Dummy Loads

[tedmich]

I had occasion recently to build a 3000w power supply for my Dad so he can equalize the big batteries in his rural home. I found 3x TDK Lambda FPS-1000 units (brand new) on Ebay for $60 each, a fair savings over the $1800 Mouser wanted. Once I figured out how to run them in parallel with remote trimming I hooked up a cheap 100 A shunt with back lit power meter and wired it all up and mounted it on the wall of Dad's battery room.

So I'd like to test it with dummy load, one that looks like one of Dad's batteries: ~0.7 ohms that can handle ~50A / >2kW

I found a bunch of old crusty GE 18" wire wound units on Ebay but I also found a mess of Vishay thick film resistors.

Specifically used LPS 300 units at 10 ohms/300w, for $2.95 each ($48 at Mouser)
Vishay LPS 300L Resistors 10 Ohms 10 LPS300L | eBay
the asking price means when paralleled you'd get the following:
# / price / ohms / wattage
1 / $10.10 / 10.00 / 300
2 / $17.45 / 5.00 / 600
3 / $24.35 / 3.33 / 900
4 / $30.45 / 2.50 / 1200
5 / $36.30 / 2.00 / 1500
6 / $42.00 / 1.67 / 1800
7 / $46.92 / 1.43 / 2100
8 / $51.49 / 1.25 / 2400
9 / $55.61 / 1.11 / 2700
10 / $59.29 / 1.00 / 3000
11 / $62.52 / 0.91 / 3300
12 / $65.31 / 0.83 / 3600
13 / $67.66 / 0.77 / 3900
14 / $69.56 / 0.71 / 4200

probably cheaper as the seller accepts best offers too.

the 5 paralleled / 2 ohm version might be just the ticket to test an iNuke!
Of course you'd want to attach them to something big and heavy, I'm trying to find one of those steel plates the road workers just leave lying around for the 14 units I have on the way...

[techineer]

Here's another idea.... a bit simpler and cheaper.

Go to your local home improvement store or hardware store and look for water heater elements. Most of them are in the 10-20 ohm range. Take a multimeter with you (and show it to the greeter when you come in!) and measure them. Select some that are appropriate and will parallel to get the resistance you need, and mount them in the lid of a 5 gallon bucket. Wire them up and fill the bucket with water, and you should be good for several KW.

http://www.homedepot.com/p/2000-Watt...5120/204219916

[J M Fahey]

And you can take a shower later

[Mick Bailey]

Select some that are appropriate and will parallel to get the resistance you need, and mount them in the lid of a 5 gallon bucket. Wire them up and fill the bucket with water, and you should be good for several KW.

Maybe if you did that in the store you could decide there and then whether to take them or not.

[defaced]

I test welding power supplies sometimes. 250 amps, 10 volts is common. We buy cheap black annealed steel wire to hold heating pads onto some of the parts we weld. I take this wire, maybe 40-50 feet of it, fold it into 4ths, and twist it with a drill. Connect it up, lay it on the concrete floor or suspend it from something, and give it a go. For $6.23 a lb, it's worked pretty well for my uses. McMaster #8870K32. Because it gets red hot, I often have to iterate either diameter or length for a given V/I condition.

I've also talked to guys who make power supplies about what they use. Often, they'll use a carbon pile load. I've never used one, but apparently by varying the pressure of the carbon stack you can change resistance and get a pretty stable load. A little more costly, but a nice tidy unit.