laminations interleaved, rather an air gap to limit saturation of the
core.

On Mon, 13 Jul 2020 at 18:39, Denny Esterline <[hidden email]> wrote:

>
> Personally, no. But the internet is full of people that have taken out the
> secondary windings and wound on 2-3 turns of heavy wire to produce a spot
> welder.
> Google around a bit on DIY spot welder and I'm sure you find lots of people
> hacking up these transformers in interesting ways. Probably something
> relevant to be learned there.
>
>
> -Denny
>
> On Mon, Jul 13, 2020 at 9:23 AM Bob Blick <[hidden email]> wrote:
>
> > I am in need of a large DC choke and thinking about making one from a
> > microwave oven transformer. It appears that the E's and I's of the core are
> > not interleaved so all I need to do is cut the weld holding the core
> > together and it should fall apart. Hopefully in just two pieces. Then I can
> > strip out the windings, put my own winding on, and, most importantly,
> > sandwich a spacer so I have a gap (I said this was a DC choke).
> >
> > Anyone here ever play with microwave oven transformers at this level and
> > learned any hard lessons?
> >
> > Thanks, Bob
> > --
> > 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] Microwave Oven Transformers

Bob Blick-5
In reply to this post by Denny Esterline-2
I've only seen one person use it as an inductor, and he did not cut it apart and add a gap. I suppose I'll just go for it, but I only have one, and I haven't seen any free microwaves on Craigslist lately. Saw one on the sidewalk on my way to work a few weeks ago, but by the time I drove around the block it was gone. Lotta scroungers out there, I guess :)
Cheers, Bob
________________________________________
From: [hidden email] <[hidden email]> on behalf of Denny Esterline
Sent: Monday, July 13, 2020 10:38 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Microwave Oven Transformers

Personally, no. But the internet is full of people that have taken out the
secondary windings and wound on 2-3 turns of heavy wire to produce a spot
welder.
Google around a bit on DIY spot welder and I'm sure you find lots of people
hacking up these transformers in interesting ways. Probably something
relevant to be learned there.


-Denny

On Mon, Jul 13, 2020 at 9:23 AM Bob Blick  wrote:

> I am in need of a large DC choke and thinking about making one from a
> microwave oven transformer. It appears that the E's and I's of the core are
> not interleaved so all I need to do is cut the weld holding the core
> together and it should fall apart. Hopefully in just two pieces. Then I can
> strip out the windings, put my own winding on, and, most importantly,
> sandwich a spacer so I have a gap (I said this was a DC choke).
>
> Anyone here ever play with microwave oven transformers at this level and
> learned any hard lessons?
>
> Thanks, Bob

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Re: [EE] Microwave Oven Transformers

Bob Blick-5
In reply to this post by Alan Pearce
Yes, that's why I thought it might be relatively easy, assuming everything didn't fall apart when I cut through the welds. This guy seems to have achieved it:
https://www.youtube.com/watch?v=rCqddXhoP4E
Cheerful regards, Bob

________________________________________
From: [hidden email] <[hidden email]> on behalf of Alan Pearce
Sent: Monday, July 13, 2020 12:51 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Microwave Oven Transformers

I would have thought that a DC choke would not want the E and I
laminations interleaved, rather an air gap to limit saturation of the
core.

On Mon, 13 Jul 2020 at 18:39, Denny Esterline  wrote:

>
> Personally, no. But the internet is full of people that have taken out the
> secondary windings and wound on 2-3 turns of heavy wire to produce a spot
> welder.
> Google around a bit on DIY spot welder and I'm sure you find lots of people
> hacking up these transformers in interesting ways. Probably something
> relevant to be learned there.
>
>
> -Denny
>
> On Mon, Jul 13, 2020 at 9:23 AM Bob Blick  wrote:
>
> > I am in need of a large DC choke and thinking about making one from a
> > microwave oven transformer. It appears that the E's and I's of the core are
> > not interleaved so all I need to do is cut the weld holding the core
> > together and it should fall apart. Hopefully in just two pieces. Then I can
> > strip out the windings, put my own winding on, and, most importantly,
> > sandwich a spacer so I have a gap (I said this was a DC choke).
> >
> > Anyone here ever play with microwave oven transformers at this level and
> > learned any hard lessons?
> >
> > Thanks, Bob

