Quick sanity check before I grumble about 12V charger

[numpty with a crowbar]

Just bought a 12V (12A) battery charger for the caravan battery. Hooked it up this morning and left it for 3 hours > came back to it and there doesn't appear to be any charge in the battery.

I've tested it with a miltimeter (while both connected to and disconnected from the battery) and the reading's coming back as around 2.5 volts - I assume it's borked and should be spitting out around 13-14V?

It's not a trickle charger BTW. Fuse is ok and the "charging" LED is lit, but nowt much in the way of power.

Just want to check before I take it back so I don't look like a divvy... Cheers

 

[ricicle]

If the battery is u/s then the charger will not attempt to charge it.

 

[numpty with a crowbar]

If the battery is u/s then the charger will not attempt to charge it.

Cheers - what about if the charger is completely unhooked from the battery - will it deliver any voltage across the terminal clamps that I can measure?

 

[Alarm]

Some will some will not.

Not exactly the answer you want is it
What does the IM say?

 

[JohnW2]

Cheers - what about if the charger is completely unhooked from the battery - will it deliver any voltage across the terminal clamps that I can measure?

As you've been told, some (probably most) will and some will not. However, it's worth a try - since if you do find something around 14V coming out of the charger (when not connected to a battery), then the charger is probably OK. If you don't measure any appreciable voltage, then you can't be sure what that means. The best test would probably be to connected the charger to an appropriate (designed for 12V) load (e.g. a 12V bulb/lamp) and see if it works.

Kind Regards, John.

 

[wotan]

most modern chargers are electronic load sensing and will not charge if the battery is extra low or damaged, you can however dummy them into working by temporarily connecting another good battery via jump leads, connected in parallel, when the charger starts to deliver, just disconnect the good battery.

Wotan

 

[numpty with a crowbar]

Cheers all - looks like I've got some testing to do tomorow morning:
1) try the charger running a 12V light
2) Hook an extra battery on (got plenty charged from some DIY solar panel rigs in the shed) and try and trick it into charging

Failing that it's back to the shop to replace and an additional grumble about the lack of a useful manual

But thanks for the advice - time to annoy the missus and setup shop on the kitchen table

 

[ericmark]

most modern chargers are electronic load sensing and will not charge if the battery is extra low or damaged, you can however dummy them into working by temporarily connecting another good battery via jump leads, connected in parallel, when the charger starts to deliver, just disconnect the good battery.

Wotan

As said many chargers have built in protection to stop burning out diodes etc should it be connected the wrong way around.

For a caravan battery one would expect some level of automatic control.

Best quality would want to charge the battery at max amps until the voltage reads 14.8v then it will hold at 14.8v until the current drops to 5A at which point it will drop the volts to 13.2v. Should the battery not take charge then likely it would quickly drop to 13.2v what is called a float charge.

Lower quality will likely just have a float charge voltage but a little higher likely 13.8v.

Car battery chargers are designed to give an equalising charge and although likely the output would be much lower it could under no or little load hit 16v not a true RMS value the battery is acting like a capacitor. Also car types can have a timed or a heat sensor to give a boost with silly currents up to 300A so they do need some safety system. 300A can do a lot of damage.

A 20A battery charger like
this will cost around £160 where as this one costs £20 clearly very different. Even the cheap one advertises having short circuit protection but to charge an 80AH battery one is looking at 3 hours to 20 hours clearly very different chargers.