DIY split charge

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96terrano

Well-known member
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Jun 27, 2010
Messages
8,022
ok so split charge kits are £40 to £65 ish, so just simply googled DIY split charge and this came up, would this diagram work? i've got a 100amp relay and everything else....or will i need a proper kit? thing is, this diagram looks too low amps :doh

thinking of this for the little Hyundai since i'll be using it for holidays

Split_charge_relay.gif

split202.gif
 
Hi Ryan,
The top diagram is the one I use, works fine, I use a 45 amp relay,

there are two thin wires from the alternator, I think you need the blue one, just put a fuse big enough to protect the wires in series at both battery and load ends

ahh ok, so charging a battery doesn't pull many amps?
 
Hi Ryan,

I run the alternator wire to the relay with around a 30 amp fuse both sides, alternator will pump out loads of amps to a flat battery
The thin blue wire on the alternator is the one I use to hold in the relay, on my Mav anyway

My first post was a wrong you saw it before I changed it.
 
Last edited:
Hi Ryan,

I run the alternator wire to the relay with around a 30 amp fuse both sides, alternator will pump out loads of amps to a flat battery
The thin blue wire on the alternator is the one I use to hold in the relay, on my Mav anyway

cheers, i'll just copy the top diagram then, thing is, im wanting to run a inverter and so on
 
It's easy enough to work out without a diagram. Just use relay, fuses and cable thats rated appropriately.
 
Depends on the output of the inverter remember watts =voltsXamps so if you want to run a power saw at say 500 watts, that's around 2 amps at 240 volts or over 40A at 12V
I am sure solarman will correct me if I got it wrong
dave
 
All I can add to the issue is a relay will charge the 2nd battery to full vehicle charge (not full battery capacity) as opposed to a diode which will only charge to a lesser capacity due to the voltage loss involved, Rick
 
Schottky diodes

Schottky diodes,...
typically exhibit a forward voltage drop in the order of one third of a normal PN junction diode.
Available from the likes of RS components etc...

These can be a sensible no moving parts option, been used on boats and leisure craft a lot. Commercial products produced by Victron, Sterling etc..
eg.
http://www.victronenergy.com/battery-isolators-and-combiners/argo-diode-battery-isolators/

This is an informative read on split charge options:
http://highfields-arc.co.uk/vehicles/auxchg.htm
 
Schottky diodes,...
typically exhibit a forward voltage drop in the order of one third of a normal PN junction diode.
Available from the likes of RS components etc...

These can be a sensible no moving parts option, been used on boats and leisure craft a lot. Commercial products produced by Victron, Sterling etc..
eg.
http://www.victronenergy.com/battery-isolators-and-combiners/argo-diode-battery-isolators/

This is an informative read on split charge options:
http://highfields-arc.co.uk/vehicles/auxchg.htm

Nice, I wanted to go with a relay as I know how to wire them up, never wired a diode before and have no experience with them
 
The main reason the diode method was preferred on small boats and the like was due to persistent high humidity and condensation.
Damp gets everywhere on a small boat and it is difficult to locate sensitive parts where they will not eventually be affected by it. Add to that the possibility of salt water and everything has to be pretty much hermetically sealed!
Solid state devices have proven far more reliable in this environment than even the best "sealed" relays.
Unless you are constantly drowning your vehicle the relay method will be fine, but there is some elegance in eliminating the moving bits!
 
The main reason the diode method was preferred on small boats and the like was due to persistent high humidity and condensation.
Damp gets everywhere on a small boat and it is difficult to locate sensitive parts where they will not eventually be affected by it. Add to that the possibility of salt water and everything has to be pretty much hermetically sealed!
Solid state devices have proven far more reliable in this environment than even the best "sealed" relays.
Unless you are constantly drowning your vehicle the relay method will be fine, but there is some elegance in eliminating the moving bits!

Interesting that, the relay on this will probably be mounted either under the dash or under the boot floor with the battery
 
What would be the best amp cable to use? I was thinking about 30?
 

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