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Old 01-21-2013, 04:30 PM   #1
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Default Drawing 20 Amps for device testing

I'm creating a test system for a device that will measure amperage drawn from a 120 Vac source. The device basically passes on the power source from the wall and uses current transformers to read how much current is flowing through mains to some piece of equipment connected to it.

I'm looking for ideas on how to draw 20 Amps off the equipment outlet of the device for a small period of time (less than 5 seconds). What was done in the past was to use a couple heaters or a bunch of light bulbs in parallel, but I wanted to see if there was a more compact solution that didn't have as high of risk for break down.

I tried looking for some current shunt resistors and combinations of transformers and resistors to do this, but I couldn't find something that worked out at least off the shelf.
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Old 01-21-2013, 05:58 PM   #2
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Do you want something to limit current?

If so, then your best bet is either something like a set of space heater elements - to limit current to 20 A, you'd need about 2.4 kW of heating elements.

If heat is a problem, then you can use magnetic ballasts like are used in fluorescent lights, but you want higher power - so something like sodium or industrial metal halide lighting. A ballast designed to run a 1 kW sodium (or halide) lamp off a 240 V mains supply will provide about 10A of short-circuit current when connected to a 120 V supply. 2 of those in parallel will provide you with about 20 A of short-circuit current. (Note the above example needs a "reactor ballast" (common in Europe) rather than the usual US style ballast which won't work. However, you might be able to find one or two.
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Old 01-21-2013, 07:40 PM   #3
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Well, amazingly enough Dangerous Prototypes had a design up just this morning to do exactly what you're looking for:
<EDIT: Never mind, that's DC only. The circuit design also only supports 7A, but 20A would be possible with minor changes>

I'd go with an electric water heater element. A 2.0KW/120V element would run about 17 Amps, and it'll be pretty rugged and pretty cheap. If you leave it bolted into a hot water tank, you could run it for hours and heat water for the sinks in the bathroom at the same time. If not, put it in a steel pipe to protect it with a fan mounted in one end to exhaust the heat, and don't run it for more than a few seconds at a time...

Last edited by FrankSchwab; 01-21-2013 at 07:43 PM.
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Old 01-22-2013, 03:17 PM   #4
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For our datacenter power system testing we have these huge heater units an wheels with fans. There are switches on it to turn on more of the elements to allow you to increase the current.
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Old 01-22-2013, 04:39 PM   #5
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Add there anything with 2400W or similar power draw.
Air compressors have high peak current, when you turn it on, it can draw 3 times higher current for few seconds.
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Old 01-22-2013, 05:21 PM   #6
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two of these will do

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Old 01-22-2013, 05:48 PM   #7
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