12V split charge system ideas

[123hotchef]

Ok so after letting the truck battery run flat late last night I am going to install a split charge system into my truck. I have installed them in the past to my cars when fitting big sound systems. I have seen these smart relays that only charge the second battery when the alternator is putting out 13.8V and it also cuts out when it is 12.8v. I dont know whether to use on of these or not. If doing so I will not be able to utilize the 2nd battery to start the truck without using jump cables from it or bypassing the smart style relay will I.

Any one got any other better ideas on how to rig up the system.

 

[Exuptoy]

I have a smart split charge relay called dura something or other installed in the camper although it is fused at 20 or 30 amps I think, so I cannot use it to back feed the starter circuit as it knocks out the fuse but it would be possible to have a set of take off leads for jumping.

Here you go...correction its called Durite.

https://bushbatteries.shopfactory.com/contents/en-uk/d58__split-charge-relay-system-kit.html

 

[123hotchef]

I have a smart split charge relay called dura something or other installed in the camper although it is fused at 20 or 30 amps I think, so I cannot use it to back feed the starter circuit as it knocks out the fuse but it would be possible to have a set of take off leads for jumping.

Here you go...correction its called Durite.

https://bushbatteries.shopfactory.com/contents/en-uk/d58__split-charge-relay-system-kit.html

yes that was the one I was looking at. Good idea in theory, but it would be good to have a switched back feed just incase. I guess I could always use jump leads

 

[carbon]

I use the ring smartcon relay in my van just as it was available locally. Has an adjustable pot if it needs to be adjusted

 

[Luke]

I've used a smart relay in my landrover for about 10 years and wouldn't go back.

When/if it fails, I'll go for a smart relay with override, similar to the following.

https://www.simtekuk.co.uk/product.php/split_charge_-_power_control_relay/?k=:::1617106

 

[Justme]

Use a Voltage Sensitive Relay VSR of about 100-140 amps. Use thick cable.

If you want to jump it use a cable to the second bat or one of the new booster packs.

If you have solar the VSR (at least the Durite type ones) will allow the solar to charge the starter bat too.

 

[knighty]

skip the split charge relay, get a bit relay or a solenoid... then there's 2 options...

wire it into the small -ve feed from the alternator (the one that works the dash bulb) - that's negative until the alternator starts putting out power, and then goes positive (optionally add a switch so you can power it on for extra starting power)

or just wire in in to come on with the ignition... this is what ford do with all the ford transit dual battery vans (dual batteries is standard on all long wheelbase rwd vans now)


keep it simple, it's more reliable that bway :-)

 

[123hotchef]

I've used a smart relay in my landrover for about 10 years and wouldn't go back.

When/if it fails, I'll go for a smart relay with override, similar to the following.

https://www.simtekuk.co.uk/product.php/split_charge_-_power_control_relay/?k=:::1617106

thats a good idea

 

[123hotchef]

skip the split charge relay, get a bit relay or a solenoid... then there's 2 options...

wire it into the small -ve feed from the alternator (the one that works the dash bulb) - that's negative until the alternator starts putting out power, and then goes positive (optionally add a switch so you can power it on for extra starting power)

or just wire in in to come on with the ignition... this is what ford do with all the ford transit dual battery vans (dual batteries is standard on all long wheelbase rwd vans now)


keep it simple, it's more reliable that bway :-)

I have a few 100, 150 and 200 amp relays and plenty of cable so that is not a problem

 

[Luke]

Both of the above will connect the batteries together when one is potentially flat and the other is not fully charged. Not ideal.

A VSR/smart relay will ensure that the cranking battery is recharged before bringing the ancillary battery in, minimising the risk of being left with two half-charged batteries.

 

[rtbcomp]

...

wire it into the small -ve feed from the alternator (the one that works the dash bulb) - that's negative until the alternator starts putting out power, and then goes positive (optionally add a switch so you can power it on for extra starting power)

or just wire in in to come on with the ignition... this is what ford do with all the ford transit dual battery vans (dual batteries is standard on all long wheelbase rwd vans now)


keep it simple, it's more reliable that bway :-)

Not quite, the lamp wire is zero, (not -ve) and as you say rises to +12v when the alternator gives an output, thus extinguishing the alt. warning light. This 12v is sufficient to power a standard 30A automotive relay, possibly larger relays, I've not tried it.

If you want to provide a boost start just wire a basic starter solenoid between the 2 battery +ves (with starter motor cable, make sure the -ve cable on the 2nd battery is the same cable). Connect the solenoid coil to the ignition switch "Start" terminal via a switch.

To cover the point @Luke makes ^^ your could fit a switch in the split charge relay coil, but you'd have to remember to use it.

