Desulf, revisited (how many times now?)

[zap]

I noticed this effect with another sla I added water to previously... it seems the cells will have a negative pressure after adding water, a slow charge, then a long rest.
Before I added water this last time, I noticed the cells all had a positive pressure.  Looking at the cells, all appear to be moist although it's noting scientific at all.
I added about a half a ml this last time from the little bit of water I had left and I've left them on charge now (24v scooter charger) for about 48 hours.  Under finish charge the standing voltage has risen from around 26.5v when I first started messing with the pair to 27.3v now.
I think I'll leave them on the scooter charger for awhile and see if the voltage rises any more then do another capacity check then maybe move them to the SunGuard and let the solar pulse them for awhile.

[wooferhound]

I threw away two 12 volt scooter batteries last year because they were fairly dry. After seeing Zap's results I am wishing I had tried to revive them.

[Madscientist267]

Yeah I think most 'sulfation' in SLAs is actually lack of water.

True sulfation in an SLA shows up (as far as I can tell) as swelling and splitting of the cases.

I had hundreds of these at work sitting on a pallet to be shipped off for dumping (who knows where), the cases swelled, and I never bothered with even trying to do anything to them. Every time I've tried to revive one with a swollen case, I ended up with a shorted cell at the very least.

Just remember that after watering, they do appear to act much more like FLAs than SLAs, as far as I can tell. Apparently it's true, others are finding it too.

Steve

[zap]

UPDATE
After a 48hr charge and 24hr rest the batteries are sitting at 12.88v and 12.82v.  They've always been charged/discharged as a pair because they've always been within 0.01v.

I'm pretty sure each had almost the exact amount of water added but with a feeble mind that get's older every day...
I suppose I now need to do more closely monitored discharge on them separately.

[Madscientist267]

Keep the load light at first, I think it plays a role in evening out the charges across the plates.

Also, don't be afraid to let them 'boil' a little bit during charge. Something like equalization.

From what I can tell, adding the water causes some striation, so they need to be stirred to get things even.

This is especially true if you've managed to get the water somewhat above the plates. Stirring can be difficult in an SLA because of the matting between plates.

Sounds like you're making progress however. Look forward to hearing your final results.

Steve

[zap]

UPDATE

So...
These are the same two 12v/12ah batteries from the first part of this thread.

these are marked as "HOMER" from HUAMAO SCIENCE & TECHNOLOGY CO., LTD

The batteries haven't been exercised much at all but both would hover around 12.85v even after months of sitting idle.

I decided to stick them in an ebike and they seemed to perform fairly well.
Yesterday I did a "no pedal" trip draining them to about 20.5v (10.25v each... although I couldn't measure them separately).
The ride yielded 4.6 miles.
This was full throttle and averaged 12.9mph.

I've never measured the draw of this motor but most sites state it as 350 watt.

What still gets me is how little these batteries weigh compared to a typical 12v/12ah sla.  The latter would be about 19lbs, these two plus the battery case with it's fuse and wiring comes in a tad under 15lbs... go figure

[Simen]

So the max draw of the motor are around 15A @ 24V. Maybe 10-12A average i'm guessing? A 12Ah sla won't give you the full Ah at 1C; maybe 1/3-1/2...

I had several 18Ah sla's of equal weight and size but different make; one from a cheap jump-start-kit. when i recycled those, i cracked open the cheap one, because there was something loose inside, and i discovered a 1kg (ca.) iron bar embedded in a compartment in the bottom!

Edit:
I used 3 of those sla's in my e-bike, and it was always the cheap one that gave out first... Now, i'm using a 36V, 16Ah LiMnCo battery wich weighs only 1/4 of the 3 sla's together, and i have 3x the riding distance...

[Madscientist267]

Another victim made it's way into my collection the other day, and so far I've seen good results.

The basic background is something like this:

12V 5AH SLA, removed from a small UPS, brand new in the box (still had prong protectors on the cord), and was returned because 'it didn't work'.

A friend of mine passed it along to me, and it sat in my car for a couple of months before I got to it. Nice hot, unforgiving trunk, going everywhere I went and then some for I don't even know how many miles, bumps and all.

Popped the UPS out of the box the other day, plugged it in, and sure enough, zip. zero. nada.

No surprise, went for the best guessed culprit. Again, sure enough, 1.4V or so at the terminals. Very nice. A star was born.

I pulled it out, let it sit for about 12 hours to let it cool off (was still rather warm from the trunk), and then laid a 2mA (no typo) charge across it (intentionally current limited to this level) and left it to sit for about 4 hours. After this, it measured about 10.5V.

Ok, time to up the current a bit. Set it up so that when it hits 12.0, it would be drawing 50mA, the C/100 rate. It was nowhere near that when charging was first resumed. Started out just shy of 10mA. After 9 hours or so, it was drawing 35mA (ish) and appeared to still be climbing. At 12 hours, it topped out just shy of the 50mA limit. Measured terminal voltage was about 12.1V.

I let it sit for another 12 hours like this, came back and the current was down a bit, around 40mA. CTV of 12.3V or so.

Ok, lets see if she'll bite.

She did. Upped the current to 100mA, took it instantly (without that recovery 'climb'), and has dropped only to 95mA or so over the course of the last 6 hours. Terminal voltage at last check was 12.4V.

Time will tell, but the math (AH accumulation) points me to about the 20% charge range at this point. Took it a while to get going, so the math probably isn't hardcore-accurate, but gives me an idea.

CTV tells a slightly different story, I'm thinking somewhere in the 35 to 40% range. If I'm right, it will have a recovered capacity of about 2.5AH at the 20 hour rate when it's all said and done.

Stay tuned, I'll inform.

No other special treatment was done. Just a really S L O W charge rate.

Steve