Club 80-90 Forums

I am thinking of putting a diode in the line between the split-charge relay and leisure batt so the current can only flow one way, ie: into the battery but cannot cycle it when the load on the vehicle electrics is heavy. I know with a decent alternator this is unlikely to happen, but with the fridge, headlights, blower, wipers etc... at low revs...

Questions: (1) this might not be necessary anyway because if the alternator is not charging the alternator warning light will come on and then the split-charge relay will open and break the circuit. Is this true, or is it a case of once it's out, it's out?

(2) If I went for the diode, would this be man enough for the job? https://www.ebay.co.uk/itm/Fast-Ultrafa ... SwywRaHBR2

(3) Am I being a bit OCD?

Mark S wrote: (3) Am I being a bit OCD?

this ^^^

A diode will drop about 0.5V not only is that 0.5V charging voltage lost with high current it means it will get hot.

You would need heatsink mounted high current diodes, these are threaded and bolt on to the heatsink. A better solution would be to use a smart relay and adjust it to switch on at 13.4v or above. In the event of high current demand on your starter battery the smart relay will disengage if the alternator output is compromised. I use a 20A type and it is connected to the coil of the original relay which is rated at 45A. You can get higher current smart relays but a bit more expensive.

I tried a voltage sensitive relay in mine and didn't get on with it as it cycled on and off when I had wipers, spotlights, blower etc on and the relay also had a feed to the fridge as well as one to the leisure battery so the fridge kept cycling every few seconds.

Now I have a split charge relay that's driven from the D+ wire of the alternator but I also have a voltmeter in the dash that tells me the voltage at the fuse box and a switch in the relay drive wire so I can disable the relay if the voltage drops too low.

Hope that makes sense and helps you.
BBB.

Thanks, All. I think I'll drop the diode idea as voltage drop can be worse than the brewer's variety and, short of running a 35 sq mm silver cable direct to the alternator, I am keen to scavenge every last fraction of a Volt going.

I think I'll buy a Voltmeter in the first instance to do some load trials and see what's going on. Then I'll decide whether to put some smart gubbins or a manual switch in the relay trigger circuit.

Slightly OT but interesting: when I burned out my old split-charge relay because of a failed leisure battery, the first indicator prior to smoke off the relay was that the fuel gauge was showing empty and I was scratching my head as I thought there was at least a third of a tank in it. It was basically dragging the whole vehicle low.

Mark S wrote:
I think I'll buy a Voltmeter in the first instance to do some load trials and see what's going on. Then I'll decide whether to put some smart gubbins or a manual switch in the relay trigger circuit.

Good idea, I use my multimeter pretty much every week, don't know what I would do without it.

I think you'll find that even with pretty much everything on at idle you'll still be charging both batteries. Expect to see best part of a volt drop when the fridge is put on which is why it is better having this connected to the leisure battery.

Things I have connected to leisure:

All interior lights
Front electric windows (now no longer need to put key in ignition to open window when camped!)
Radio/MP3 player
Propex heater

By the way, those strings of LED lights you can get in poundland etc (run on 3v) can be powered by one of these.
https://www.ebay.co.uk/itm/DC-to-DC-buc ... wcafWlTiQg" onclick="window.open(this.href);return false;

They make excellent low-level lighting and bright enough to read by and have little to no affect on leisure battery state of charge as they draw milliamps. Have several sets in mine connected to a bank of switches. Just make sure the dropper is AFTER the switch:
https://www.youtube.com/watch?v=78H_GsSyG64" onclick="window.open(this.href);return false;