Split Charge Systems and batteries

[Topple]

I know this has been discussed before and probably at some length. while I'm waiting for my winch to turn up I've started to look around at what battery and split charge system to deploy.

Just being reading the National Luna website at their intelligent solenoid, I don't think I'll go the whole hog and buy the battery management system though.

Came across this diagram amonst others suggesting hoe to wire up a winch.

[Bob696]

that diagram begs the question "why bother with a 2nd batt.?"

[davidlandy]

thats how i have wired mine up

never let me down

the second battery is there via the touch of a button to support the first when needed ie to jump start , or a temp connect to assist when winching.

[isle of man]

i have a www.painlesswiring.com set up on my wrangler, very nice bit of kit.

peter henry

[Bulli]

If you are only connecting the second battery when winching how does the connection cope? most winches can draw upto 500 amps which will kill most things.
Why bother with all the faff. I connected both batteries all the time, the benefit is that the voltage doesn't drop as quickly when winching so the ampage drawn is less....as voltage drops ampage increases in direct proportion. As for running ancilleries i have power to spare....and my fridge runs of lpg once ive pitched camp.

[Bob696]

the winch on the 110 is wired to the 2nd battrey. The split charge relay has a cut out switch so if I need engin power and the winch I can isolate the aux battery saving the alternator and relay.

[Bulli]

I know what you are saying but then you are relying on an unsupported(no alternator or 2nd battery)battery to run your winch. The voltage will drop like a stone and thats when the increased ampage can damage BOTH your battery and your winch.
What kind of extras are you running that require a battery all to themselves? If you go on long camping trips and dont want to flatten your main battery i can see the point but for winching the system doesnt make that much sense. Plus its way more expensive than connecting the 2 batteries.

[SimonR]

Although connecting two batteries in parallel seems a good idea - it is only a good idea with two accuratly matched batteries.

What tends to happen on un-matched batteries is they charge / discharge at slightly different rates.  This leads to an imbalance in the voltages after you have stopped charging /  discharging.  The battery with the higher voltage pumps charge into the other one.  It over-shoots a bit leading to charge being pumped the oher way.  The other battery over-shots and so the process continues.  Over a period of time, both batteries discharge to the point damage occurs.

The next simplest solution is just a heavy relay / solenoid which connects the batteries together while the alternator is charging.

A stalled 8274 draws about 170A between the batteries across the split charge relay.  Thus a relay capable of carrying 200 or so amps is sufficient.

Most of the people running a split charge in competitions use this setup.  It is not affected by water and you can fix it with a hammer (well, nearly!).  Neither applies to a computerised charge control system.

You can of course spend a few hundred quid extra on something with an anodised box and a blue LED - but personally, I go with the relay!

Si

[Bob696]

What kind of extras are you running that require a battery all to themselves?

Fridge, cdplayer, interior lights, dvd player CB and a few other things that are required when stationary (its a camper van conversion)

Plus its way more expensive than connecting the 2 batteries

My heavy duty relay, all the wire and connectors cost me under £20

[Bulli]

You will have to let me know where you got the cable from i paid 25 quid for one length of winch cabling!I looked at doing exactly the same as you and even have the relay sat in my garage.I spoke to Richard at scorpion who does a lot of extreme events and he recommended linking the 2 batteries. My winch has been the difference between staying put (forever seemingly) and getting home so I just dont want to compromise it for anything.
 I run all the same stuff but i switch my fridge to lpg as it if far more efficient than whilst on 12 volt.Too effiecient ....the first time i used it on gas it froze the milk and eggs solid by morning!

[Bob696]

The £20 was for the relay and all the wires to link the 2 battries together. Didnt have to bother with ultra heavy cables as the 2 battries arnt linked whilst the winch is working.

We got our fridge on an ultra special offer £150 instead of nearly £500. It is super efficient and even over 3 days it never drained the yellow top we use :-)

As too linking the 2 battries together wouldnt it be more sensible to just buy a bigger battry?

The nice thing about the 2 isolated battries is that even if you completly run the battry flat by using our inverter plus play station etc you can still start the engine

When/if i ever put a winch on the 90 I am just going to fit a bigger/better battry and strap the winch to that and not bother with a 2nd battry at all

[Bulli]

what fridge is it? There are some realy nice ones around.
I have 2 very strong deep cycle batteries and it spins the starter no matter what. Just to give you an idea even with a truck type normal battery, like i used to have, the engine would stall after prolonged winching...there wasnt enough juice to run the efi.
Horses for courses as ever but you will kill a battery if you winch from it without the support of the altenator.....im more concerned with getting unstuck than anything.Even at the expense of not being able to start the car. I can always walk and borrow a battery if i need to.
I winched ALL of these through this section.....