Voltage Matching

[Alan Zoff]

I have a portable jump starter/air compressor which contains a sealed 12v lead acid battery. It comes with a mains charger unit to keep the battery topped up. There is no data plate on the charger and I was surprised when I checked the output with my multimeter that it gives out 22v. Given that the battery is 12v, I was expecting the output to be around 13.5v as would be the case with an alternator charging a car battery.

I tested my meter with other plated chargers and it seems to be reading correctly.

Am I missing something? More importantly, is it safe to use a 22v charger to charge a 12v battery?

[Dave&Olive]

hi ok

  That's the no load voltage....[:D]

  Dave

[Alan Zoff]

Thanks Dave. I'm sure you are correct but does that mean that it's the correct output to charge my battery.

Sorry. Not my subject.

Alan

[Dave&Olive]

hi ok

 Going back to my college  days ...a dynamo will fully charge a battery an alternator can only half charge one ..it`s only amps that can kill you not volts ....so if the amps drop when you are charging then it looks like it`s working ok ,if not ?? lead/acid batteries are hardy little sods just think of the temp changes and conditions they put up with ..just charge it and keep your eye on it ....but make sure it is not connected to your car /? if you think it`s dicky

 dave 

[Alan Zoff]

Thanks again Dave. As usual, I am better informed if none the wiser.

[Chancer]

Mmm, more like less the wiser when it comes to the properties of dynamos and alternators!

Lead acid sealed batteries will certainly tolerate a higher charge voltage than that given by a car alternator, from memory the no load charging voltage on most burglar alarm panels which use the same batteries was in the high teens.

Editted, same story for ni-cad chargers for battery drills, 18 volt ones typically produce 24volt off load.