I need a high wattage dummy load

Thread Starter


Joined Feb 3, 2014
I built one here (called Big Dummy);

The two heatsinks came from a junkyard piece of equpment and were already populated with the big transistors, already wired as darlingtons. That was common in high power linear power supplies, 1960's 70's 80's etc.

It uses a pot to set the current. The biasing is set up at the moment to work with about 5v-48v and 0A to 30A.
I'm interested in Big dummy load. Has circuit to look at some pls.:D


Joined Feb 11, 2008
I didn't use a circuit. :) I'll go have a look at it.

The heatsinks have 16 large NPN power transistors (equiv 2N3055) driven as darlington pairs by 16 smaller NPN transistors. Then the 16 emitters are tied to ground through 16 emitter resistors, each is 1 ohm 5W.

That whole array is in parallel; so all collectors, bases and grounds connected together. Then the collector to the red terminal and ground to the black terminal.

To make it conduct there is a pot and a couple of resistors from red to black terminals, making an adjustable voltage. That pot is connected to another NPN base, in "trilington" with the main array so its collector joins their collectors, and its emitter goes to their bases.

The thing is so simple I never bothered drawing a diagram.

It works well for 6v, 12v loads up to about 20v. But I remember grabbing the soldering iron and changing a resistor value on the pot circuit at least once, possibly to test a 24v or 36v high current supply. :)


Joined Jan 20, 2014
Just make it like a standard current limiter from any powersupply.
Then You will have a coarse scale for Your potmeter to determine what load You are to put to test.
And actually, with a wide voltage range too.
Supply the load with a thermoswitch or two to protect Your devices, and you are good to go.


Joined Nov 3, 2012
This is heating element wattage.
You might want to use water cooling, so one choice would be a modified electric water heater using multiple heater elements as power resistors.

You could switch these with some high current Mosfets.
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Joined Nov 12, 2008
I'm find the power load for test battery 48v 100A
I'm guessing you are talking about 4 big lead acid batteries in series???

If so most are specified at a constant current discharge rate of either 25 amps or 75 amps. You will need to test each one separately to get good data on their capacity.

Tell us more about your final objective.


Joined Nov 7, 2013
I may have access to a bunch of these.

This is my private stash.:)

Half are .5 ohm and half are 1 ohm.

The .5 ohm are the ones bracketed together making the pair .25 ohm.

~ 300 watt each.


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