16 Nov
2004
16 Nov
'04
11:57 a.m.
Ok for the ones of you that didn't get it I was being sarcastic. That's why the
smiley at the end of the message. I just wondered what the reaction to trying to find a
.0333 Ohm 750 Watt resistor would be. FWIW I once made such a resistor out of paralleled
incandescent heaters when I was in a small town in Virginia that didn't have anything
other than a small town hardware store. IIRC it took about ten or eleven heaters in
parallel to get a low enough resistance.
Incandesent bulbs are a good idea but you have to be careful. Their resistance
isn't linear and varies widely depending on the voltage. That makes them dammed
difficult to use accurately. The same applies to the heaters that I used but luckly I had
a GOOD ampmeter and voltmeter.
Joe
At 12:30 AM 11/17/04 +0000, you wrote:
OK I just
picked up some computers with 150 Amp 5 volt supplies. Now
figure out the necessary resistrance and wattage and go find me a
resistor :-)
Now what I'd do there is very simple...
6V car headlamp bulbs tend to have 36W filaments, and double-dippers with
2 36W filaments are not uncommon. For short periods (like testing PSUs)
you could run both filaments together. And light bulbs approximate to
constant current devices, so I would guess they'd take 6A (each filament)
from a 5V supply too. Or thereabouts.
I'd normally test a PSU at around half its rated current, so around 75A.
Each bulb (both filaments) takes 12A, so use half a dozen of them. And
yes I do keep such bulbs in stock for testing such PSUs (my I2S image
processors have such a PSU module for each crate...)
-tony