batt bank losing voltage-not running anything?

apexcarl
apexcarl Registered Users Posts: 7 ✭
in Solar Beginners Corner #1
Hi, Im a newbie, with 2 small (probably stupid) questions..i have 6 us-l16hc 6 volt batteries hooked up in series/parrallel to get a 12 volt bank...they are rated @ 420 amphours each...so running at 12 volts do i have 2520 amphours or 1260 amphours?
also, my voltage drops during the night, 1-2 volts, even when the inverter is turned off..? im using a sunforce 12v 30 amp charge controller.. fed by 4 sharp 123 watt panels on da roof...should be about 500 watts (30 amps) supply. is the voltage drop normal? or do i have a batt issue?
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #2
    Re: batt bank losing voltage-not running anything?

    Two six volt L16, 420 A-H batteries in series yields twelve volts at 420 A-H.

    For your three strings you have 3 X 420 A-H's or 1260 A-H.


    The voltage drop depends on what your starting point reference is.

    With no load, the battery equilibrium state should be about 12.7 vdc.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: batt bank losing voltage-not running anything?

    I suspect your batteries may be damaged due to chronic under-charging.

    Here's why:

    4 @ 123 Watts = 492 * 80% efficiency = 394 Watts usable / 14.2 Volts charging = 27.7 Amps maximum.
    That's enough to keep 550 Amp/hrs of battery 'happily' charged; i.e. reduce sulphation to a minimum and get the electrolyte stirred. For 1260 Amp/hrs it is woefully inadequate.

    This is why I say charging batteries is more than just replacing the 'used' Amp/hrs. It is more important to get the current to acceptable levels (5%-13%). Generally if you can achieve that then replacing the Amp/hrs is easy.
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  • 1965GMC
    1965GMC Registered Users Posts: 8 ✭
    #4
    Re: batt bank losing voltage-not running anything?

    I am a newbe too, but is seems that you have a draw on the batteries or they could be bad. Some things I would check out is the water level in the batteries, check the solar panels to see if they are drawing on the bateries at night. If all of this checks out, I would check the wiring. Oh if you have a voltmatter make sure it off when not in use, although I don't think it should drain the batreies over tight chexk it any way.
    If the diodes in the your panels have done bad for some reason, they will drain your batteries.
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  • apexcarl
    apexcarl Registered Users Posts: 7 ✭
    #5
    Re: batt bank losing voltage-not running anything?

    i don't understand why my panels are not enough, when i am not running anything off the bank..i have watched them put out 32+ amps...for hours...gets the bank up to 15+ volts....but by nightfall, we are at 12.6 volts..or is 12.6 volts a 'good' starting point?..i only plan on draining about 3-4 kwh off the bank overnight..i thought i just needed that big a bank so i would not be draining them past 75% reserve...or mabey i lost my mind somewhere...
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  • apexcarl
    apexcarl Registered Users Posts: 7 ✭
    #6
    Re: batt bank losing voltage-not running anything?

    thanks for the input. i have a "charge controller hooked up, its supposed to stop the panels from vampiring the power at night...mabey its bad...all equipment and batteries are brand new...guess i will have to check some more...65GMC? i have a 67cadi limo....luv it..
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: batt bank losing voltage-not running anything?
    apexcarl wrote: »
    i don't understand why my panels are not enough, when i am not running anything off the bank..i have watched them put out 32+ amps...for hours...gets the bank up to 15+ volts....but by nightfall, we are at 12.6 volts..or is 12.6 volts a 'good' starting point?..i only plan on draining about 3-4 kwh off the bank overnight..i thought i just needed that big a bank so i would not be draining them past 75% reserve...or mabey i lost my mind somewhere...

    Nope; you're sane. It's the world of physics that is nuts! :p
    Just replacing the 'used' Amp/hrs isn't enough.
    The problem is if the charge current isn't high enough, sulphation sets in. That is the sulphur in the sulphuric acid in the battery coating the plates. This means the exposed area becomes smaller and smaller - essentially like getting a lower Amp/hr battery with every 'bad' recharge. As this happens, it gets easier to 'recharge' the batteries - apparently. Hitting 15V from time to time is good; it's actually the equalization Voltage for a 12V system and helps knock some of the sulphur back into solution.

    I'm probably not explaining it well. There's good, in-depth infor at the battery FAQ: http://www.windsun.com/Batteries/Battery_FAQ.htm#Battery
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
    Re: batt bank losing voltage-not running anything?

    the batteries are being under charged as the charge rate to them is about 2.23%. we usually recommend between 5% and 13%. when the charge rate is as low as 2.23% it just does not charge it properly if at all at that rate as it it is not exactly linear when down low. in fact some batteries can lose that much just sitting and no loads on them. add to that the sulfation that has developed and they are heading downhill fast. you have the 1260ah battery bank and 5% of that is 63a. your pvs are rated for an imp of 7.16a and you have 4 of them for 28.64a and that does not include any losses or efficiency factors. you need more than double what you have. battery failure is the cost of having more ah capacity than you can charge properly. had they been agms you may have gotten away with it up until now as they are more efficient and they don't lose as much on the shelf, but even then you are far too low in the charge % than i'd have normally recommended.
    it is possible you may be seeing the batteries come to full charge only because of the lost capacity and lifespan.
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  • apexcarl
    apexcarl Registered Users Posts: 7 ✭
    #9
    Re: batt bank losing voltage-not running anything?

    aahhh,... thanks for the input...i really do appreciate it...so im thinking, should i cut back on the batt bank size till i get more panels hooked up? & what size would be right?...im trying ....
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: batt bank losing voltage-not running anything?

    You could start by fully charging each battery (or in series two since they're 6V) and check the Specific Gravity on all cells. See how many you can get up to 1.275 SG or near. Some of them are likely to be irretrievable.

    Your panels could handle only one set of these 420 Amp/hr batteries, as per my comments in post #3.

    Hope that helps.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #11
    Re: batt bank losing voltage-not running anything?

    What Marc and Niel said,, only again:

    Chronic undercharging

    Read and understand the following as best you can:

    "http://www.batteryfaq.org/

    http://www.batteryfaq.org/

    We have ~400 watts of Pv and that is really not quite enough to provide enough amperage into 450 ah of battery. We get the batteries charged most every day to full, mostly because we manage our loads quite carefully, but on the best days we get ~25 amps (+5%) but on many days we might only eek out only 20 amps.

    As for cutting back on the battery size, consider how you are going to keep them all up to charge. What other charge source do you have/use? I would charge the hell out of them until the specific gravity is as high as possible for the batterys. My guess is the damage has already been done.

    Good luck,

    Tony
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  • 1965GMC
    1965GMC Registered Users Posts: 8 ✭
    #12
    Re: batt bank losing voltage-not running anything?

    apex, keep in mind I am a newbe as your self. You seem to have good amps but what is you voltage like? If your running a 12V system you should have 13 to 14 Volts to charge 12V batteries. I would get out my multimetter and start to check over the whole system to see what is doing what what. As a newbe, did you hookup your charge controller to the battery first? I did not do the math, but at 30+ amps you may have enough volts. Be sure your charge controller in connected right. If you have a dump load on the contrller be sure it goes to a dump laod, or other wise it may cook your battries for having no where to dump the load. this is as far as my knowledge can take you without seeing the system. so go through your system with fine tooth comb and take nothing for granted, even wire size.

    67 Limo ha, that 555 must keep you at the pump. Lots of power there, ever thought of putting a feul cell in it, with a fiew bubelers to keep the engine clean?
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