[ARC5] [Milsurplus] Old Dynamotors- Don't be a DooFuss Like Me....

Mon Apr 1 19:58:58 EDT 2013

Thermal inertia can be your friend too. I worked on an air-to-air missile
for a while. The PS only had to work for about 5 minutes. The transformer
was wound w/ Cerroc insulated wire. At the end of maybe 5 minutes, the
thing was glowing red, but still working.

-John

===============

> Thermal inertia, yeah, it's real.
>
> I had a sobering experience on Field Day several years ago, 2008.  I
> always take a vintage rig, and that time was using a WW2 HRO powered from
> the rack-type supply used with an RAS.
>
> There was something very funky about the juice coming from the
> Chinkee-Chinee-made generator the club was using.  Either it was not a
> sine wave, or perhaps was producing two different waveforms simultaneously
> which were "adding" to produce too much peak voltage (my Weston meter --
> RMS of course -- read 118 volts), or maybe some IDIOT had decided that
> reducing the generator RPM would reduce gas consumption but didn't affect
> the voltage (such is the mind set of the Kodeless n Klueless), no thought
> whatsoever about the frequency -- whatever was going on, I started
> noticing that my receiver was getting unstable (it NEVER had, before) and
> that the power supply was hot enough to cook an omelet on the top cover.
> So was the power supply in my LM freq meter.  And the transmitter!
>
> I shut down my rig at 9 pm, and never turned it back on.  At 7 am the next
> morning, the RAS/HRO power supply -- specifically the transformer -- was
> still very noticeably warm.
>
> It took me a week after Field Day to get up the nerve to try the power
> supply on my work bench.  I brought it up slow with a variac, and it never
> even hiccupped.  Nor did it ever get warm.
>
> Had that not been a mil-spec transformer, it would have fried for sure.
>
> 73
> Mike
> W4DSE
>
> --- On Mon, 4/1/13, J. Forster <jfor at quikus.com> wrote:
>
>> From: J. Forster <jfor at quikus.com>
>> Subject: Re: [ARC5] [Milsurplus] Old Dynamotors- Don't be a DooFuss Like
>> Me....
>> To: "Dennis Monticelli" <dennis.monticelli at gmail.com>
>> Cc: "Military Radio Collectors Association" <mrca at mailman.qth.net>,
>> "milsurplus" <milsurplus at mailman.qth.net>, "ARC-5 List"
>> <arc5 at mailman.qth.net>
>> Date: Monday, April 1, 2013, 5:53 PM
>> Yes, but you should limit the power
>> to a few to a few tens of watts. If
>> you put too much power in, you may not notice it until too
>> late.
>> Transformer have a lot of thermal inertia and DC heats them
>> from inside.
>>
>> You can do this with many dynos also. Just pull the input
>> side brushes, so
>> only the shunt field is powered..
>>
>> -John
>>
>> ==============
>>
>>
>> > Another trick that works is to apply DC current to the
>> primary in a
>> > sufficient amount to heat the interior via the temp
>> rise of the windings.
>> >  Put several watts into it and let it sit for a
>> day or more.  Proportion
>> > the current to the size of the transformer.
>> >
>> > Dennis  AE6C
>> >
>> >
>> > On Mon, Apr 1, 2013 at 7:09 AM, J. Forster <jfor at quikus.com>
>> wrote:
>> >
>> >> For years, I've always baked out stuff with
>> non-hermetic magnetics.
>> >>
>> >> I put the thing on a few bricks, put a couple of
>> 100 Watt incandescent
>> >> lamps underneath it, and a big cardboard box with
>> some holes in the top
>> >> over it, and let it sit for a week or more.
>> >>
>> >> You want the thing to get up to about 130F for
>> several days, at least.
>> >> Longer is better, IMO.
>> >>
>> >> YMMV,
>> >>
>> >> -John
>> >>
>> >> ==============
>> >>
>> >>
>> >> > On Mon, Apr 1, 2013 at 12:50 AM, David Stinson
>> <arc5 at ix.netcom.com>
>> >> wrote:
>> >> >
>> >> >>
>> >> >>
>> >> >> I thought about putting the whole thing
>> sans end bells into a
>> >> 200-degree
>> >> >> oven for a couple of  hours to dry it
>> out
>> >> >>
>> >> >
>> >> > This is  a problem with big chunks of
>> iron in old transmitters, too.
>> >> Many
>> >> > do not realize how similar to a sponge the
>> laminations and windings
>> >> are.
>> >> > And old transformer left sitting in a damp
>> cellar or storage shed is
>> >> an
>> >> > accident waiting to happen if you just haul it
>> out, hook it up, and
>> >> apply
>> >> > voltage. Might happen in 5 seconds, 5 hours,
>> or 5 days, 9.9999 times
>> >> out
>> >> > of
>> >> > 10 it'll zorch.
>> >> >
>> >> > The oven works great as is provides a means of
>> getting rid of the
>> >> moisture
>> >> > without introducing more. On bigger pieces it
>> can take a day or two,
>> >> maybe
>> >> > more, to feel safe enough to put power to it.
>> And there's never a
>> >> > guarantee, of course. But recovery rate is
>> far, far better when dried
>> >> out
>> >> > than when not. The trick is to heat it up long
>> enough for the heat to
>> >> > reach
>> >> > the core and drive out the moisture. It's all
>> about the mass. Smaller
>> >> =
>> >> > faster; hours vs days.
>> >> >
>> >> >
>> >> > A good reminder as many of my dynamotors are
>> out in the garage here in
>> >> > humid NC. Though lately humidity has been
>> amazingly low.
>> >> >
>> >> > ~ Todd,  KA1KAQ/4
>> >> >
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