A slightly worn 52 Ah battery, any experiments worth doing? - Page 1
Forum section: electronics / projects

author: jitter
author_rank: Frequent Contributor
timestamp: June 20, 2016, 05:48:40 pm
content: Okay, so now I have an almost worn spiral cell 12 V 52 Ah car battery that I replaced a couple of days ago because it would no longer crank the engine.I've had it on a dumb 12 V 6 A battery charger (basically just a transformer and a rectificier). It started out at 4 A but now it won't drop below 1 A while simultaneously it won't rise above 14.0 V. At the same time, the battery gets lukewarm. I guess that's what you get with that type of charger, or is it indicative of a problem with the battery (assuming I didn't already know that)?Just after it had stopped cranking the engine, there was still a voltage on it high enough to not cause sulfation and it would spin the ventilation fan and light the control lamps just fine, it's just that it no longer had any real grunt. So does that mean that one of the cells has gone higher internal resistance?So, before I chuck it out (read: recycle) I plan to see what capacity is left, and at what currents (to a max. of 300 W, still 25 A).I have a 300 W electronic DC load. What would be a good current to drain the battery with to, say 10.5 V, and measure the remaining capacity?Other things I can do (short of shorting the battery or other dangerous things)?

author: Gyro
author_rank: Super Contributor
timestamp: June 20, 2016, 06:08:38 pm
content: The first thing I'd do is try to gain access to the filling ports on the cells, I'd bet that one of them has got too low. A bit of distilled water could potentially restore it to a reasonably useable battery (with some loss of capacity obviously).

author: jitter
author_rank: Frequent Contributor
timestamp: June 20, 2016, 06:36:29 pm
content: Uhm, this is a completely sealed type that can be used upside down (if need be)...

author: SeanB
author_rank: Super Contributor
timestamp: June 20, 2016, 07:53:04 pm
content: Warmest cell will be the dry one. That top does come off, but it will not go on again well without copious amounts of silicone sealer afterwards.most likely is that the one cell has cracked a connection internally and this has isolated most of the cell, which is why it will not deliver high current.Test it to see just how much capacity it has left, and as you can do 300W of test go for the full 25A, which will give a good comparison to the C20 rate, and is the manufacturers test in any case. My bets are it will fall off after 2 hours or less

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 20, 2016, 10:37:30 pm
content: The 25A rate is only 110 minutes brand new. It is lower than what would be predicted from the Ah rating (measured at C/20 rate) due to internal losses.What terminal voltage do you get if you disconnect the charger for an hour or so? One common failure mode is one cell going partial short.

author: jitter
author_rank: Frequent Contributor
timestamp: June 21, 2016, 04:02:50 am
content: I will give those things a try, but I must first get some heavy gauge wire. What cross section am I looking at for 25 A max, say roughly 1 m/3 ft long?After a night on the charger I had it disconnected for a couple of hours, and it went to about 12.7 V. Now the patient has been on life support for another day, so when I'm off to work I'll check what its vitals are and disconnect it. Then, say, in another roughly 9 hours I'll see how it survived on its own....

author: jitter
author_rank: Frequent Contributor
timestamp: June 21, 2016, 06:34:01 pm
content: Quote from: SeanB on June 20, 2016, 07:53:04 pmWhen I came back from work, the battery voltage had stabilized at 12.5 V, about 9 hours after having been disconnected from the charger.I found a piece of 2x 6 mm2in my stash that I used to hook up the battery to the electronic load. Then I ran the battery programme @ 25 A and a minimum voltage of 10.5 using remote sensing at the battery terminals to account for the voltage drop in the wires (which turned out to be only 0.35 V @ 25 A).@25 A, the fun didn't last long, not even 10 mins. The load clocked up a mere 5.5 Ah before the 10.5 V limit was reached and the discharge aborted.I'm going to repeat it at a far lower current, but first the long wait for the recharge...Edit: I removed "slightly" from the title. I think this battery is in far worse shape than I imagined. It did not just fail all of a sudden, it had worn to the point where it could muster one start, and I had been lucky for a couple of months now...

author: SeanB
author_rank: Super Contributor
timestamp: June 21, 2016, 08:20:32 pm
content: 5.5AH says at least one cell has got a cracked plate and this left only a small area of usable active material on it.I had a similar thing this morning, I left a SLA on the float charger overnight to refresh it, and this morning I walk in and sniff that toasty battery smell, with the battery being warm and unhappy. Disconnected it, put it in the recycle shelf and connected one of the other 5 spares in it's place. I guess it too has got a broken plate connection, but then the remaining cell developed a short and thus the 1A charge from the float charger did the rest and cooked it gently.

author: jitter
author_rank: Frequent Contributor
timestamp: June 22, 2016, 07:07:04 pm
content: At a much lower current of 10 A, it still doesn't even make 10 Ah, so yeah, this looks like most of the capacity has gone.I'm going for one more charge and discharge, but now at 1 A. Just out of curiosity.

author: jitter
author_rank: Frequent Contributor
timestamp: June 27, 2016, 05:37:05 am
content: Even at a low current of 1 A the capacity is way down to less than 14 Ah.So yes, I'm convinced the battery wasn't just flat when I replaced it, it really is worn beyond a usable point.

author: jitter
author_rank: Frequent Contributor
timestamp: October 14, 2016, 07:52:43 am
content: Quote from: SeanB on June 21, 2016, 08:20:32 pmA quick revisit to this thread.I was just tidying up some rubbish and found this battery again.I had put it away charged and it was still sitting around 12.5 V, so I decided to do one good deep discharge at high current. First I topped it off with a new automatic charger (€ 15 Lidl cheapo) to test if that worked and then put it on the electronic DC-load.I could feel after a few minutes that one of the six cells got noticeably warmer than the rest (@ 30 A discharge), which after about 15 minutes had become quite pronounced. The one cell was now warm while the other five remained cool to the touch.So yeah, SeanB's diagnosis has been confirmed.Edit: I just realized: the bad cell was the one sitting closest to the radiator...

author: tautech
author_rank: Super Contributor
timestamp: October 14, 2016, 08:05:37 am
content: Quote from: jitter on October 14, 2016, 07:52:43 amProbably just coincidence.