Other uses for Microwave oven transformers?
terry
scrapped parts from old (UNREPAIRABLE/NOT-WORTH-FIXING) microwaves!
e.g. the transformers, fans, fuse holders, overheat switches. And even
occasionally have used some of them for repairs to other microwaves!
I applied 115.7 volts AC to what had been the HV winding of one of
these scrapped transf. recently and got about 6 volts on what had been
the original primary. That established the ratio between the two
windings as approx 20:1.
Also a small voltage (about 0.185 volts) across what had been the
magnetron (Approx. 3 volt?) heater winding. Which gives ratio of about
1:33 to the original primary winding; also a ratio of about 1:700 from
the original HV winding.
So the idea of using the transformer backwards comes to mind????
Depending on the unit they are typically rated as follows?
Input winding 115 volts at whatever total wattage of the magnetron
circuit is. Assume say 1000 watts requiring about 8.7 amps primary
current! Usually intermittent use.
The original HV secondary operates at around 2200 volts, so 1000 watts
(ignore the magnetron heater current for a moment) would average about
400 to 500 milliamps? And pretty peaky because of the half wave high
voltage doubling circuit???
More moderately; at 115 volts and say 400 m/a into the old HV winding
the transformer might be able to supply around 6 volts at around 5 to
7 amps from what used to be the 115 volt primary?
Or at 115v/250 m/a maybe 3 to 5 amps? For 6.3v heaters?
Alternatively could such an ex-microwave power transformer be used in
the plate circuit (non-push/pull) of an audio amp using say a 6v6 or
6L6 (perhaps triode connected?) with a DC plate current of 45 to 75
milliamps?
Thus in such an arrangement the 20:1 ratio to the original primary
could provide something of a match for an 8 ohm speaker? (20)^2 x 8 =
3200
Problems; the laminations of such transformers do not seem to have air
spaces as in some audio transformers carrying DC? The bottom (neutral)
end of HV winding is sometimes at cabinet 'ground'. Hence a problem;
unless the transformer is isolated and even then the transformer frame
could be 'hot' whenever the unit is plugged in if that winding now
used as the primary! Therefore unsafe.
Have also heard of cutting off the old HV winding etc. and using the
remainder of transformer to make battery charger; down rating a
typical transformer to say 500 watts (continuous) for battery charging
that's sort of around 30 to 40 amps at 12+ volts. Not sure what the
turns per volt would be but should be possible to poke a few turns
around the partially stripped core until one gets around 14 to 15
volts RMS.
This is all supposition at this stage! Any comments criticism????
JC Morrice
s.com>, terry <tsan...@nf.sympatico.ca> writes
>Trying to clear out some 'junk' but have always tended to keep
>scrapped parts from old (UNREPAIRABLE/NOT-WORTH-FIXING) microwaves!
>
>e.g. the transformers, fans, fuse holders, overheat switches. And even
>occasionally have used some of them for repairs to other microwaves!
>
>I applied 115.7 volts AC to what had been the HV winding of one of
>these scrapped transf. recently and got about 6 volts on what had been
>the original primary. That established the ratio between the two
>windings as approx 20:1.
>
>Also a small voltage (about 0.185 volts) across what had been the
>magnetron (Approx. 3 volt?) heater winding. Which gives ratio of about
>1:33 to the original primary winding; also a ratio of about 1:700 from
>the original HV winding.
>
>So the idea of using the transformer backwards comes to mind????
snip.......
>Depending on the unit they are typically rated as follows?
>This is all supposition at this stage! Any comments criticism????
Seems there are quite a few uses for them!
Other uses:
good:
http://www.rhunt.f9.co.uk/Electronics/Spot_Welder/Spot_Welder_Page1.htm
Neat, but not so good - has he never heard of screening mains supplies?:
http://www.youtube.com/watch?v=Wp7JF2sANsw
Sheesh - doing this over large metal sheets with live mains involved an
apparently zero mains insulation / isolation box / separation. Would
*LOVE* to see his kilowatt linear; but perhaps not:
http://www.instructables.com/id/Build-a-Microwave-Transformer-Homemade-
Welder/
John
--
JC Morrice
jo...@pentode.demon.co.uk
Stray Dog
Your concepts are good, and if you do google searches on "microwave oven
transformers" you will get websites that talk about their experiences.
I did buy a couple of used microwave ovens at local thrift stores for $5
each and played with the big transformers inside.
I was not satisfied with the result. One of the things some of the
websites talk about is that you have to remove the "magnetic choke" that
is part of the core. This needs a good hammer and a "punch" and was much
harder to do for one transformer than another. And, after taking it out,
it still did not perform.
The problem I found in both of my transformers is that at low voltages and
a reasonable load, it was fine, but from about 50 volts and on up to line
voltage into the primary, the primary current went up much faster than it
should have considering the load that I put on the transformer secondary.
I do not know what kind of load magnetrons put on power supply
transformers but i suspect it is not like a continuous load. I tried to do
google searches on magnetron current-voltage relationships but could not
find anything. Certainly those "magnetic chokes" must be doing something.
In the end, I wound up buying my plate transformers at hamfests and also
one, new, made by Hammond in Canada. Peter Dahl is out of business, and
Ameritron (I think) will sell plate transformers and some are reasonably
priced for the power and voltage. Fair Radio Sales (Lima, Ohio) and
Radio-Daze (NY) are two that sell Hammond transformers, including large
plate transformers (many types, specs all over the map, too).