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Re: [EE] Microwave Oven Transformers

Richard Prosser
Even with the welds cut I'd thought that the laminations would be tight
(Not fall apart). They may be epoxied in place as well. Otherwise there
would be a strong buzz when operating. I haven't used microwave
transformers (yet), but had a holiday job assembling speaker transformers
and power supply chokes.
RP

On Tue, 14 Jul 2020 at 08:17, Bob Blick <[hidden email]> wrote:

> Yes, that's why I thought it might be relatively easy, assuming everything
> didn't fall apart when I cut through the welds. This guy seems to have
> achieved it:
> https://www.youtube.com/watch?v=rCqddXhoP4E
> Cheerful regards, Bob
>
> ________________________________________
> From: [hidden email] <[hidden email]> on behalf of Alan
> Pearce
> Sent: Monday, July 13, 2020 12:51 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Microwave Oven Transformers
>
> I would have thought that a DC choke would not want the E and I
> laminations interleaved, rather an air gap to limit saturation of the
> core.
>
> On Mon, 13 Jul 2020 at 18:39, Denny Esterline  wrote:
> >
> > Personally, no. But the internet is full of people that have taken out
> the
> > secondary windings and wound on 2-3 turns of heavy wire to produce a spot
> > welder.
> > Google around a bit on DIY spot welder and I'm sure you find lots of
> people
> > hacking up these transformers in interesting ways. Probably something
> > relevant to be learned there.
> >
> >
> > -Denny
> >
> > On Mon, Jul 13, 2020 at 9:23 AM Bob Blick  wrote:
> >
> > > I am in need of a large DC choke and thinking about making one from a
> > > microwave oven transformer. It appears that the E's and I's of the
> core are
> > > not interleaved so all I need to do is cut the weld holding the core
> > > together and it should fall apart. Hopefully in just two pieces. Then
> I can
> > > strip out the windings, put my own winding on, and, most importantly,
> > > sandwich a spacer so I have a gap (I said this was a DC choke).
> > >
> > > Anyone here ever play with microwave oven transformers at this level
> and
> > > learned any hard lessons?
> > >
> > > Thanks, Bob
>
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> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
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Re: [EE] Microwave Oven Transformers

Bob Blick-5
Hi Richard,
The laminations aren't interleaved, and I can't imagine they'd want to weld if there were varnish or epoxy. So they probably varnish after the whole thing is assembled. In that case I can't imagine the bond being very strong. I can always cook it in the toaster/reflow oven for a while to soften it up.
Cheers, Bob

________________________________________
From: [hidden email] <[hidden email]> on behalf of Richard Prosser
Sent: Monday, July 13, 2020 1:36 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Microwave Oven Transformers

Even with the welds cut I'd thought that the laminations would be tight
(Not fall apart). They may be epoxied in place as well. Otherwise there
would be a strong buzz when operating. I haven't used microwave
transformers (yet), but had a holiday job assembling speaker transformers
and power supply chokes.
RP

On Tue, 14 Jul 2020 at 08:17, Bob Blick  wrote:

> Yes, that's why I thought it might be relatively easy, assuming everything
> didn't fall apart when I cut through the welds. This guy seems to have
> achieved it:
> https://www.youtube.com/watch?v=rCqddXhoP4E
> Cheerful regards, Bob
>
> ________________________________________
> From: [hidden email] <[hidden email]> on behalf of Alan
> Pearce
> Sent: Monday, July 13, 2020 12:51 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Microwave Oven Transformers
>
> I would have thought that a DC choke would not want the E and I
> laminations interleaved, rather an air gap to limit saturation of the
> core.
>
> On Mon, 13 Jul 2020 at 18:39, Denny Esterline  wrote:
> >
> > Personally, no. But the internet is full of people that have taken out
> the
> > secondary windings and wound on 2-3 turns of heavy wire to produce a spot
> > welder.
> > Google around a bit on DIY spot welder and I'm sure you find lots of
> people
> > hacking up these transformers in interesting ways. Probably something
> > relevant to be learned there.
> >
> >
> > -Denny
> >
> > On Mon, Jul 13, 2020 at 9:23 AM Bob Blick  wrote:
> >
> > > I am in need of a large DC choke and thinking about making one from a
> > > microwave oven transformer. It appears that the E's and I's of the
> core are
> > > not interleaved so all I need to do is cut the weld holding the core
> > > together and it should fall apart. Hopefully in just two pieces. Then
> I can
> > > strip out the windings, put my own winding on, and, most importantly,
> > > sandwich a spacer so I have a gap (I said this was a DC choke).
> > >
> > > Anyone here ever play with microwave oven transformers at this level
> and
> > > learned any hard lessons?
> > >
> > > Thanks, Bob


