Charging a 12v 72ah car battery with a PSU

[Darren Hibbert]

Hi.

Hope I'm in the right section.

I have a discharged 12v 72ah sealed car battery and want to charge it up full. I don't have a car battery charger but have a bench power supply 0-20A 0-30v.

What should I set on the LED display? I believe about 14.5v but what about the amps?

[stj]

14.8v
amps depends on how long you want to wait.
and how thick the wires are
dont forget if you charge it you need to allow for hydrogen-release - so dont do it in a closed space or near sparks/fire

[petehall347]

battery will take what it takes amps wise .it should drop as it charges it if its a good battery . you can go up to about 16v but nor recommended really .old cars often went that high . 13.8v will charge it . 14.4v will charge it a bit more .

[sam_sam_sam]

It depends on how low on charge this battery is and how long it has been in this discharge state
if its very low voltage and it has been in this state for a long time more than a week

I would recommend that you slow charge it set your voltage at 14.5 and your current for about 5 amps until you voltage goes above 12 volts and then you might be able to go to 10 or maybe higher as long as your current does not go down and your voltage does go up drastically if the voltage goes drastically turn your current down and let it charge longer at 5 amps

One note if you have very high voltage from the beginning trying to charge the battery it might not be very good anymore
Another note do not leave it charging with this voltage for a long time if your current is below 3 amps because you can have a situation where you might be boiling the liquid out of the battery cells a safer voltage might be 13.8 volts and a current less than a amp or less concerned it fully charged now weather or not it pass a load test is another story

I hope this helps you with your battery issues

[petehall347]

if battery is still good the voltage should come back up in short order like seconds to a few minutes . if its well discharged it might take a week or so before it charges fully . if so never let it discharge again as it will likely kill it .been there done that enough times . if its relatively new and hasn't been frozen whilst discharged it should come back to life .

[redwire]

any bench power supplies get damaged charging batteries. Especially those chinese ones.
Anytime you get backfeed from the car battery back into the PSU, it kills it. They can even catch fire and burn up. I have seen it happen if you power off/mains fail while charging. Or if the PSU voltage is far below the battery voltage like a few V and you then connect the PSU to the battery, it can damage pass transistors, IC's etc. in linear PSU's.
I would recommend using an inline fuse and series-diode if you are really not sure about the PSU being ok "charging". But check its user manual. Most will say if it's OK for charging batteries or not.

If the battery is old or was totally drained, it needs extra care. It could be sulphated. You can't charge it hard and fast.
AGM most makes is 14.40-14.70V bulk charge, float 13.50V and temp compensation -5.00mV/°C/cell. Max. current is 10% of C₂₀ or 7.2A here.

Roughly, I would set the PSU to 14.40V and current-limit to 3-7A or less if the battery needs reconditioning. Leave if for several hours and see what charging current drops down to.

Here are smart charger algorithms, which are basically what people here like me will advise.

[Darren Hibbert]

Excellent answers. Thank you very much.

The battery is only one year old and has only been discharged for 24 hours. Ideally I'd like to put it on a 14 hour charge overnight.

[redwire]

If it's only been dead 1 day I would charge at low current until terminal voltage comes up past 12.0V try a few amps.
It will take more than 14 hours to recharge unless you are over 6A.