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Solar DC Pump voltage drops to 4VDC when turned on

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  • Solar DC Pump voltage drops to 4VDC when turned on

    I have a 284W solar pump (with built in MPPT), connected to 400 Watts of solar (2 strings of 2 x 100Wp 12Volt panels), according to the manufacturer, it can be operate this way, because it has a wide voltage range and has the controller inbuilt. The specified pump head is 30m, I am pumping from a shallow well to a 3000 L tank (total head is 12m). I switched on the breaker yesterday morning at 10am and it ran perfectly, very powerful water delivery, for about 2 minutes, then turned off, never to turn on again, until today.

    When I checked solar array voltage (breaker in OFF position) it is giving me 40Volts (this is within working voltage range of 18-45V), but when I turn on the breaker, voltage immediately drops down to 4Volts. I have checked cabling, connections, debris, but could not find anything.

    The only thing i can imagine is I have somehow burnt the motor out, it would be really helpful to have some other ideas from you who may have encountered a similar situation with DC solar pumps.

  • #2
    When I searched for 284W solar pump the only one that came up was a cheap pump listed as 24V.

    You may have a pump that failed or panels that are not supplying enough power.

    If you have a couple of 12 batteries configure them to 24 V and try the pump to see if its still working.


    • #3
      Even with a shorted motor, the MPPT should keep the panels at about 30V. Having two strings of panels go bad at the same time is unlikely. That leaves a really bad connection from the panels or the MPPT function has gone south. Load test the voltage at the pump with two headlights in series for about a 5A load.