"Don Foreman" wrote in message
...
On Wed, 30 Mar 2005 13:21:49 -0800, Jim Stewart
wrote:

Ken Finney wrote:
Off-topic, but the learned denizens here are pretty good at asking
bizarre
questions.

I need an inductive load to switch a 28 VDC 12 A circuit into. Note
that
this is a one time test circuit, and I don't want to break the bank.
My
initial thought was to parallel a couple of 28 VDC relay coils to get
the 12
A current. What I'm finding is that most of the relay coils draw less
than
an amp, and I don't want have to parallel 16 relays to draw that much
current. Does anyone have a better suggestion for me? I'm having zero
luck
finding out how much an automotive starter solenoid draws, if I could
find a
24 VDC diesel starter solenoid that requires 3 or more amps, that would
probably be doable.

Just a quick back-of-an-envelop calculation
shows you'd need about 500 feet of 16 gauge
wire for a dc resistance of 2.3 ohms in your
coil. I'd not want to use anything less than
16 gauge and even then for just a short time.
It's going to have to dissipate 336 watts once
the core is saturated.

That's a big coil, either to wind or to find
in an existing device.

The induction motor winding will have some resistance. The rest can
be made up with 1/16" dia stainless TIG rod. I measured one such 36"
piece to be about 0.313 ohms. I don't think it'd overheat at 12
amps. It's probably settle out at about 315C. .

The flaw with that theory is that while a "real inductor" is indeed
inductance
in series with the resistance of the winding, putting a resistor external to
the
winding takes away from the amount of inductance you would have if that
was all in the coil -- taken to the extreme, you could say 1 turn of wire
and
a 2.3 ohm resistor is the same as the 500 feet of 16 gauge wire -- from
a DC viewpoint, that would be true, but for the purposes of an inductive
load
with a changing field, they are definitely NOT the same circuit. Of
course it also depends if it is wound on an iron core or air core or ...
Your best bet to meet your requirements as stated would probably be to
find a large transformer with 2-2.5 ohms dc resistance and use that.
There is still the part about liability that you need to make sure you are
covered there -- as another poster said, probably UL, or others.

mikey