dual battery problem

Hi,

30 Amp seams a small fuse, the charge form the alternator is most likely lots more,

Try at least a 60Amp fuse

HTH
Ray

Gooday crusty,
the fuse definitely seems to small... hence it's getting hot. Another thing you need to check is the size of the cable between the two batterys and isolator. If that is too small, it will also generate heat problems with the high amperage that takes place during charging.
regards

Check out this thread and the answers by ABR Sidewinder - here

Rgds

Mandrake

I'm not familiar with the Projecta isolator, but if it works like many others, after you switch the ignition off, the starter and aux battery remain connected till the starter drops to a predetermined level (around 12.5 V usually). This is to use excess capacity in the starter battery, but still protect it from getting too low to start the motor.

If you have no load, it can take a long time (sometimes days) for the starter battery to drop. To check this, after running the car for a while and switching off, turn your head lights on. This will put a load on the starter battery (and aux while they are connected). The voltage will drop fairly quickly due to the load (high beam even faster). After a few minutes, you should hear the solenoid (if the isolator has one), click out and the 'charge' light will go out.

The reason you are reading 13.9 Volts without the engine running is you have just switched off the motor and have no load. This is normal. Without load, it will drop over time as the battery rests. This is why you cannot get an accurate reading of a battery's charge with a voltmeter unless it has been at rest (no charge, no load) for about 12 hours or more.

Like the other posters, I suspect the fuse is too low. Fuses take time to blow at currents not a lot more (like several times more) than the rating. There are charts available that show this. If I can find one, I'll post it. In your case, if the actual current going into your aux is 40 to 50 Amps (which is very likely), it will take a few minutes at least for the fuse to heat up enough to blow. On the other hand, if there was a short circuit and several hundred Amps was flowing, it would take a second or 2 at most.

In the situation you have described, I use a 60 Amp reset circuit breaker.

Hope this helps.

Norm C

wow thanks for the quick replies guys,
hmmm I'm getting the hang of these things bit by bit,I'll take out the "glass fuse" holder that comes as part of the box and replace it with a quality blade fuse holder and throw a 60amp fuse in ... see if that cures my ailments.

You say: "Disconnecting and reconnecting the isolator to the starter seems to reset it"
I believe you have an Isolator (wiring) problem, it should be the exact same voltage when it is re-connected again.

As stated above the 13.9v is ok under the conditions stated.

However, check out the actual wiring connections of *ALL* the battery cables associated with the batteries concerned, make sure the positivevs are secure and all earths are tight without loose wire anywhere.

Maîneÿ . . .

My sparky told me if you want to runany more than 15amps always use a curcuit breaker instead of fuse it has never let us down.