Mountain DonMountain Don Solar Expert Posts: 494 ✭✭✭
This will sound like a dumb question I'm sure. I have always made certain my batteries are fully charged before I do an equalization charge. I use a hydrometer and keep a log and normally only equalize when there is a cell to cell difference of 0.010 or more. The exception to this is spring. Our system sits mostly unused over the winter; the FM60 keeps the batteries full. I equalize in spring just to stir up the electrolyte.

My question stems from a discussion with another person with an off grid cabin. He claims it is not necessary to have the batteries fully charged before doing an equalization. I say that is wrong. Trojan states that batteries must be fully charged before equalizing. A few other websites seem to have copied and used Trojan's information. Some other battery sites (Crown for example) do not state anything about what to do, if anything, before equalizing.

So, what is the best practices recommendation from the fine folks here? And maybe some plain english explanation as to why the recommended best practise is true?

Thanks very much. PS; My batteries are golf cart types (not Trojan) in a 24 volt configuration, installed in July 2009 and they still perform quite well.
Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M


  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Equalizing

    Pretty simple:

    If you have parallel strings of batteries it is essential that you have the bank up to a reasonable charge before you equalize. If you do not you will have a risk of one or more strings getting too high a current when you apply the equalization voltage to them.
    If your equalize cycle is current limited to the bulk current or less and just changes the voltage end point, it probably will not cause any problems with a single battery or series string.
    But you will need to add the time needed to get the bank up to full charge to the recommended Equalize cycle time.
    SMA SB 3000, old BP panels.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Equalizing

    Since EQ is a controlled overcharge, if you start an EQ on a battery bank that isn't fully charged, you're not equalizing them, you're charging them, at least until they finally get to the fully charged state. Therefore, (for arguments sake) depending on their initial state of charge, you could select EQ (for example one hour) and end up doing actual EQ for perhaps only 10 minutes, the rest of the time the batteries were just getting charged up.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Equalizing
    inetdog wrote: »
    If your equalize cycle is current limited to the bulk current or less and just changes the voltage end point, it probably will not cause any problems with a single battery or series string.

    This has been discussed recently over at Midnite's forum:

    The Midnite Classic can be configured to do automatic EQ and it does just what you mention... starts out in the morning with an EQ. Effectively it is just doing bulk with a higher voltage set point.

    Some of the reasons NOT to do that are mentioned in that thread, and Midnite will probably get around to inserting an absorb before auto EQ.

    Your point about EQ uncharged parallel strings is well taken.

    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Equalizing

    You are right - you need to finish absorb first.

    If you don't, what happens is that the battery that still needs charging ramps up too quickly to the EQ voltage rather than staying at the absorb voltage. Now, it spends most of it's time gassing, and not really finishing the charge efficiently, nor doing a good job of equalizing.

    A bad drag-strip analogy would be that you have to finish the absorb to be in the right gear when you start. Otherwise, when you stomp on the accellerator voltage, all you do is spin your wheels, and travel slowly. Lots of smoke and rubber. Or in this case, battery damage because it isn't finishing the charge nor really equalizing properly.

    Sorry guys, I couldn't help it. :)
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