Battery Balancer

lazza
lazza Solar Expert Posts: 336 ✭✭✭
in Off Grid Solar & Battery Systems #1
HI

We are still having issues with 12V batteries in series to make 24V systems. As the single 12V batteries are much cheaper than OPzS, everyone seems to go for them.

However there are problems with these batteries dying in series, particularly if they are over-discharged a few times and/or are unequal to begin with and voltages vary on charging.

I've come across these so-called Battery Balancers, and just wondered if anyone has had experience with them and if they are effective??

http://www.aliexpress.com/item/Battery-balancer-for-In-series-connected-Lead-acid-battey-24V-36V-48V/1265574756.html
http://www.victronenergy.com/upload/documents/Datasheet-Battery-Balancer-EN.pdf

Cheers
Larry
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Comments

  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #2
    Re: Battery Balancer
    lazza wrote: »
    HI

    We are still having issues with 12V batteries in series to make 24V systems. As the single 12V batteries are much cheaper than OPzS, everyone seems to go for them.

    However there are problems with these batteries dying in series, particularly if they are over-discharged a few times and/or are unequal to begin with and voltages vary on charging.

    I've come across these so-called Battery Balancers, and just wondered if anyone has had experience with them and if they are effective??

    http://www.aliexpress.com/item/Battery-balancer-for-In-series-connected-Lead-acid-battey-24V-36V-48V/1265574756.html
    http://www.victronenergy.com/upload/documents/Datasheet-Battery-Balancer-EN.pdf

    Cheers
    Larry
    Interesting technology, and something that is regularly seen built into a Lithium chemistry battery pack, since they are far more sensitive to over or under charge.

    For Lead Acid, whether FLA or sealed, the normal use of a three stage charger, with a suitably set Float voltage should be all the balancing that is needed unless one or both the series connected batteries is defective or nearing the end of its useful life.
    The traditional way to avoid problems of this sort with Lead Acid strings (including individual cells within a battery) is to observe the voltages and when they get too far out of balance do a higher voltage equalizing charge. This forces current through any high voltage cell groups to make sure that the other cells get a full charge.
    This is not damaging to FLA batteries as long as current and temperature are kept within limits, but needs to be done with some serious care when sealed (AGM) batteries are involved. It is possible to safely equalize AGM batteries, but the current and temperature have to be closely monitored to make sure that the internal pressure does not rise to the point where the cells vent. Just cranking the voltage up to some nominal "Equalize" setting will not work.

    All that said, the balancers may have some use when the batteries are different ages from the start or when you are taking a small 12V load from the midpoint of the battery stack.
    There are also power balancers that let you drive large 12V loads from a 24V stack without causing any imbalance, even when the batteries are not being charged at the time. The DC equivalent of autotransformers, made with active circuitry.

    One other comment: The Victron brochure mentioned that a high leakage battery could unbalance not just that battery but others in parallel with it. That is a risk, but is mitigated by avoiding parallel batteries in the first place or by paralleling strings instead of making up strings of parallel groups. (Series-parallel contrasted to parallel-series.) :)
    SMA SB 3000, old BP panels.
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  • CDN_VT
    CDN_VT Solar Expert Posts: 492 ✭✭✭
    #3
    Re: Battery Balancer

    Whats the pricing Larry ?
    Good read & points also

    VT
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #4
    Re: Battery Balancer
    inetdog wrote: »
    Interesting technology, and something that is regularly seen built into a Lithium chemistry battery pack, since they are far more sensitive to over or under charge.

    One other comment: The Victron brochure mentioned that a high leakage battery could unbalance not just that battery but others in parallel with it. That is a risk, but is mitigated by avoiding parallel batteries in the first place or by paralleling strings instead of making up strings of parallel groups. (Series-parallel contrasted to parallel-series.) :)

    HI, dont quite understand what you mean by paralleling strings instead of making up strings of parallel groups??
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Battery Balancer

    Correct way to increase battery capacity by paralleling is to create strings of batteries to equal the necessary Voltage, then connect the strings in parallel.

    The other way is to build parallel sets of batteries to create the desired Amp hour capacity, the connect these sets in series to get the right Voltage. It doesn't work very well and is what Victron is warning against.

    Of course no matter what solution you implement people who misuse the system will simply find a different way to misuse it, and probably kill all the batteries at once.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #6
    Re: Battery Balancer
    lazza wrote: »
    We are still having issues with 12V batteries in series to make 24V systems. As the single 12V batteries are much cheaper than OPzS, everyone seems to go for them.

    Hi Larry, I recently specced a small system for a client and had a look at the 12v batts. The reason they're so cheap is that they're rated at a MUCH lower cycle life than OPzS or even the Trojan or US Battery 6V units. The cost looks much better when it's per cycle, or per expected lifetime :)
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #7
    Re: Battery Balancer

    OH man - it's 1998 all over again - shades of the EVDL list with guys trying to balance their Pb batteries for EV use. Lee Hart's circuits were popular, until people figured out not to buy trash, not over-discharging, and charge each battery individually first before placing them into a string, and then doublechecking for high-resistance jumper cabling.

    I knew it would be just a matter of time until the Pb industry got around to reviving the "balancing" act now that 1998 is long forgotten. :) What they found then was that actively "balancing" a pb string was merely masking problems, until they just outright went completely dead or plasma ball.

    http://www.evdl.org/lib/

    Ah, the good 'ol days of pb balancers.....

