Cant put load on system

machineman
machineman Solar Expert Posts: 129 ✭✭✭
in Off Grid Solar & Battery Systems #1
Just got up to my cabin and seems I can't put a load more than a few lights on my system or it will crash. Voltage is good >26VDC. If I turn on the fridge the voltage drops to zero and the inverter shuts down. I have a Magnum 4024 inverter and 8 6V batterys totaling 440 amp hours at 24VDC. Is my inverter dead or my batterys?

Off Grid Cabin, 24V 440ah 6V GC battery bank, Xantrex MPPT60-150 CC, Magnum MS4024 inverter-charger, >1200w Solar bank

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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #2
    Re: Cant put load on system
    machineman wrote: »
    Just got up to my cabin and seems I can't put a load more than a few lights on my system or it will crash. Voltage is good >26VDC. If I turn on the fridge the voltage drops to zero and the inverter shuts down. I have a Magnum 4024 inverter and 8 6V batterys totaling 440 amp hours at 24VDC. Is my inverter dead or my batterys?
    Sounds like your batteries have high internal resistance and/or low capacity. Or else you have a very bad wiring connection somewhere.

    If the batteries were left too long without charging they will be sulfated and probably not recoverable. At least check the SG and the water level to see if you have an obvious problem like one bad cell in your battery bank.
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Cant put load on system

    The Voltage drops to zero measured where and how? AC Voltage? DC Voltage?

    You need to put a meter on the batteries and see if they are actually dropping or if the inverter input is showing low Voltage; it could be bad wiring between the two causing excessive V-drop.

    If it is the AC output that just drops then we need to know if the inverter is staying on or a fault is triggering it to shut off. If it is on and has zero AC output Voltage under load then the inverter has died. If a heavy load is triggering a fault shut down of the inverter you have to determine what the fault is.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #4
    Re: Cant put load on system

    Could also be bad electrical connections to the batteries (loose/dirty/corrosion)--If it is the DC voltage collapsing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • machineman
    machineman Solar Expert Posts: 129 ✭✭✭
    #5
    Re: Cant put load on system

    I see the voltage drop to zero on my trimetric and the inverter shuts off probably because it reaches the Low voltage cut. The flooded batterys are over 5 years old and my water maintenance hasn't been that good. But I only visit this place one weekend a month so the solar has been keeping them charged while Im gone. If I measure the voltage on each battery it ranges from 6.5 to 8.0 volts. I have 2 banks of 24V in parallel and I've tried each bank by itself hooked up to the inverter and same issue. So if its the batterys then more than one of them is messed up. Or the inverter cant handle a load anymore than a few light.

    Off Grid Cabin, 24V 440ah 6V GC battery bank, Xantrex MPPT60-150 CC, Magnum MS4024 inverter-charger, >1200w Solar bank

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Cant put load on system

    Reading 8 Volts on a 6 Volt battery is a clear indication of a problem: it means one of the batteries in that string is very low which forces the Voltage on another (or all others) high. 8 Volts indicates a possible shorted cell.

    Flooded cells = get the hydrometer out and check each one for SG. I suspect you will find significant imbalance on more than one.

    Inverters don't suddenly drop from being able to handle full output to being able to handle only partial output. Batteries do. Most likely given the age and symptoms the whole bank is scrap metal.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #7
    Re: Cant put load on system

    6.5 to 8 volts on batteries--Something is wrong. The 8 volt battery may have, for example, an open cell (if this is voltage during charging) and the 6.5 volt battery near dead (or 1/2 charged--don't know from what you have here).

    Or, the 6.5 volt battery may have a shorted cell--Together they add up to 14.5 volts volts--A very reasonable charging voltage. But the 8 volt battery would be getting "way over charged" (equivalent to 16 volts on a 12 volt battery bank).

    You may have to mix/match batteries to get a single string that will keep you going for a while. If you had a DC Current Clamp DMM, you could tell if the problem is an open or shorted cell (almost no current flow, or a lot of current flow).

    I have "cheated before" by setting a DMM to 2 volt (or 200 mVolt scale) and measure the voltage drop across a battery interconnect cable. The voltage drop will be proportional to the current flow--And if you have the same length jumper in different strings--The are your "current shunt/power resistor" to measure voltage drop on between string.

