How to get low battery SG up?

kaipo_boy · July 2015

I have a small string of Interstate GC2 6v x4. 3 of them had SG of between 1.270 and 1.290 after my first EQ (they are about 2 months old). 1 had consistently low readings of nearer 1.240-1.250 on one of the batteries so I figured costco had 1 older battery in the batch that had been sitting there awhile. So I just took it back last week and exchanged it for a new one.

When I got it home, the SG of the new battery indicated it was near 60-70% SOC but I have no way of charging a lone 6v battery; so just wired it into the string with the other 3 and have been using it like that for a week.

The string seems to be behaving noticeably better as the voltage readings seem to be holding up longer overnight. However, last night I took an SG reading on the new battery and it was near 1.220-1.230 (the bank was not at float but it was close, the other batteries were near 1.280 ish. So this morning I ran an EQ for 2 hours and the new battery came up to 1.240ish; so I ran it 2 more hours on EQ and it came up to 1.245-1.250 on all 3 cells. However, now when I check my other batteries they are all near 1.290-1.300.

My gut tells me it needs longer EQ on that one battery but I have no way to do it without involving the other 3 batteries too... it appears (other than taking it off and taking it back) my only options are to run it like that, or else run another EQ cycle tomorrow and it sounds like it will need at least 2 or 3 more hours... but I don't want to subject the other batteries to that. I was careful to watch temps and battery temp never exceeded 84 F. Ambient is closer to 95F today.

What would you guys do?

zoneblue · July 2015

Well it stands to reason that if you overcharge the rest of the pack long enough it will come up. But do you really wanna do that?

How bout hacking together a crude charger from an adjustable DC to Dc converter ($5 ebay one)?

vtmaps · July 2015

One thing to keep in mind is that it may take 50 cycles before a new battery behaves normally. In other words, it may take many EQ cycles before the new battery gets to where you want it to be. Your old batteries (2 months old) are already at least 50 cycles ahead of your new battery.

What would I do? If you can isolate the new battery and have a spare solar panel and spare time, you can hook up the spare panel directly to the battery. Watch it carefully... you don't want to boil it dry. Don't try to get the SG all the way up in one cycle... as I mentioned, it may take many cycles. Of course, while you are doing this, your system is inoperable

--vtMaps

kaipo_boy · July 2015

vtmaps wrote: »

One thing to keep in mind is that it may take 50 cycles before a new battery behaves normally. In other words, it may take many EQ cycles before the new battery gets to where you want it to be. Your old batteries (2 months old) are already at least 50 cycles ahead of your new battery.

What would I do? If you can isolate the new battery and have a spare solar panel and spare time, you can hook up the spare panel directly to the battery. Watch it carefully... you don't want to boil it dry. Don't try to get the SG all the way up in one cycle... as I mentioned, it may take many cycles. Of course, while you are doing this, your system is inoperable

--vtMaps

Hmmmm, you know what they say. A little knowledge.....
I actually do have a spare panel, but I think it runs at near 35v in full sun... let me check zoneblue's suggestion.

BB. · July 2015

Get some 6 volt brake lamp bulbs from the autoparts store. And install some spring clips and wiring each bulb.

When the sun is up, clip a bulb on each "high sg" battery. And do not clip a bulb on the "low sg" battery(ies). The brake lights will "bypass" current around the fully charged batteries and put 2-4 amps into the low SG battery.

Note, when connecting the clips, wear a face shield/cover the battery cells so that a spark will not light any hydrogen gas (I like to use a fan to blow gasses away when making/breaking electrical connections).

You can remove the bulbs after the sun sets--Although, you can leave them on even at night--They will discharge the "high sg" batteries down to the low SG batteries. Then the batteries will all be "matched" level of discharge--And the next day's sun will recharge all of them together.

Of course, don't forget the lamps--If left on too long, you can create more unbalanced batteries.

-Bill

SolarPowered · July 2015

You can balance all batteries by completely disconnecting the bank from the cc, and inverter.
Allow 12 hours to have all batteries to equalize to DOD equalization no matter what that percentage is.
After equalization plug the cc back into the bank, do not plug the inverter in until after bulk and float charge are complete.
Then you are ready to rock and roll

Photowhit · July 2015

If you can live with out electric for a while, I'd rewire your bank to put all the batteries in parallel for 24 hours or so, this should allow the low battery to "catch up" being pulled up by the other batteries. In addition the other batteries will be drained by the low battery. This should get you into the ball park of equalizing them as a group with out boiling out having to repeatedly charging the full batteries. This might be what SolarPowered is suggesting, but we don't know what voltage your system is, it will only bring up / equalize across the cells if you have a parallel system.

Another option is to pull the battery and take it to where you bought it or some auto part stores shore side, and have them charge it, it will often be a 'hot charge' but it should help bring up the SG. Let whom ever is doing the charging know it's a deep cycle, some, a few will have chargers designed for deep cycle batteries.

waynefromnscanada · July 2015

Had a situation where one battery out of 6 had significantly lower SG. Ran a battery charger off the inverter while the sun was shining, wired a car headlight in series to limit current (charger was 6 volt while battery was 2 volt) to put extra charge in that one battery. Took a number of days to get the SG up, and from the beginning of this process, one of the other batteries had high SG. Will go with BB's suggestion of a load on that single high SG battery to bring it down. Feel foolish I hadn't thought of that.
The spread in SG took place over Winter when I wasn't keeping close tabs on things. Several EQ cycles did not change anything, thus the alternative, heavy handed approaches.

kaipo_boy · July 2015

Excellent suggestions, all! Thanks BB, you are a gem. I'll try that one first, if I can find some 6v brake lamps... haven't looked for any of those in decades, not since the last time I worked on an air cooled VW! Photowit, your suggestion also is interesting, I'll keep it as a backup plan as well. Thank you everyone.

SolarPowered · July 2015

Photowhit wrote: »

This might be what SolarPowered is suggesting, but we don't know what voltage your system is, it will only bring up / equalize across the cells if you have a parallel system.

Yes you are correct sir. I should of stated that they have to be broken down to each cell, and paralleled.
This is the best way to do it with old or new batteries for equalizing, it doesn't all ways mean it will maximize SOC 100%.

zoneblue · July 2015

Yep, that sure is a colorful range of possibilities there!

kaipo_boy wrote: »

actually do have a spare panel, but I think it runs at near 35v in full sun

Thats ok, PV is a current source, the voltage will just slip down the IV curve to the match the battery.

ZoNiE · July 2015

I have a vintage Sears Craftsman car battery charger that has 6V option. You may be able to find one on CL. Worth a shot.

waynefromnscanada · July 2015

kaipo_boy wrote: »

I'll try that one first, if I can find some 6v brake lamps... haven't looked for any of those in decades.

Doesn't have to be 6 volt bulbs, a 12 volt bulb will work, just will run cooler and take longer to do the job - - - unless you use a headlight bulb.

vtmaps · July 2015

ZoNiE wrote: »

I have a vintage Sears Craftsman car battery charger that has 6V option. You may be able to find one on CL. Worth a shot.

You may be able to use a 12 volt charger. Many chargers will not charge a battery that is too far below nominal voltage, but some chargers have a "dead battery" option. This means that a 12 volt charger will try to charge a "dead" battery that is at only 6 volts.

Of course, you must monitor the situation to avoid overheating or boiling the battery dry.

--vtMaps

How to get low battery SG up?

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