How do I charge this battery?

[David_Web]

I have 29 of these double 6V packs that I want to use. They are from an old 4KW UPS but I don't know their condition or how old they are. I took a measure and one of them where 0.6V (that's in series). I have no experience with these kind of batteries. Carge them in paralell or series is up to you, you know what's best. What charger should I use? how should it charge? And while I'm at it, how many A can you put on it as a load?

 

[London Lad]

Charge a single battery or multiples in series. Don't charge in parallel.

Charge with a constant voltage charger or power supply. I.E. set the voltage and let the current vary.

If you are going to cycle the battery (i.e. charge it then use it to empty) then charge 2 batteries in series at 14.4 volts.

If you are going to float charge (i.e. keep them on charge all the time) then use 13.5 volts.

If you are measuring 2 in series at 0.6 volts then they have probably had it. They don't like being left in a discharged state.

 

[winny]

If all of them read 0.6 V, they are dead. If you would manage to charge them, their capacity would be very very low. I would advice against trying to revive them when the voltage is that low.

If the other ones are ok:
Charging two in series, like they are connected on the picture with a 12 V charger should be ok. Any 12V lead-acid charger should do, and try to keep the charge current low, like 0.5 A perhaps.
A bit better is to charge each 6 V battery one by one, but 6 V chargers are not as easy to find.

EDIT: Hey, you're from Sweden! I missed that one. God jul på dig!
Biltema has one fully automated 12 V SLA charger for about 250 SEK which would work fine. CTEK has several, both 6 V and 12 V, but they are expensive. PM me if you need to borrow one or need any assistance!

 

[London Lad]

I don't mean to be rude but "Any 12V lead-acid charger" will NOT do.

You must use a purpose built SLA charger or a bench power supply as I detailed above. Constant VOLTAGE is the key.

However as winny says at 0.6 volts they are almost certainly useless.

 

[Ra]

Hi David_Web,

These SLA batteries should be kept fully charged at all times, London Lad already said how to charge them properly.

The only thing I can add is that they don't like fast-charge !! The nominal charge current should be 1/10 C, so 330mA in your case. If you really are in a hurry then max 1/5 C is acceptable, but not recomended.

If you know how, they are very easy to maintain: A constant voltage charger at 13.5-13.7 volt can be hooked up for ever !! Charge them after every use, no matter how short, they don't have a memmory-effect like NiCads do.

However, when they are stored empty, sulfates are forming inside, permanently decreasing capacity. And with 0.6 volts total (in series) I'm afraid yours are quite dead!! Cycling them can propably bring back only a few % of their capacity !


Regards,

Ra.

 

[David_Web]

I suspected that they where done fore. But it would not hurt to try.

I read around a little on the net and apparently you can pulse charge it to revive nearly dead batteries.

"Reviver is a compact small electronic device, Employing microprocessor Technology, it is guaranteed to dissolve sulfate crystals back into the battery’s electrolyte solution. Reversal of sulfating accumulation in the existing batteries, and also prevents sulfating formation in new batteries."
"The Reviver units are manufactured according to the approved International Standards. The rating can be continuous or intermittent. The Reviver current is between 0-4 Amp and the Reviver frequency is 8000-12000 cycles/sec."

Winny: God fortsättning!
Do you think that the biltema charger would work? "Max. 2 A Charge current. Charge capacity 6–20 Ah." It says it can revive nearly dead batteries. I'm worried it will fry it instead.

I have a benchsupply that I can set the current/ and or voltage on. not sure it would help without removing some oxidide/goo/whatever first.

 

[London Lad]

...................
I have a benchsupply that I can set the current/ and or voltage on. not sure it would help without removing some oxidide/goo/whatever first.

No you are right, it won't!

In my experience it is very hard to recover a SLA battery to any usable performance once it is as low as yours are.

But I have never tried the Reviver!

Years ago people used to built SLA chargers which produced 'rough' DC (1/4 wave rectifiers and no smoothing) and claimed they could reverse sulphating but I never had any luck with them.

Good luck!

 

[MrAl]

Hi there,

I charge my 6v LA battery at a rate of C/8.
The charger must be voltage regulated yes, but also current limited.

 

[London Lad]

The important thing is to keep the voltage constant (the opposite to charging NiCads or NiMh where constant current is used)

If you set the charge voltage correctly (as described above) then the current will look after itself.

Having said that, if the battery is very flat you may have to limit the initial charge current for a few minutes but constant voltage throughout the charge is the most important thing. If in any doubt opt for the float charge voltage as above.

 

[winny]

David_Web,

I actually built one of these devices which pulses the batteries in order to disulfide them. I have absolutely no use for it at the moment so if you want to, you can have it as a late Christmas gift. Drop me a PM.
Yes, the Biltema charger might push a bit too much current. You won't fry the cell as in setting it on fire, but it will probably get unnecessary hot and shorten their lifespan. Your CV/CC power supply will do the trick as the other ones explained.

 

[65535]

CC/CV is a great way to charge batteries just stick an Ampmeter on the output and watch it when it starts going down in current that means its charged and set the voltage to 6 .1 volts for good measure.

 

[London Lad]

.....nevermind

 

[David_Web]

Just to see if it is of any use I hooked one battery up. I starts up at 0.1A so I will see how it goes. Running at 14.36V
The A is ticking up slowly so hopefully it works.

Winny: I will see how well this one takes charge and if it looks like it takes charge ok I will contact you on your offer.

Thank you all for all the help. I appreciate it.


*Edit*
It is now pulling 0.8 A so I lowered it to 13.61V And it it still pulling 0.8A
The battery is slightly warmer then the surrounding things but it's nowhere near hot.

 

[London Lad]

The rise in current you see is probably some sulphide breaking down. You should then see the current start to drop as the battery takes the charge.

If the battery was in good condition the current would start high and slowly drop off.

You will probably get a charge into the battery but I would be vey supprised if you get any capacity worth having. Good luck and keep us posted!

 

[London Lad]

BTW the battery is fully charged when the current stops dropping not when it starts dropping.

 

[David_Web]

I edited while you wrote.

The current is now at nearly 1A. I have set the limit at 1A so the voltage is dropping, should I let it be like this or should I abort?

*Edit* One battery takes 7.5V while the other takes 5.57V

 

[winny]

FAST EDIT:

Decrease! C/3 is too high for an old SLA battery.

David_Web,

Just in case:
Looks like you have been charging for half an hour. I don't know how much current your power supply can, err, supply but it might be a good idea to not just only voltage charge the battery, but current limit it as well. Something like 0.3-0.5 A might be good. Leave the voltage setting as it is and just decrease the current (well, you don't actually decrease the current, but I'm too lazy to explain) if you happen to have it set to max.
Otherwise, if something bad might happen in your battery and if you PS can deliver 20+ A and the battery shorts (does happen occasionally), well, I wouldn't want to stand near it.

 

[David_Web]

Thanks. I have now set it at 0.3-0.4A and it is now feeding 10.4V

 

[Ra]

BTW the battery is fully charged when the current stops dropping not when it starts dropping.

Yep, it is fully charged when it stops dropping.

If the batt is in good condition, and you apply the right voltage, the current stops dropping at a few milliAmps...

EDIT: In most cases, when your batt is not in good condition, the current also stops dropping at a few milliAmps.. Only much sooner..


Regards,

Ra.

 

[London Lad]

BTW the max charge current for that battery is 1 amp (0.99 amps to be exact!)

As the batteries are obviously out of balance it may be better to charge them individually at half the voltage I gave in my first post (max current still 1 amp)