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Load testing

Discussion in 'General Electronics Discussion' started by Purepower, Mar 24, 2017.

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  1. Purepower

    Purepower

    2
    0
    Mar 24, 2017
    Hi guys,

    It's been well over a decade since I've had to think physics or electronics, and honestly never used it at all after studying.

    Spent most of the day wracking my brain trying to pull something useful out and thought I'd turn to forums!

    Using 12v, 75Ah sealed batteries (I've got over a hundred to test :/ ) and 'currently' using a 100A load tester to test how healthy the batteries are. The thing is, I only need to draw 2A from them at maximum use.

    At the risk of sounding like an idiot, surely drawing 100A to test them is wrong? The vast majority of them have failed. Assuming it is wrong, what's the best / easiest way to test them under 2A load?

    Sorry if this is in the wrong section!
     
  2. AnalogKid

    AnalogKid

    2,520
    718
    Jun 10, 2015
    The battery datasheet should have a number for the peak current allowed. Due to different internal constructions and materials, some batteries are specifically designed for very high discharge currents, and some are not.

    Ohm's Law gives you 6 ohms. Watt's or Joule's Law gives you 24 W. Therefore, use a 6 ohm resistor rated for a minimum of 50 W, such as six, 1 ohm 10 W resistors in series. A new fully charged battery should stay above 10 V for approx. 40 hours.

    For a more accelerated test, consider a 7.5 A load. This is C / 10, or 1/10th the current of the amp-hour capacity (C) rating, a common test condition for rechargeable batteries. As above, for long term reliability be sure the resistor or resistor bank is rated for at least twice the power your are dissipating.

    From there you can build or buy an electronic timer and a voltage monitor so the batteries discharge overnight and the monitor system holds the time it took to discharge below a setpoint.

    ak
     
  3. Purepower

    Purepower

    2
    0
    Mar 24, 2017
    Thanks alot mate. It's been so long since i touched on anything, I was starting to wonder whether I kept all my old textbooks. Must admit, reading through the topics here, I wish I kept up with it.
     
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