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Re: [EE] Microwave Oven Transformers

RussellMc
In reply to this post by Bob Blick-5
On Tue, 14 Jul 2020 at 04:23, Bob Blick <[hidden email]> wrote:

> I am in need of a large DC choke and thinking about making one from a
> microwave oven transformer. It appears that the E's and I's of the core are
> not interleaved so all I need to do is cut the weld holding the core
> together and it should fall apart. Hopefully in just two pieces. Then I can
> strip out the windings, put my own winding on, and, most importantly,
> sandwich a spacer so I have a gap (I said this was a DC choke).
>
> Anyone here ever play with microwave oven transformers at this level and
> learned any hard lessons?
>
> Have done the obligatory spot welder -  less oomph than desired for task
in mind.

Falls apart when welds removed.
No hard lessons in this application.
DC choke may have some of it's own :-)- let us know.


    Russell
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Re: [EE] Microwave Oven Transformers

Harold Hallikainen-3
We had a microwave oven with an interesting problem. When the timer timed
out, the fan would stop, but the high voltage and RF would keep going. We
finally smelled the transformer overheating. Luckily it would stop when
you opened the door. I thought it would be an interesting to use it as the
high voltage supply in an amateur radio RF power amplifier. It looks like
the transformer is typically about 2.8 kV RMS. But, as stuff piled up in
the garage, I eventually took it the the electronic recycler and bought an
amplifier at a local hamfest ( https://w6iwi.org/DentronClippertonL/ ).

Harold
https://w6iwi.org



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Re: [EE] Microwave Oven Transformers

Bob Blick-5
In reply to this post by RussellMc
Immediately after bemoaning the dearth of free ovens, one popped up in the local craigslist. Although smaller than the transformer I already had, 900W vs 1200W, it is more suitable for disassembly due to the placement of the mounting bracket. Here is a picture of the two of them.

The fattest enameled wire I have in any quantity is only 15AWG, so my plan is to use 4 strands of 12AWG conventional house wire in parallel and just wind until it's full. Then I will experiment with different air gaps. I need it to work at around 120 Amps DC.

I know the insulation of house wire will waste as much space as the copper, but that's the way it is. It's hard to find thick enameled wire, and it would be very hard to wind 8AWG or thicker wire.

Will follow up with my observations.

Cheerful regards, Bob

________________________________________
From: [hidden email] <[hidden email]> on behalf of RussellMc
Sent: Monday, July 13, 2020 3:39 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Microwave Oven Transformers

Have done the obligatory spot welder -  less oomph than desired for task in mind.

Falls apart when welds removed.
No hard lessons in this application.
DC choke may have some of it's own :-)- let us know.


    Russell

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TwoTransformers.jpg (34K) Download Attachment
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Re: [EE] Microwave Oven Transformers

sergio
https://www.wires.co.uk/acatalog/TX_3000-5000.html

On Wed, 15 Jul 2020, Bob Blick wrote:

> I know the insulation of house wire will waste as much space as the copper, but that's the way it is. It's hard to find thick enameled wire, and it would be very hard to wind 8AWG or thicker wire.

A good place for wire:

https://www.wires.co.uk/acatalog/TX_3000-5000.html

They used to do much more so I guess they can get hold of a lot more than
they advertise.

