How to charge a lead acid bat. - Page 1
Forum section: electronics / general

author: Mo3tasm
author_rank: Contributor
timestamp: May 20, 2016, 08:45:43 am
content: I have this battery that belongs to a ride-in kids motor, I need to charge it, but not sure what kind of charger I should use,What are the ratings for such a charger?Thanks in advance..Note to admins: If this is not the right section for such a topic, please move it where appropriate.

author: tautech
author_rank: Super Contributor
timestamp: May 20, 2016, 09:08:30 am
content: Standard recommendations for charge rate are C/10. (C = battery capacity A/hrs)In this case 2 amps for ~10hrs.....theoretically.Your case is Cyclic use and when the current drawn is minimal @ 7.5V consider it charged.In lieu of a dedicated charger any bench PSU can do it, just be sure to keep within the max initial current.

author: Mo3tasm
author_rank: Contributor
timestamp: May 20, 2016, 09:18:48 am
content: Great thanks, one last thing. How exactly the the wiring should be?, the battery as you know only has two terminals, one + and one -.

author: tautech
author_rank: Super Contributor
timestamp: May 20, 2016, 09:30:26 am
content: Quote from: Mo3tasm on May 20, 2016, 09:18:48 amIthinkyou mean polarity WRT the charger.+ to + and - to -

author: Ian.M
author_rank: Super Contributor
timestamp: May 20, 2016, 09:57:05 am
content: If its been left flat too long and its terminal voltage is under 5V, its probably FUBARed.If you are using a bench PSU to charge it you *MUST* have a power diode in series, otherwise loss of mains supply with the battery connected is likely to damage the PSU. I'd use a 3A 1N5400 series diode. Its 10AH, so C/10 would be 1A, not 2A as previously suggested. The acceptable charging voltage range is conveniently printed on the case, but you need to allow for the diode drop, so add 0.5V. I'd set the PSU for 7.9V, with a 1A current limit before connecting the battery. If you are using the cyclic charging voltage, stick it on a time switch set to cut power after 12 hours. If the battery is not fully discharged reduce the charging time accordingly. If you need to trickle charge it continuously you must use the standby (float) charging voltage.

author: tautech
author_rank: Super Contributor
timestamp: May 20, 2016, 10:13:15 am
content: Quote from: Ian.M on May 20, 2016, 09:57:05 amYep, eyes need testing.

author: ion
author_rank: Regular Contributor
timestamp: May 20, 2016, 11:03:07 am
content: IIRC the maximum current you can safely charge a lead acid battery at is C/4. So you can go up to 2.5A on that battery if you use a proper charger that will not overcharge it, although it's better to charge it slower if you're not in a hurry.If you just use a current limited DC supply, I'd agree with the above posters and go with a maximum of C/10.

author: Jeroen3
author_rank: Super Contributor
timestamp: May 20, 2016, 11:25:53 am
content: Quote from: Ian.M on May 20, 2016, 09:57:05 amNot anymore for modern batteries. I've had some NP1.2-12 (12V's) accidentally discharged to below 6. You'd think it is over when it's that low.But charging it at 100mA for a day fully revived it.

author: Ian.M
author_rank: Super Contributor
timestamp: May 20, 2016, 11:42:30 am
content: Its worth a try, if there are no visual signs of distress and they haven't been left flat for months or years in a hot place, but once they get down to a voltage where its likely one or more cells have reversed + extended storage flat, the odds aren't very good.Also, recovering severely discharged sealed Lead Acid batteries is more of an art form than a science - If you can get them desulphated enough to take charge, over-charging can pop the vent valves or seals, which may not reseat properly, resulting in rapid failure, and there is always a small risk of a hydrogen explosion when attempting to recover an abused battery.The advice I gave in the previous post is far from being an adequate tutorial on battery charging - it was merely aimed to improve the O.P.s odds of success while doing no harm to the O.P, their equipment or the battery.

author: tautech
author_rank: Super Contributor
timestamp: May 20, 2016, 12:00:52 pm
content: Quote from: Ian.M on May 20, 2016, 11:42:30 amIn the past Iimproveda few with desulphation but only enough to learn that the process was only postponing the inevitable purchase of a new unit.IMHO desulphation was a waste of time for small SLA's.

author: Ian.M
author_rank: Super Contributor
timestamp: May 20, 2016, 12:25:23 pm
content: Quote from: tautech on May 20, 2016, 12:00:52 pmYes. Even if you get reasonable success, the result for sealed batteries always has that 'gypsy' feel and similar life expectancy, and leaves you thinking of paint-on driveway 'resurfacing' or second hand trucks with the differential 'fixed' by adding sawdust.There's a fair chance of recovery with a flooded battery with removable caps if you can drain and filter the electrolyte, flush out the sediment, replace the original electrolyte, fully charge till it gasses heavily, cycle it a few times and finally recharge and replace the electrolyte with new at the correct S.G. but you always loose some capacity, and the self-discharge rate tends to increase. Its also a nasty, dirty PITA to do with the risk of acid burns, and results in toxic waste.