Split charge realy with diode. How many amps?

Post by **Westy.Club.Joker** » 27 Nov 2006, 19:14

Been reading the Wiki on heavy duty charging and split charging. lots of good info from Irish dave, Tonytech and others. Got me a bit concerned about the split-charge wiring and relay on my Westy.

Anyone know where to get a heavy rated split-charge relay with the diode in it, can only find 30amp ones at the moment, and after reading the tech. stuff it does look like it may be under-rated if both leisure batts. get run down. The alty is the standard 65amp one, so in theory it could be pushing up to 65amps down the system

If Irish Dave or Tonytech read this, can you give me some idea on where I might get a heavier relay with diode fitted? Also, Dave mentioned that he thought the factory-fitted split-charge wiring on his Westy was under-rated in his opinion. What rating of wire was originally in there Dave?

Just had a quick look in the Bentley manual (Yank spec) and it says the charge cable to the split-charge relay is 6.0mm, which I have found rated anywhere between 42amps and 75amps??

Does this sound right?

I have had a look at the leisure battery wiring in the batt. box, and the brown earth lead does look very puny, which I`m going to change to a braided earth strap. I`ve wired the second leisure battery in with 80amp cable, braided earth strap and maxi-fuse holders capable of taking big-rated fuses, got 50 amp fuses in there at the moment.

Post by **Simon Baxter** » 27 Nov 2006, 20:15

Thing is..
If you have 2 totally flat batteries, and a 65A alternator, and the batteries are the same capacity then you will get 32.5A max down each wire to each battery. The current will be shared between the batteries.
The alternator will only put out what it needs to do, if the batteries are in good shape and charged then the alternator output will be very low.
You really have to load the electrical system on a vehicle to get them to reach their maximum output, this rarely happens.
If you protect the wire that goes between the batteries (through the relay) with a 30A fuse, the only time you will manage to blow it is if you run your leisure battery right down, again rarely happens.
I have run my liesure battery right down in sub zero temperatures and the 30A fuse has coped.
I have been running the normal 30A relay with a 30A fuse and 3.0mm (28's) for years (10?) and never had to replace a charge fuse.
I have wired countless split charge systems in for customers with the tried and tested 30A relay with good results, and an 80-90 speciality, it's cheap!
If it's a Westy, don't worry too much, VW rarley get things wrong it's only when people start messing that problems arise.

Post by **irish.david** » 27 Nov 2006, 20:20

As far as relays with built in diodes go, i haven't found any over 30amps but if you get a R70 relay you can add a 5p diode from Maplins and get the same thing. The diode isn't going to be carrying any significant current so a cheap low spec power one will do. I know it's a bit more messy, but it's the best solution i found.

As far as split charge wiring goes, the original wiring in my westy was spec'd at about 40 amps (when new) and the relay was about 20A. When driving along with the fridge and 600W inverter running at maybe 10% the current draw on the was a maximum of 20A so it looks like everything is ok (fridge has it's own relay). Problem was that due to the age of the wire their resistance had increased so there wasn't enough voltage across the leisure battery to charge it meaning when i got to the campsite the eber wouldn't run and the lights went out way too fast.

The only solution was to re-wire so while i was doing that anyway i over-spec'd cause that way the new wires will last longer, voltage drop will be less and if i want to add any high current devices in the future (like a microwave for example) the wiring will be up for it. You could probably get away with re-wiring with the same spec wire, but seeing as your doing it anyway why not pay an extra couple of quid and do a proper job.....

As a extension to what Simon said, just charging batteries isn't going to get the alternator to maximum current output, but you have to remember that there are other things going on than just charging batteries. Driving along at night in the winter, you might have the lights, stereo, heater and fridge all on and if the wiring isn't up to it the batteries ain't going to get charged. Also the maximum value of 32.5A per battery isn't totally correct. If you have a flat leisure battery and a full main battery and you start the engine, the batteries are both suddenly connected to the alternator so the leisure battery will get most of the current til it's at more or less the same charge as the main battery

Dave

Post by **Westy.Club.Joker** » 27 Nov 2006, 20:22

Thanks for the info Si

Post by **Simon Baxter** » 27 Nov 2006, 20:34

irish.david wrote:
As a extension to what Simon said, just charging batteries isn't going to get the alternator to maximum current output, but you have to remember that there are other things going on than just charging batteries. Driving along at night in the winter, you might have the lights, stereo, heater and fridge all on and if the wiring isn't up to it the batteries ain't going to get charged. Also the maximum value of 32.5A per battery isn't totally correct. If you have a flat leisure battery and a full main battery and you start the engine, the batteries are both suddenly connected to the alternator so the leisure battery will get most of the current til it's at more or less the same charge as the main battery

Dave

Yep, note sharp end to my reply! had to go!

was coming to that!

Nice thing about Westies, plug them into the mains and the charger charges both batteries. Nice.

Post by **Westy.Club.Joker** » 27 Nov 2006, 23:23

Thanks for that Dave. That was my main concern, I have 2 leisure batts, wired in parallel, so if they get discharged quite a bit over a weekend, then when the motor is started there could be a lot of amps trying to get down the original single cable to the batteries. If the alty is trying to push anything like it`s output into the batts, which will be capable of accepting the charge due to being flat, then the main split-charge wiring and relay could overload? Or is it just unlikley due to the alty never going to put anything like 65amps into them?

Is there a fuse in the split-charge wire from the main battery to the leisure side of things? Also, looking at the wiring diargram in Bentleys (yank spec. camper) the split-charge relay doesn`t have the diode!

Maybe I`m just looking for a problem that I`m never going to have?

Post by **irish.david** » 28 Nov 2006, 01:26

The original relay has the diode built into it. If you remove the relay the diode symbol should be marked on the side of it.

The chances are that you are never going to have a problem using your set-up with a 30A relay. My reason for over specing is my system is that i was re-doing it anyway and a 70A relay didn't cost a lot more. In the future i can put up to 840W of electrical load to my split charge system and not worry about things breaking. Plus with my upgraded wiring i will be arriving at the campsite with fully charged leisure batteries.

Remember that when you start your engine that the leisure batteries and the main batteries are suddenly connected regardless of their state of charge. If your leisure batteries are totally empty, your main battery is going to try and equalise the voltage on all the batteries and your main battery can supply a whole lot more than 65 amps. In a this situation if you had a the fridge and some other load on the split charge system you could get quite a bit more than 30A through the relay.

The other thing to be aware of is inverters should you choose to fit one. A 600W inverter is capable of adding a 55A draw (90% efficient) on your split charge system.

Dave

Post by **Westy.Club.Joker** » 28 Nov 2006, 09:49

Thanks Dave. Got a 1500W invertor, so had better be careful what I plug into it