Best Regards
Sergio
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Re: [EE] Microwave Oven Transformers

Bob Blick-5
That's pretty nice! I guess I shouldn't give up on finding a source for enameled wire. I will start with my current plan and see how much inductance I get, since I have lots of house wire.
Thanks, Bob

________________________________________
From: [hidden email] <[hidden email]> on behalf of sergio
Sent: Wednesday, July 15, 2020 10:13 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Microwave Oven Transformers

https://www.wires.co.uk/acatalog/TX_3000-5000.html

On Wed, 15 Jul 2020, Bob Blick wrote:

> I know the insulation of house wire will waste as much space as the copper, but that's the way it is. It's hard to find thick enameled wire, and it would be very hard to wind 8AWG or thicker wire.

A good place for wire:

https://www.wires.co.uk/acatalog/TX_3000-5000.html

They used to do much more so I guess they can get hold of a lot more than
they advertise.

Best Regards
Sergio
-

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Re: [EE] Microwave Oven Transformers

graham foulkes
HI
120 amp windings at low voltage, you don't need thick insulation on the
wire. Maybe strip off the house cable insulation and lap wind with thin
tape, electronic polyamide high temperature tape preferrably. I have used
thin cotton tape to insulate scondary coils in a home built welder, still
running 30 years later.
Shellac lacquer is also an alternative, does not soften much with
temperature increase and has good dielectric properties. Avoid PVC
electrical tape, softens too easily and punctures when winding, stretches
and so thins out.

On Wed, Jul 15, 2020, 7:38 AM Bob Blick <[hidden email]> wrote:

> That's pretty nice! I guess I shouldn't give up on finding a source for
> enameled wire. I will start with my current plan and see how much
> inductance I get, since I have lots of house wire.
> Thanks, Bob
>
> ________________________________________
> From: [hidden email] <[hidden email]> on behalf of
> sergio
> Sent: Wednesday, July 15, 2020 10:13 AM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Microwave Oven Transformers
>
> https://www.wires.co.uk/acatalog/TX_3000-5000.html
>
> On Wed, 15 Jul 2020, Bob Blick wrote:
>
> > I know the insulation of house wire will waste as much space as the
> copper, but that's the way it is. It's hard to find thick enameled wire,
> and it would be very hard to wind 8AWG or thicker wire.
>
> A good place for wire:
>
> https://www.wires.co.uk/acatalog/TX_3000-5000.html
>
> They used to do much more so I guess they can get hold of a lot more than
> they advertise.
>
> Best Regards
> Sergio
> -
>
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Re: [EE] Microwave Oven Transformers

Bob Blick-5
Hi Graham,

The choke is only going to be used at low voltage so you're right, I don't need to worry too much about insulation.

I could strip off the insulation and bundle the four strands together before insulating. It would be rather stiff, but I've got tough fingers. Would use a lot of polyimide tape, I expect it to be about 30 turns. The widest I have is 30mm I think.

Varnishing it is an interesting thought. I've got no experience with varnish or shellac, so finding something that would work from my local hardware store will be an interesting experiment.

I have some 8AWH battery cable too. But probably not enough.

Thanks for the ideas!

Bob
________________________________________
From: [hidden email] <[hidden email]> on behalf of graham foulkes
Sent: Wednesday, July 15, 2020 10:57 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Microwave Oven Transformers

HI
120 amp windings at low voltage, you don't need thick insulation on the
wire. Maybe strip off the house cable insulation and lap wind with thin
tape, electronic polyamide high temperature tape preferrably. I have used
thin cotton tape to insulate scondary coils in a home built welder, still
running 30 years later.
Shellac lacquer is also an alternative, does not soften much with
temperature increase and has good dielectric properties. Avoid PVC
electrical tape, softens too easily and punctures when winding, stretches
and so thins out.

On Wed, Jul 15, 2020, 7:38 AM Bob Blick  wrote:

> That's pretty nice! I guess I shouldn't give up on finding a source for
> enameled wire. I will start with my current plan and see how much
> inductance I get, since I have lots of house wire.
> Thanks, Bob
>
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Re: [EE] Microwave Oven Transformers

Alan Pearce
Rather than bundle the wire together before binding it I would try to
lay the four lots side by side and then bind it so it is a flat wide
strip. This will make it easier to wind on the core.

