I have been reading with great interest your question and answer pages and this has helped me enormously during my recent wiring of my 1935 narrow boat. When I first bought the boat last year it was set up to be permanently moored and it had one starter battery, one domestic battery and a shore line. Only the starter battery was charged from the engine as the system was existing from the 60’s and all that had been added was an independent Domestic battery.
I use my boats for cruising and therefore wanted the system to be less reliant on a shore line.I have therefore increased to 4 x 110AH leisure batteries and fitted a Phoenix Combi inverter/charger and a split charge relay from the alternator.
Now, my question is regarding the good old fridge. I have 240v/12v/gas fridge which is currently only connected to the 240v. It would be far easier to wire it to 12v rather than connect the gas which due to the positioning etc would be a little awkward. Also I’m far more comfortable wiring than doing gas. Obviously I don’t want the fridge draining everything so I was thinking that I might put in a dedicated battery with another split charge relay so that it could discharge itself without affecting everything else. Would this be a good solution or am I coming at it sideways? Or overcomplicating things? Would this battery be up and down too much and harm it and therefore the others when they were all connected via the relays?
Just for interest I’ve attached the wiring diagram I drew for the system. I’ve learnt as I went along by asking questions and researching etc. and am really quite pleased with what I’ve managed to achieve. The only other thing I am worried about is 240v leakage which I have read about. What should I have to ensure that the inverter in particular is safe when operating and unlikely to electrocute anyone!
Once again I would like to thank you for your advice I’ve managed to find on net. It has been most useful and has helped someone with a mere basic knowledge now have almost completed a project of which I am very proud.
Thank you for all that.
I am almost certain that your fridge is an Electrolux unit and that it is only supposed to use 12 volts whilst driving to a site in the caravan. In this mode it does not need a thermostat, so one is not fitted to the 12v heater coil.
As an absorption fridge it is not very efficient, so draws something in the order of 6 to 8 amps the whole time it is turned on. I think you will draw your own conclusions.
If you can not continue to run it on gas, then practically you have two choices. Even if you run it off 240 volts, the loading on the batteries is likely to be the same or worse, except it should have a 240v thermostat so may only work draw current for 50% of the time.
1. A 12v compressor fridge. This will cost £300 plus and if its any distance from the batteries will require getting on for £150 for the cables.
2. A domestic 240v fridge plus inverter. As you have the inverter already I think this is the way for you to go. The only things I would be concerned about are:
a. Can the inverter cope with the fridge starting surge (probably yes for your inverter)
b. How high is the inverter “stand by” current when its turned on, but the fridge is turned off.
As far as using another split charge relay and separate battery, you really need to do the calculations to find out how low you would discharge it. These are in the electrical notes mentioned above. I am happily running a TV, waterpump, lights and 12v compressor fridge on a cruising boat with a 60 amp alternator and 2 x 110ah domestic batteries.
