Electrical novice has a 12V boat related question....

tom_on_a_boat · Jul 9, 2014

Hello all,

I am new to the forum and am searching for some help and advice for an electrical challenge on my house boat.

I currently have to run my engine to power the oven (it runs off 240V circuit) and want to wire the oven into my 12V circuit to save time, fuel and my sanity. I have an existing 12V circuit which powers lighting and some applications and wondered whether it is safe to run a feed off 12V wiring going into the same fuse board.

I have thought up a solution which will be easy to do, and will involve running a feed off my fridge cable to connect up the oven. I am currently have a Waeco 80L 12v Fridge (spec at the bottom of this post), which is powered from my leisure batteries. (3X ABS LP110 12 Volt 110Ah Leisure and Marine Battery).

I wondered whether it would be safe to run a feed from the cable that powers the fridge (which is 12volt cable and 8mm thick). The feed would be to a small inverter which would then power the Oven. The cable I was planning to use for the feed is slightly thinner at 5mm thick.. The inverter is a MayaTech ,Spec - 12V -30A Max, Output220-230HV – 50Hz 400VA/330W.
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The oven is a Belling XOU60LPG and according to their tech support team, has a requirement of 37W including Cooling fan, LED, ignition, light etc.

1. Firstly would the feed from the fridge cable be OK?
2. Is the cable for this sufficient or should it be the same thickness?
3. Would a connector block be the best way of doing this?
4. Finally, is this inverter safe/capable to use to power the oven? (it has an on/off switch and would only be used when the oven is in use)

Any help, comments or advice would be gratefully received.

Thanks
Tom

The spec for the Waeco is:

Voltage	12/24 volts DC
Average Power Consumption	Approx. 48 watts
Current Consumption (12 volts DC):	1.8 Ah/h at +25°C ambient temperature, 2.1 Ah/h at +32°C ambient temperature, both at +5°C interior temperature and -18°C in the freezer compartment
Insulation	Full foam insulation in CFC-free polyurethane foam
System	Fully hermetic Danfoss BD35F compressor with integrated control electronics, low-voltage protection, electronic fuse/automatic reverse pole protection, dynamically ventilated wire tube condenser, mechanical, continuously variable thermostat

Adam W · Jul 10, 2014

I'm no expert, in fact I've never worked on a houseboat before, but I'd run a separate supply from the dc board using the largest cable you can fit in - 10mm if possible.
Maybe someone will be along in a minute to tell me I'm talking rubbish...

Marvo · Jul 10, 2014

When we talk about the size of wiring we usually refer to the cross-sectional area of the conductor so a 2.5mm wire actually has a cross sectional area of 2.5 mm² if you cut it and look at it end on. The actual thickness of the wire with the insulation on isn't really an indication of how much current it can carry.

Chances are you probably can run your oven from a small inverter supplied by battery power because the oven only needs 37watts for the fan, ignition and light. You'll be taking a lot more than 37 watts from your battery though because of the inefficiencies of the inverter but even if the overall energy consumption is double it should still be fine.

I can't comment on your suggested wiring method, it sounds a bit rough to be honest but whether it complies with the UK regs I couldn't say, maybe one of your fellow countrymen will have some comments on this.

telectrix · Jul 10, 2014

is the oven gas? because if it's electric heating, 37watts ain't going to boil an egg before it hatches.

happysteve · Jul 10, 2014

Hi,

Ideally, run a separate feed to your 12V fuseboard, as Adam W suggests above.

If this is problemmatic, you could do as you suggest. What size fuse (in terms of amps) supplies your fridge? You fridge will be drawing about 4 amps. The inverter, running your cooker, will pull the same again, or most likely more than that. This 8mm... presumably you have two of these, a red and a black? (or is it one cable with two wires inside)? What's the diameter of the actual copper? If two separate wires, sounds plenty, and will be that big not for current carrying capacity, but to ensure minimal voltage drop.

Adding an inverter to your fridge circuit will make the voltage drop worse, which your fridge might not like. On the other hand, it might be fine - particularly if your batteries are well topped up.

An alternative is to fit a change-over switch to select either fridge or cooker. Some boats have big versions of these to swap between leisure and starter battery (or both, or off). You won't need anything that big, but if you did go down this road, make sure it could handle 10A or more.

Whether the inverter is suitable or not, I can't say. It will probably have a step wave output (rather than sine wave) - some appliances don't like these. I would definitely switch it off when not in use (it'll probably have a noisy fan anyway!). If you used a 12V changeover switch at the input - to select either fridge, or cooker - you could use this to turn it on and off.

Hope this was helpful.

(Used to live on a boat)