//////////////////////////////////////////////
On Sun, 21 Jun 2009, terry wrote:
> Date: Sun, 21 Jun 2009 16:21:03 -0700 (PDT)
> From: terry <tsan...@nf.sympatico.ca>
> Newsgroups: rec.radio.amateur.homebrew
> Subject: Other uses for Microwave oven transformers?
mikea
> In the end, I wound up buying my plate transformers at hamfests and also
> one, new, made by Hammond in Canada. Peter Dahl is out of business, and
> Ameritron (I think) will sell plate transformers and some are reasonably
> priced for the power and voltage. Fair Radio Sales (Lima, Ohio) and
> Radio-Daze (NY) are two that sell Hammond transformers, including large
> plate transformers (many types, specs all over the map, too).
Well, yes, Peter is out of the business, but the transformers and other
items are still being built to his specs:
<http://forums.qrz.com/showthread.php?t=153611?
<blockquote>
Peter Dahl Company has NOT been sold. It is NOT moving across the border
to Mexico. Gary no longer works for the them. The Peter Dahl Company has
stopped production, is closing their doors, and will become part of
Amateur Radio History!
But the NAME lives on!
Jeff Weinberg, W8CQ of Harbach Electronics, has purchased the rights to
the name, the original transformer and choke specifications and designs,
and the design equipment.
The transformers will be built by MagCap Engineering using the original
PWD specs, and sold through Harbach Electronics under the Peter Dahl
name. The transformer and chokes will be FOB Canton, MA and shipped
directly to the customer from MagCap.
This is great news for the Amateur Radio Community and a great way to
memorialize the Peter Dahl Company who's innovations and designs have
brought so much to our hobby.
To nullify any further rumors or innuendos about the status or future of
the Peter W Dahl Company, let me share the following e-mail with you
(edited for content)...
Quote:
Re: Harbach Electronics and Peter Dahl
From: "Jeff Weinberg W8CQ"
Date: Wed, February 20, 2008 2:30 pm
To: "Dino Darling"
Hi Dino,
Yes, the deal is finally completed. I have purchased all of the
transformer
designs and design equipment from Peter Dahl. I am moving the equipment
here to Ohio. Once all of the computer design work has been updated and
cataloged, I will be selling Peter Dahl transformers and chokes.
I should be up and running in a couple months.
(snip)
MagCap will be building the transformers according to the original Peter
Dahl designs and specs and will be sold by Harbach Electronics under the
Peter W. Dahl name.
Regards,
Jeff Weinberg W8CQ
Harbach Electronics
http://www.harbachelectronics.com
I've heard great things about Jeff and his company from people I know
and respect. To me this is a great day in Amateur Radio and I look
forward to the future with Peter W Dahl firmly rooted in our hobby!
</blockquote>
--
Mike Andrews, W5EGO
mi...@mikea.ath.cx
Tired old sysadmin
JIMMIE
They are a great source of a core and primary for DIY transformers.
Thes transformer were designed as a constant current source and have
magnetic shunts that must be removed for most power supply
applications
Jimmie
Stray Dog
On Mon, 22 Jun 2009, mikea wrote:
> Date: Mon, 22 Jun 2009 10:55:05 -0500
> From: mikea <mi...@mikea.ath.cx>
> Newsgroups: rec.radio.amateur.homebrew
> Subject: Re: Other uses for Microwave oven transformers?
Thanks for the info. It goes beyond what came out in QST at the time and
that was that production was going to end, period. There was no hint at
all in the QST anouncement that there was even any possibility for
continuation.
raypsi
> On Mon, 22 Jun 2009, mikea wrote:
> > Date: Mon, 22 Jun 2009 10:55:05 -0500
> > From: mikea <mi...@mikea.ath.cx>
> > Newsgroups: rec.radio.amateur.homebrew
> > Subject: Re: Other uses for Microwave oven transformers?
>
Hey OM:
The only way to do them is to tear them down to the lams re insulate
the lams and re stack them.
Only because they put weld shunt shorts on the lams that act as
shorted windings, plus the welds hold the lams together, because they
don't interweave them.
73 OM
de n8zu
JIMMIE
>
> - Show quoted text -
I f you can find some of the older ones and they are getting harder to
find you can just knock the shunts out with a hammer and punch. I have
given some thought to trying cutting the welds out but I havent had a
project lately that I am in that desperate of a need of a
transformer..
Jimmie
raypsi
Hey OM:
I grind the shorts off on a grinder with 6 inch diameter grind stones.
Then I have to take the burrs off each lam. All the bear metal has to
be insulated. Then you can make like Tesla and series 3 transformers.
Talk about the air becoming alive. 7500 volts AC will show you how
much leakage there is in the air.
stan
> > project lately that I am in that desperate of a need of a
> > transformer..
>
> > Jimmie
>
> Hey OM:
>
> I grind the shorts off on a grinder with 6 inch diameter grind stones.
> Then I have to take the burrs off each lam. All the bear metal has to
> be insulated. Then you can make like Tesla and series 3 transformers.
> Talk about the air becoming alive. 7500 volts AC will show you how
>
> - Show quoted text -
Years ago, to my regret (got fed up with stubbing toes on oversize
door stop) I dumped a 115 volt input neon sign transformer that was
capable (IIRC) of some 15,000 volts?
Great big insulators on each end. Probably a few milliamps output.
Don't see them 'open wired' to the neon signs any more as we did many
years ago?
JIMMIE
>
> - Show quoted text -
The local skating rink uses them. One toasted a couple of moonths ago
when someone splashed it with a milkshake.Fire Brigade was called. I
noticed the new transformer has a plexiglass cover . They are a lot of
fun to play with. I got my hands on one when I was about 12. I made an
electric sword with it and an old automotive radio antenna. Touched my
brother on the butt with it. I knew it would shock him, I didnt know
he would collapse to the ground .My mother always wondered how I made
it to adulthood.
Jimmie