From: graham foulkes <bespoken1@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Thu, 10 Sep 2020 07:27:58 -0700
Subject: Re: [EE] Microwave Oven Transformers
Thread-Topic: [EE] Microwave Oven Transformers
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HI Bob
There is a YouTube video, one of many about these Chinese inverter welders
,which addresses this issue of arc stability. It notes the poor arc strike
capability at low current settings, no facts on electrode coatings, but
similar solution, series inductor, which they miraculously cram into that
miniature enclosure. They use, I think, a 30 mm powder iron toroid with a
double layer wind of stranded wire.
I bought two of these tiny welders, one 220 and a 120 volt version to see
how well they perform. Not able to kill them so far!
BTW, tyraps tend to stretch over time on stuff that warms up, good old
fashioned cotton string works better, look at electric motor windings, they
are always laced with twine.

On Wed, Sep 9, 2020, 7:32 PM Bob Blick <bobblick@outlook.com> wrote:

> Hi Ryan,
> I needed an inductor good for over 100 amps.
>
> One of my welders is a tiny thing as small as a lunch box. It's very
> convenient and efficient but doesn't like cellulosic electrodes, I want t=
o
> see if adding inductance in series improves things. More likely, it will
> kill my welder after it kills the MOVs I add as protection :)
>
> There's very little real information available about why inverter-based
> welders usually don't work well with cellulosic electrodes. A lot of talk
> about open-circuit voltage not being high enough. That's clearly wrong,
> since the open-circuit voltage only affects the starting of the arc, and
> the problem here is the arc dying out. Cellulosic electrodes produce a lo=
t
> of hydrogen, which does raise the arc voltage slightly, but it should be
> well within the welder's capability. I've run the welder on both 120 and
> 240 volts to see if that changes things, and it doesn't, which it would i=
f
> the arc voltage was the problem. I think the real problem is the current
> limiting in the welder getting confused by the aggressive percussive arc
> that cellulosic rods produce.
>
> There is a whitepaper by ESAB(a welding equipment manufacturer) about the
> topic, and they suggest that inverter-based welders need large inductors =
in
> order to use cellulosic electrodes. So that fits in with my hypothesis.
>
> Even if it works out, the inductor probably won't become part of the
> welder, since it weighs as much as the whole welder. Just a little work
> avoidance exercise here in my little corner of the hobby-sphere.
>
> Friendly regards, Bob
>
> ________________________________________
> From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of Ryan
> O'Connor
> Sent: Wednesday, September 9, 2020 9:42 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Microwave Oven Transformers
>
> That's not many turns. What are you going to use it for?
>
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