Brain Droppings: Battery Rotation -- is it worth considering?

2twisty2twisty Solar Expert Posts: 199 ✭✭✭
I was just thinking.. (Yeah, I know -- dangerous!)

Would there be any advantage to periodically rotating the batteries in a given string? Would that have any advantage in terms of extending the battery life so that their charge uptake is more balanced?

Clearly, monitoring SG in each cell is the best way to keep track of that, but is there anything we can do proactively to ensure that a battery's charge uptake is optimal? If so, what would be a good battery rotation plan? Just "reverse" the wiring every now and then so the battery that was providing the outbound negative lead is now the one with the outbound positive lead? Or should we shuffle the batteries around so that they get new "neighbors," or some combination of both?

Or, is the gains that may (or may not) be had from this activity so minimal that it's not worth the work of turning everything off, undoing all the connections, shifting batteries and redoing? One advantage I can think of is that it will help you make sure that your battery contacts and cables are clean, since you'd be taking them all apart and redoing them.

Thoughts?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,190 admin
    There are a few people here that rotate their batteries--They find they have "problems" (low SG readings) at one end of their battery strings. For them, it was worth it.

    There is no electrical reason I can think of why a series string would have specific gravity problems at one end of the string vs the other... Possibly uneven cooling/air circulation (hot batteries self discharge faster than cold batteries)?

    If you have a battery or two that reads low SG consistently on one end of the string, swapping batteries around and seeing what happens for you--Not going to hurt anything.

    As always, be careful with wiring and acid.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • 2twisty2twisty Solar Expert Posts: 199 ✭✭✭
    OK, so there's no theoretical reason to do it -- only as a specific solution to a problem with SG thay may be related to battery temp.. OK. I'll see what the SG does and if I have an issue, I'll look into it further. I'm not looking for MORE tasks on my maintenance list unless they go (or at least could/should) produce a worthwhile effect.

    Thanks!
  • BB.BB. Super Moderators, Administrators Posts: 30,190 admin
    I will say that I cannot think of a primary cause of string position dependencies other than thermal/cooling issues. That a few people here have seen/reported their banks have string position issues even after they rotate the batteries (i.e., location dependent, not battery dependent)--It does appear to be real for some folks.

    I could think of secondary issues with capacitive coupling and grounding (i.e., ripple current/voltage coupling/capacitive coupling is "worse" for positive string batteries vs those near the negative bus terminal--if you have a negative ground system). But I have no idea if that is what the issue is (coupling effects would seem to be very small and not capable of causing battery issues)--Or if there are some other reasons.

    Somebody else may have some good theories or knowledge of why something like that could happen.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • verdigoverdigo Solar Expert Posts: 428 ✭✭
    If you do shuffle them (I have), give them a good thump or two to get the gas bubbles to the top. Then you can even out the water levels for more consistent SGs. I think I read that one user would take his for a ride on a trailer he keeps them on.
  • jonrjonr Solar Expert Posts: 1,360 ✭✭✭✭
    I'd only do it if you had some batteries in parallel.

    I am available for custom hardware/firmware development

  • mike95490mike95490 Solar Expert Posts: 8,661 ✭✭✭✭✭
    batteries in series, I can not think of any engineering logic to suggest they be "rotated" unless it's to remedy poor thermal design.
    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    mike95490 wrote: »
    batteries in series, I can not think of any engineering logic to suggest they be "rotated" unless it's to remedy poor thermal design.
    Or high leakage current because of totally dirty battery tops and cases?

    SMA SB 3000, old BP panels.
  • mike95490mike95490 Solar Expert Posts: 8,661 ✭✭✭✭✭
    inetdog wrote: »
    Or high leakage current because of totally dirty battery tops and cases?
    Rotating batteries won't fix sneak current paths. You can fix that with a rag and leave the batteries in place.

    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Dave AngeliniDave Angelini Solar Expert Posts: 5,086 ✭✭✭✭✭
    mike95490 wrote: »
    batteries in series, I can not think of any engineering logic to suggest they be "rotated" unless it's to remedy poor thermal design.


    I can think of good reasons not to. The first is someone stressing a terminal and causing a leak. Next would be causing an internal shedding of plate material. If battery maintenance is done right, the only time you should have to disconnect a terminal is to replace the battery bank. I am speaking of large L16 and up batteries in 79 applications over 35 years.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • BB.BB. Super Moderators, Administrators Posts: 30,190 admin
    I agree that moving batteries every year is a nightmare and could possibly cause damage to terminals/batteries (ever crack a case?) during handling. I would try to avoid it if at all possible (my suggestion of placing a 12 volt (or 6 volt) break lamp across "full batteries" (particularly AGM/GEL/Li Ion) to allow current to bypass the full battery and charge the "weak ones" would be a possible manual solution).

    On the fact that batteries may show positional charging issues in a series string--Enough people here (a hand full?), that I respect for, have seen the issues in their banks--So I cannot say it never happens. I just don't understand why/what they are seeing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    BB. wrote: »
    Enough people here (a hand full?), that I respect for, have seen the issues in their banks--So I cannot say it never happens. I just don't understand why/what they are seeing.

    I think you do understand, and you mentioned it earlier in this thread... thermal issues. Blackcherry04 has reported this problem several times and I have replied to him (several times) that it is likely caused by temperature differences in his battery box.

    Even the placement of a venting system can cause temperature gradients in a battery box.

    --vtMaps

    by the way, I posted on this thread earlier today (in reply to inetdog's post) and the post seems to have disappeared. Mike95490 made the same point that I did, so I will not repost it.
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 30,190 admin
    vtmaps... Hmm, that is weird. I don't see any signs that your post was deleted (and I remember it too--No other moderators/admins logged in today).--Posts can be permanently deleted and there would be nothing left for me to see).

    I know that NAWS is having some folks work on the server over the last few days in background for an eventual upgrade (fingers crossed) for the VBB bug fix.

    That should not have dissappared your post.... Well, anyways, if anyone sees more disappearing posts, let me know.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,086 ✭✭✭✭✭
    Bill, VT's post was there just before I posted. Right after Mike's. Good title for this post BTW
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • BB.BB. Super Moderators, Administrators Posts: 30,190 admin
    I will save "lost post" thread for the VBB person when he comes by to check the forum and upgrade software (should be soon, last I heard).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    the only time you should have to disconnect a terminal is to replace the battery bank.

    I agree... except for my system :cry:

    I have a Midnite ePanel in my NEC compliant system. The ePanel has an extensive UNFUSED battery bus. It terrifies me. I will not open the door on my ePanel (not even to look for cobwebs) without first disconnecting a battery cable in the battery box.

    Someday when I need new batteries, I will cut the conduit between the battery box and the ePanel and install a switch or breaker.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 30,190 admin
    Yeah, I am more terrified of a large unfused battery bank bus than working on the 120/240 VAC lines coming down from the power pole (which terrified me enough thank you very much).

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