Series battery balancer

jonrjonr Solar Expert Posts: 1,266 ✭✭✭✭
What do people think of devices that balance the voltage across each battery in a series string?  Cheap insurance?   Will destroy your bank?

(note: I have no relation to the seller here)

I am available for custom hardware/firmware development


  • BB.BB. Super Moderators, Administrators Posts: 29,006 admin
    Not sure how helpful this would be... For a 12 volt battery, it is still across 6x cells--So it is not cell to cell balancing (would only support 4x cells if you used 2 volt lead acid cells).

    In general, flooded cell batteries allow "higher leakage current" through cells to equalize lower state of charge cells... At 2.5 to 5% rate of charge (20 hour rate capacity for battery).

    For AGM batteries which have much lower ability to force current "through" cells by over charging--Something like this could be use on blocks of batteries that may have different states of charge for some reason (putting a mixed/used bank of AGMs together may work).

    For Li Ion type cells (such as LiFePO4 batteries), you would not use this type unit... You need to monitor minimum/maximum voltage per cell to be useful (plus some sort of full cell bypass capability).

    I don't see much use for this unless you have an AGM battery bank with, for example, multiple voltage taps (i.e., a 24 volt bank with 12 volts from 1/2 the bank). Apparently, this unit could support upwards of 10 amps of charging current... I would not recommend doing this--But it appears it could work to a degree.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Solar Expert Posts: 1,266 ✭✭✭✭
    edited July 2016 #3
    But balancing across 6 LA cells instead of 24 sounds 4 times better.   Actually much more, since battery to battery variations are much larger than cell to cell variations.    Sure, equalization will re-balance them, but the battery with the least capacity is going to be discharged to a lower voltage and have a shorter life.   And eventually be the cause of the whole string being replaced.

    That being said, would be nice to see some real data on the benefits and ROI.  But it doesn't take much with a $55 device vs say $1600 in LA batteries...

    I am available for custom hardware/firmware development

  • BB.BB. Super Moderators, Administrators Posts: 29,006 admin
    edited December 2018 #4
    More or less, Flooded Cell Lead Acid Batteries can take equalization current without damage, and to a degree, it is "good for the battery" (within limits--Around 2% to 5% "leakage rate" through charged cells). In any case, whether it is 2-3-6 cells in series (4-6-12 volt batteries), there still are cells in series. Just fewer.

    AGM and various Li Ion batteries cannot support "over charging" without damage or destruction. So, for equalization to work, it really needs to be on a cell to cell basis (and most modern mutli-cell batteries do not have the ability to connect on a per cell basis--The bus bars are sealed under the battery top). So, AGM to a degree, and absolutely for Li Ion, you cannot "over charge" to balance cells. And Li Ion cells need to be actively monitored (high/low voltage alarms/cutoffs) to prevent damage (or worse).

    So--While I do not think that unit will hurt anything (assuming it works as designed)--It only offers limited advantages for flooded cell L.A. batteries, and no over/under voltage alarms.

    For "high voltage" lead acid battery banks (say 48 volts or higher), it is very difficult to "see" a shorted 2 volt cell (2 volts out of ~60 volts charging--looks like a "low charge battery bank"--And much worse for 96 and higher voltage battery banks)... So, I would tend to look for, at least, an "monitor/alarm system" that could warn if a battery block (2/4/6/12 volts) was out of balance with respect to the other batteries in the string (one battery at 14 volts, another at 12 volts, or any battery below 11.5 or over 15 volts).

    Problem is that if you have, for example, a 2 volt (per cell monitor) on a 48 volt battery bank, that is 25 wires from each cell back to the monitor--Lots of messy cabling.

    I have not seen one yet, but have thought that a per cell (or per 6/12 volt battery block) Bluetooth monitor device. Wire one to each cell/battery, and use the B.T. to send the data to a central monitor--At least get rid of a spider web of wires.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,422 ✭✭✭✭✭
    There just is not a need to over engineer this with flooded. They work really well already when the designer knows what they are doing and the client follows the basic maintenance. 

    With Lion technology, there are plenty of good places for engineers to work on making these amazing batteries safe and predictable in failure mode.

    They are really amazing and will change quite a bit as there really is not a reason that they can't be much more inexpensive than flooded. Much more!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • MGarMGar Registered Users Posts: 14 ✭✭
    Don't put too much trust, as I had a "BMS" totally fail, and nearly trashed some LiFeP04 cells. It ran about one year.
    If you can't repair don't buy it..
    It most likely will have con formal coating, unless you have it x rayed you could end up with non_fixable unit.
    And all it takes is 1 bad little mosfet and the whole thing is much worst than nothing.
    You should ask them for the repair systematic..

    I ended up having to make my own, which is down to .00x volt on load or charge but a few cells are maybe 2% lower C.
    and that will show up at lower voltage and full charges of .0x volt.
  • South AfricaSouth Africa Solar Expert Posts: 295 ✭✭✭
    edited July 2016 #7

    Victron with their BMV 702, has midpoint measuring. It turns out that it does happen a lot more than one would expect, even with the carefully crafted Trojan T105RE batteries.

    As a result, a bunch of guys here in SA, all using 48v lead acid banks, have started using those Ebay balansers, having opened them and checked them. Must say, the where much cheaper few months ago. And some have bought Victron Battery Balancers.

    All have reported a marked improvement on the volt differences between batts, having monitored their banks very carefully, as all are using software written to specifically manage their systems, protecting their battery investment.
  • EstragonEstragon Registered Users Posts: 3,588 ✭✭✭✭✭
    I didn't see anything about current limit or fusing.  Are there no failure modes in which those little wires coming out of the thing could be a problem?
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
Sign In or Register to comment.