2nd battery

[darryl]

hi my brothers just brought a t2 l reg 1994 hes got 2 batteries in his my question is i have plenty of room to fit second battery under air box his leads are earth to body then positive to positive on first battery would this be the same setup for my mav thanks darryl

 

[zippy656]

Should have a split charge

One for a caravan would work

 

[solarman216]

problem with just connecting two batteries together is that if say you leave your lights on and drain the battery you drain both, if they were split then you will have a good reserve start battery should you need it, there a several ways of connecting these, but it will depend on your reason for having a 2nd battery, Rick

 

[kitchenman]

I did mine by picking up the live that goes to the charge light, this triggers a 45 amp relay, wired to the alternator
pics are possible, on my phone somewhere

 

[solarman216]

I did mine by picking up the live that goes to the charge light, this triggers a 45 amp relay, wired to the alternator
pics are possible, on my phone somewhere

that i great but unless you have a very high amp switch/relay you cannot use second battery to start the motor if primary battery dead, Rick

 

[darryl]

to be honest i saw his and thought that looks like a good idea plus i have another battery in the shed thats only 12 months old is it not worth putting on then? thanks darryl

 

[rustic]

that i great but unless you have a very high amp switch/relay you cannot use second battery to start the motor if primary battery dead, Rick

My second battery is charged via a 45 amp relay, powered from the radio circuit supply, that goes off whilst starting is in progress.

To activate the battery in the event of flat battery, I have a starter solenoid with a push button in the cab.
Simples..
Oh and all the cable is suitably rated for the current, and the charge circuit is fused too.

Best regards,
Rustic

 

[jims-terrano]

Rustic, I like your style:thumbs

What sort of battery do you use? wont cranking an engine over kill a leasure battery unless it's a deep cycle marine type battery?

 

[Lazy-Ferret]

The main thing is, if you do put two batteries permanently in parallel, they need to be identical, and of the same age...

Like you see on every battery powered appliance, it is bad news to mix types and ages, and with the currents available to a car battery, it really could be bad. If one battery is older and is packing up. It will draw power from the good one, killing that as well, so you then have no advantage.

If you do it with a proper split charge style relay, either commercial or as mentioned above, a standard heavy current relay taking it's trigger from a circuit that is only live when the car is running, then the voltage is buffered by the alternator before the second battery comes into circuit, so stops the second battery does not get discharged by it.

The only problem with using lower amperage relays to switch, is if the second battery is the one that is dying, when switching it into circuit, it will draw a high current, and blow the fuse to it.

here is how I did mine

another discussion on the subject.

Personally, for what I require, having the batteries as two separate circuit is much better, as I can run the second battery flat, if I like, and still start the car, and for the few occasions that I may need to jump start the car from the second battery, I will just use my Jump leads to connect the two together.

 

[Thomas-the-Terrano2]

check your insurer first, many have declined such a mod!

 

[rustic]

Rustic, I like your style:thumbs

What sort of battery do you use? wont cranking an engine over kill a leasure battery unless it's a deep cycle marine type battery?

My battery is my previous Mav Battery

 

[solarman216]

Yes Rustic that is the answer, don't see to many separate start solenoids today though, I have just fitted a second winch to the rear of the off roader, was going to just run long cables to the winch battery on the front but decided that a second winch battery in the rear will be better, will use the body as earth connection and run a heavy cable between the two battery positives with a start solenoid like you describe, so begs the question where did you source your solenoid? Rick

 

[solarman216]

Jim's Terrano, there is no such thing as a leisure battery, it is a start battery being called something else, with the exception of some gell batteries, they are the only ones that come anywhere near, a true leisure battery should withstand repeated full discharge to 80% with no damage, a start battery loses a large % of its capacity ever time it is run flat, that in essence is the difference, so for true leisure read full traction, Rickl

 

[rustic]

so begs the question where did you source your solenoid? Rick

Hi Rick, got mine from ebay, search "starter solenoid" many British Leyland cars of the 70's used them.

Ok some are only on engines half our size, but since both batteries will be contributing to the start current, these should be ok.

Also the number of times it will be used will be quite low, but gives that extra security.
Best regards,
Richard (Rustic).

 

[solarman216]

Hi Rick, got mine from ebay, search "starter solenoid" many British Leyland cars of the 70's used them.

Ok some are only on engines half our size, but since both batteries will be contributing to the start current, these should be ok.

Also the number of times it will be used will be quite low, but gives that extra security.
Best regards,
Richard (Rustic).

guessed it had to be oldish, the other thing I need to bear in mind for my application is that it will be powered all the time the alternator is charging as when I use the rear winch it draws 90 amps approx and most of this will come direct from the alternator, many starter solenoids will overheat if on constant so may need to make a device that once the initial pull has been achieved, power it through a dropper resistor just enough to keep it in, Rick

 

[darryl]

seems complicated think ill stick with what i got just the one thanks all darryl:thumb2