From: email@example.com (N. Thornton)
Subject: Re: Any good uses for old microwave over parts?
Date: 8 Nov 2002 11:07:14 -0800
References: <firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: 8 Nov 2002 19:07:14 GMT
firstname.lastname@example.org (John Crighton) wrote in message news:<email@example.com>...
> On 7 Nov 2002 05:50:15 -0800, firstname.lastname@example.org (N. Thornton) wrote:
> >email@example.com (John Crighton) wrote in message news:
> >> On Wed, 06 Nov 2002 14:53:23 GMT, Al wrote:
> >> >I disassembled my old microwave oven because the interlock became
> >> >But what can be safely done with the microwave tube and supply? I once
> >> >Any ideas, even funny ones?
> >> Where ever you need a transformer you have a
> >> good sized core with a primary winding all ready
> >> on so all you have to do is knock off the secondary
> >> winding and fit another secondary to suit you.
> >Sadly that is not true. There are nowhere near enough turns on the
> >primary for the TF to run continuously. Even fan cooled it can only
> >manage typically 15 minutes before thermal protection must act. Its a
> >real shame.
> >But, if you put 2 in series, then you're cooking.
> >Hey, I just saw you said "Where ever you need a transformer". I'm not
> >putting one of them in my portable radio! :)
> >Thanks for the welder sites, must have a look.
> >Regards, NT
> Hey Mr NT,
> I think you are taking the piss out of me. I don't like that.
That was never my intent, I am sorry if you took it that way. I have
no wish to offend you at all.
My comment about using one in a radio was only meant to be a good
natured smiley. We have many threads here on s.e.d. where we pick up
on the trivial errors we all make. I hope you know I mean nothing
against you in any way John.
Onto the transformers:
Microwave TFs are something I have looked at somewhat, as they do look
as if they could be very useful at first sight. But the problems with
them are so many that at the end of the day, there is almost nothing
one can do with them, sadly. Many tron enges here have discussed
zapper TFs here.
I think it is a good idea to let the OP know not to try using the TFs
in the way you suggested: I do appreciate your good intention, and I'm
sure the OP does too. I guess ocasionally we all overlook something, I
know I do now and then. The trouble is, if a zapper TF were run in a
wood or plastic box, continuously with no fan, there would soon be a
house fire. So I do think its sensible to mention it.
> AL asked for suggestions. I gave him some.
> If a person has gone to the trouble of dismantling an oven and
> dismantling the welded cores of the transformer with a saw and chisel,
> pushed/knocked out the windings, he has some imagination,
> skills and determination to save a quid/dollar/peso.
> So adding some more turns of similar sized primary wire "if needed"
> is no big deal to the practical hobbyist. So, add a supplementary
> winding of 30 or 60 or whatever turns to the original primary.
I think it would need much more than that, thats the problem, and
there won't be enough room to add enough extra winding. Microwave TFs
are seriously underwound, to cut down on size, cost and weight.
OK, but several people already have, and regrettably microwave TFs are
much worse than they appear.
> Now you are going to say, "where do I get the wire from?"
> From another scrapped transformer, your junk box,
I have tried that too in the past. It never works. TFs must always be
wound with new enamelled wire. Reused wire inevitably shorts out. Used
enamelled wire is something else thats good for almost nothing. The
insulation just won't hold. I have even used old enamel wire as bell
wire: even that is not reliable, somewhere along the run it shorts. It
is hopeless unfortunately.
> Put two "similar" sized "E" sections together with DIY clamps
> and series both of the primaries if you wish, wind a secondary
> to suit your needs.
But DIY clamps are solid steel, and you will have horrendous core
currents if you do that. The net is a very big place, and there are
people who have tried these things.
I did try a solid iron core transformer once (non laminated) at
school, and its power efficiency was something like 5%. Yes, it got
very hot! IIRC, something like 12v 2A out for 240v 2A in!
> Snip the grounded side of the secondary winding so that it
> becomes an isolated winding. Apply mains to the original
> HV secondary and use the original primary winding as a 20 Volt
> (or whatever you get in your part of the world) secondary.
Yet another problem with microwave TFs is there is no insulation
between secondary and core. Doing what you suggest would result in
rapid arcover from seconadry to core, resulting in electrocution or
RCD popping, depending on whether you earthed your case or not.
In theory you can run it with the core live, as long as its safely
sealed away, but IRL mounting such a heavy beast securely without
using metal fixings is pretty difficult.
But even if you do that, the original primary winding is rated at
what, 6A (for a 240v TF): and that is with fan cooling. So you'd get
something like 24v ac at perhaps 3A: is it worth all the aggro for
such a moderate output? Proper TFs with those sort of ratings can be
had out of your average domestic stereo, they're free, small, and
> Might be good for a simple car battery charger. Ideal for
> lending out to friends and neighbours who like to strike the
> clamps together to see if the juice is present.
> Inefficient, yes it is.
> Achh ....I am not going to repond anymore to someone
> who nit picks my words and pees on my suggestions.
> The transformers are free. Work on them.
> What do you expect for nothing?
We have John. This is a wordwide group. The only half practical way I
have come across is to run 2 in series and rewind the secondaries to a
very low voltage. You just can't win with these things, they simply
have too many problems.
If you look at a 1.5kVA building site transformer, and compare it to a
microwave TF, you'll see just how much difference there is.
Perhaps you can come up with a practical use for them yet: so far I
have seen this subject tackled repeatedly in s.e.d., and still no good
use has surfaced. A welder is about the only one that flies.
I keep wondering if a single TF would be enough to make a really small
spot welder. It could be overrun much more heavily than in an oven,
since it would only run for a second per minute ish. It would
certainly be a more reliable and quicker way to do the heavier point
to point wiring than soldering.
How would one do that?