 

[normspanners]

The problem with having two batteries connected together is one will always be dominant and the other will not receive enough charge and suffer for it, like the pajeros etc do with twin batteries, the dominant battery closes down the alternator early and the second battery doesnt get enough charge. the best way is a 12v to 12v charger or two alternators. or change over relays so that only one battery is connected to the alternator at one time. but then we do not usually drive far enough for long enough to properly charge the batteries anyway, with most alternators the battery is only 80-90% charged at best with some being as low as 60-70%.

 

[langy]

Not quite, the lamp wire is zero, (not -ve) and as you say rises to +12v when the alternator gives an output, thus extinguishing the alt. warning light. This 12v is sufficient to power a standard 30A automotive relay, possibly larger relays, I've not tried it.

If you want to provide a boost start just wire a basic starter solenoid between the 2 battery +ves (with starter motor cable, make sure the -ve cable on the 2nd battery is the same cable). Connect the solenoid coil to the ignition switch "Start" terminal via a switch.

To cover the point @Luke makes ^^ your could fit a switch in the split charge relay coil, but you'd have to remember to use it.

That's how I've done it in the past, works fine

 

[wookie]

Ok so after letting the truck battery run flat late last night I am going to install a split charge system into my truck.

First question which nobody has bothered asking is what were you doing to run the battery flat ?

Split charge setups etc are all well and good but unless you change your wiring so that whatever flattened your battery can only get power from the aux battery then you wasting your time and money.

 

[knighty]

Both of the above will connect the batteries together when one is potentially flat and the other is not fully charged. Not ideal.
A VSR/smart relay will ensure that the cranking battery is recharged before bringing the ancillary battery in, minimising the risk of being left with two half-charged batteries.

when your alternator is happy to put out 80 amps or more, it doesn't really matter, alternator will pull the voltage up enough that the flat one doesn't have a chance to discharge the full one

The problem with having two batteries connected together is one will always be dominant and the other will not receive enough charge and suffer for it, like the pajeros etc do with twin batteries, the dominant battery closes down the alternator early and the second battery doesnt get enough charge. the best way is a 12v to 12v charger or two alternators. or change over relays so that only one battery is connected to the alternator at one time. but then we do not usually drive far enough for long enough to properly charge the batteries anyway, with most alternators the battery is only 80-90% charged at best with some being as low as 60-70%.

alternators charge as 14+volts - which is more than enough to keep both batteries equally charged



I've run dual batteries on loads of different stuff, (love dual batteries) couple of relays powered by alternator for when I might run the 2nd battery flat (when it's used for lights etc. with engine off)

rest just have both batteries joined together with nice big cables

never had a problem with any of them

batteries always seam to last much much longer... not sure if it's twice as long (to justify cost of 2nd batter)

started with dual batteries for work vans with tail lifts on, just to give them a happier life really - each one only having to out out half the current/ah needed

 

[normspanners]

A car alternator is not designed to charge a flat battery and will not fully charge the battery if it has dropped too low batteries should receive afull charge every so often from a proper charger to fully reload the battery.

 

[normspanners]

when your alternator is happy to put out 80 amps or more, it doesn't really matter, alternator will pull the voltage up enough that the flat one doesn't have a chance to discharge the full one

wrong

alternators charge as 14+volts - which is more than enough to keep both batteries equally charged

wrong
Twin battery set ups batteries do NOT last as long as single BTW

 

[rtbcomp]

when your alternator is happy to put out 80 amps or more, it doesn't really matter, alternator will pull the voltage up enough that the flat one doesn't have a chance to discharge the full one

Correct.

A car alternator is not designed to charge a flat battery and will not fully charge the battery if it has dropped too low batteries should receive afull charge every so often from a proper charger to fully reload the battery.

If the cranking battery is too flat to start the engine, what the alternator can do is irrelevant. If the engine starts, the alternator will charge the cranking battery and when the relay clicks in, both batteries will charge. The extra load of the 2nd (flat) battery will not stop the alternator from working. @Luke 's post #10 is the ideal way to go if you're worried about having a completely flat battery.

Never had a problem, the only time when I've had to put a battery on a charger is when the battery is near the end of its life or the car's been stood for over a couple of weeks. I've never had to charge one up as a matter of routine.

 

[Robotstar5]

I always ran the winch, extra lighting etc. off the auxiliary battery so I could always use the main battery to start the engine. Aux battery was charged with a split charge diode (70's technology )

 

[normspanners]

Sorry but you are both wrong, a battery that is below 60 % charged will not be charged properly by the alternator,and if coupled together the higher charged battery will prevent the second battery receiving full charge because the higher voltage battery will limit the charge given by the alternator. thus not charging the lower condition battery
most batteries on vehicles are only 80% charged at best. because the vehicles are not run long enough in normal day to day running to charge them properly.

https://www.optimabatteries.com/en-...nators-are-not-designed-charge-dead-batteries