Sealed led acid battery wont charge?

[Darren]

I have pulled an old 7ah 12v sealed led acid battery out of a UPS
When I put it on the charger the volts jump up to 40v, why is this? is the
battery stuffed?


Thanks
Darren

 

[Wild Wizard]

I have pulled an old 7ah 12v sealed led acid battery out of a UPS
When I put it on the charger the volts jump up to 40v, why is this? is the
battery stuffed?

yep and so is your charger (shouldn't be giving 40v to charge a 12v battery)

 

[Arpit]

Well maybe the charger isn't stuffed. Its probably a current limited
supply or equivelant, relying on a proper battery to bring the voltage
down to a sane level without sinking too many amps.

 

[Terry Collins]

I have pulled an old 7ah 12v sealed led acid battery out of a UPS
When I put it on the charger the volts jump up to 40v, why is this? is the
battery stuffed?

Well, you probably need a better charger.
If you want to try and recover the battery, you will need to leave a
charger attached for a a few weeks. Some batteries occcissionally come
back to "life" but quality varies.

 

[L Chung]

I have pulled an old 7ah 12v sealed led acid battery out of a UPS
When I put it on the charger the volts jump up to 40v, why is this? is the
battery stuffed?

One of more of the series connected 2-V cell(s) have developed a high
impedance. No charging can return the battery to normal.

Before you bin it, see what I have done to such a battery to get some
of its life back.

<A
href="http://www.chunglim.freeserve.co.uk/c/sealedbat.htm">http://www.chunglim.freeserve.co.uk/c/sealedbat.htm</a>


L.Chung

 

[John Crighton]

One of more of the series connected 2-V cell(s) have developed a high
impedance. No charging can return the battery to normal.

Before you bin it, see what I have done to such a battery to get some
of its life back.

<A
href="http://www.chunglim.freeserve.co.uk/c/sealedbat.htm">http://www.chunglim.freeserve.co.uk/c/sealedbat.htm</a>


L.Chung

Hello Mr Chung,
you are a man after my own heart

Darrren,
on some of my old sealed batteries, sonnenshien brand,
like the ones shown in Mr Chung's web page, you can
see the outline of the connecting link between the cells.
It is very easy to drill and separate the link between the
cells. Turning a 12V battery into a larger capacity 6 V
battery was easy. I have successfully hack sawed away
one complete side where there were two dud cells to make
a slim 6volt battery.

Darren,
about charging. Bypass the dud cells first as Mr Chung
described. Drilling and soldering is easy.
Try your charger with some series resistors to limit the
current.

I like the constant current method. Fixed current for 12 to
14 hours or whenever I remember days later.

Here is a simple circuit for a constant current charger.
http://wlan.sdvanime.com/wireless-leeuwarden/img/zelfbouw/LM317_datasheet.pdf
Look at figure 7 on page 5.
Resistor R1 sets the maximum current.
For 1 amp, find a resistor around 1.2 ohms 2W or slightly more
in your junk box. Parrallel up whatever you have in your junk.

If you want to make your charger even nicer, you can add
a normal voltage regulator after the constant current regulator.
Build up Figure 5 on page 5.
That way your charger would be set and forget ( almost.)
Constant current of around say 1 amp when the battery
is dead flat and then the current drops to a trickle later on. So
you can float charge at whatever voltage is recommended.

You will need two LM317s one for the constant current section
and one for the constant voltage section. You could probably
use your existing charger as the supply to the two additional
current and voltage regulators.

Have Fun,
John Crighton
Hornsby

 

[Darren]

Thanks for your replies

The charger I have is fine (super nova 250s) I guess it thought there was a
bigger battery installed so it put the volts up.

Thanks Chung I will take a look at your site.

Darren

 

[Russ]

Thanks for your replies

The charger I have is fine (super nova 250s) I guess it thought there was a
bigger battery installed so it put the volts up.

The Super Nova is a constant-current charger, so in an attempt to get the
current up to a target value (I don't know what that charger does in Pb
mode - 1 amp or something?), it pumped up the volts - what you should have
noted was the charge current at 40 volts. As others have mentioned, it is
probably stuffed (or one cell is), but letting the Super Nova have a go at
it for a day or two certainly won't hurt it, as it will automatically drop
the voltage once the battery starts to charge.

Russ.

 

[Darren]

was

The Super Nova is a constant-current charger, so in an attempt to get the
current up to a target value (I don't know what that charger does in Pb
mode - 1 amp or something?), it pumped up the volts - what you should have
noted was the charge current at 40 volts. As others have mentioned, it is
probably stuffed (or one cell is), but letting the Super Nova have a go at
it for a day or two certainly won't hurt it, as it will automatically drop
the voltage once the battery starts to charge.

Russ.

You can set the nova to charge at any current.

It wont charge the battery at all, it just jumps up to 48V and says "battery
voltage to high" or somthing like that.

Darren

 

[Russ]

You can set the nova to charge at any current.

Sure, that's kind of what I meant - you specify a fixed charging current,
and following the I=V/R thing, the charger ramps up the voltage to the load
(battery) until it sees the target current being drawn.

It wont charge the battery at all, it just jumps up to 48V and says "battery
voltage to high" or somthing like that.

Which means, as others have said, that the battery, or at least one of the
cells, is buggered. I was assuming the Super Nova might keep trying to
charge the battery at that maximum voltage until something happens, but it
sounds like the charger is deciding to give up straight away.

As I mentioned before, one method I've heard of is to try a high voltage for
a sustained period in the hope that the battery will come good, but
obviously you need to be around to drop the voltage once it starts charging,
or else it will draw excessive current and something will probably blow up.

Russ.