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EEVblog #102 – DIY Constant Current Dummy Load for Power Supply and Battery Testing
Dave grabs a few junkbox parts and builds a useful constant current load for switch mode power supply, battery testing, and other applications.
Video Rating: 4 / 5
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Something like this should be easy to? scale up by increasing the number of MOSFETs fitted and by using fan-cooled heatsinks. I use a CPU heatsink from an Xbox 360, although it’s not fan-cooled, but I don’t need to dissipate 150W like you do! You may have to get creative when clamping a CPU heatsink, though. Mounting back-to-back might make it easier (I have a spare, unused MOSFET under mine, so each TO220 epoxy block faces the other one’s metal tab, with legs sticking out opposite ends).
Update: I’ve now built one. Meter from eBay, multiturn pot from eBay, IRFZ44 and other components from spare parts, all built into an old British Telecom NTU 11A case (and using its original PSU). Beauty!
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Useful, I think I’ll build one of? these.
I’m surprised not to find anything like this on eBay.
Hi Dave,
I need to variably load my small wind? turbine while testing it in a wind tunnel. My electronics skills are not that good, I am a simple aerodynamics engineer. Could this little device be scaled up to dissipate about 150W?
Hi Dave, I put together one of these on a? breadboard using similar components, but the transient response seems to be pretty bad. Also, there is steady state error. Any ideas why?
Excellent…might have to put one of? these together.
What are the values for the? resistors?
10 Ohms, 1%, and 1 W?
What is the value? of the capacitor?
I built something like this a few years ago. Micro-controlled. Only good up to 50W though. This year I want to construct a larger load bank with which I can test large power supplies up to 1200W. It will consist of 6 individual loads each capable of 200W and current up to 40A. The tricky bit is that all electronic loads in the bank will need to be floating/isolated for maximum flexibility. This? means transformer-coupled power to the driver circuits and opto-isolated control lines.
Hi Dave.
Would it be possible to use an op amp and a logic mosfet to give a variable constant current source rather than a load? I have built a similar circuit with the LM317 and fixed resistors selected by a rotary? switch to give me 10mA, 20mA, 30mA, 40mA etc. But it would be nice to have a completely variable current source from 1mA up to 1A perhaps?
Cheers, John.
I’ve found out on how? to get the LCD cx101b to work reading millivolts even though it’s one millivolt offset, I think is due to the lcd +-1%.
Hi Dave I’m trying to use the CX101b LCD but it’s a pain in the ass to configure, can you tell me what resistor values you use to get it to read 1999???? I know that your schematic values are not the same as? what you use.
Thanks.
What’s the bypass cap for? on the LM324?
Correct, that’s what the original board does. Micro with constant? current/resistance/power and logging capability.
Pretty awesome little project. I want to make one but I think I’d like to “crank it up a notch” and have a? microcontroller involved that varies the current, takes measurements and spits them out back to a computer. Press a button, capture data and graph
. The original use of your board seems to do something along those lines where the uC controls the current, unless I misunderstood.
of course … all you need is an opamp like an lm358 that controls a large n-fet, like an IRFP460, source grounded via? a current measuring shunt. you feed the voltage from the shunt to the inverting input and a reference voltage to the noninverting input. you connect the positive of the DUT to the drain of the fet and the negative to ground. you can power the circuit from a 9v battery, the whole device draws only a couple mA.
Aint there no way to have a variable “artificial” load without the need of power resistors? in series?? some semiconductor that burns all the heat just into the cooler and not into the power resistors?
Great Idea Dave!
I want to build one!
A request:
Please add 17:17 to the next “how to entertain a geek Highlights!
Especially the part? about doing it with “intelligent control”
Thanks a lot Dave.
What? is the use of the extra op-amp?
Why does the MOSFET need to be logic-level?
DaveCAD ?
Where can i download it?
How to determine the require gate voltage in order to obtain 1v source voltage?
is there? any source available?
How many ampere is the max? discharge for this design?
Hi! I need to build a dummy load for a PC power supply that can draw up to 100A and another unit that can draw up to 30A that are adjustable in steps of 10A and 5A respectively. I know my basic electronics but I would have absolutely no idea on where to start with this. I have heard MOSFETs are very scalable and can achieve this? with adequate cooling, but I need a circuit diagram or something so I can make it. Please help!