My boat was built with a design spec of 72 hp to achieve waterline speed in normal conditions. My experience with a conventional engine confirmed that it was about right. I know that many folks recommend using smaller electric power but I felt than the extra power is good to have when you are in rough conditions, a fast moving river, breaking inlet, etc. Admittedly, an electric motor has much more torque at low power, but that doesn't really help the top end.
On the other hand, my generator is only half that power, to get 50kW or 100kW requires either using all electric or syncing the generator voltage with the battery output to maximize the combined power to the motor while minimizing battery drain. My boat has a single battery bank and is charged at 352 volts.
We're doing the propulsion for a second boat which is a 110' schooner with twin screws. That system will be using two 480 vdc battery banks with 64 kW-Hrs of capacity in each bank. There's some more stuff about my boat at http://barbara-ann.com and about the design approach at http://hybridpropulsion.com.
To a large extent what we've been doing is a research project so far. However, each iteration gets better and better. We're on our third go round on the battery management and we've reduced the size and cost by two thirds. Also, our all of our designs have been able to keep the batteries in balance to within millivolts. We've found that a very high percentage of the total system cost is wire, connections, and labor. Since all the DC cable must be armored and floating, cable costs can range from $7 to $23 per foot. Each connection and the manhandling of cable and hardware take an inordinate amount of labor. We're trying to eliminate most of this with our latest design. The telecom style batteries (like the Odyssey P1800) help this a lot. We've been very happy with our choice of using AC generators. At the current time, they are much less expensive and familiar to most installers. The only disadvantage has been the weight of the alternator versus a PMDC motor.
We are still ambivalent on the propulsion motors. We've used both the UQM and EVO motors. Both of these are great (EVO is a little better), but both are expensive. The drives, in particular, are optimized for automotive use and have more cost and features than we need. We are gravitating towards maintaining variable frequency AC in the system and only doing the DC conversions and the point of use. Try Googling 400 to 600 volt DC 200 amp circuit breaker and check the cost. Typically it's in the thousands of dollars, versus hundred for AC. Carrying around 3-phase greatly reduces the cost of breakers and safety electronics. Ideally, we'd like to stay at around 450 volts at 250 to 400 hz. This would be straightforward in the generator if we can find the right 12-pole motor, or maybe use a 400hz alternator. We try to stay at under 200 amps wherever possible for the same cost reasons. We're also interested in exploring induction motors for propulsion. The systems we are working on are right on the borderline where induction makes more sense than PMDC.
I'll post some more pictures next week. The contractor panel that I posted is the main DC bus. One connection goes to the battery bank, one to the generator, one to the motor, and the rest are various loads and sources like the shore charger, HV to 12VDC power supply, HV to 24VDC power supply, AC inverter, and a 10 kW induction motor for the hydraulics pump.
- Bill
On Aug 17, 2011, at 1:16 PM, R Hampson (MottramGroup) wrote:
Hey Bill,
Sent: Wednesday, August 17, 2011 11:35 AM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] 100kW hybrid installation
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