"Owen Duffy" wrote in message
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"Jimmie D" wrote in
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wrote in message
ups.com...

Jimmie D wrote:
I was cleaning up today and came across an old dummy load I had that
looks
like it is made from 2 watt resistors. ITs mounted on a quart size
paint can
lid and looks to be a 50 watts worth of resistors. This looks like
it may have been a commercially built unit and I was wondering what
the power handling capability would be if the resistors were
submerged in mineral oil.

Jimmie

Hi Jimmie, It would probably take a kilowatt, the question is for
how long? I was looking at my old Heath "Cantenna" manual and it
says it will take 1000 watts for about 1 minute in mineral oil. The
resistor element appears to be ~50-100 watts. The Cantenna is in a
gallon paint can. If none of the 25 resistors "fuse" out due to
current, your load should take a kilowatt for at least 15 seconds,
and take 100 watts ~forever.

Gary N4AST

Thanks Gary
Would it be worth my while to remount it for a gallon container. I was
thinking of doing this anyway because the local paint store sells
gallon paint cans, Im not sure about he avaiability of the quart size
cans. I have access to lots of mineral oil. At work we use about 100
gal a year and I can have all the used oil I want


Hmmm, what is used oil? Used engine oil is regarded as carcinogenic in
these parts, hypoid gear oils similarly whether used or unused. Further,
it is full of conductive particles that may affect the load's its
performance, water and metals that may form corrosive products, and
possibly volatiles that will "boil off" when heated.

I don't know what automatic transmission fluid costs in your part of the
world, but here it is not an unreasonable cost to fill a load with new
ATF. Air tool oil is a source of light grade mineral oil that does not
contain detergent agents.

Long time ago, I favoured refrigeration (compressor) oil for filling
loads, but it is expensive, and the low moisture quality is soon lost if
the load is not as good as hermetically sealed. It is possible to do
that, I still have a load that I made using a hermetically sealed BNC
connecter (yes, a true glass seal) and the whole enclosure was brazed /
soldered up, closed like a 'fridge. I also experimented with refrigerant
in the loads, a lot more fuss and they didn't work any better than
compressor oil. Today, you would not be allowed to do that with R12!

I used to work on some fron cooled equipment. When the equipment got hot the
freon boiled and the vapor went up pipes into a radiator where it was cooled
by fans then driped back down the pipes. I guess you could do a dummy load
like this too.

I have a couple of the glass BNC connectors, I think they are like the ones
you are talking about. They are bulkhead connectors female on both sides. I
keep them around because I have never seen any others like them. They are
isolated. the shield doesnt connect to the mounting flange.


Anyway, to your original question of how much increase in power rating
with oil immersion. In the long term, it is determined by the ability of
the load to dissipate heat from the outside for a tolerable rise in
temperature of the oil and the resistor element. In the short term, it
comes down to the resistor element, and different constructions will
behave differently (eg metal film vs composition).

Owen