Inverter/Charger not charging due to Battery Voltage

ashton
ashton Registered Users Posts: 3
in Off Grid Solar & Battery Systems #1
Hello, first time using the forums here.

I had a question regarding charging my off grid battery system. I have a 24v battery bank that I used all winter to power my house. It is recharged with a generator through a magnum magnasine inverter/charger. The inverter reads the voltage and determines the battery state of charge as well. Thus worked fine until I added solar panels this summer. The panels run through an outback flexmax60, sand the voltage output from the charge controller typically ranges around 30v. This seems to confuse the inverter, causing it to enter float charge mode even if the state of charge reading on the batteries are low.

even after disconnecting the solar panels or at night the voltage remains high enough to cause the generator to not charge the batteries. The state if charge is now below 50% but the voltage is around 27 when the panels are off. Which reading should I use? Thank you for any advice.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Inverter/Charger not charging due to Battery Voltage

    Welcome to the forum.

    Usually one uses either solar or an AC powered charger. When you use both some confusion is bound to arise. In this case it is the Magnum getting confused because it doesn't know about the charge contribution from the solar panels.

    The question is: does the Magnum charge based on Voltage or on its own internally calculated (and now inaccurate) SOC number? I'm not sure if the Magnum uses (or can use) an external shunt for measuring SOC, but if it does the charge controller output should be on the inverter side of the shunt so that its output to the battery is included.

    What you really need is correct measurement of the SOC. Voltage is not a very good indicator of this, but Specific Gravity is (providing these are flooded cells you can dip a hydrometer in to).

    You say Voltage is around 27. Is that with the generator running or with all charge sources off and the batteries just sitting? If it is, that's rather high for a 24 Volt system at rest. If it's with the gen on it is a normal Float Voltage for a 24 Volt system. But you don't want to be running a generator to maintain Float; it's very wasteful.
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  • ashton
    ashton Registered Users Posts: 3
    #3
    Re: Inverter/Charger not charging due to Battery Voltage

    Thanks for the reply. That gives me a place to start. The magnum inverter does use a shunt and I have the solar on the wrong side. I will make that switch.
    These are gel batteries so no hydrometer.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Inverter/Charger not charging due to Battery Voltage
    ashton wrote: »
    Thanks for the reply. That gives me a place to start. The magnum inverter does use a shunt and I have the solar on the wrong side. I will make that switch.
    These are gel batteries so no hydrometer.

    Oh dear. GEL are not a good choice for RE use. Not being able to check them isn't the only reason. They are very picky about charging and easily damaged. Only a few of them are recommended for this kind of application.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: Inverter/Charger not charging due to Battery Voltage

    Check the specifications for your GELL batteries (mfg. website, etc.).

    In the US, most GEL batteries appear to be rated for around C/20 Hour (5%) maximum rate of charge (i.e., 200 AH battery bank, 10 amps maximum rate of charge). Higher charge rates can cause gassing, which makes permanent bubbles in the GEL (as I understand)--Which reduces capacity of the battery.

    For solar and generator charging, it is usually nicer to have faster charging (typically 10% to 13% rate of solar charging) to quickly and fully recharge the battery bank when you have limited hours of sun per day.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ashton
    ashton Registered Users Posts: 3
    #6
    Re: Inverter/Charger not charging due to Battery Voltage
    Cariboocoot wrote: »
    Oh dear. GEL are not a good choice for RE use. Not being able to check them isn't the only reason. They are very picky about charging and easily damaged. Only a few of them are recommended for this kind of application.

    Oops, Agm not gel. That was a brain skip on my part. Hopefully those are better (universal battery ub4d to be exact). It has been a while since I bought those and I got mixed up.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    Re: Inverter/Charger not charging due to Battery Voltage

    AGM are very nice lead acid batteries--They can be damaged by over charging (too high of absorb/float charging voltages, too many hours of elevated charging voltage, or equalized like a flooded cell lead acid battery).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Inverter/Charger not charging due to Battery Voltage
    ashton wrote: »
    Oops, Agm not gel. That was a brain skip on my part. Hopefully those are better (universal battery ub4d to be exact). It has been a while since I bought those and I got mixed up.

    Very much better than GEL! They can take a lot more current in/out and are only sensitive to Voltage. Although looking at the specs it gives a pretty wide range of 14.5 to 14.9 Volts. Maximum charge rate appears to be 30%.
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