Club 80-90 Forums

Hi all,

I am renovating a camper and I would like some advice about the electrical system.
The camper had a Zig cf unit. So I am thinking of still using it.
However after reading a lot about the different systems I am a little confused about some aspects:
- 1st- Fridge connection. It is recommended to connect the fridge directly to the main battery, the Zig instructions recommends using a relay RM12 or RM14. However I did not find information about how to connect these relays to the alternator of my van (I am not quite familiar with the van wires). So I decided to use a sensitive Smartcom relay instead (more simple to install).

- 2nd -Battery charging: I read that the Zig is a trickle charger. I also read that this type of charging needs a lot time and it is not able to charge the battery completely. So once I have the Smartcom relay for the Fridge I thought of using it also to charge the battery a little faster or to complete a final charging step. This will have a switch to use only when required. No idea if this is right. I am also wondering if the fact that the battery is charging from the Zig and the Smartcom relay at the same time can be bad for the leisure battery.

-3rd- Cables sizes. This seems easy regarding the famous formula: Cable size=(Amp*Calbe length*0.017) / 0.3. However it s not clear to me what is the right size for the cable coming form the engine battery to the Zig and to the Smartcom relay as I do not how many amperes this cable will use.

I read that the battery should be connected using 10-16 sq mm using for example the Smartcom, obviously the Zig unit does not allows this cable size. So my question is what is the right cable size from the engine battery to the Zig unit if they are separated by 5m and what are the Amps that would support this cable.
Same question for the 30Amp Smartcom relay.

Attached is a diagram of the system that I´m thinking of installing, please give some feedback if this is right .The cables size, cable length and max amps expected are also included. An option B for the Smartcom relay is also included. I do not which option is better.

https://club8090.co.uk/wiki/Ca ... _Zig_Units" onclick="window.open(this.href);return false;

look at the fuse sizing and calculate your cable sizes from there.

I used 35A cable for all my split charging stuff and have very little volt drop between points.

Zig instructions (CF6 and CF8 are identical):

http://www.club80-90.co.uk/pages/downlo ... ig-cf8.pdf" onclick="window.open(this.href);return false;

RM212 fridge instructions:

http://www.club80-90.co.uk/pages/downlo ... xRM212.pdf" onclick="window.open(this.href);return false;

Fridge 12v electronic ignition instructions (if fitted):

http://www.club80-90.co.uk/pages/downlo ... 2Elect.pdf" onclick="window.open(this.href);return false;


General wiring:

https://club8090.co.uk/wiki/Ca ... _Zig_Units" onclick="window.open(this.href);return false;


Split Charge system for charging a leisure battery. Same wiring for fridge incidentally; just substitute the leisure battery connections for the fridge 12v heating element connections. I wouldn't use a smart relay for the fridge personally.

https://club8090.co.uk/wiki/Ca ... it_charger" onclick="window.open(this.href);return false;

Club 80-90 'Wiki' at the top of the page and useful downloads in the 'Club Stuff' tab at the top of the page too – all very useful.

AlexIRL wrote: - 2nd -Battery charging: I read that the Zig is a trickle charger. I also read that this type of charging needs a lot time and it is not able to charge the battery completely. So once I have the Smartcom relay for the Fridge I thought of using it also to charge the battery a little faster or to complete a final charging step. This will have a switch to use only when required. No idea if this is right. I am also wondering if the fact that the battery is charging from the Zig and the Smartcom relay at the same time can be bad for the leisure battery.

I believe the Zig is a 'constant voltage, variable current' charger. I think the voltage it uses is around 13.5V - I'm not sure, 13.8V maybe? - which means it will get charge into a flat battery quite quickly (it provides up to 12A), but will, as you say, take a very long time to get it fully charged.

The smartcom relay only operates when it senses that the starter battery voltage has risen over a specified threshold, which indicates it's being charged. If your Zig is wired up conventionally, then the only way your starter battery is going to get a charge is if the alternator is running. So yes, it's possible that the smartcom relay will allow the leisure battery to be topped off (by the possibly higher voltage alternator), but only when the engine's running. You won't need a switch - it's voltage sensing and therefore automatic.

The Zig's 'Touring' switch will simply link the leisure battery to the starter battery, so that any charge from the alternator will also reach the leisure battery. It's doing the same job as the smartcom relay, except it relies on you remembering to set the switch, rather than being automatic (voltage sensing). Having a Smartcom relay AND the Zig 'touring' switch is not a problem - you're just providing two paths between the batteries instead of one.

Have you seen the schematic for the Zig CF8?

1664 wrote:I wouldn't use a smart relay for the fridge personally.

I thought that was one of the good things about the Smartcom relay. The one I fitted had separate outputs for the fridge and the leisure battery.

CJH wrote:

1664 wrote:I wouldn't use a smart relay for the fridge personally.

I thought that was one of the good things about the Smartcom relay. The one I fitted had separate outputs for the fridge and the leisure battery.

It's purely personal preference Chris, whilst the wiring is (only slightly) easier for a smart relay the 'smart' introduces complications into an otherwise simple arrangement. Should it be set incorrectly or go t!ts up there is the possibility that the fridge (which is the largest electricity consumer in most vans) could be sucking the life out of the battery if the fridge switch is left ON. With simple the relay is energised when the engine is running and not when the engine is off; the worst that can happen is the relay fails 'open' leaving the fridge disconnected. Maybe not a problem with your van - you have it set up like the national grid and are more likely to run out of fuel before you run out of 12v

Now I'll be the first to admit that I may have that completely wrong, but like with vehicles, I believe the simpler the better as there is less links in the chain to break and if a link does break it's usually a simple fix.

bottom line is I'm a bit of a dinosaur

Thanks all,
Much clearer now about the Battery charging options. My Smartcom relay also has independent outputs for the battery.
http://www.ebay.es/itm/370837856330?ssP ... 1497.l2649

Regarding the fridge I see that there are different opinions and I suppose that each one has advantages and disadvantages. Personally, I am not familiar at all with the van wiring such as the ignition cable and so on. For this reason I chose the Voltage sensitive relay option.
Regarding the cable size it seems that the Zig is not sensitive to the drop voltage, so I will use a 4.5 sq mm. For the Smartcom I will use a bigger one (6-7 mm). I think this will be enough to have a small voltage drop using 5m of cable.

