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I have a 1440VA (980W) Uninterruptable Power Supply (UPS) which I bought a while back to protect my computers from power fluctuations and possible outages. Recently the battery failed and so I acquired a replacement. The replacement battery came with instructions saying that after installing the battery I need to recalibrate the UPS so that it learns the total discharge time of the new battery. The procedure for doing this involves:

  1. allowing the battery to charge for 24 hours,
  2. applying a 30% load to the UPS,
  3. unplugging the UPS from the wall, and
  4. allowing the battery to completely discharge while powering the load.

Performing this procedure is apparently a condition of the warranty on the battery. I'd like to perform the procedure, but the problem is I do not know what to use as the test load. I obviously do not want to have my computers plugged in because when the battery runs out at the end of the test, they will crash hard, the same as if there were no UPS and the power failed. So I guess I need something that will consume about 300 watts of power that will not harm the UPS electronics and is not itself harmed by a power failure scenario.

What would be suitable to use for a test load?

My first thought was maybe a small heater of some sort, but I think most heaters draw too much current and I think that might be bad for the UPS. However, I think I might have a couple of halogen construction lamps in my basement; is that safe to use as a load? Anything else I should consider?

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  • \$\begingroup\$ 30% then a load of about 300W that is constant... \$\endgroup\$
    – Solar Mike
    Commented Mar 21, 2020 at 5:56
  • \$\begingroup\$ @SolarMike right, I got that part. My question is, what device can I plug into my UPS safely that would consume the 300W? \$\endgroup\$
    – Brian Rogers
    Commented Mar 21, 2020 at 6:01
  • \$\begingroup\$ @downvoter, Would you care to comment on how I could improve my question? \$\endgroup\$
    – Brian Rogers
    Commented Mar 21, 2020 at 18:04
  • \$\begingroup\$ I'm also curious about the downvote, can't see any problems with the question really \$\endgroup\$
    – pipe
    Commented Mar 21, 2020 at 18:14

1 Answer 1

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Heater or halogen lamps are a very good candidate. If you are worried about accuracy, you should find a way to measure the power they actually draw, if you have a multimeter it is not that hard since those are purely resistive loads.

Another candidate is the good old incandescent lamp, you probably would need two or three of those.

The "best" way to do this, as in how a professional would do it, is using a rheostat rated for at least 300 W. Those are basically big chunky variable resistors that can dissipate somewhat high loads, but I guess the price would be too high.

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  • \$\begingroup\$ I'm not so much worried about accuracy as I am about plugging in a load that the UPS is not designed to handle. Sounds like I might have been overthinking this a bit. Using lamps should work fine then for my purposes. I appreciate your answer. \$\endgroup\$
    – Brian Rogers
    Commented Mar 21, 2020 at 18:03
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    \$\begingroup\$ Watch the cold resistance of the lamps. The resistance will be very low when cold and cause an initial switch-on surge. Switch the lamps on one at a time and you should be OK. \$\endgroup\$
    – Transistor
    Commented Mar 21, 2020 at 18:29
  • \$\begingroup\$ @Transistor Thank you for the tip. If that is a concern I could plug the lamps into something else first to let them warm up for a few minutes and then quickly move them over to the UPS. \$\endgroup\$
    – Brian Rogers
    Commented Mar 21, 2020 at 18:33
  • \$\begingroup\$ Nope, you won't be fast enough. We're talking about a few cycles of the mains for filament to heat up and cool down. \$\endgroup\$
    – Transistor
    Commented Mar 21, 2020 at 18:35
  • \$\begingroup\$ @Transistor oh wow, I did not know the filament would cool that quickly! \$\endgroup\$
    – Brian Rogers
    Commented Mar 21, 2020 at 18:36

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