Checking on-board charger output

[takisawa2]

Hi.
After a few issues that I thought were all down to the battery, I dropped a meter on the battery leads on the caravan expecting to see the normal 13.8 volts (or so), but only reading 0.2v.
(The battery is off the van at the moment, connected to my CTek unit in the garage).
With the leads just lying loose in the battery compartment, & the on-board charger on, should I see a reading ? Do they need to be connected to a battery to give a reading ?
Am I right in thinking the on-board charger may be duff ? The 12v side from the transformer looks ok, I'm getting 12v at various points.

Elaborating on the issues I mentioned, I found a dry cell after the winter storage, I topped it up & let it charge on the van. We noticed a smell & the battery getting hot, so I removed it from the battery locker to cool it down. Moments later the battery exploded, sending shards of plastic all over the pitch, & coating the underside of the van in battery fluid. :-(
Hence the cautious approach. I wonder if the charger might have been over charging also.

 

[Jaydug]

We noticed a smell & the battery getting hot, so I removed it from the battery locker to cool it down. Moments later the battery exploded, sending shards of plastic all over the pitch, & coating the underside of the van in battery fluid. ...................... I wonder if the charger might have been over charging also.

I had this happen a couple of years ago. When I set off on my journey the battery was fine since it powered the mover to get my van from its parking spot onto my drive. The van was parked for 36 hours on the ferry followed by a 120 mile drive to Salamanca. It was during the night that the gas triggered the CO alarm followed by the smell by morning and eventually I found the battery hot - so hot that I couldn't touch the terminals. Fortunately mine didn't explode. With a new battery fitted the voltage was showing 13.8 and the charger was ok. I suppose one cell had suddenly died.

 

[ProfJohnL]

Hi takisawa2

It very difficult to diagnose this sort of issue and whilst you have tried to give us information, the results you have are insufficient for me to form a probable scenario.

Depending on how old your caravan is, the type of charger fitted can be substantially different, older ones may just be a rectified sine wave from a transformer, which relies on a battery as a smoothing element for the circuit. Without a battery a meter may detect 21 or 22V,

Others have a regulated smoothed output of 13.8V dc which will not only keep a battery topped up, but are capable of running a limited nuber of 12V appliances without a battery connected.

Some of the very latest units have smart charging included.

I would have expected to see 13 to 14V on the battery wires, but it may be you have a smart charger which looks to see if there is a battery connected before trying to charge it. Perhaps you have some of your switches set incorrectly, of may be a fuse has blown.

Again you tell us the batter now has a dry cell, what we can't know is if that is is either the result of a charger problem or the cause of the problem.