AlexIRL wrote:Thanks all,
Much clearer now about the Battery charging options. My Smartcom relay also has independent outputs for the battery.
http://www.ebay.es/itm/370837856330?ssP ... 1497.l2649

That's the one I used. Once I'd got the thresholds set it worked fine for me. I installed a little check light in the dash, fed from the fridge output, so that I could see when it was switching in and out. It takes a little getting used to, since it doesn't come on immediately when you start the engine, and doesn't switch off immediately when you stop the engine.

AlexIRL wrote: Regarding the cable size it seems that the Zig is not sensitive to the drop voltage, so I will use a 4.5 sq mm. For the Smartcom I will use a bigger one (6-7 mm). I think this will be enough to have a small voltage drop using 5m of cable.

My Zig unit had the original Motorhomes International wiring, which was 4mm2. Voltage drop isn't too much of an issue because a) there isn't much with that size cable (see here), and b) you've got an alternative link between the batteries (the Smartcom). The DC circuits fed by the Zig will all work some way below the battery voltage.

6-7mm2 cable is going to be a tight squeeze in the Smartcom connectors - it may not fit. Do you have some that you can try before routing it around the van? I used 30A cable, with 25A fuses, and never once blew a fuse. You'll have to fuse it to protect the 30A relay anyway. I'd be the last person to advise using cable that's too small, but I'm just pointing this out in case your 50A cable won't fit in the relay's screw terminals. You'll see the biggest current flow if your leisure battery is depleted when it gets connected to the starter/alternator, but I don't really know what sort of current might be involved.

1664 wrote:Maybe not a problem with your van - you have it set up like the national grid and are more likely to run out of fuel before you run out of 12v

Well yes, I've taken steps to minimise the chances of running out of battery power, but with a 100W solar panel I don't think I need to worry too much about feed-in tariffs. Mind you, there's still a lot of unused space on my roof......

CJH wrote: 6-7mm2 cable is going to be a tight squeeze in the Smartcom connectors - it may not fit. Do you have some that you can try before routing it around the van? I used 30A cable, with 25A fuses, and never once blew a fuse. You'll have to fuse it to protect the 30A relay anyway. I'd be the last person to advise using cable that's too small, but I'm just pointing this out in case your 50A cable won't fit in the relay's screw terminals. You'll see the biggest current flow if your leisure battery is depleted when it gets connected to the starter/alternator, but I don't really know what sort of current might be involved.

I've just remembered - the last change I made before pulling it all out and starting again, was to use the battery output from the Smartcom to trigger a bigger relay, wired in with fatter cable, so that the split charging circuit could handle more than 25A. It probably wasn't necessary (given that I never blew a 25A fuse), and it rather defeated the object of the Smartcom relay, but it did still leave me with the fridge output and the voltage sensing smarts, without the need to run a trigger from the alternator.

6-7mm2 cable is going to be a tight squeeze in the Smartcom connectors - it may not fit.

Thanks for your help, I now have my Smartcom and I have started to do some work on my camper.
I was confused about the Voltage Drop Calculators that you can find online (e.g. http://www.bulkwire.com/wireresistance.asp). According to this for 8m cable (distance between the main battery and the leisure battery) and 25Amp a 8sq mm is recommended. However this is not possible to fit it in the Smartcom. I am not interested in higher Amperes so I will follow the easier way and follow your recommendations about using a 4 sq mm cable.

AlexIRL wrote:I was confused about the Voltage Drop Calculators that you can find online (e.g. http://www.bulkwire.com/wireresistance.asp). According to this for 8m cable (distance between the main battery and the leisure battery) and 25Amp a 8sq mm is recommended. However this is not possible to fit it in the Smartcom. I am not interested in higher Amperes so I will follow the easier way and follow your recommendations about using a 4 sq mm cable.

That's a useful site. It recommends a cable size to keep the voltage drop to less than 4%. So yes, if your 8m cable was passing 25A all the time you'd be losing around a volt with 4mm2, or less than half a volt with the recommended 8mm2. In reality, you'll rarely be passing 25A I believe - if there's a big voltage difference between your starter battery and your leisure battery the current will be high, but how high I don't know.

I doubt that the alternator will provide 25A to your leisure battery. Most of the time it would be lower, but I'm not sure how much lower. If it was, say, 10A (like a decent mains charger), the voltage drop over your 4mm2 cable would be more like a third of a volt, and if it was only 5A it would be half that again.

All of that is according to the calculator on that website. I can't vouch for that, and I'd even be hesitant to 'recommend' 4mm2 for such a long run, except to say that it was considered sufficient by Motorhomes International when they installed my Zig unit - in total I think there was about a 10m run between my starter and leisure batteries via the Zig.

If you wanted to make use of your Smartcom AND use thicker wire, don't forget that you could use the Smartcom's output for the leisure battery to trigger a conventional relay that could handle thicker wire. Just take a thinnish wire from the smartcom to the relay's energiser circuit, and another from the relay to earth, then your thicker battery wire would go via the other two (switched) terminals.