Friday, Jan 23, 2004 at 21:05
Moose
Here's how I've done the job on my diesel landcruiser,
1. the wire which activates the solenoid is live when the key is ON (ie normal driving)
2. install 2 relays in this wire, configure them to work in the normally closed mode using the 87a terminal. This means that when power is applied to the relay, it opens or turns off.
3. switch one of these relays from the glow plug circuit , and the other from the starter solenoid.
All of this means that the 2 batteries are isolated from each other; when the glow plug circuit is live (this is on a timer and will vary depending on the ambient temperature and the engine temperature) and also when the starter motor is in operation - or both.
This system is simple, cheap and it works ok. Using the oil pressure switch (as noted above) is another option.
Over the years I've tried various methods of wiring up an aux battery with varying degrees of success. FYI I list these below.
a) Use 1 huge size truck battery to do everything (start ute & run auxillaries) - simple, heavy, hard to mount, expensive, worked ok on petrol engined ute.
b) Hella solid state battery isolater - simple enough & provided isolation between the 2 batteries , but dropped about 0.8 v from input to output - not a problem IF your alternator has an external, adjustable voltage regulator - just crank it up a bit.
c) Cole Hersey battery switch - was already installed when I bought the ute - worked sort of ok, used lots of battery cable resulting in voltage drop, relied on my memory to operate it !!
d) ElectronicsAustralis battery isolater kit - looked impressive with flashing leds but didn't work as required on a long trip away, not sure why , I just binned it and used method e)
e) a wire link between the 2 batteries - a tempory measure which worked ok but isolation required the remembering to remove/ replace the link each night/morning.
f) solenoid between the 2 batteries - the same electrically as e) but controlled via the ignition key, furthur refined by the addition of the 2 relays as detailed above.
I hope above ramblings are of some use to you, and others.
Cheers , Brownie
AnswerID:
44149