Split Charge Relay

Veg_Ian · Post by **Veg_Ian** » Fri Oct 27, 2006 1:57 pm

I know this has been asked before but I've not been able to find an answer in the archives.

I bought a relay from Towsure but when I came to connect it to the alternator, instead of finding one low current wire coming out of the alternator as anticipated, I found two. Being a coward and not liking the 50/50 odds, I decided to connect directly to the vehicle battery instead. Consequently, after repeatedly replacing fuses, I now think I've fried the relay.

I've got a more robust unit on order and this time I would like to do the job properly by connecting the feed to the alternator not the battery. Does anyone know for sure which alternator wire I should connect into please?

moonshine · Post by **moonshine** » Fri Oct 27, 2006 5:33 pm

As an alternative to connecting to the alternator, you could connect the tag which energises the relay to an ignition-fed source so that it becomes live and energises the relay when the ignition is switched on. The disadvantage with this is that if you sit with the ignition on, and the engine not running, both batteries will be connected together and the main battery will drain into the leisure battery. Provide that you only switch on the ignition when you intend to start the engine, this should cause no problems.

If you try this system, make sure however that you connect to the "ignition" terminal and not the accessory terminal, as you don't want the relay to energise if you just want to listen to the radio.

Veg_Ian · Post by **Veg_Ian** » Fri Oct 27, 2006 6:04 pm

That's not a bad idea Moonshine - thanks. It just occurred to me to look in the manual (keep forgetting I have one) and it shows the L and S terminals as the possible contenders on the alternator. It's still not clear which one to use though. If I were a betting man I would go for the L terminal but I don't want to take the chance as there's too much at stake. If no one can give me a definitive answer I'll go with your idea.

Thanks again
Ian

Mark & Shelly · Post by **Mark & Shelly** » Fri Oct 27, 2006 7:51 pm

The ignition source feed is a simple solution, but also don't forget that if your starter battery should become significantly more discharged than the leisure battery then your starter moter will try to pull some serious amps through your split charge wiring, hope it would only fry a fuse but you better get plenty more in stock.

madmile · Post by **madmile** » Fri Oct 27, 2006 9:33 pm

You will find more information than you possibly need on 'kampenwagen.co.uk' - if I could remember how to post a link I would

Best method and simplest is to use the alternators 'no charge' feed from the back of the alternator. On the bongo there is a double pin plug which is near the main positive cable. If you disconnect the plug and then make up a small length of wire with spade crimps on the end you can tell which of the wires is the no charge feed by connecting one side at a time and then switching ignition on(not start). Normally the no charge light comes on when the ignition is switched on, then goes out once you start the engine and the alternator pushes a charge in. With one of the two wires not connected by your temporary extension wire you will find which one is the no charge light, as it will not light up when the ignition is on. I think its the thinner of the two, but best check.
You then use this wire via a scotch lock to run a wire up to your relay.
This way your leisure battery is only charging / possibly drawing from your starter battery once the vehicle is actually running.

Veg_Ian · Post by **Veg_Ian** » Sat Oct 28, 2006 10:05 am

That's what I was after - many thanks Madmile

Veg_Ian · Post by **Veg_Ian** » Sat Oct 28, 2006 2:33 pm

Job done. For future reference the required feed wire is the thinner of the two - purple and black I think.

Veg_Ian · Post by **Veg_Ian** » Sat Oct 28, 2006 4:45 pm

Hmm job not done. Came to drive away and the charge and sediment lights are faintly glowing. Disconnected the feed to the coil in the split charge relay and both lights are out but of course the leisure battery isn't charging. Ideas? I know I got the right wire from the alternator.

ChrisEm · Post by **ChrisEm** » Sat Oct 28, 2006 9:43 pm

Not done anything similar on the Bongo but from experience would say you've possibly got an earth fault or a backfeed, without looking at a wiring diagram it's a bit tricky too pinpoint. IIRC the wire on the indicator light circuit is required to give the alternator a 'kick' on startup, you may find that connecting to the split charge relay has created too much of a voltage drop across the circuit, therefore causing the light to illuminate. I know some alternator circuits have 2 feeds whereby the light will remain out when both are energised but when one loses a feed to earth it will illuminate. Hope this helps

Veg_Ian · Post by **Veg_Ian** » Sun Oct 29, 2006 8:20 pm

Well I've wired it as per the Kamperwagon site and checked the no charge light wire from the alternator (which was correct) and also checked the earthing point by trying different earthing points as well as a different wire. So it's not a bad earth but there would appear to be a voltage drop as a result of connecting the relay to the no charge wire and hence the charge, sediment and glowplug lights to come on when running. So not much else I can do on that front. My only option would appear to be to use an ignition feed such as from the stereo but then I'm back to square one with blown fuses. I'm at a bit of a loss now ..........

