One half (side) of battery bank low?

StorminNStorminN Registered Users Posts: 12
Hi there,

I looked at a friend of a friend's system the other day that's having low-voltage problems. System has eight L-16's, wired in series-parallel for 12V nominal, with a Trace C40 and an Outback VFX2812.

The batteries are arranged such that all the negative posts on the far left are tied together in parallel, and the main negative lead comes in on left side at the rear... the batteries are wired in series left to right, so all the positive posts on the far right are tied together in parallel, with the main positive lead exiting from the front right.

The voltage readings on the batteries were interesting... the four batteries on the left side of the battery bank had close-to-normal readings... 6V±... but the four batteries on the right side of the bank (the batteries with their positives tied together and main positive cable going to the inverter) had the low readings... 4V±.

When I got there, the C40 was blinking red / green, which means it's trying to equalize, correct?... the bank voltage was 10.5V. There wasn't much sunlight, and when I tripped the disconnect coming from the PV's (eight Siemens, look like 75W panels from afar) and measured the no-load voltage from the PV's, it was 16V+. Closed the breaker again, and the voltage dropped back down to battery voltage, about 10.5V.

Started the generator (Honda EX6500) and the Outback recognized it and started charging at about 75ADC, which dropped to about 56ADC after a bit... about 8.5A in on the AC line (generator is only wired in on one leg, no autotransformer). The owner ran the generator for about six hours, up to ~14.1V with generator running. The next morning (six hours later), she said the bank voltage was back down to 12.1V. She ran the generator again for a about 40 minutes, then ran into generator problems (another story, see below)

SO... my question is... when batteries start to fail - go bad, lose a cell, etc... has anyone else seen this pattern of the batteries on one side of the bank all being lower than the batteries on the other side of the bank, or could this be some other issue... cabling, connections, etc.? All the cables and connections look good, no corrosion present, everything seems tight. Right now I'm thinking of removing the four worst batteries and rewiring the good ones, so the system is usable, albeit with less capacity.

The story with the generator is that it ran fine for six hours (into the night), then the owner turned it off, and restarted the next morning after seeing the bank voltage was down to 12.1V... owner says the genny ran for 40 minutes or so and then "got really loud", so she immediately turned it off. I went to take a look at it later that day, and it appears the governor for the generator is failing... start the genny up, and it tries to run at full rpm. This is a Honda EX6500 with a propane conversion. There's a factory Honda vacuum actuator that controls the throttle, the vacuum going to the actuator is controlled by an electric solenoid. I tested for power going to the solenoid, got power there. I tested for vacuum going to the solenoid and vacuum coming from the solenoid, got vacuum both places. There's an older EX5500 there also (parts machine), I tried swapping the identical parts (solenoid and vacuum actuator) from the EX5500 to the EX6500, and it still didn't work. It seems as though there just isn't enough vacuum to hold the governor... if you push it closed by hand, it will hold it for a little bit, but then it slips and the genny overspeeds. If you pull a vacuum manually on the actuator, it will hold it, so I don't think there's a leak there (besides, I took the actuator apart and the diaphragm looks good, and besides that, I swapped the whole actuator out with another actuator and it still didn't work. My hunch is that the mechanical governor is broken, and the vacuum governor isn't designed to hold it on its own... the mechanical governor coming out of the side of the motor is designed to push on the back of the vacuum actuator arm. Anyway... I was stumped, I'm not a strong generator guy... so she's going to bring it to the local Honda dealer.

Now if I can just figure out what to do with the batteries...



  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: One half (side) of battery bank low?

    I would charge and test each battery separately.

    Do like you said, take the four weak ones out and test them first.

    Batteries dead/weak on the same side would lead me to one or more got hot and damaged its neighbor.
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: One half (side) of battery bank low?

    Connecting on the "diagonal" will extend the life of the batteries by helping share the loads. see :
    What you described, if i understood it, should be good.

    Lots of batteries in parallel, is "not desireable"
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: One half (side) of battery bank low?

    The very first thing I would do is to test each cell with a good hydometer to establish that there are no bad cells. After that, I would charge and eq each battery or pair of batteries if you only have 12volt charging capability. Once all the batteries were fully charged,, I would wire them diagonally as Mike suggests (Or some other way that ensures that the loading/charging is as equal as possible on every battery). As you wire them back together,, I would pay particular attention to the quality of each cable/connector assy.

    Finally I would monitor the system performance for the next several months to see if any of the effected batteries were damaged.

  • rplarryrplarry Solar Expert Posts: 203 ✭✭
    Re: One half (side) of battery bank low?

    Just out of curiosity how old are the batteries? If she dosen't know, then you can look at the date code stamped into one of the terminals on each battery. A=January B=February etc. Then there will be a number which will lndicate the year of manufacture, ie a battery with the code L9 would be November 1999. If the batteries are too old then they may be beyond recovery, or maybe you will get lucky and they will recover. The age of the batteries will tell you alot.
  • RCinFLARCinFLA Solar Expert Posts: 1,479 ✭✭✭✭
    Re: One half (side) of battery bank low?

    Batteries can fail toward 'open' state or 'leaky' state. A battery with a cell with high/moderate leakage will usually take other good batteries out whether series or parallel connection.

    Open or high resistance battery is usually positive plate grid corrosion where there is high resistance connection from lead plate and terminal grid. Leakage is usually plate separator failure or lead/ lead sulfate particulates collected at bottom of battery finally pilling up until it reaches bottom of plates creating leakage/short.

    Definitely taking a specific gravity measurement is best. Doing a load test will show a high resistance (open) battery.

    My experience, which might just be random draw, is sealed batteries usually fail toward open where flooded cells fail toward cell short/leakage.
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