T-Pain Is On A Boat: Re: [Electric Boats] Repowering 40' 1975 20,000 lb sailboat

Sunday, October 11, 2009

Re: [Electric Boats] Repowering 40' 1975 20,000 lb sailboat

Keith, et al,
Perhaps the answer to charging strings equally would be to provide the bulk charge via a high voltage charger, then use smaller chargers on each battery to allow equalization. I've been using twin output 12v chargers for my 24v installation, and the batteries are very close. Add two more chargers for 48v systems, and now every battery gets a full charge. The outputs must be isolated, however.
The last special application vehicle I built had 16 12v Odysseys, bulk charged during operations, and equalized every night. I had one cell soften up, but otherwise ran the pack was run from 100% to 20% several times a day. Without the overnight equalization, I'm certain the string would have unbalanced quickly.
Arby

________________________________
From: aweekdaysailor <aweekdaysailor@yahoo.com>
To: electricboats@yahoogroups.com
Sent: Wed, October 7, 2009 1:23:52 PM
Subject: Re: [Electric Boats] Repowering 40' 1975 20,000 lb sailboat

Don

I would caution against running too long on just these 4 batteries (unless they are quite larger than I expect). I made that mistake, so maybe you can learn from my experience. And apologies in advance if this is already known to you or you've got monster 4D's in or something.

First - you should take the Peukert effect into account. If your batteries are typical 100AH (for example), and you normally cruise at 30AH you might think you have 2.5 hours of capacity at 80% depth of discharge ((100*.8)/30) . But...because of Peukert (I'll use a value of 1.25) your batteries will only give you 1.7 hours - only 70% of what might have been predicted.

Second - you should never run your batteries much past 50% so you really will only get ~1 hour. Because I didn't understand Peukert I once ran my original pack down probably well below 80%, damaging it.

Third - once your current batteries are used for a while and you then try to double up - you'll find your battery pack to be pretty unstable where it's difficult to get the old batteries charged correctly and balanced. Your pack will then act as if every battery has only the energy capacity of the weakest.

So I would make the investment in extra batteries now (I know space is limited in an e27). If you do you'll get 2.5 hours @50% DOD. So on a dollars/range basis - that second bank is much cheaper than the first and well worth it.

regards and welcome to the e-boat club!

-Keith

--- In electricboats@ yahoogroups. com, postal6@... wrote:
>
> I have just installed four batteries powering an ElectricYacht 48 volt
> system on an Ericson 27.

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