Aux. battery & split charge.

[Dormy]

Hi Guys,
Some of you may have read a post I put up on the S2 Forum about doing some rewiring to my alternator (Lucas ACR) so that it will charge a bit better. This is because I will be fitting a leisure battery to our Esterel this year and might as well put the facility to use it in Dormy (especially after getting caught out by our Waeco fridge last year !), where it can also be recharged on a run if necessary.

I have already researched most available systems (some are very expensive), but I like to tinker so am swayed by two cheap DIY possibilities: -

1. Use a H/D relay switched by the alternator's charge lamp circuit (with an isolator when the aux. battery is removed) and some suitable gauge wiring from the alternator's spare output terminal.

This would be the simplest option. But I know it could allow a heavy current after starting as the vehicle battery tries to discharges itself through to the aux. battery, if it is sufficiently discharged.

2. Install a couple of Zener diodes as above without needing the relay, but still with an isolator for when the aux.battery is removed.

Because of the voltage drop through the diodes a battery sensed conversion would also be a must for the alternator. I might want to do this anyway as it should improve the charge to both batteries in the first system too.

Any thoughts/advice ?

Thanks
Ian

[RMS]

What about an auto-sense relay like THIS

I've used cheaper versions, like THIS on Patrick's and my Carawagons, but both failed after a few months use so replaced one with a better one, like the first item, pulled from a Disco donor.
The other I replaced with a heavy duty relay, alternator switched, from another Disco donor (marked Land Rover so hopefully ok).

Does your Waeco fridge have a High/Low switch - both of ours do. If set to High, it will cut out when the battery voltage drops to less than 12V so still leaving enough to start the engine (apparently )

Cheers,
Robin.

[Dormy]

Hi Robin,

The relay I was thinking of is http://www.maplin.co.uk/p/12v-40a-dc-sp ... elay-n02aw 1/10 the price of the 70 amp. It will also be auto sensing if wired from ALTs. warning lamp circuit (as I guess you have done) and at 40 amps should cope with the output of the ACR.

Not surprised the other relays burned out. Can't see how any manufacturer can possibly suggest their gizmo is suitable for split charging batteries when it is only rated at 15 amps !

Yes the Waeco does have the switch, but I must confess to setting it wrong.

Ian

[RMS]

The point of the auto sense ones is that they only start charging the auxiliary battery when the starter battery has recovered from starting the engine. They also 'soft-switch' and control the amount going to the auxiliary battery which means they can limit the charge rate to 15A, or whatever.
The expensive one does that, but can send up to 70A to the auxiliary circuit so heavy duty wiring is required. On the smaller one, lighter wiring can be used as it will only send 15A maximum, though that does mean it takes longer to charge.

Neither of the cheap ones showed any signs of being burnt out (I dismantled both), but they were poorly made with surface mount integrated circuit and components badly soldered to the circuit board

The other one I used is basically what you are suggesting, though an electronic switch rather than a mechanical relay, with the switching circuit taken from the alternator charge lamp.

I've certainly used heavy duty relays in the past, switched from the alternator charge lamp circuit, and they have worked ok, but as we're using Optima Yellow Top batteries, I thought it best to protect them, and I had the units from the Discos anyway

Cheers,
Robin.

[Dormy]

Hi Robin,

OK, controlling the relay by switching it from the alternator is crude compared to the sensing units, but I haven't read anything about limiting the current on any of the basic ones. Did find another here http://www.brocott.co.uk/split-charge-r ... h78-1.html which may be more reputable but at a good price (too good to be true !?).

However, I take it you are happy with the alt. switched electronic system you are currently (scuse the pun) using ?

Ian

[RMS]

I think so Ian,

I replaced mine mid 2012 and Patrick's early 2013.

Both have proved ok since then, whereas the original cheap units failed to charge after just a few months.

We have both attended long weekend shows (Thursday to Sunday) without running the engines and the auxiliary batteries have held up well using fridge, lights and Eberspacher (mine more than Patrick's caus I'm soft ), so must be getting charged properly on the way there

Cheers,
Robin.

[RobW]

Is this something that can be added to the main battery? I'll have both main & leisure batteries under the bed so can just link the two via some gubbins?

[DrivingDutchman]

I have a question relating to this topic…

Can you make a split charger system with the original dynamo opposed to an alternator?
I have a six pot with still its original dynamo fitted and need to install a split charger system to run my fridge.

Michiel

[Dormy]

I'll have both main & leisure batteries under the bed so can just link the two via some gubbins?

Yes, should work like that too.

Can you make a split charger system with the original dynamo opposed to an alternator?

Absolutely no reason why not. It might look more complicated because of the extra wiring with the control regulator on the bulkhead, but it should just be a case of tapping your aux. supply at the right point. Using the terminal where the main battery cable joins the starter button is probably best.

The advantage of the Dynamo is they are usually set to a slightly higher voltage so should maximise the charge a little. The disadvantage is the Dynamo's lower output which means charging will take longer.

HTH
Ian

[Dormy]

Another question for Robin: -

Do you still need some form of isolator for the sensing type relay when the aux. battery is removed ?

Ian