Wiring relay for split charge & leisure battery

I'm planning to wire a relay on to the supply feed (positive) cable running from starter batterty to leisure battery, so that the connection is only made when the engine is running. I have seen many previous posts on this subject, and I think I know what I have to do. My one question is this: Can anyone suggest where I should connect the relay - ie where is only live when the engine is running, and not cranking. I have a multimeter and a Haynes, but I expect someone out there can point me a bit closer!

thanks.

John London, UK

--

1980 Land Rover Series 111 109 Station Wagon + Dormobile mod cons 1964 Lambretta Li 150
Reply to
John S
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Take a signal feed from anything on the ignition. some will reckon there'll be a surge as the relay opens and the two batteries say hello to each other (for the few seconds before the engine starts and alternator kicks in) but to be honest, I've run such a system for a good few years without any problems.

Reply to
Mother

But if you wire the relay so it comes on when the ignition is on AND the ignition light goes out then the alternator will already be doing it's stuff thus reducing any surge in the pre-startarooney stage. :-)

Lee D

Reply to
Lee_D

Stop talking sense Davies...

Reply to
Mother

So, er, how would I do that?

Reply to
John S

On Tue, 20 Apr 2004 at 05:25:48, John S caressed the keyboard thus: [SNIP]

Why not use a voltage sensing relay - one less wire to worry about.

Reply to
**SPAM**

Have your big solenoid for the charging circuit.

Have it controlled by a wire which has 2 relays in it.

One relay makes a circuit when it has power attached - wire this one to your ignition controlled circuit - the feed for the radio or somesuch.

The other breaks a circuit when it has power attached - wire this to the ignition warning lamp.

What now happens is that you turn the ignition on and the first relay engages and tries to pass power, however the 2nd relay breaks the circuit until the ignition warning lamp goes out and then lets the circuit complete.

Any questions?

P.

Reply to
Paul S. Brown

None other than "what's the point" as the chance of the warning lamp being on when the ignition off is zero, so you're adding complexity for no reason.

Have a look at

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which explains pretty well how to wire it up.

Reply to
Paul Everett

Connect the wire from the coil on the relay to the B+ terminal on the alternator, job done, no faffing about, robert's your dad's brother and all that.

What happens in this circuit.. when you turn the ignition on, the alternator no charge warning lights, but the relay does NOT trigger, the reasons for this.. the no charge warning light dosent work how most people seem to think, when it's lit and everything is normal, just the alternator is not turning, 12 volts is fed from the ignition switch, through the bulb, and it goes down the wire to the alternator B+ terminal, where it makes it's way to earth through the field coils and all that, thus the bulb lights,

When you start the engine, and give her a blip of the loud pedal to extinguish the no charge light, the alternator is producing voltage, and sends it up the no charge light wire, where it gets to the bulb in the dash, and meets the 12 volts that's coming from the ignition switch, thus it has no way to get to earth, and the bulb can't light, In this situation the 12 volts can get to earth through the relays coil, so it triggers the relay, and connects the 2 batteries together to charge them as one,

When you turn the engine off, the voltage is removed from the no charge lamp via the ignition switch, the light will glow untill the engine stops fully, this is because the voltage the alternator is feeding the light, can now get to earth through the ignition switch being in the off position, in this situation, the split charge relay disconnects, smae happens if you throw the alternator belt, or the alternator dies, if the light's on, the split charge relay is off,

light off, and ignition on, the split charge relay should be on,

This is the way it's been done on motorhomes for years, boat's are usually wired like this too, but they seem to love split charge diodes more nowadays, ok if you have a battery sensed alternator to compensate for the voltage loss through the diode, but most car alternators are not battery sensed.

i personaly don't like the voltage sensing relays, but then there are some who don't like triggering the relay from the alternator, for me, i'm buildign a motorhome, and have a large 4 stage mains charger to charge the leisure batteries, i can also switch that over to the starter battery if i ever needed to charge that battery too, doing this with a voltage sensing relay in the circuit will cause the relay to trigger when the charger applies 14.4 volts to the starter battery, thus making the starter battery charge time last 5 times longer than it should, not to mention i will have at least 330 AH of leisure batteries, and only 88 AH of starter battery.

But the same thing happens when jump starting a car, you'll be connecting the leisure battery to the starter battery, and making the slave battery doing the jump starting work even harder.

But it's horses for courses.. my van has 2 alternators on it, keeping hte leisure battery bank total seperate from the starter battery at all times, but that's considered over the top my most apparantly :)

Reply to
CampinGazz

On Tue, 20 Apr 2004 at 21:23:50, CampinGazz caressed the keyboard thus: [SNIP]

Just a thought

You need to set the relay a bit below 14.4v for reliability under varying temperature conditions. Connecting your charger won't trigger the relay until the starter battery voltage rises above the trigger voltage by which time it is nearly fully charged. It can then go on to charge the leisure batteries in parallel saving you a switch.

Jump starting is a different issue. With the voltage drop across the jump leads you'll be lucky to have 12v across a flat battery (a lot less once you key the starter) so there's little chance of the relay being triggered until after the engine has started.

So - if you use a voltage-sensing relay you save not only a wire - but a switch as well and semi-automate charging of your vehicle batteries. What a bargain....

Reply to
**SPAM**

I have a bit of info and a wiring diagram for a split charging system. Can I attach it to a post?

Wolverine Big Red '93 110 CSW

Reply to
Wolverine

You would be much better off putting it online somewhere and then giving us a link to it.

Reply to
Tom Woods

Twas Wed, 21 Apr 2004 18:30:56 +0100 when Tom Woods put finger to keyboard producing:

I'll host it for you if you like.

-- Regards. Mark.(AKA, Mr.Nice.) ___________________________________________________________ "To know the character of a man, give him anonymity" - Mr.Nice.

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110 CSW 2.5(na)D___________________________________________________________

Reply to
Mr.Nice.

Reply to
tomtom

From... ?

Reply to
Mother

Thanks Gazz, that wins the Simplest Solution award. So I tap the relay trigger wire into the B+ terminal, or presumably anywhere between B+ and the low charge light.

Thanks all .

Reply to
John S

"CampinGazz" wrote

Me too, send me an e-mail.

Reg

Reply to
Reg

It all seemed to go very well, until the long journey home from Cumbria to London, when the alternator burnt out on the M6 (smoke, smells, No Charge light on).

- The no charge light is now lit all the time I have checked wiring from alt to battery, and looks OK, so it's the alternator that's burnt out I think.

- The 30A fuse in the split charge relay had blown. Clearly, this must have happened when the alternator was OK (and triggering the relay switch). Not sure why though; I was drawing a few amps to stereo and cool box (each with their own fuses).

Could the blown relay fuse cause the alt burn out? Surely not..?

Confusingly, it also coincided with my forgetting to replace oil cap at last refuel, so engine bay was very hot and splattered with hot oil. Are they by some chance related? I'm hoping so, as it means my wiring might be OK after all.

Any suggestions as to the most likely chain of events? I don't want to do the same again when I replace the alternator!

Reply to
John S

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