72 volt lead acid pack won't charge over 74 volts

[cboy]

I have a pack of 6 12-volt deep cycle batteries. These were purchased new in October 2017 but have been sitting while I finished construction of the trike they are in. The batteries all tested around 12.8 volts when new. I did not put these batteries on a charger during the construction period but did monitor them from time to time to insure each remained above 12 volts. The trike is now virtually completed. My Cycle Analyst says the pack has 74 volts as does the meter on my throttle. I want to charge the pack up to full capacity but after repeated attempts the batteries will not charge above 74 volts. My "smart charger" (three charging phases) immediately shows the batteries as "fully charged" and turns on the green LED. I left this charger on for 19 hours and it did not raise the voltage above 74 volts.

My assumption is that the batteries sulfated during the construction period and even though they never fell below an average of 12.33 volts per battery which is where they are at now. Am I correct in assuming that sulfation is the most likely culprit?

To try to desulfate I currently have my Schumacher "dumb" charger hooked up to the battery pack and first set it at 72v and 5 amps. I put a clamp meter on the positive wire from the charger and it read 5.1 amps when I first turned the charger on. After about 20 minutes that fell to about 4 amps and after an hour it fell to about 3.4 amps.

I then switched the charger over to 10 amps. The clamp meter reads between 6-6.3 amps. It hasn't been on the 10 amp setting long but it appears the amperage reading will slowly continue to fall.

My question is, am I on the right track in trying to desulfate the batteries and am I "safe" if I continually monitor my dumb charger in terms of the amperage being applied to the battery pack. I will be shutting off the charger and checking the "charge state" every hour or so. Am I correct that the batteries should not "boil" as long as the total voltage of the pack remains within reasonable limits (like 77 or 78 volts)? My hope is that I can recover the batteries using the dumb charger and then put my smart charger back on the pack to finish off the charge without fear of over charging. Any suggestions or alternative approaches I ought to looking at?

My thinking is to try to "desulfate" using the dumb charger, get the voltage to rise by a volt or two, and then try to switch back to the smart charger in order to prevent over charging and boiling off the battery acid.

Is there something I am missing or misunderstanding here? Could the problem lie elsewhere

 

[cboy]

Update...and sort of answering my own question.

I've had my dumb charger hooked up to the pack for four hours, checking along the way, and it has now charged to 77.5 volts, or about 12.9 volts per battery. So it is getting close to being fully charged. I have now removed the dumb charger and put the smart charger back on. The LEDs on the smart charger are indicating the batteries are at full charge, but then they indicated the same thing when the batteries were only at 73 or 74 volts. I'm leaving the smart charger hooked up over night to hopefully top off the pack and get a true "full charge" into the system.

My theory is that the batteries had, in fact, sulfated to a degree and it required the higher amperage of the dumb charger to get the charging action going again and undo the sulfate accumulation.

 

[999zip999]

Charge each pack separately to 13.6v. Then see which one falls low. The pack should hit 80volts off the charger. Don't ask how I feel about lead.

 

[cboy]

Don't ask how I feel about lead.

Ha. I'm actually with you on that...if my checkbook were big enough. Also just curious, can all 12 volt lead acid batteries be expected to charge to 13.6 volts without any negative side effects? I'll see what my smart charger does overnight (if it will get the pack up to 80 or more). It may automatically throttle itself back before that. But I could force the pack to 80 or more with my dumb charger...if I watched over it closely. I'm just wondering if 13.3 to 13.6 is safe and sane for the battery itself.

 

[amberwolf]

Whatever it says on the side of the battery is what I'd recommend. All of the SLAs Iv'e ever seen in person have their recommended voltage and current right there. If it doesn't say, then you'd have to check with teh manufacturer for their spec sheet.

But generally, 13.6something volts is full for a cyclic charge on SLA. 14.4v for a float charge. If they're FLA (water-fillable) then it can be different (as can be the sulfation removal).

If they're actually only at 12-something volts, they're not nearly full. 10v is pretty much dead.


Keep in mind that high charging currents don't remove sulfation, but they do outgass the electrolyte (which you can't put back in the SLAs), and can damage the cells.

Low currents (couple hundred mA) at a higher voltage (15-16v) for a long time can reverse some sulfation. Warming up the batteries can help, too, but you don't want them really hot (or nonreversible outgassing will occur).

Hard sulfation isn't removable or reversible; hard to tell teh difference without just trying it; if it doesnt' come back after a long time (hours, maybe couple days) of the low currrent, it's probably not going to.

 

[999zip999]

I do back in believe A.W. but with all the different electrolytes in SLA batteries there could be many different situations current voltage and milliamps of high voltage. Nobody was talking about Epsom salts I remember when that was the hot deal 4-5 years ago Epsom salt don't know nothing about it. Find an Egyptian from 6000 years ago and see what he thought of his batteries the upside and the downside I think we lost something overtime.

 

[cboy]

Problem solved.

Turns out I may have been a bit premature in asking this question. Late this afternoon I discovered the root cause of the problem. As noted above, I had put my smart charger on the battery pack for 19 hours and there had been no change in the pack voltage. It had started at 74 volts and ended at 74 volts. This had led me to believe I had a sulfate problem. That wasn't the case at all. I was using a brand new smart charger which has a "house" style female plug on the end instead of typical clips. The manual for the charger says the brown wire is the positive wire. Unfortunately, all the wires are permanently encased in a plug cord...so you can't see the individual positive and negative wires without cutting the cord open (and messing with the warranty). So I had gone by the notation on the end of the plug, figuring the terminal marked "N" was the negative side and the terminal marked "L" was the load or positive side. And I had wired the male receptacle for the plug accordingly. Wrong. The factory had wired the encased plug the opposite way. (I know, I should have put my meter on it to test but I figured who would wire a plug the opposite of how it was marked.) As a result, I had immediately blown the fuse on the charger at the beginning of the 19 hour charging session. But the LED lights all came on and stayed on...so I figured the thing was working. In fact, nothing was happening at all. So the culprit was a blown fuse and not sulfate.

Anyhow, at this point the pack is charged to 80 volts using my dumb charger and tomorrow I'll rewire the receptacle for the smart charger and I should be off to the races for future charging. As always, thanks for the wealth of knowledge you are all willing to share.

 

[999zip999]

A 50 cent fuse.