# Fridge 12v feed & split charging. Smartcom v standard re



## 88826

I'm contemplating installing a split relay charging system with 12v feed to the Dometic fridge while "on the move". Both vehicle and leisure batteries are 120AH with the latter in a secure area behind the passenger seat. 
I would be grateful if some learned member can extol the virtues and problems of both systems. Being simple minded the Smartcom appeals as there are no connections to the alternator with only five connections on the relay. However all the literature I've read seem to indicate that it is primarily used for the caravan towing fraternity. Can it be adapted to my needs and if so how would the circuitry be modified? The other alternative to the Smartcom is a Combi Master dual relay system. Other considerations are location of relay, (near leisure battery or engine compartment) cable and fuse capacities.

Thanks
Bonza


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## safariboy

Split charge and the fridge are two separate things. You need is a relay for each. Remember to fuse each line where you take it off the battery.
There are diode systems which are simpler to fit but if you use one of these you loose some volts and so they will work less well.
I would tend to put the relay in the engine compartment.
If you do not want to make the alternator connection you can connect to the Key on line but this will mean that the fridge comes on and the habitation battery is connected when the engine is being started. The key on line may well be as difficult to find as the alternator.
I would tend to put a 1A fuse where I branched off from the Alternator on line for the relay.
Make sure that there is a fuse as close as possible to all batteries, that the wire is large enough to take the current, and that it is routed so it is protected and cannot chafe. Where is goes through a bulkhead ther should be a rubber gromet.
Fuse sizes for the split charge 20A and the fridge 15A seems about right but I expect someone else will come back on that one.

Best of luck hope all goers well.


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## safariboy

I have just looked at a smartcom site. It seems that it is not a diode device as I thought but a relay that senses the increase in voltage when the alternator starts working. This should be OK and is simpler to install but in the long run it might be less reliable as it depends on a fine adjustment of the voltage sensing relay. The unit has two switched outputs. 
If I was putting that in I would include a small indicator lamp to reasure me that it was working correctly!


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## DABurleigh

Bonza,

If you can locate the "alternator is charging" sense wire, or its connection at the alternator, there is no point in using a Smartcom. If you really can't locate it, by all means do use one.

However, if you think you will really benefit from being able quickly to charge your leisure batteries at up to a sustained 50Amps, even from tickover (leisure batteries take a long while to recharge from depleted via a normal split-charge relay arrangement, even with thick cabling), then consider a Sterling battery-to-battery charger, which from a connection point of view can be regarded as a Smartcom relay with even fewer connnections, and none to the alternator. Bit of a bigger box though! 

Dave


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## 88826

safariboy said:


> I have just looked at a smartcom site. It seems that it is not a diode device as I thought but a relay that senses the increase in voltage when the alternator starts working. This should be OK and is simpler to install but in the long run it might be less reliable as it depends on a fine adjustment of the voltage sensing relay. The unit has two switched outputs.
> If I was putting that in I would include a small indicator lamp to reasure me that it was working correctly!


Thanks safariboy. I was aware that the Smartcom wasn't a diode device but I would be very interested in the website link which you viewed the information. Do you know who actually manufactures the device?
Bonza


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## 88826

DABurleigh said:


> Bonza,
> 
> If you can locate the "alternator is charging" sense wire, or its connection at the alternator, there is no point in using a Smartcom. If you really can't locate it, by all means do use one.
> 
> However, if you think you will really benefit from being able quickly to charge your leisure batteries at up to a sustained 50Amps, even from tickover (leisure batteries take a long while to recharge from depleted via a normal split-charge relay arrangement, even with thick cabling), then consider a Sterling battery-to-battery charger, which from a connection point of view can be regarded as a Smartcom relay with even fewer connnections, and none to the alternator. Bit of a bigger box though!
> 
> Dave


Hi Dave,

I've had a look at the Sterling battery to battery charger. It looks the 'bees knees' and very simple to install but I was hoping for a cheaper but effective option. It is also very subsceptible to temperature which affects the operation of the device. Hence the Smartcom v standard relay query. I know, 'What you pay is what you get' and sometimes isn't the best option.

Bonza


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## safariboy

http://www.thecampingwarehouse.com/information/articles/smartcom-type-voltage-sensing-relay.html
was the site I looked at. there may be others. I simply put "smartcom caravans" into google and out it poped.

Bets of luck with your project.


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