Fairly short cruise this morning to waterpoint below Atherstone locks. A bloke on a narrow boat said his mate on a short Springer would be along soon and we could do the locks together. So we did. Still took all morning, I think we cleared the last one about 1pm. After that another long lock-free section down to Marston Junction (Ashby Canal) then about 3 miles further to Hawkesbury Junction where I turned onto the Oxford Canal via the Sutton Stop Lock.
Moored just past Sutton Stop, sandwiched between David and (wife?) who accompanied me through the locks earlier and their friend +1 +another (mother-in-law?) who is very old, crooked and unsteady on her feet. They’ve all gone to the pub at the junction to eat but I had stuff in the fridge to use up.
The fridge is still giving me grief. I’ve done a few measurements with the gear I have and come to the following hypothesis:
The fridge uses 0.6A at 220-240V running off mains (at Llangollen) or off the inverter.
To get 12V from the battery to 240V the inverter steps up 20 times the input. Therefore the current must go up the same. 0.6 x 20 = 12A
But the inverter is about 80% efficient so consumes more like 15A.
That’s more than my little meter can handle so I can’t check, I’ll buy an ammeter when I get home.
I suspect 15A is close to the charging current into the battery from the alternator (via split diode circuit) and solar panel (200W or about 15A on a sunny day).
So in the morning if I check the leisure battery voltage it’s usually around 10-12V. Start the engine and wait a while for the alternator to replenish the engine battery and the relay to close to start charging the leisure battery and it goes up to 12.x or even 13V. But that’s from the alternator and solar panel the battery state is still showing empty. (Or close to empty, it’s not very precise).
Now I can switch on the inverter and the fridge and it works. But if I have a prolonged period without the engine running (waiting at locks for example) the fridge goes off even though the inverter is still running and draining the battery. I need to repeat the morning routine to get it working again. Turn it off. Run the engine, wait for the voltage to rise and restart the inverter.
By the end of the day the battery state is showing a low charge, or if I’ve not had the engine on much, empty. I can run the fridge for a few minutes – ½ hour maybe, but then the volts tail off and the fridge stops working.
When I get a real ammeter (using a little multi-meter at present) I’ll check the alternator output and charging current into the batteries. I might need a more powerful alternator (I think it’s a standard car model and few people have fridges in cars). I might need another battery in parallel with the first to hold more charge.
Anyone reading this got any more ideas / info, please comment below.