Badger

Badger

Well-Known Member
Yeah yeah it's been covered a hundred times, but a quick question regarding cables as nothing is black n white in the search's ;)

using a small 30Amp relay i want to stop the 2nd battery leeching from the 1st cranking battery, wiring it up is simple enough, but from what i've read the cable joining the 2 batterys (v+) should be of a fair thickness, fitting this to a small relay is abit, ahem, ****e.

Is there a way to check the alternator current back to the battery and which cable thickness to use to bridge between the 2 batteries?

Ta
 
30 amp rleay won't cut it as cranking amps can be over 150amps. (IIRC) simple way to do it would be an isolating switch in cab. and turn it on/off manually
 
redhand said:
30 amp rleay won't cut it as cranking amps can be over 150amps. (IIRC) simple way to do it would be an isolating switch in cab. and turn it on/off manually
Click to expand...

2nd batt shudnt be used for cranking - but relay needs to take full alternator output current.
 
2nd battery will be isolated via the relay from cranking ( battery light on dash ) ie it wont open until the dash alternator light goes out, i was concerned at the amount of current flowing back into the battery through a thinner lead.

Will check the FAQ's

:edit:

Is it me or are the FAQs having a bad day? Searched ' Split charge, Relay, Charge, Relay charge ' and all came back with zero results....
 
Last edited:
I've just wired 2 batteries in using normal Battery Cables no fancy relays or split charging systems for me. and it's working perfectly fine.
 
redhand said:
I've just wired 2 batteries in using normal Battery Cables no fancy relays or split charging systems for me. and it's working perfectly fine.
Click to expand...

yu risk having catestrophic failure on one tho - because one will always be weaker than the other and the stronger will constantly try and compensate by "charging" the weaker one, causing a temp rise within the weaker cell.
 
Found your relay guide MHM, although useful it doesn't answer the question on cable thickness, a standard charger doesn't use that thick a cable, in fact mine at home ( which is a 5amp ) has piddly little cables. Does the alternator give back a large current ( i imagine it would ) ?

As above this was the reason i want to do this, with a new battery fitted, my older one is sub par and fine for general use, but not enough for cranking etc and my new battery was charging the older one whilst the Landy was garaged. i found this out when i went to start her yesterday after a day if being not used and the battery was seriously under charged.
 
An alternator on a Landy can put out between 45 Amps and 110 Amps - depending on what Alternator it is.
 
redhand said:
tis a lot of money for a relay and a bit of wire though??
Click to expand...
but it works tho.

and even in winch comps it was faultless and you have the facility to link both batteries if ya need the extra oomph..

i dont think summit like this can be skimped on,i went thru 3 of said cheaper kits and none done the job i wanted it to or work how i wanted it to,and you had no visual way of knowing wheter the systm was working or at what charge the batterys were,the tmaxx for me fitted the bill perfectly..
 
I have a X-eng split charger. For the 300TDi it does not get connected to the battery warning light circuit, but just a switched live, It does not energise the realay when you turn the starter as the starter switch (ignition barrel) cuts of the feed to it, I a m running 2 numax heavy duty batteries, one for starting and one for the winch and the other bits and bobs. I suppose a display to shopw the charge of the batteries would be good but i think it is one more bit of kit to go wrong, or to get drowned when going through big puddles.
 
Paul,
I use a 60 amp relay with 60 amp wire - that was worked out using the maximum demand plus 10%. However, either side of the relay has a 30 amp fuse at the moment as that is all I currently require. The cable that connects to the alternator is rated at 15 amp and has an inline 10 amp fuse.

The theory behind the fuses is that they will blow before the wire starts to melt (and potentially burn).

I used:
http://gm7rqk.org/t25/split_charge_wiring.htm

Hope that helps....
 
Thanks for the links etc, will look into them although i do have a 30Amp relay here atm.

Having a visual isn't really an issue for me as i got a spare multimeter which is kept in the vehicle and my batteries are easily reached. It's not for winching or even a fridge, just for a few 12V sockets, radio, cb and a few spots so i'm not too fussed about the battery itself, i'm more concerned about fooking up the new battery by it being leeched to charge the older one.

I'll give it a few experimental tests and use inline fuses to keep it safe and see how i get on, in the meantime i'll keep an eye out for a heavy duty relay :D
 
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