A bit of data (see image) from yesterday's small sail, which included anchoring for lunch and testing my generator. I electric motorsailed with just a tiny bit of headsail. The total distance was 14 NM. Average speed there and back was 4 Knots. Top speed was 5.87 Knots. I used 3,500 Wh from my battery so that is 250Wh/NM or 1,000 Watts average for the 4 Knots average speed. My battery started at 100% charged. I put 10% back in at my lunch stop and had 40% SOC at the finish. Being Lithium I can go down to 20% SOC. I was going with/against the current as it was a round trip, plus headwinds of up to 20 knots. There was little wave chop as it is in sheltered waters. You can see how I varied the throttle settings by the current draw in the graph and how that affects battery voltage.
Comparing the graphs in the image (click to enlarge) you can see how voltage drops as the charger is switched off and when current is started to be used for motoring. Max current drawn was around 70 Amps as you can see and max power used, at the voltage at that time, was around 1750 Watts .You'll also notice the voltage drop due to load, this just over 1 volt, starting at 26.6 and dropping to 25.4. The nominal voltage of this Lithium bank is 8 cells x 3.2V=25.6V. Voltage drop would be far worse if AGM.
At the lunch stop you can see I was putting around 20 Amps back in (about 900 Watts, which is my generator's continuous output) and once back on shore power around 43 Amps in (as I can use more chargers). I have a 10 Amp breaker for the charge and AC appliances side at 240V. I have a further 6 Amp breaker for other AC supplies. 240V/1Amp marina supply.
Battery temperature was between 12C to 18C during the trip,due to charging and electric motoring use.
John
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