Electric Cooking

In common with many boats, MARLIN had a LPG gas cooker (2 ring; grill and oven). LPG is inherently dangerous on boats: it collects in the lowest place since heavier than air and it is flammable. LPG gas bottles must be stored in a locker that vents overboard and pipes (plus flexible connectors) must be checked and kept up-to-date. I fitted a LPG gas detector and had the recommended number of fire-extinguishers and a fire-blanket.

I would feel happier without LPG aboard: no risk of fire or carbon monoxide poisoning. Since I do little cooking (I never used the oven, prefering to eat ashore whenever possible), I investigated using electricity to cook/boil/toast/..

MARLIN has 24 volt electrics and has 100 Ah (at 24 volt) service batteries. My first step was to obtain a 24 volt electric kettle. These are mainly targetted at truck cabs. With a 15 amp consumption, the kettle uses 320 watts. This level of current is NOT appropriate for a "cigar lighter" type plug connection. After some exploration, I wired the kettle in permanently (with a 20 amp fuse and on/off switch rated at 30 amps). I find that 320 watts is quite slow - a mug of water takes 6 minutes to boil. That is OK for when I am aboard alone and only want a hot drink occasionally.

To have more options, I decided to fit an inverter: this generates 240 volt AC and can power a faster electric kettle; microwave; power tools; toaster; etc. I chose a 2KW rated inverter: there is a choice to be made about "modified sine-wave" versus "pure sine-wave". The former is cheaper and is perfectly suitable for heating applications but may not work properly with motors and microwaves. I went for the latter to have microwave oven capability and to be able to use all my power tools.
Note that for a non-resistive load (motors and some power supplies in TV's, etc) the starting load can be up to 3 times the continuous load and some inverters may cut-out unless sufficiently highly rated. My previous experience was that an inverter rated at 700 watt was unable to start a 600 watt power drill.

LCD DISPLAY Pure Sine Wave power inverter 4000W Peak 2000W DC 24V TO AC 220V - 240V [cost £155 in 2016 from China].

This needs around 100 amps (DC at 24 volts) to drive it - so I sourced 25 mm2 cable [voltage drop at 100 Amp of 0.18 volt per metre] and suitable fuses, switch (main DC switch of the battery master switch type), connectors and contact breakers. It has a [UK-style] mains plug on the front panel.

With this installed successfully, I removed my LPG cylinders and oven unit. This gave me plenty of room to fit a 240 volt "travel kettle" of 900 watts as well as a toaster. I made a retaining fixture to hold the travel kettle in place when under way.

I have tested it with power tools and found it successful. If the engine is not running, you have to keep an eye on the total use to avoid running the batteries down too much.

I have yet to try it with a microwave oven - mainly because most microwaves are of a size that will not fit comfortably in the space I have available. Also microwave ovens usually have a turntable which might misbehave in a bouncing boat - though "flatbed" microwaves are starting to appear that might suit better.

One small tip: this inverter has a large capacitor (0.02 Farad) to store energy (6 Joules) and when switched off it will still be full of charge (at 24 volts) for a while - so can give quite a nasty shock/spark, particularly since you are not expecting it. Also when first switched on at the DC switch, the DC current flow to charge this capacitor can cause some sparking in the switch. To ameliorate these issues, I fitted a suitable resistor (eg 3 KΩ) across the DC switch to provide a small current: to slowly precharge the capacitor for a softer start and to slowly drain the charge when the master battery power is switched off.

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