split charge system

I want to build a split charge system for my series 3 diesel. Does
anyone have plans for such a system?

Peter Blaabjerg

This is very easy. Use a relay that operates from the ignition switch. This
only energises when the engine is running and connects the second battery to
the main battery for charging. When the engine stops and the ignition is
switched off the relay disconnects the second battery from the first and
prevents it discharging the main battery when using the second battery.
Heavy duty relays for this purpose are available from caravan shops.
Cheers,
Peter

It is better to take a feed of the alternator. That way the two batteries
are connected after the engine has been started (and the alternator starts
to charge). If you take the feed for the relay of the ignition switch the
two batteries will be connected before the engine is started and part of the
current for the starter motor will be taken from the second battery. Since
this often is a leisure battery (for low currents but deep discharge) it is
not made for these large currents and will quickly deteriorate.

Pieter

"MR!PETER.F CAPLEN" <[email protected]> wrote in message
news:[email protected]...
> This is very easy. Use a relay that operates from the ignition switch.
> This
> only energises when the engine is running and connects the second battery
> to
> the main battery for charging. When the engine stops and the ignition is
> switched off the relay disconnects the second battery from the first and
> prevents it discharging the main battery when using the second battery.
> Heavy duty relays for this purpose are available from caravan shops.
> Cheers,
> Peter
>
>