2 batteries 1 alternator?
 

I have a question to any body that knows about electrics. I have a transit recovery that when very cold won't start with just it's own battery but will with a jump. It does'nt need alot even a small bike battery is enough just to give it alittle bit more. I need to run various work lights and the winch from another battery so I don't need the engine running while I'm using the lights or winch. I'm planning on making a perminant jump lead between the two with a cut off switch in the middle. The idea being that when it needs it I can joint the two together and use the second as an on board jumper pack, then remove the key so it does not kill both batteries.
If I run another wire from the alternator to the second battery will one alternator charge both batteries?
As the batteries are joined together through the alternator by a light weight wire compared to the starter cable, will the first battery try and draw power through the alternator wire when the starter motor is in use and melt it?
Is it going to be easier to just have two seprate charging systems ( I have a choice of 3 spare alternators) and run the switched jumper lead between the two?

Think unless you have a high output alternator it may struggle ..the smaller of the two batterys will always draw the charge current before the larger one does (to work the two batteries must be identical)...might be easier to get a new transit battery ...

Just my opinion someone my know better though !!

What you need is a split charge circuit, a feature of all motorcaravans. Quite simply it is a relay between the positives of both batteries. The relay is usually energised by the D signal from the alternator. Your alternator should be quite capable of charging two batteries. An alternative is to use a voltage sensing relay. This simply fits between positives of both batteries but when the engine battery voltage rises due to alternator charging the relay will detect the increase in voltage and close to couple both batteries together and allow them both to charge. If you need more info or a wiring diagram just ask:D .

D.

like davey says. ebay split charge system they are about £15-20

Phil have a look on some of the marine websites you can get some nice battery change over switches this allows you to charge both batteries
and isolate each in turn so that you could run your lights or winch off one then turn over to the other or bring both into use at the same time
that way you will always have one battery fully charged
HTH
cheers les g

Just Kampers do a neat split charging doodah :cool:

A split charge system doesn't need to be anything special, a 40 Amp automotive relay, two 30 Amp fuses and holders to suit and some heavy-ish wiring will do the job nicely.

D.

if you want to use the second battery to jump start the transit you need to link the battery to the vehicle battery with heavy starter cable via a master switch with a 250a minimum rating. The alternator will charge both batterys with the switch joined and you can split the batterys when using the winch.

if you want to do this with a flick switch on the dash you can use a electromagnetic master switch

I wouldnt use a 40amp relay having a split charging circuit on my van i used a 70 amp relay and after a year it burnt out (120,000 miles) Ive just replaced it on hind site i would have mounted it better to prevent it getting hot.

Don't worry chaps I've got it sorted now. Truck now has twin batteries using smart split charge system , on board self help jump lead with the aid of a kill switch and I've even added an Anderson connector on the beaver tail so I can run jump leads from the back. So now I can use the rear work lights,winch and jump leads with out leaving the keys in the ignition, very handy for when out on your own or in buisy streets.