noisy cooling fan

ThomasThomas Solar Expert Posts: 291
I have a cooling fan connected to my array to cool my inverter, it is dioded so that when the sun goes down the fan turns off and leaves the batteries alone. Problem is
during the day there is small surges[most annoying] resulting from my line voltage increasing for some reason.
My MSView software says the line voltage surges from 28.8V to 32V and the amps stay constant.
could this be the result of MPPT in my inverter?:grr:confused::p
Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
2.3kW [10] Enecsys SMI-240-60 micro inverters

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,090 admin
    Re: noisy cooling fan

    How many Amp*Hours of AGM batteries do you have? (12 volt battery bank?)

    It sounds like your AGMs are starting to sulfate/dry out/fail/failing parallel wiring among batteries/etc.... And/or you have a lot of charging current for a (relatively) small battery bank.

    How long does it take for the battery bank voltage to swing from 28.8 to 32 volts? Less than 1 second, a few seconds, or a few minutes?

    Solar charge controllers (sometimes?) appear to have relatively slow control loops and feedback/sample only once every second (or few seconds).

    If you have a lot of charging current and/or a small/failing battery bank, simply the sample/feed back time of a few seconds can let the battery bank voltage rise very quickly.

    You could also have too long of Absorb timer set (or other absorb termination setting) which is overcharging your AGM battery bank.

    Also, if you have an AC Inverter running at the time--It may cause the charge controller to think the batteries are not full (poor battery bank AH capacity can also cause this problem) and not terminate to float correctly.

    And with an AC inverter, they are (for the most part) constant power converters Pin=Pout=Vin*In=Vout*Iout

    So, if you have an issue with constant charging current causing a rising voltage at a battery bank, the AC inverter will start cutting back on in load current (P=V*I, increased battery voltage, decreased AC inverter current) and you will get even more current flowing to the battery bank (causing voltage to rise even faster until the charge controller cuts back on current).

    In any of these cases, if you are using a DC fan connected to the solar array or to the battery bank (not sure--Array?)--A fast changing DC voltage will, for more simple DC fans, cause their speed to "hunt" with the voltage changes. Most of the simple DC fans will settle on an RPM based on the voltage at that moment in time... If the DC voltage moves around a bunch, the fans will keep varying in speed too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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