Thanks. That all make perfect sense. Given that 80W is optimal, is anybody really achieving that. Are the vendors over selling the practicality or functionality? That recharge rate will not please many owners, but it would be fine for me. Can I achieve it with a single motor or do I have to design in an auxiliary towed-type generator?
On the other hand, a secondary generator combined with the primary motor might get me above 80W?
-jak
>
> From: Eric <ewdysar@...>
> Subject: [Electric Boats] Re: Experiences with Sail-powered Regeneration?
> To: electricboats@yahoogroups.com
> Date: Saturday, March 26, 2011, 12:48 AM
>
> Jak,
>
> You already have reasonable experience with regen while sailing. If you stop and think about your towed generator, it is optimized for power generation and it produces about 80W (13.5V x 6A) at 6kts, probably considerably less at 5kts. I would not plan on doing any better than that with a system that is designed for propulsion, the regen has to be a secondary consideration.
>
> So you need to ask yourself, how much of the time do you expect your 26' boat to be able to sail at 6kts? We'll assume that your 7kW motor is driven with 48V, that means that your max power will be around 145A. If your drive is somehow as efficient as your towed generator, then your max regen will be 1.5A at 6kts. I think that this is optimistic, but we'll go with that number for now.
>
> We have no idea where on earth you sail, but let's assume that you'll be satisfied with a capacity of only 1 hour at 4kts under power or a practical range of 4nm. You'll probably need about 2kWh of usable energy to cover this distance. So how long will it take to recharge 2000Wh with an 80W charger? The answer is 25 hours of sailing at 6kts to recharge from 1 hour powering at 4kts. That assumes no other electrical load during the recharging period, house loads will make the recharging process take longer.
>
> So far we've been estimating with best case scenarios, in practice, your results will probably be somewhat less due to prop inefficiencies, drive train friction, controller losses and charging losses going into the batteries.
>
> Larger (faster) boats can do more with regen, there are a number of 40'+ catamarans that are pretty successful at collecting power at sailing speeds around 8kts and faster, but your 26' boat won't be able to do that. 8kts is hull speed for a 45' waterline length in a displacement keelboat.
>
> So I would guess that Niki was getting as much regen as the laws of physics allow for, which is nowhere near the expectations that drive manufacturers set when they say "you can recharge your batteries while you're sailing". I find electric drive manufacturers to be disingenuous when they pitch regen in small (less than 30') sailboats
>
> Therefore, I think that it is pretty safe to say that 2kWh of regen is a theoretical maximum for 24 hours of 6kt speeds, regardless of the size of the boat. In practice, the results will probably be somewhat less.
>
> I want regen as much as you do (maybe more), so please, somebody, prove me wrong.
>
> Fair winds,
> Eric
> Marina del Rey, CA
> 1964 Cheoy Lee Bermuda 30 ketch
> 5.5kW Propulsion Marine drive, 8kWh LiFePO4 batteries
>
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