Mark F.
I should have clarified, those "balancing tricks" are not in any particular order, can be mixed and/or matched, and can be used on all lead acid batteries, AGM and gell included. Desulfating may or may not be effective on gell batteries, but it would not hurt them.
AGMs and other sealed batteries vent fine. But once they vent, you can't get those lost hydrogen and oxygen molecules back in there. Overcharging dries "maintenance free" batteries out, ruining them.
The re-cabling process (#1) starts all the batteries off at the same voltage, since they were all paralleled together, making one large 12volt battery (or very large 6volt battery if that is what you have). Then when you re-string them as a series for 36 or 48 or whatever your system voltage is, they MAY discharge and recharge more evenly. This desperate strategy ('cause its hard and probably needs repeating) counters the divergent tendency of cells (the strong cells grab more of the charge AND the weak cells give more of the discharge). Since each battery is usually 3 or 6 cells, this technique only approximates cell balancing, which is the real need.
That is probably one of the tremendous advantages of lithium battery packs: proper ones manage each cell individually with Battery Management Systems (BMS).
Trick #6, if you've made it this far, is overcharging, also called equalizing. The theory is to get each cell to the highest voltage chemically possible. Since they are chemically identical, they should eventually arrive at identical voltages. Then the cells later can start even in the charge/discharge cycle. This is a great longevity technique for FLA batteries (if you let them cool, then add distilled water, then stir), but a horrible technique for "maintenance free" batteries.
Cool, water, stir? Equalizing also overheats the batteries. The water level of hot batteries is slightly different than room-temp batteries. Also cooling gives the bubbles (hydrogen & oxygen) a chance to rise and dissipate. Water level with bubbles is different than all water. Stirring helps homogenize the acid/water solution, which otherwise stratifies over time. Equalizing helps stir the electrolyte with the bubbling action. If you just add distilled water to the top, without somehow mixing it in, you inadvertantly create electrolyte stratification, where the top part of the cell is taking a vacation, while the acid rich bottom part gets overworked. These concerns are admittedly marginal, but they do add up over time.
Why do I drone on so?
Mark Stafford
--- In electricboats@
>
> Thanks for your reply Mark.
>
> I should have mentioned that my batteries are AGM's. As I understand it you shouldn't "overcharge" sealed batteries because they can't vent effectively.
>
> What does the recabling parallel do?
>
> Thanks again,
> Mark F
>
> --- In electricboats@
> >
> > Mark F.
> >
> > Tricks for balancing an unbalanced battery pack:
> > 1. labor intensive: uncable, recable parallel, wait an hour, uncable, recable serial.
> > 2. put a 10-20amp load on the high battery for 1/2 hour.
> > 3. build an electronic flying-capacitor charge equalizer
> > 4. buy a charge equalizer:
> > a. resistive load (akin to #2 above)
> > b. charge re-distribution (PowerCheq or BattEQ)
> > 5. de-sulfate the other batteries (BatteryLifeSaver or other electronic desulfator)
> >
> > My BattEQ from two years ago will not balance an unbalanced pack, but it will keep a pack balanced as long as the batteries are not too disparate. My PowerCheq only touches two batteries, so to do a whole string (series wired), you need 7 PowerCheqs for 8 batteries. My BatteryLifeSaver(
> >
> > Mark Stafford
> >
> >
> > --- In electricboats@
> > >
> > > "Finally - let's say you find one bad battery as I did. Are there any strategies for adding it into an existing "aged" pack."
> > >
> > > Great question Keith. I'm dealing with that right now after finding a bad battery in one of my two banks. The bank is the newest set of batteries so it's about 9 months old.
> > >
> > > I put a new (exact same battery) battery in the bank and tried charging. My PakTrakr showed the new battery being charged at a higher rate than the older batteries so I turned the charger off. I was told to try running the motor full out for about 15 minutes then cruise for a long time and try charging again. I did the 15 minutes full on in the slip and tried charging. It worked for a while (45 minutes?) then showed the new battery at a higher voltage (1 full volt) than the others. I turned it off. It seems it will take a while of vigilant monitoring while charging before I get a nice "patina" on the new battery so that it plays well with others :-).
> > >
> > > Does anyone have any tricks?
> > >
> > > Mark
> > >
> > > --- In electricboats@
> > > >
> > > > I'd like to add a section on my site about troubleshooting - particularly battery/range issues. But this seems like it's pretty much dark magic.
> > > >
> > > > To make it particularly tough I have a complex pack for both space and charging issues. It's 4 sets of (3 parallel) batteries cross-connected in series for 48V. From reading it seems this is sub-optimal but I'm not clear exactly on why (charge imbalance is the stated reason). I charge each set as a if it were a single 12V battery. One issue I suspect I face is sulfation because my charger output is so low (6amp) in comparison to the size of the set (345amp) - the batteries are sitting around in a discharged state for probably 3-4 days.
> > > >
> > > > I recently have been having trouble with greatly reduced range, and rapid voltage sag (like 40 down to 30 volts within 5 minutes). Reduced range I could expect due to sulfation, but the voltage sag was more troubling.
> > > >
> > > > First I checked water - I found a dry cell in one of my batteries a few weeks ago and thought that was the cause, but I dropped 1/3 of my pack (so now I am 4 sets of 2), that cell included, and it didn't help.
> > > >
> > > > Next I ran a load test after charge - couldn't see anything. (Sears has a nice 130amp load tester for about $50)
> > > >
> > > > Then I ran a load test after dropping the batteries pretty low. Bingo - 1 battery showing a dramatic difference. Pulled that battery and now I've got a range much closer to the predicted value (about 10AH down from "ideal"). And that's a string that has the "dry" cell battery in it (after refilling)
> > > >
> > > > Other than "divide and conquer", load testers, specific gravity and voltage meters - what other tools, strategies and processes can be used to diagnose battery issues?
> > > >
> > > > For example, I hear about "shorted" cells - what does that look like?
> > > >
> > > > Finally - let's say you find one bad battery as I did. Are there any strategies for adding it into an existing "aged" pack. All the stuff I've found basically says "don't do it"
> > > >
> > > > Thx
> > > >
> > > > -Keith
> > > >
> > >
> >
>
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