Generator not charging batteries

js_70hjs_70h Registered Users Posts: 5
I've got an off-grid system here using a bank of ~4100Ah of Concorde AGM batteries (16 PVX-2580L units, 258Ah each), a Xantrex SWPlus 4024 inverter, 790W of PV panels, and a Cummins/Onan 5kW gas generator. Out power demand has jumped in the last week or so, and we've discovered that the generator is not charging the batteries. The system will allow the panels to charge up the battery bank when there is sun. Our practice was to use the generator to recharge the batteries when there wasn't much solar input, and that is no longer happening. When the generator is turned on, it will provide power for appliances/lights/etc that are turned on, but it doesn't appear to be charging the bank, even when there is no other draw at all on the generator. We can watch the inverter's battery voltage reading, and it doesn't change when the generator comes on, which it used to.

We've looked through the inverter menus, and can't find anything that changes this. We also can't see any change in the wiring of the system.

Any ideas what might be going on?



  • Solar GuppySolar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: Generator not charging batteries

    I think this sets a new record for undersized charging of a battery bank ... 4100 ah .. holy crap that's big

    It would take your generator running full bore at least 20 hours without any other loads to charge that battery bank ... the PV ... couldn't even do anything for the self discharge let alone help in charging ... 4100ah * 24V that's almost 100,000 watt/hour of storage
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Generator not charging batteries

    Max charge rate on the SW4024 is around 100 amps, so if your batteries are 50% down, it will take over 20 hours to recharge. Your panels supply a max of around 30-35 amps, depending on what controller you have (way undersized for the battery bank you have).

    There should be a place on the inverter menu to see what the charging rate is going to the batteries.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Generator not charging batteries

    As the experts have noted; you don't have enough PV or Gen to recharge that bank. What's been happening is; you've drawn off the batteries for a long time, putting back tiny amounts of current, and the bank has gone down, down, down. This is a kind of torture which batteries don't like.

    What you have to do now is check every battery individually, recharge them one at a time or in a configuration your genset can handle in a reasonable # of hours, let them rest overnight, and see which ones have survived.

    For reference: I have 700 watts of panels that can just keep up with 300 Amp/hrs of battery capacity. That's roughly the same size array as yours, feeding less than 1/10 the bank.
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Generator not charging batteries

    Oops! Sort of puts to rest the notion that bigger is better.

    I have run into this before. A friend of mine scored about a zillion ah's of telco batteries. He was going to run his entire camp off of them,,, which he did. Worked fine for about 4 weekends,, then he kept getting low voltage shut downs. He kept asking,, "what's the deal? I got big batteries,, and the solar panel charges them during the week,, how come after 4 weeks they are dead?"

    There is a reason that the "rules" have evolved,,, they make sense. You can push them a bit, I myself am, under the recommended adult daily dose for my batteries,,, but I know it,,, and I cycle them shallow,,, and watch them pretty closely.

    Get the batteries fully charged as Marc suggests and see what happens. Then maybe wire a number of smaller banks. Charge one,, move on to the next, and so on until you can afford some more Pv or you get a bigger generator charger or both.

  • Dave AngeliniDave Angelini Solar Expert Posts: 6,627 ✭✭✭✭✭
    Re: Generator not charging batteries

    OK the math,

    (16 PVX-2580L units, 258Ah each), a Xantrex SWPlus 4024 inverter

    Looks like 12V 8D's so we really have 2,064 AH if the spec is a 20 hour rate.
    8 in series = 2,064AH

    Definately not sized right unless you have very low usage. You should be able to charge this with the SW4024 if you keep your usage small.

    So, does the SW pick up the generator? Is the AC2 light flashing?

    when you say the gen powers the lights how do you know that? Do you hear the transfer switch after 30 seconds?

    For now I would push the defaults button on the front panel (enable it) You do have a manual? They are on-line at X

    Good Luck!
    "we go where power lines don't" Sierra Nevada mountain area
    E-mail [email protected]

  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Generator not charging batteries

    Anyone with a Solar Renewable Energy System of any useful size should have a DC Clamp Meter in there tool kit, there not expensive about $45 even in Spain and UK.

    It is a quick and simple way of checking Solar Output from PVs .Charging output Dc from your inverter, without dismantling wires . I can check my full array and inverter output in a couple of minutes.

    Plus most of these DC Clamp Meters are also Digital Multimeters

    No Brainer with the cost and longevity of batteries being a major $$$ drain.
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