Charging individual batteries in a string.

In a string of 6v batteries wired for 48v can you charge an individual battery with a 6v charger without disconnecting the cables, and the battery main.

Comments

  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Charging individual batteries in a string.

    I think not.

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 29,967 admin
    Re: Charging individual batteries in a string.

    I just typed a lot of hand waving below that says yes you can in some cases... However, if I answered no instead and told you to disconnect the battery you want to charge and do each one at a time--you will probably be safer and not confused by reading my wordy reply.

    --read following at own risk--- :roll:

    Assuming the charger is isolated from Ground/AC Line--yes.

    Probably would recommend that the batteries not be charging or under load during the charging period because of unknowns with your system (charging one battery in the string will probably cause other batteries to under charge from the 48 volt controller; if charging under load, you may draw more current from the charger and cause it problems; etc.).

    If you have parallel strings. Charging one battery in one string could cause the rest of the batteries in the same string to discharge into parallel connected strings. So, I would also recommend that if you have parallel strings, that the one string being charged should be disconnected from the other strings.

    Obviously, any dangers from "faults" (shorts, dropped clips, sparks near charging batteries, etc.) and battery safety warnings all apply.

    Of course, you want to get all batteries charged to the same level. So charging when the string is under load or under charge is going to make that difficult to balance.

    As always, batteries are dangerous and I don't know your setup, hardware, or if your charger is isolated or not. The end result of charging should be that all batteries end up with the same state of charge so they remain balanced.

    With all of the caveats--it may be better to just disconnect the one string and charge each battery until full/equal. :roll:

    -Bill

    PS: See Tony's safe, short, and sweet answer.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • woodrosewoodrose Registered Users Posts: 7
    Re: Charging individual batteries in a string.

    Bill: I have 2 strings of 460a Surretts in my system and extensive periods of very little load and solar charging. A couple of batteries are continually lagging and I'm paying a heavy price in overcharging the rest during equalization and it's a pain in the ass to isolate them for charging.
    The battery system far from ideal now so I'm not looking for a perfect solution, so i"m just trying to minimize the damage to the good ones, and save some propane on my generator when equalizing.
    The one question I have from your response is what is meant by:"the charger isolated from Ground/AC Line"
    Thanks for going into detail.
    Larry
  • BB.BB. Super Moderators, Administrators Posts: 29,967 admin
    Re: Charging individual batteries in a string.

    I would guess that most (all?) modern UL/NRTL listed batteries chargers are isolated by transformers from the AC line (Hot/Neutral and grounds).

    If a charge controller where to have the DC output referenced to (typically--if done) the safety/ground wire--and your DC battery bank was also ground referenced--you would have a short between battery bank ground and your battery charger leads when clipped to intermediate batteries in the bank.

    Assuming your battery charger output is not ground referenced, it should be perfectly safe to connect to any one of your 6 volt batteries.

    Although, I would disconnect the string under charge from the other string as the "high voltage" of the one battery under charge could cause the others in the sting to begin "charging" the lower voltage string.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,563 ✭✭✭✭✭
    Re: Charging individual batteries in a string.
    BB. wrote: »
    I would guess that most (all?) modern UL/NRTL listed batteries chargers are isolated by transformers from the AC line (Hot/Neutral and grounds).

    I wonder if the switch/mode chargers (Vector) are isolated ? They likely have a tiny switching transformer in there, so maybe they are.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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  • BB.BB. Super Moderators, Administrators Posts: 29,967 admin
    Re: Charging individual batteries in a string.

    I am always careful about grounding--because there were still a few old positive grounded British and American cars around when I was young(er). Had to be careful when the owners put in negative grounded aftermarket stuff (sitting on rubber pad on floor for isolation and such).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BrockBrock Solar Expert Posts: 633 ✭✭✭✭
    Re: Charging individual batteries in a string.

    Mike the Black & Decker / Vector ones I have are isolated. I have the 2/4/6 and the 2/6/10 and the 4/10/25 and all three varieties are isolated.