pippin · Post by **pippin** » Sun Oct 29, 2006 8:25 pm

I would not worry too much as long as you recognise the difference between faintly glowing and the fault condition when they will glow at normal brightness.
You might of course get fed up with the lights glowing faintly all the time .........

moonshine · Post by **moonshine** » Sun Oct 29, 2006 11:36 pm

Hi Veg_Ian,
Don't use a feed from the stereo as this is connected to the accessory terminal. You will energise the relay if you just want to listen to the radio without the engine running. This will discharge the main battery into the leisure battery until they balance out. Use a feed from something that is only live when the ignition is fully on, as you only want the relay to energise when you are about to start the engine.

If you have wired it correctly, no fuses should blow unless you are using too low a rating. The cable you use to connect the relay to each battery should be cabable of handling at least 60 amps, and the fuses I would recommend would be around 35 amp rating.

Yamaha · Post by **Yamaha** » Mon Oct 30, 2006 12:59 am

Hi Veg_Ian

I have just also wired up a split charge relay - and had the same problems as you mention - ignition light glowing, but more importantly, the relay was dragging the voltage down to about 5v, not enough to energise the relay! It was definitely wired correctly - the thin black/ blue? wire from the alternator.

After wasting a day trying to get it to work reliably ( sometimes it worked - then it didn't ), I decided to take a live feed from the radio - now it works every time.

Not the most perfect solution, but it was driving me nuts!!

Mike

grumpo · Post by **grumpo** » Mon Oct 30, 2006 2:21 am

The ignition lamp takes a supply from the battery and completes the
circuit by earthing it through the auxilliary connection on the alternator.

When the alternator is charging, it opposes the battery voltage and so
puts the lamp out, ( 12V + both sides of the lamp).

If you connect any other low impedance source to this alternator terminal
it will backfeed other warning devices which rely on this output.

A battery not being charged can only maintain 13.8 volts - fully charged -
and usually about 13 volts at best. The split charge relay includes a
comparison circuit which switches the main relay at just over 14 volts and
can only do so when the alternator is supplying sufficient voltage. This
also causes the relay not to switch when the traction battery is severely
discharged, this ensures that the traction battery gets all the charging
current from the alternator before diverting some to the leisure battery.

The correct way to connect a split charge relay is via an ignition "ON"
circuit which is usually available at the radio. As the current is a few
milliamps it would not require additional fusing. The main charging
cables should be be of sufficient size to carry the maximum output current
of the alternator and should be fused accordingly, bearing in mind that you
could have a situation where the traction battery may be fully charged and
the leisure battery is fully discharged, in this case the leisure battery will
be taking almost the full output from the alternator.

Listening to the radio without the engine running will not cause the split
charge relay to energise as explained above, although you will draw a
few negligable milliamps for the comparison circuits while you do so.

Sorry about that Moonshine, but if yours does then there's something
wrong with it.

Veg_Ian · Post by **Veg_Ian** » Mon Oct 30, 2006 8:38 am

Well that's just how I had it wired before, the ignition feed from the radio. Result ? - blown fuses when the leisure battery charge is low. Having read the Kamperwagon site I'm off the opinion that you don't want to charge the relay until the engine is running but the alternator is out because of the need to balance both sides of the charge light with equal voltage. The wire from the no charge wire to the relay is obviously too long and causing the voltage drop and as you say Grumpo - backfeed. It's not just the charge and sediment lights that glow, the glowplug light is also flashing (I'm afraid that would really get on my t*ts).

Yes I could fit higher rating fuses as the SCRelay will take 100A but would also have to rewire as I've only used 25A cable at present. Other than the alternator I can't think of an ignition controlled circuit that doesn't kick in after the engine starts. So it appears I have one of three options.

Use the ignition feed from the radio and:
1. Add a manual switch connected to the ignition controlled circuit and switch it to on after the engine has started (which would be a bit naff).
2. The above but with a timer in the ignition circuit.
3. Upgrade the wires from the traction battery to relay and from relay to leisure battery.

Option 3 looks like being favourite but what about the fuse holders? I'm currently using blade fuse holders but they won't take 35A. Is there something special I have to buy, hopefully not too expensive as I seem to have spent a fortune on this already?

Thanks for the input (sic) everyone BTW. It's surprising how it all starts to make sense when you kick a few ideas around.

Cheers
Ian