On Wed, 15 Jul 2020 at 19:29, Bob Blick <[hidden email]> wrote:

>
> Hi Graham,
>
> The choke is only going to be used at low voltage so you're right, I don't need to worry too much about insulation.
>
> I could strip off the insulation and bundle the four strands together before insulating. It would be rather stiff, but I've got tough fingers. Would use a lot of polyimide tape, I expect it to be about 30 turns. The widest I have is 30mm I think.
>
> Varnishing it is an interesting thought. I've got no experience with varnish or shellac, so finding something that would work from my local hardware store will be an interesting experiment.
>
> I have some 8AWH battery cable too. But probably not enough.
>
> Thanks for the ideas!
>
> Bob
> ________________________________________
> From: [hidden email] <[hidden email]> on behalf of graham foulkes
> Sent: Wednesday, July 15, 2020 10:57 AM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Microwave Oven Transformers
>
> HI
> 120 amp windings at low voltage, you don't need thick insulation on the
> wire. Maybe strip off the house cable insulation and lap wind with thin
> tape, electronic polyamide high temperature tape preferrably. I have used
> thin cotton tape to insulate scondary coils in a home built welder, still
> running 30 years later.
> Shellac lacquer is also an alternative, does not soften much with
> temperature increase and has good dielectric properties. Avoid PVC
> electrical tape, softens too easily and punctures when winding, stretches
> and so thins out.
>
> On Wed, Jul 15, 2020, 7:38 AM Bob Blick  wrote:
>
> > That's pretty nice! I guess I shouldn't give up on finding a source for
> > enameled wire. I will start with my current plan and see how much
> > inductance I get, since I have lots of house wire.
> > Thanks, Bob
> >
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Re: [EE] Microwave Oven Transformers

Bob Blick-5
That makes a lot of sense. 12AWG wire is 2.05 mm diameter. The winding space is 45mm by 15mm. Maybe I can get 5 quad turns per layer by 6 layers or 4+ turns per layer and 7 layers for 30 total turns. If I am lucky, perhaps a few more.

Stretching the wire ahead of time so it's straight and binds tightly together would be good to do. I can make a couple of wooden(or 3D printed) channels to hold the wires flat and together while I tape them, and slide them along as I tape.

Thanks, Bob

________________________________________
From: [hidden email] <[hidden email]> on behalf of Alan Pearce
Sent: Wednesday, July 15, 2020 12:16 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Microwave Oven Transformers

Rather than bundle the wire together before binding it I would try to
lay the four lots side by side and then bind it so it is a flat wide
strip. This will make it easier to wind on the core.

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Re: [EE] Microwave Oven Transformers

Alan Pearce
Yeah, i was thinking along the lines of flat or rectangular enamelled
copper that is sometimes used on switchmode chokes for high
current/low resistance use. I believe the same trick has been used in
speakers but with the rectangular wire wound on edge to maximise the
number of turns within the gap of the magnet to try and make the cone
movement more linear.


On Wed, 15 Jul 2020 at 21:04, Bob Blick <[hidden email]> wrote:

>
> That makes a lot of sense. 12AWG wire is 2.05 mm diameter. The winding space is 45mm by 15mm. Maybe I can get 5 quad turns per layer by 6 layers or 4+ turns per layer and 7 layers for 30 total turns. If I am lucky, perhaps a few more.
>
> Stretching the wire ahead of time so it's straight and binds tightly together would be good to do. I can make a couple of wooden(or 3D printed) channels to hold the wires flat and together while I tape them, and slide them along as I tape.
>
> Thanks, Bob
>
> ________________________________________
> From: [hidden email] <[hidden email]> on behalf of Alan Pearce
> Sent: Wednesday, July 15, 2020 12:16 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Microwave Oven Transformers
>
> Rather than bundle the wire together before binding it I would try to
> lay the four lots side by side and then bind it so it is a flat wide
> strip. This will make it easier to wind on the core.
>
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Re: [EE] Microwave Oven Transformers

sergio


On Wed, 15 Jul 2020, Alan Pearce wrote:

> Yeah, i was thinking along the lines of flat or rectangular enamelled
> copper that is sometimes used on switchmode chokes for high
> current/low resistance use. I believe the same trick has been used in
> speakers but with the rectangular wire wound on edge to maximise the
> number of turns within the gap of the magnet to try and make the cone
> movement more linear.

