Has anybody fitted a diode between their leasure battery and engine battery so that when on hook up they both charge but the engine battery can't be discharged by the TV etc when not on hook up.
I'm thinking it would also need a current limiting resistor in series with it to protect the diode during engine cranking. Diodes have a small voltage drop across them but it's only about 0.5v.
Well I've connected it up roughly to measure what happens.
The engine battery was sitting at about 12.5v and leisure at 13.8v
If I connect them directly, the engine battery charges at 3.7a
After connecting the diode the engine battery starts charging at 1.1a but steadily falls. Last time I looked it was 0.7a
With the 10ohm resistor in line it only charges at about 50ma so the resistor is a bit too big.
With the EHU switched off the engine battery still takes a small charge from the pleasure battery, about 20ma. But that would drop to nothing after a while I think.
Hi
I have a similar system using a solar panel connected to the leisure battery only
To top the engine battery i use a 12 volt charger from leisure to engine battery
it basically charges the engine battery when the leisure reaches 13.3 volts.
No problems when engine running
would work on electric hook up.
Quote: Originally posted by saxo1 on 27/11/2014
On Hymer motorhomes when on hookup the vehicle battery is trickle charged and the habitation battery is charged via a 3 stage charger.
knarf
My charger will be three stage but it doesn't charge the engine battery which seems a bit silly for the sake of a bit of wire and a couple of 50p components.
I suppose unless you're parked up for a month you don't need it to. We park up for longer periods abroad because you get a cheaper rate.
I've left it charging all afternoon and it's dropped down to a 270ma charge now, I'm going to have to test it with the engine running at some point, but I can't see there being a problem with it.
I tested it this afternoon with the EHU off and all the lights and inverter on inside and the engine battery showed no discharge at all
I've fitted this, it works a treat....it's a split charge device that will charge the engine battery, wether on ehu or solar, once the leisure battery reaches 13.6v.
Yes mine has 3 wires ground and the 2 battery positives. I've put a little volt meter module in the circuit to see the engine battery voltage. It all fits in an old PIR light connector box so it's quite small. I've opted to have it free standing and the connection wires are on insulated croc clips.
Total cost is about 3 quid tee hee.
I can post pics and diagram if anybody's interested.
The forward voltage drop on a standard diode is about 0.6 - 0.7V, less if the diode is the Schottky type.
Obviously it will reduce the voltage from the leisure battery, but it will do the job required if the leisure battery is up on charge at 13.5V or so. Otherwise it won't do much at all.
Remember also that on starting the vehicle, the diode will try and pass a fairly large current as the starting battery volts fall sharply.
If the leisure electrics share a common negative with the vehicle electrics then a small DC-DC converter would do the job.
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Topic: Charging engine battery
