caravan charger.

[Deleted member 9648]

I have a mate with a towing caravan battery charger problem. Scenario is the original fixed charger failed while he was away and he replaced it with a new straight swap unit...(3 stage 18a max unit). The battery is a 110ah unit which takes a charge fine on a separate trickle charger.
The issue is that as soon as the new charger is switched on the 15a fuse in the caravan fuse bank (wired into the battery + line from charger to battery) gets very hot and blows. I have checked wiring and connections and all appear ok....faulty charger? or is it the fact that the new charger is capable of 18a the problem?
With no experience of car/caravan 12v electrics advise appreciated.

 

[Richard Burns]

Drawing 18A on a 15A fuse certainly does not sound good but I would not really expect the fuse to blow quickly.
That fact that it is getting hot seems to indicate that the circuit at that point cannot cope with the current, is there enough time to measure the actual current drawn or to fit a higher fuse for a short while to allow the measurement (sorry, really bad practice!).
Is the fuse seating correctly in the holder? As it may just be damage, dirt or corrosion at the fuse holder causing a high resistance localised heating and accelerating the fuse blowing.
However I am in the same boat (car?) regarding 12V electrics.

 

[tazz]

Sounds more likely the battery has gone dry......shunt test the battery first.

 

[Deleted member 9648]

Thanks for the replies,battery takes a charge fine and works caravan electrics when charged remotely,it's only when connected to the caravans integrated charger that the problem happens.All connections and fuseholder appear ok.
I think that the new chargers max current of 18a is the problem,but I am not sure whether this current is actually what it supplies constantly when charging. Checking with manufacturer today.

 

[tazz]

With lead acid or gel...the voltage must remain constant @ 13.8v the charging current can then be variable or fixed. The battery will therefore charge at a given rate.... say 2 or 4 amps.
If one or more battery cells fail, they usually fail short circuit. Giving rise to a lower internal resistance and hence more current.
We see this daily with fire and security batteries, blowing the charging fuse after aprox 5 years of use.

 

[Deleted member 9648]

Just in case anyone is interested I contacted the charger makers who informed me that the charger detects a low charge and goes into boost mode and does indeed chuck 18a into the battery,hence the existing 15a fuse getting hot! I now have to upgrade the fuse and wiring to 20a spec...a mate in need and all that lol.