Smartcom / split charger confusion???

[orangebooboobearcrew]

Hi,

Seems to be quite a popular topic at the moment but I finally got around to fitting my Smartcom / second battery at the weekend and I am a bit confused by something.

I thought it would be a good idea to fit an l.e.d. on the dash to light when the Smartcom relay kicked in so that I could check that this was in fact working and actually charging the second battery. So I wired up the whole set up as follows (sorry not diagram but I tried and don't know how to do one!) :-

Starter battery positive feed to Smartcom relay '12v positive input' terminal (with fuse)
Smartcom relay '12v earth input' terminal earthed to bodywork (should this be fed instead direct from starter battery negative terminal?)
Smartcom 12v switched (not 'permanent live' or 'fridge output' terminals) output terminal (with fuse) to leisure battery positive terminal
Leisure battery negative terminal to vehicle earth
Leisure battery positive terminal then to secondary fuse box
Secondary fuse box to additional electrical items (work fine as tested)

My logic was to take the l.e.d. positive feed from Smartcom 12v switched output terminal, just after the fuse so that it would only light if the Smartcom relay was 'switched open' i.e. greater than 13.2v so that I could tell it was working. I then wired the negative of the l.e.d. to the same earth point as the negative input side of the Smartcom
relay.

However, when I switched the battery back on from the isolation switch, the l.e.d. is on all of the time, regardless of whether the engine is on or not!? How can this be? Surely the relay only produces voltage output at 13.2v unless it is faulty and 'leaking' voltage all the time and hence will flatten the starter battery fairly quickly I would imagine as it will be trying to charge up the leisure battery? What am I doing wrong?

All help would be greatly appreciated - many thanks in advance.

Chris

[VWCamperfan]

The voltage from the leisure battery is supplying the LED... Simples!

[bigherb]

As above, should have connected it to the fridge outlet.

[orangebooboobearcrew]

Thanks both for your replies.

How does that work then? I know this will sound stupid but doesn't the voltage just 'flow' in one direction from the starter battery, through the relay and then to the leisure battery, then down seperate wire from leisure battery to secondary fusebox?

Also, if I do connect up the l.e.d. to fridge output, when I wire the fridge up tomorrow (12v fridge only), will this make any difference to how the l.e.d. should work?

As I say, sorry if I am being a numpty (again) but still learning!

Cheers,

Chris F

[VWCamperfan]

Electricity will always take the easiest route and as you have a copper wire coming from the leisure battery back towards the relay, that is the route it will go. Whenever a wire is connected to a battery you will have power running through it.
Say, for example, you disconnect your main battery live terminal. You still have power running from the leisure battery to whatever equipment/device is connected to it. In this case, its your LED.

[orangebooboobearcrew]

A-ha! I see (said the blind man!). That makes sense now - thanks for your invaluable help. I'll try wiring to the fridge output tomorrow and hopefully all should be okay...

cheers,

Chris

[AngeloEvs]

The smart com relay has two outputs rated at 15A each, (incidentally, I complained to their tech support as the relay is listed as 30A) which is fine for the fridge but falls short for charging the leisure battery. Simple mod is to use one output from the smartcom to power the fridge and the other to drive a higher rated relay for the charge function. You can then wire your led across the same output as used for the charge relay (which should have a 30A minimum rating).

[bigherb]

Like angelo using the smartcom to switch a normal relay is the best configuration and as the electricity will flow both ways down the wire, there should be a fuse next to each battery.

[Oldiebut goodie]

......used for the charge relay (which should have a 30A minimum rating).

Ideally the charge relay should have a rating equal to or greater than your alternator output if you think about it.
Yes, I agree about Smartcoms marketing hype. There are 100A voltage sensing relays available - I picked one up on fleabay for £15.

[matty o]

you could put a diode in line with the led this will only allow the current to travel one way.

[VWCamperfan]

you could put a diode in line with the led this will only allow the current to travel one way.

An LED is a diode!

[orangebooboobearcrew]

Thanks for all the advice guys.

So let me get this right, are you saying that my leisure battery will not actually charge up sufficiently using this Smartcom set up (also now using the fridge output from Smartcom to power 12v fridge)?

Cheers,

Chris F

[1664]

No, not necessarily. The arrangement you have will allow the leisure battery to draw up to 15amps from the alternator to recharge it. This is perfectly acceptable if you've only run your leisure battery down to a point it does not demand more from the alternator when you start the van and the relay switches in. If you have run the leisure battery to near flat it will demand a lot more than 15amps and will blow the fuse.

This has been happening a lot to me since I bought a TV for the van. I need to upgrade my rather feeble split charge wiring - what I've been doing in the meantime (which is far from ideal and I do not recommend this in any way) is removing the fuse, starting the van and chucking a set of jump leads betwen the batteries terminals - and the jump leads get quite warm too so there's probably 50ish amps flowing through them initially until the leisure battery has at least partially recharged.

So the bottom line is, the more you flatten your leisure battery the more it will demand from the alternator during the initial stage of the recharging process, and if it's more than 15amps it's going to rupture your fuse.

[orangebooboobearcrew]

Thanks for that 1664.

We're going on holiday on Friday so don't want a total nightmare with electrics while we're away!

Crikey - I think I'll pass on the jump lead solution you have been using as I haven't got any rubber boots!!

So in terms of a longer term solution, would you an option be to upgrade the relay to say 30a and use 27a wire with 25a fuse? The reason I ask is I have used 27a wire right through and apart from the cost it would be a nightmare to have to rip this out and uprate this now

Would the 25a this would provide(?) be sufficient? sounds like possibly not if you say battery is drawing 50amps? What are the aternatives?

Cheers,

Chris

[1664]

It all hinges on how far you run your leisure battery down. Theoretically, If you utterly flatten it, it will have all the juice your alternator is capable of giving it. My 15amp split charge system performed perfectly adequately for years - it was the addition of a TV that sucked 4.5amps for long periods that 'broke the camels back'.
Before that I was just running the camper fluorescent lighting and the water pump which only slightly discharged the leisure battery so when the relay switched in the leisure battery demand was not more than 15amps. I did have to keep an eye on how long the propex was running though.

If you're not going to be pulling any great load from the leisure battery and the van is not parked up for days on end without being driven you should be fine. If you drive from place to place every day of your holiday this shouldn't be an issue unless like I've said you are running a heavy load for a substantial amount of time.

If your existing wiring is capable of carrying 25amps then upgrading the relay to say 30amps and re-fusing to 25amps would certainly improve the situation - gives you another 10amps leeway, but ultimately if the leisure battery is run right down it would still cause the fuse to rupture. Simplest solution is not to treat your leisure battery like the National grid. Some people install an additional leisure battery to give extra capacity.

No, I don't recommend the use of the jump lead method................... that's strictly a rare 'once in a blue moon' get me out the doo-doo type of risk only mad electricians might take