How does the leisure battery charge through alternator

[sharkjazz]

Have tried to find this information through search but couldn't find anything.

Van is 1988 Westfalia, no zig unit as I have seen mentioned in over threads, just a black box under the rear seat.

When I am driving, the alternator goes to the relay thing and then charges up the batteries. Will this top up the leisure and starter battery to full power, i.e. does it know how drained the batteries are and charges accordingly. Or will it only charge the batteries up, if power is being taken from them at that time? i.e. stereo on, so alternator puts the charge back in the stereo took out, but it will not put back the power the stereo took whilst the van was parked up?

Thus, eventually after a while, the batteries may be very empty and will need to be plugged into a charger overnight? If this is the case, is there anything I can buy / modify that will allow the lesiure battery to take additional charge whilst driving?

[ghost123uk]

When I am driving, the alternator goes to the relay thing and then charges up the batteries. Will this top up the leisure and starter battery to full power,?

The simple answer is = yes

It will give a high charge to either / both batteries if they are low on charge and will settle to a trickle charge once they are charged up. = Nothing to worry about

Just don't run either of them dead flat as that is not good for them.

[Red Westie]

The starter (main battery) charges directly from the alternator, where as the leisure battery charges through a relay that connects both leisure and main batteries together WHEN triggered by the alternator.
This connection (main to leisure) doesn't happen until the engine is started, hence in theory the starter battery should never become flat as it is kept seperated whilst camping (as you have carried out the radio/interior light mod)
The regulator part of the alternator senses charge state (how discharged the batteries are) and the charge rate (how much power is put back) is regulated accordingly until both batteries are fully charged.
Fully charging both batteries from a fairly discharged state can take many hours of driving especially if you running with ancillaries turned on (lights/stereo/blower/heated rear screen etc) so a quick hours trip home will only part re-charge if they were flat discharge state.

Martin

[ghost123uk]

A good and more comprehensive reply there from Martin

If you have any sort of multi meter you can check if they are fully charged.
They should measure around 12.6 volts after a couple of hours at rest when fully charged.