    I have a 60v electric scooter that uses five 12v 40ah batteries in series. I had read that many people were complaining about early batteries failures, not sure if it was the supplied charger, sting charging, cheap batteries or some combination. In any case I added individual leads out and charge them with five 2/4/6 Black & Decker chargers in 2 amp mode (2.8 amps to the battery). I haven't had any issues and have about 400 cycles usually to about 25% discharge.

    I think the real trick if you going to charge them individually is to make sure you are not loading or charging them via some other source while doing this. I also would recommend if you charge one up to charge them all up, even if one takes 10 minutes verify one is topped off and the bad battery is taking 4 hours.
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Charging individual batteries in a string.

    A question I might ask, (in fact am asking) is why are the batteries in the string lagging so badly and so consistently? Are they wired in such a way as to make sure that the cabling and connectors are equal to all batteries (as much as possible anyway)?

    Are they wired such that they are being charged/loaded from one end or the other rather than such that they are evenly loaded/charged? In post number 4 you mention that you have two strings, but don't mention how many batteries in each (8?)

    There are of course a number of different ways that you could wire 2 strings that would deliver 48 volts.

    Tony
  • woodrosewoodrose Registered Users Posts: 7
    Re: Charging individual batteries in a string.

    Tony;
    When you get one or 2 batteries underperforming out of 16 the better chance is that one way or the other they have been abused. In my case I suspect it was in the original shipping. Another way is if all the batteries weren't shipped from the same lot and some might have set uncharged for a while.
    From my experience (bad) only buy a battery set that was shipped direct from the factory.
    Larry
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Charging individual batteries in a string.

    if you just recently got those batteries then you should be contacting the people you bought it from, but before you do be sure your wires and connections are not at fault. if unsure then try placing the questionable batteries where the good batteries are in the bank and then re-equalize it to see if they come up. if they do and after some use the same original battery positions that were in question show a problem then it may be your wire/connections. if the original problem batteries continue to show themselves not up to snuff then it is most likely a fault with the battery. be sure water levels are good too.
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Charging individual batteries in a string.
    woodrose wrote: »
    Tony;
    When you get one or 2 batteries underperforming out of 16 the better chance is that one way or the other they have been abused. In my case I suspect it was in the original shipping. Another way is if all the batteries weren't shipped from the same lot and some might have set uncharged for a while.
    From my experience (bad) only buy a battery set that was shipped direct from the factory.
    Larry

    I quite agree, unless you have a cabling issue as Niel suggests. I had thought about moving them to different positions as well, but forgot to mention it.

    Good luck
  • woodrosewoodrose Registered Users Posts: 7
    Re: Charging individual batteries in a string.

    Thanks for all the advice.
    I already replaced 2 of the set of 16 after 18mo. (under warranty) and they cost more than what I originally paid for them. Pays to read the fine print.
    On the cabling I've installed a new set of cables and nothing changed so I don't think thats the problem. My cabling is a standard 2 strings of 8 then connected to double the amps.
    The following is an answer from the tech people at Surrette.
    I assume from their answer that I would have to move the battery from the middle of the string to the negative end of the string.
    I really don't want to gas the critter, just goose it a little so it's not such a problem come equalization time. The spark/gassing comment really got my
    attention.

    Larry,

    Under 2 very specific circumstances you may but in general no.

    A real concern is connecting and disconnecting the charger when there is current passing through the leads. If the hydrogen concentration in the vicinity is between 4% and 75% there will be an explosion. You and the batteries will be damaged and acid and plastic parts will be flung about the space.

    1) The battery charger positive and negative leads are isolated output leads. They BOTH must be isolated and be able to tolerate whatever the offset is from ground. You will have to get this information from the charger manufacturer. A properly wired isolation transformer could be used to accomplish the isolation.
    2) The battery you are attaching this charger to is on the negative end of the string such that the negative lead of the charger is at ground potential and the positive lead is attached to the 6 volt terminal of that same battery.

    Fred King, PE
    Surrette Tech Support
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