    A cheap hydrometer (if you can get one locally at an auto-parts store--a glass float version if they have it) will help you weed out bad cells/batteries too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • machineman
    machineman Solar Expert Posts: 129 ✭✭✭
    #8
    Re: Cant put load on system

    Measured the SG. 2 Banks of 4 6V batterys in parallel. I've tried both banks separately and same voltage drop out issue under load. Clearly there is one bad battery in bank 1 but bank 2 has same issue if isolated from bank 1.

    Bank1

    1180
    1150
    1250

    1230
    1230
    1230

    1235
    1235
    1245

    1240
    1235
    1235


    Bank 2

    1260
    1225
    1250

    1265
    1270
    1260

    1250
    1230
    1225

    1265
    1250
    1265

    Off Grid Cabin, 24V 440ah 6V GC battery bank, Xantrex MPPT60-150 CC, Magnum MS4024 inverter-charger, >1200w Solar bank

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Cant put load on system
    machineman wrote: »
    Bank1

    1180
    1150
    1250

    That battery is in trouble. It has a problem with that first cell.
    1230
    1230
    1230

    1235
    1235
    1245

    1240
    1235
    1235

    These three are far from charged with minor cell imbalance.

    Bank 2

    1260
    1225
    1250

    Another battery in trouble; the middle cell is very low compared to the first.
    1265
    1270
    1260

    Best battery in the bunch, and it shows the others are dying because this one clearly is not and they were all part of the same charge routine.
    1250
    1230
    1225

    Another with significant imbalance.
    1265
    1250
    1265

    Second best, and as before indicative of over-all failure.

    Have you got a 12 Volt charger you can use to try and bring pairs up with? The total imbalance for Bank 1 is 0.070 and for Bank 2 0.045. Bank 1 should not be charged as a unit if possible, and Bank 2 is pretty dicey.

    Don't get your hopes up.
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  • machineman
    machineman Solar Expert Posts: 129 ✭✭✭
    #10
    Re: Cant put load on system

    I've tried isolating Bank 1 and only running on Bank 2 and have the same issue. I know the batterys are tired but is Bank 2 alone bad enough to cause this issue? I want to troubleshoot this thing so I know what parts to bring up next time I visit. Still not convinced yet that the invert doesn't have a problem.

    Thanks,

    Off Grid Cabin, 24V 440ah 6V GC battery bank, Xantrex MPPT60-150 CC, Magnum MS4024 inverter-charger, >1200w Solar bank

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: Cant put load on system
    machineman wrote: »
    I've tried isolating Bank 1 and only running on Bank 2 and have the same issue. I know the batterys are tired but is Bank 2 alone bad enough to cause this issue? I want to troubleshoot this thing so I know what parts to bring up next time I visit. Still not convinced yet that the invert doesn't have a problem.

    Thanks,

    Use Bank 2.
    Check Voltage at battery terminals and at inverter input.
    Load inverter with something it can handle and recheck Voltage at both points.
    Increase load and check Voltage at both points again: you're looking to see if the two points change equally or if the inverter input falls off more drastically.
    Load the inverter until it faults while watching Voltage at batteries. Do the same thin while watching Voltage at inverter.

    If the inverter is shutting down for low Voltage then when it does so the input V at the inverter (and at the batteries if it isn't due to wire loss) should actually be low as read by the DMM. If it isn't, the inverter is not 'interpreting' the Voltage correctly and is at fault.

    At this point I don't want to say this is the third Magnum failure I've heard about in the past three months.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #12
    Re: Cant put load on system
    machineman wrote: »
    Still not convinced yet that the invert doesn't have a problem.

    The inverter may well have a problem, but if it does, then you have two different problems, because your battery bank is frigged.
    The only way to properly check your inverter is with a known good battery bank, and that's something you unfortunately do not have.
    I strongly suspect that when the batteries are replaced you'll find the inverter will work fine.
    I went through basically the same thing when my 3 parallel strings of 11 year old batteries were finally dieing. Light loads were still fine, but anything heavy sagged battery voltage badly, and of course the inverter shut down, as it should.
    Wishing you best of luck.
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  • Skyko
    Skyko Solar Expert Posts: 121 ✭✭✭✭✭
    #13
    Re: Cant put load on system
    Cariboocoot wrote: »

    At this point I don't want to say this is the third Magnum failure I've heard about in the past three months.

    I rather hope it isn't an inverter problem as I also have just installed a new Magnum MSH4024M and would hate to think it unreliable. It *seems* well made and is silent.
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