Some Details of mehitabel's Installation, and Results
Batteries - Concorde SunXtender 6V x 8 in a row for 48V nominal.
Rated for 5000 cycles to 20% discharge; 1200 cycles to 80% discharge.
"220Amphours" at 24hr rate (drawing 9A) but practically...
204Ahrs at 8hr rate (drawing ~25A) - so usefully, 9.8kWhrs.
At that latter rate, mehitabel's been going at roughly 2.5+ knots in flat calm, has gone maybe 20 nautical miles, and the batteries are totally dead. (So we don't do it that way. We very seldom go even half that long.)
Our 48V battery bank weighs 250kg.
The 8 batteries are set forward of the old diesel's mount, 10cm from the hull. I'd double it without overload worries, only cost worries, and the angst of one more step away from minimalism...
Total Solar Panels - 520 Watts, with fancy MPPT Solar controllers to 12V house bank, which stores 440 Ahrs = 5.3kWhrs.
Wind Generator - SW WindPower Breeze 48V - 200 Watts continuous when it's windy, around 20 knots I think. (no wind instruments...)
If all those inputs are working at max, we can charge the batteries to full after a 50% discharge, in about 7 hours. Never happens. 2 or three days would be roughly right, but 50% discharges are actually very rare. Usually more like 10%, which can recharge in a sunny-and-windy afternoon.
'Soaking up diesel' like this, is as hard a job as 'letting the glue set.'
Battery Charger - Meanwell 600A 48V from a Xantrex 1800W inverter.
This is about 75% efficient, drawing from the house bank. So actually, sunny late morning through afternoon...
Fuelled Generator
(Not installed. I'm not sure whether we'll finally install the petrol-propane Honda motor with DC generator. It could keep up with ~3 knots as long as fuel lasted. I have an even better generator component to try... I haven't felt the need sufficiently yet. To Tonga next year? We'll likely be fine without it.)
Motor - Mars ME0913 Dual Stator, Brushless
Its maximum output is 10.5kW=14HP Continuous; 21.6 kW=29HP for 2 minutes. Heaps of torque. Heaps, at any RPM. Maximum RPM is 2550.
Controller - Sevcon Gen4-4845, which is a good match to the motor's maximums. It's mounted on a good heat-sink, and only ever gets warm.
I slightly regret that the motor is useless without the electronic controller. Brushed DC motors can be hooked up directly to batteries and will go.
Drive Train - Belt reduction 3:1 motor:propeller, 2550:850 at maximum.
(2:1 is recommended if speed is a priority &/or a small propeller is used.)
Propeller - Kiwi Feathering Propeller 18.5" diameter. Pitch (in forward) is adjustable.
Our big prop doesn't get to maximum RPM. We're only going about 5 knots at maximum throttle, but we're hard to stop...
Performance
Now, before I give performance figures, don't take these super-seriously.
Preparing to design the motor system, we towed the boat with another yacht, measuring the force to pull mehitabel at up to 5 knots. Calculated... deducted propeller drag... guessed efficiencies... to arrive at predictions of electrical power required to go at various speeds. I recommend the exercise, because the predictions came true!
Predictions:
Knots ::: Electrical Power Input (at batteries)
Total efficiency assumed: 44%
1 ::: sheesh! Hardly any. A Yuloh would do fine.
2+ ::: 0.5kW
3+ ::: 1.5kW
4 ::: ~3kW
5 ::: ~6kW
6 ::: ~10kW
Actuals:
Tested figures have met or exceeded predictions, markedly exceeded since installing the big Kiwi propeller.
I need to test more. It's on the list. But bringing together a clean bottom, polished propeller, crew to take readings, flat water, working calibrated knotmeter, time and inclination... well, we've done a few tests with some rigour, and none perfectly.
I now reckon with the new propeller we may assume 50% efficiency (battery input to actual propulsion) and be very close.
You'll note the dramatic energy cost of going fast. So we go slowly, typically 3 knots or less. The ammeter is staring at me all the time.
Imagine a fuel-use gauge for a diesel. If you could deduct the overhead of running the thing at all, the display would tell how much can be saved or spent by varying your speed.
Our old Bukh used about 1 L/hr idling, and our long-term consumption averaged 1.5 L/hr. That glaring truth was one motivation for changing to electric.
Oh, Cost
Including everything listed above and fabrication, wires, a new shaft, bearing, seal and all... a little less than a new 20HP diesel installation, complete. I would have done most of the work in either case.
That's imprecise, but in line with what the Groves have committed to EasyGo's motor system. There are differences, because the solar panels and wind generator provide all our electrical energy, not just for the motor. Many people would want a diesel as well, to generate continuous electricity and so dissolve the biggest compromise - limited range.
Individual components can seem cheap, with smaller motors around US$400, but you'd have to price it out right down to the (many) battery cables and the terminals on the ends, to really cost it properly. We didn't. Once the decision was made, we simply did what we had to do until it worked. And when it smoked, we did some of it again.
It's been interesting.
Cheers,
Kurt
I dealt with Brian, Mark & Co. there for the motor and controller we have now.
They're very savvy about electric vehicles, and are learning more about boats all the time. Decent folks, and busy.