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I feel like I have a simple question that hopefully can be answered quite quickly. I have a 24V power supply that is supposed to achieve a max output of 200W. Recently, I have reason to believe that the supply has gone bad, and rather than damage anything down-line from this supply, I want to test the output with a dummy load.

Currently, I have just been making a dummy load by wiring a bunch of resistors in parallel, which gives me one net resistance of 13ohm (~45W of power). Ideally, I would like to make a dummy load that will cause the supply to consistently output ~80W of power. I feel like the bundle of resistors is really cumbersome, and that there is an easier way to do this, I am just unsure because I am a novice.

If anyone knows an easier way to make a dummy load that can undergo up to 200W, and is less cumbersome that would help me out a lot. Thanks!

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  • \$\begingroup\$ Heating elements from clothes iron, owen, underfloor heating, or buy some resistive wire. \$\endgroup\$
    – user208862
    Commented Feb 20, 2021 at 3:01
  • \$\begingroup\$ Several different power resistors that you can combine in series and parallel as needed. If you get 500 or 750 W resistors, they will not get TOO excessively hot when you test the supply. An example is the TE connectivity TE series of resistors: te.com/commerce/DocumentDelivery/… \$\endgroup\$
    – user57037
    Commented Feb 20, 2021 at 3:08
  • \$\begingroup\$ Maybe heater from old car do the job. \$\endgroup\$
    – user208862
    Commented Feb 20, 2021 at 3:09

3 Answers 3

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12 volt halogen light bulbs are cheap and have cheap fittings. Two 50 W bulbs in series gets you to 24 volts there's a load of 100 W.

enter image description here

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  • \$\begingroup\$ Thanks! I have two 55W bulbs readily available! \$\endgroup\$
    – Dayman
    Commented Feb 19, 2021 at 23:51
  • \$\begingroup\$ this probably will trip the supplies short circuit protection, check the resistance of the lamps when cold. \$\endgroup\$
    – Jasen Слава Україні
    Commented Feb 20, 2021 at 2:23
  • \$\begingroup\$ Except they are 10 times this power when cold and may trip the OCP \$\endgroup\$
    – D.A.S.
    Commented Feb 20, 2021 at 2:23
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    \$\begingroup\$ I used this to test a 24V motor drive board I designed. A couple of incandescent car headlights worked just dandy as a load. But the thing was controlled to a current and voltage both, so when the commanded voltage wasn't yet reached, it'd go into current limit. A typical supply may well trip, unless you use lots of little bulbs and switch them in one by one. \$\endgroup\$
    – TimWescott
    Commented Feb 20, 2021 at 4:57
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    \$\begingroup\$ The two 55W bulbs I have are car headlight lamps. I was able to use this as a test without tripping the short on the supply. The supply does not have separate controls for current and voltage. From my understanding, it outputs a constant 24V and will adjust the current automatically. \$\endgroup\$
    – Dayman
    Commented Feb 20, 2021 at 21:27
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For testing high power low voltage supplies I use a cheap inverter connected to the appropriate number of mains voltage quartz light bulbs. This forms a compact dummy load you just need to be careful about how you mount the bulb holders. I have them screwed to a piece of plywood.

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4 ohms will get you about 144 watts dissipation, so use that much steel wire strung between nails on a board as a resistor.

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    \$\begingroup\$ Better recheck that value. It’s too low \$\endgroup\$
    – D.A.S.
    Commented Feb 20, 2021 at 2:35

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