From: Jason White <whitewaterssoftwareinfo@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Sat, 18 Jul 2020 16:29:35 -0700
Subject: Re: [EE] Microwave Oven Transformers
Thread-Topic: [EE] Microwave Oven Transformers
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Thanks for sharing Bob! It's interesting to see your progress.

On Saturday, July 18, 2020, Bob Blick <bobblick@outlook.com> 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 u=
se
> a lever or other human invention. Keeping four 8-meter wires parallel whi=
le
> taping will be challenging. I may tack-solder it at intervals along its
> length. Spiral wrapping the Kapton tape seems to be easier than lengthwis=
e.
>
> In the meantime, a friend gave me a transformer he had stripped the
> secondary from(in anticipation of making a spot welder) and then abandone=
d.
> I decided to do some tests just for giggles. It is a 120V 60Hz model, fro=
m
> 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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Jason White
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