advice on what to do next

martinf
martinf Registered Users Posts: 5 ✭
in Off Grid Solar & Battery Systems #1
So, please excuse my lack of important facts when describing this system....
I'm helping out a friend who's got a cabin off grid. He's got a small diesel gen a solar panel of about 8x8, a battery bank of rolls wired series parallel, a xantrex MX60 solar charger and two xantrex inverter/chargers....sorry don't know the models other than to say they are like long horizontal shoe boxes with about eight LEDs Ina row that come on red then green if things are good.

Here's what happened: his system went down while he was gone. I went to look at it. The inverters had powered off I am assuming because the voltage was so low. He had told me that he thought one of the batteries was bad, so I separated then and load tested each one. All were at 5.5 volts and held steady at 5.2 with a 6 volt load tester on it for one minute. One battery, when checked this way went down to 3.8. I assume this battery has a bad cell.

Now I know about not replacing one battery in a bank, but this guy is getting grid power down his road in a year and there's no way he as gonna buy 8 new rolls or even cheaper ones. But he does need alt power for this next year, so I installed one new battery of the same amp hr and size, L16.

But, heres the problem...with this new battery in place, the inverters wont power up. When i flip off the two main breakers and thwen back on, the inverters go thru their initial check with red lites coming on scrolling thru to green...and thwen they shut off.

The mx60 shows its stuffing power into the batteries (im getting a 6.8 volt reading on the cells). I thought maybe theres not enough power yet in the batteies, so i cranked up the generator. But, with thwe gen running the inverters still wont stay on.

Questions....
Does the charger part of the xantex inverters function even when the lights tuen off so that the gen can be charging the batteries?

And, most importantly, any ideas on what could be wrong and where i go from here?
This guy is hoping to come up to his cabin with family to spend some of the christmas holiday and i am hoping to get him up and running.
Thanks for hanging in there with thias long post and for any advice.
Martin
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: advice on what to do next

    Martin;

    A six Volt battery that measures 5.2 Volts is dead. If they have been down for long they probably won't come back up no matter what you do. A good one will read over 6 Volts at rest.

    If the battery bank Voltage is below the minimum for the inverter-charger it won't fire up. As far as it is concerned it doesn't have minimum Voltage, so it just stops trying. If it won't fire up, it won't do anything including function as a charger from the generator.

    L16's are big batteries and need a lot of current to charge them. I don't know what you mean by an "8x8" array but even a single string of 320 Amp hour L16's on a 12 Volt system (i.e. two batteries) would need 500 Watts for proper charging. How much current is coming through that MX60?

    One thing you might try is getting an automotive charger that can do 6 & 12 Volts and running that off the generator, charging each battery individually. It will take many hours to do this and there's no guarantee it will help. It would also be a good idea to take the caps off and look inside: make sure the plates are still covered with electrolyte and if possible check the specific gravity of each one. Maybe you can find enough 'good' batteries (possibly after charging) to power up one inverter, but don't expect miracles.
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  • martinf
    martinf Registered Users Posts: 5 ✭
    #3
    Re: advice on what to do next

    Thanks for the quick reply.
    Wow. You mean that if the battery level is below the minmun to run the inverter, the charger sidewwon't allow the generator to recharge the batteries? If somebody let's their system go below the threshold, how does one ever get it back up if the charging circuitry also won't function? It will be pretty impossible to pull these big boys out and take them some place that is on the grid for recharging as the cabin is so remote.

    The solar panel is about 8 ft square, sorry don't know how many watts output. Then diesel gen is a smaller Isuzu. I assume that would have. enough kW output but if the charger inverter won't function is there a way to rigg up a temp bypass to hook the gen straight up to the batteries to get them up past the low cutoff?
    OK, here's a stupid question. If the gen is on, doesn't the inverter have enough juice to run and power the 110 circuits in the house. I mean, it doesn't need healthy batteries to run gen powering inverter, does it?
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  • martinf
    martinf Registered Users Posts: 5 ✭
    #4
    Re: advice on what to do next

    Oops. Sorry, I didn't read your reply carefully enough. Iso I see how you could go off the gen ac supply, plug in an automotive charger and bring the batteries up one or two at a time. But I am surprised that this makeshift approach is what would be required in this situation wherein you get below critical minimum.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: advice on what to do next

    Off grid inverters' default mode is "invert". Without enough battery power to fire up the control circuitry they sit there like bricks. Loads attached to the AC OUT will not be powered because the relay that does it is normally connected to inverter output and needs the control circuitry powered in order for it to recognize that there is AC available on the input and switch over. Dead batteries are the same as no batteries as far as the inverter is concerned, and without batteries they do absolutely nothing.

    If the batteries are too low to activate the solar charge controller you can bypass it and have the PV feed unregulated current to them until they come up enough to power the controller, but there's no way around the inverter's controls.

    You need a stand-alone battery charger that can be connected to the generator and push up one or two of the batteries at a time. It would be slow going because most automotive chargers are about 10 Amps, which is pretty low current for an L16 (they tend to be >300 Amp hours) but it's better than nothing.
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  • martinf
    martinf Registered Users Posts: 5 ✭
    #6
    Re: advice on what to do next

    OK, I get it...kinda like what part of no don't you understand. Sorry bout that.
    So I'll set up that work around. I appreciate the help and a merry Christmas to you!
    Martin
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: advice on what to do next

    A lot of people don't realize inverter-chargers don't have a separate battery charger added in: it's the same circuits that do the inverting only operating in reverse. That's what causes confusion.

    One of the things anyway. :roll:
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #8
    Re: advice on what to do next

    And you said that he will be getting utility power in about 1 year... Probably time to start looking at a second solution. Bascially, figure out how much wattage of solar panels he has, and design a battery bank and AC inverter that can use that amount of energy.

    You might be able to justify getting a few of the L16's together for a 12 volt or 24 volt system, and use a "small" AC inverter that can power "quiet time" loads (evening/overnight/etc.).

    Then use the AC generator for larger loads (tools/office during the day/cooking in the evening, etc.). And a separate AC to DC battery charger (if needed) to add some power to the battery bank while the genset is running anyway (and during winter when the sun is hiding).

    For a small home, a 300-600 Watt inverter would give a nice amount of power and would work with 2-4x 6 volts @ 220 AH "golf cart" batteries.

    Anyway--Food for thought.

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