https://www.wires.co.uk/acatalog/rt_ec_wire.html

>
>
> On Wed, 15 Jul 2020 at 21:04, Bob Blick <[hidden email]> wrote:
>>
>> That makes a lot of sense. 12AWG wire is 2.05 mm diameter. The winding space is 45mm by 15mm. Maybe I can get 5 quad turns per layer by 6 layers or 4+ turns per layer and 7 layers for 30 total turns. If I am lucky, perhaps a few more.
>>
>> Stretching the wire ahead of time so it's straight and binds tightly together would be good to do. I can make a couple of wooden(or 3D printed) channels to hold the wires flat and together while I tape them, and slide them along as I tape.
>>
>> Thanks, Bob
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Re: [EE] Microwave Oven Transformers

Bob Blick-5
In reply to this post by Bob Blick-5
Just a quick update.

Cutting apart the transformer was easy. Hacksawing along the two welds a little more than a millimeter deep was enough.

Making my own flat wire is a bit challenging. I experimented on a 1 meter length. Stretching 12AWG solid wire to make it straight is hard. I will use a lever or other human invention. Keeping four 8-meter wires parallel while taping will be challenging. I may tack-solder it at intervals along its length. Spiral wrapping the Kapton tape seems to be easier than lengthwise.

In the meantime, a friend gave me a transformer he had stripped the secondary from(in anticipation of making a spot welder) and then abandoned. I decided to do some tests just for giggles. It is a 120V 60Hz model, from an oven rated either 900 or 1000 watts. I connected it to a Variac and a low-quality AC volt/ammeter on the primary, wound 5 turns of 12AWG for a secondary, and put an RMS voltmeter and oscilloscope on it.

Applying up to about 90 volts, primary current was 0.8A and I got something resembling a sine wave on the secondary, about 4.2V.

By the time I got to 120V the primary current was 5.8A, there was minor annoying hum and the output waveform looked rather stressed-out 5.3V. See attached photo. 2V/division.

The transformer still had its shunt blocks(search the internet and you will see what they look like and where they go). Removing them and retracing my steps gave me similar results at lower voltages but less voltage compression and 6.8A input current with 120V in. At 117V the current was 5.8A and output voltage was 5.27V

Very little heat was produced, it appears that most power was reactive.

More fun to follow some other day. I need to fix my chainsaw and do other important chores.

Bob
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Waveform.jpg (52K) Download Attachment
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Re: [EE] Microwave Oven Transformers

Jason White-20
Thanks for sharing Bob! It's interesting to see your progress.

On Saturday, July 18, 2020, Bob Blick <[hidden email]> wrote:

> Just a quick update.
>
> Cutting apart the transformer was easy. Hacksawing along the two welds a
> little more than a millimeter deep was enough.
>
> Making my own flat wire is a bit challenging. I experimented on a 1 meter
> length. Stretching 12AWG solid wire to make it straight is hard. I will use
> a lever or other human invention. Keeping four 8-meter wires parallel while
> taping will be challenging. I may tack-solder it at intervals along its
> length. Spiral wrapping the Kapton tape seems to be easier than lengthwise.
>
> In the meantime, a friend gave me a transformer he had stripped the
> secondary from(in anticipation of making a spot welder) and then abandoned.
> I decided to do some tests just for giggles. It is a 120V 60Hz model, from
> an oven rated either 900 or 1000 watts. I connected it to a Variac and a
> low-quality AC volt/ammeter on the primary, wound 5 turns of 12AWG for a
> secondary, and put an RMS voltmeter and oscilloscope on it.
>
> Applying up to about 90 volts, primary current was 0.8A and I got
> something resembling a sine wave on the secondary, about 4.2V.
>
> By the time I got to 120V the primary current was 5.8A, there was minor
> annoying hum and the output waveform looked rather stressed-out 5.3V. See
> attached photo. 2V/division.
>
> The transformer still had its shunt blocks(search the internet and you
> will see what they look like and where they go). Removing them and
> retracing my steps gave me similar results at lower voltages but less
> voltage compression and 6.8A input current with 120V in. At 117V the
> current was 5.8A and output voltage was 5.27V
>
> Very little heat was produced, it appears that most power was reactive.
>
> More fun to follow some other day. I need to fix my chainsaw and do other
> important chores.
>
> Bob



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