fishsponge

fishsponge

New Member
I understand that a split charge relay is designed to (a) protect one of your batteries so you can always start your engine even if you can't turn anything else in the vehicle on and (b) charge up whichever battery needs charging the most.

Do they do anything else? Do they even do what I describe above?

Are they cheap?

Does anyone actually use them?

Are they worth having?

etc...

Oh, and I should add that I have two batteries already, both of them just connected to each other with wire. No idea which bits are connected to which battery, so I assume i'd have to figure out what each wire was for if I were to fit one...
 
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With the set up you have at the mo-if one battery goes down,it will discharge the other as well-only a good idea if both batteries are same age and identical capacity
 
I do have a winch, and am about to fit a CB (maybe), and have 6 spotlights on the front which I use occasionally of an evening while camping at events throughout summer...

Also, I believe both batteries are identical and of the same age... but you are right - if one battery dies and then takes down the other battery, will I need two new batteries?

If so, would the cost of a new battery be better spent on a split charge relay?
 
I fitted one to mine, so it charges 2nd battery when the car is running, cost me about £30.00 in all for the relay etc, and took around 10mins to fit :D A lot cheaper than shelling out for batteries......
 
So long as you wire the accessories you might want to use while the engine is not running, to the other (non-starting) battery, including the winch, then it makes sense to have one. However, you need to ask yourself do you really need the extra hassle and expense of 2 batteries + split charge + wiring. And are 2 batteries better than one big battery?

If you wire it up so the split charge connects the battery with ignition on then a problem you might see is that during starting, the current draw across the split charge relay (ie from non-starting to starting battery) is high (due to the voltage difference) and blows the fuse. For this reason, motorcaravans have it wired off the alternator lamp, ie so it stays disconnected until the alternator is charging, ie not during starting but when the engine is running normally (eg at idle or higher speeds).

I imagine the same might occur during using the winch, but the other way round?

Hence the suggestion that one big battery instead of 2x batteries and split charge etc has some merit.
 
Well I already have 2 batteries with no split charge, so I guess that's similar to one large battery. Plus, I don't intend on using the winch with the engine off, so I should be ok without...
 
i have 2 072 batts, and a durite 120 amp relay acting as a split charge.
both batteries are connected together at -ve and both earth strapped to the body.

the starter motor/car ius connected to drivers battery as factory, the winch is connected to auxiliary battery.

basically connect one battery +ve to one side of the relay, the other +ve to the other, and then the relay to earth and the switch wire to the back of your alternator, connected to the charge indicator terminal.

split charge is far better for the reasons already outlined.

you may end up winching with the engine off: you stall the car in a pond and it wont start again, you winch yourself out on battery 2 and have plenty of power left to try to get the car running on battery 1.

it really is worth sorting out, the flexibilty of knowing youre not risking a flat battery when thye engines off is very nice.

remmeber you should fit a maxifuse next to each battery, in case either of the cables wear through on their route around the engine bay (or you'll get a major fire issue)

i also have 2 separate LED voltmeters on the dash, these are wired to either side of the relay, so when the engine's off you know how your two batteries are looking.

cost me about 100 quid for relay, fuses, cable and voltmeters, but its a very tasty system that works and performs pretty much in the same way as them very expensive battery management systems...

that said, even a simple split charge setup might save your bacon.

cheers.
 
I`ve just fitted some of these for a customer eBay - The UK's Online Marketplace They work by sensing the increased voltage when the engine is running then automaticaly charge the 2nd battery. Simple to fit and work well. Will be fitting one to my disco to run accesories and a small heater as i sleep in the back of mine when we go laning/doggin!:D
 
Voltage sense relays are great but I dont think that those caravan type ones are really man enough for the job,they are tiny little 30a units inside that box.

My opinion (note that please!) is that you need a minimum 70a for an aux battery in this situation and if you are running stuff like winches you need min 120,better 180a relays....and cable to match.

Of course you CAN buy heavier duty voltage sensing relays.Or use a low power one to trigger a heavy duty plain relay,if you like lots of wiring.The alternatives are to trigger the one heavy duty relay from an ignition live,or (my fave) from the alternator using the lead to the rev counter - this will mean it only works when the engines up and running.You can put switches in line with the ignition live type trigger but then you got to remember to actually switch it on....and you can bet the time you REALLY need it.....

Anyway,if you do a search there are excellent sticky instructions and info for all this on here that tell you ALL you need to know.
 
mine is even simpler - I have a 2 battery system in my 110, 1 for starting and 1 for accesories including winch, just seperated by a Hella heavy duty cut off switch, switch key out only accesory battery works, key in and start battery works anorl - no relays to go wrong + bit of security with dash mounted volt meter to monitor = simple
 
shocker said:
Voltage sense relays are great but I dont think that those caravan type ones are really man enough for the job,they are tiny little 30a units inside that box.

My opinion (note that please!) is that you need a minimum 70a for an aux battery in this situation and if you are running stuff like winches you need min 120,better 180a relays....and cable to match.

Of course you CAN buy heavier duty voltage sensing relays.Or use a low power one to trigger a heavy duty plain relay,if you like lots of wiring.The alternatives are to trigger the one heavy duty relay from an ignition live,or (my fave) from the alternator using the lead to the rev counter - this will mean it only works when the engines up and running.You can put switches in line with the ignition live type trigger but then you got to remember to actually switch it on....and you can bet the time you REALLY need it.....

Anyway,if you do a search there are excellent sticky instructions and info for all this on here that tell you ALL you need to know.
Click to expand...

I agree, but don't even think 180A is enough, most low line winches will draw atleast 300A or more when pulling near max load.

There are some relays "out there" marketed at 180A, but I for one am very sus ref their suggested rating, especially when you compare them to a "commercial" type heavy duty contactor from Albright for example.
 
I admit I was dubious whether my 120A relay would suffice. I actually run 100A fuses in the link cable, to protect the relay.

AND my 10000lb superwinch was supplied with a 3x50amp fuse setup on bussbars.

This was a bit of a daft arrangement so I got a 150amp maxifuse to go in the winch power cable instead. I have done numerous near winch stalling pulls and it's never blown that fuse, so I think my 120amp relay will be coping nicely.

Current draw is probably closer to 100amp, maybe even less.

Cheers.
 
i like it!

no moving parts, thats a good thing for offroaders.

also, in theory no chance of the batteries draining each other.

what are the negatives (no pun intended) of these diodes then? gotta be more cons than just the cost...?

cheers!
 
Hi Noisy
From what I can see they use Mosfets so there is very little voltage drop :D
They charge the batteries in parallel but isolate them so no danger of one discharging the other one:D:D
The current rating of the diodes only depends on the charge current the batteries take.
I am sure someone can tell us what current the batteries actually take to charge ;)
Wiring looks very straight forward too-Disconnect lead from main batt + that connects to the alternator the and connect to diode pack.Connect a new lead from pack to main batt.
Connect extra lead from pack to 2d batt
Connect winch/fridge/tv to second batt (with suitable gauge cables)
Job done and will main batt wont be run down :D:D:D
 
Most decent battery chargewrs charge at around 30-40 amps, i wonder what the battery draws from the alternator when it's dead flat?

if you stick jump leads on a flat car, you can hear your engine slow down as the alternator loads up.

cheers :)
 
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