    Side note - li-ion packs like those used in tools, RC, and EV applications are far different from a lifepo4 solar housebank - which does NOT need constant balancing. If you do, you are doing something very wrong, or treating them like "drop in replacements" with too high a voltage.
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  • CDN_VT
    CDN_VT Solar Expert Posts: 492 ✭✭✭
    #8
    Re: Battery Balancer

    Ahh Thanks PNjunction , It comes back .
    I had a DUH moment

    VT
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #9
    Re: Battery Balancer

    Thanks for the replies

    It seems that this issue of 2x12V batteries in series to make 24V is becoming more and more critical- every time I look at an installation, even after a very short time, one battery very often is 0.2V above or below the other in the series.

    Each 12V battery is 250Ah at C100. In a 500Ah system at 24V, by parallelling not just the strings but also each series at its midpoint (i.e. 12V), similar to as seen in the picture below (ignoring battery balancer).... could this help mitigate somewhat large variations in my battery strings?

    Attachment not found.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #10
    Re: Battery Balancer

    I really don't like "cross connecting" the middle batteries of parallel battery strings. It makes it virtually impossible to monitor individual batteries for any failures.

    If everything is working normally, there should be zero current flowing through the cross connect(s). If there is a bad connection in the main series wiring, or an open/shorted battery--Current will flow through the cross connect masking the open/shorted battery (cell) or bad series connection (for example, if one battery cell goes open, you will have effectively three batteries on the "high side" with two batteries on the low side in parallel/series connection--Very difficult to catch failures).

    You can use a DC Current Clamp on the cross connects to check for zero current flow--And if you see any "significant" current flow, figure out why it is happening.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: Battery Balancer
    BB. wrote: »
    I really don't like "cross connecting" the middle batteries of parallel battery strings. It makes it virtually impossible to monitor individual batteries for any failures.

    This is something of an understatement. It creates 'shadow' parallel paths that can really unbalance the batteries. So in fact it may aggravate the very problem it is trying to alleviate.

    It sounds like the problem originates with batteries that either aren't any good (cheap and inconsistent) or aren't commissioned/maintained properly. Many of us run strings of multiple batteries without issues, so the configuration is not at fault.

    Here's a somewhat unusual solution for you: wire the array and charge controllers as two 12 Volt systems in series. Yes you have to be 100% certain there's no shorting such as common negative, but it will put each battery or battery segment on its own controller. With parallel strings you could use dual controllers per segment if within parameters.

    Overly complex? Yes. And I can't help thinking from the diagram given that the problem may be sourced in using three parallel strings. Just how expensive is that balancer?
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #12
    Re: Battery Balancer

    The balancer costs about 50€. That's for the Victron, the Chinese one is about half the price.

    The doubt I have with the Victron one, is that the maximum balancing current is only 0.7A. Surely this will be insufficient to alleviate a 0.2V imbalance between two 12V batteries in a series??
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: Battery Balancer
    lazza wrote: »
    The balancer costs about 50€. That's for the Victron, the Chinese one is about half the price.

    The doubt I have with the Victron one, is that the maximum balancing current is only 0.7A. Surely this will be insufficient to alleviate a 0.2V imbalance between two 12V batteries in a series??

    That would depend on the size of the batteries. 0.7 Amps is not very much for 200 Amp hours (typical small RE bank), really.
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #14
    Re: Battery Balancer

    With only two batteries in series, I'd much rather fix the balance inequality by using standard techniques, like EQ or at least fully charging two nearly identical batteries individually, and of course fixing any poor interconnects.

    The same issues existed back in the 90's with EV's, and even today with lifepo4: do you want to introduce another possible point of failure into your system?

    Common failure modes included latching into the discharge mode, even worse if it was a short when the mosfet or other internal dummy load blew or burnt up. RFI / EMI ingress from nearby cellphones, vhf radios, etc caused a few of the diy ones to get confused. If it fails, or is in a constant state of balancing masking poor battery quality issues, are you going to get the balancer manufacturer to pony up for a new set of batteries?

    If anything I would go Victron and not the cheap one. Still, I see this setup being totally abused by those wanting to pair crap or dissimilar batteries together to see if it would relieve them of proper initial engineering or maintenance. How does the balancer handle a PB battery with an internally dropped cell that you can't acess for evaluation or individual rescue charge? Will it continue to try and balance a good one with a bad one forever?

    Ok, looks like a difference of over 200mv will trigger an alarm relay on the Victron. One had better be within earshot of the alarm, and/or use it to trigger the CC or charger OFF and let you dig into the problem. Not sure if the other el-cheapo units have this function.
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #15
    Re: Battery Balancer

    The idea i had for use of the battery balancer was to apply it to new installations- ie batteries that are well-balanced initially, to prevent them from becoming imbalanced once the installation is up and running. (As opposed to applying them to already imbalanced systems, where problems may exist.)

    Do you think it could work to that effect ??
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #16
    Re: Battery Balancer
    lazza wrote: »
    The idea i had for use of the battery balancer was to apply it to new installations- ie batteries that are well-balanced initially, to prevent them from becoming imbalanced once the installation is up and running. (As opposed to applying them to already imbalanced systems, where problems may exist.)

    Do you think it could work to that effect ??

    If they start out balanced they should stay balanced, at least within the range that the balancer could handle.

    The problems we repeatedly mention regarding parallel strings notwithstanding. Even so, if done correctly they should be within tolerance providing they are maintained. You can not build an off-grid system that can be ignored for years without it suffering any degradation.
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