I also have 2 banks set up to run both at the same time..I have the option to shut one bank down if there is a problem in one string.. You need to have both strings using the same size batteries to do this..
If I remember right Mark has different sizes in both strings and this may cause them both to behave like the smaller batteries..It would still reduce the draw from each battery though.
Richard
From: chris Baker <chris@currentsunshine.com>
To: electricboats@yahoogroups.com
Sent: Friday, July 22, 2011 4:44:29 PM
Subject: Re: [Electric Boats] Re: two banks
Hi Mark and Pat.
I can suggest a couple of good reasons why you might want to combine your banks...
The first is that by drawing from two banks you'll be discharging to a lesser amount and so the batteries are left in better condition after your use. We keep hearing that its better for lead acid batteries to not discharge them too deeply. So instead of discharging one bank by, say, 50%, you'd be discharging two banks by only 25%. This is better for the health of the batteries.
The second reason is to do with peukerts effect. By discharging at a half the amperage you actually have more capacity available in the batteries. Depending on the typical amperage that you'd be drawing this effect may be significant. It would mean that you actually have more useful amphours available by operating batteries as one large pack.
Overall both these effects combine to leave your batteries in a better state of health than if you use them separately.
The disadvantage of course as Mark mentions in another message, is the loss of a backup bank, and the peace of mind that comes with that.
Perhaps that peace of mind that comes with knowing you have a 'reserve tank' could also come from good instrumentation that will give you a reliable sense of how much is in the tank.
After all, with motor vehicles we have got to the point now that we trust our fuel gauges to not need the reassurance of having an actual reserve tank of fuel.
Thinking of an emergency situation where you might want to get back to harbour in a hurry, the best way to do this would be to combine the banks, so that you can get every last drop of available power, and not lose it to peukerts.
I know this goes against conventional thinking, but I suspect that comes from the days when we did not know how much power was in the batteries, and could easily run them down without being sure what's there. But now with devices such as amphour counters perhaps we could rethink this point of view.
Cheers
Chris
On 22/07/2011, at 8:42 PM, greenpjs04 wrote:
Hi Mark,
Yes, you would have one bank at 200 ah. But, be very careful doing that. Make sure both banks are at the same state of charge before turning on both switches. If one bank is fully charged and the other is discharged, a huge amount of current will flow from the charged bank to the other. There is nothing to control how much current flows other than the internal resistance of the batteries and wiring. That is not a good situation. I think most people here would recommend keeping your setup as two separate 100 ah banks. In fact, I can't think of any good reason to combine them. You might want to Google batteries in parallel for more information.
Pat
--- In electricboats@yahoogroups.com, "acsarfkram" <acsarfkram@...> wrote:
>
> My EP system has two separate 48 volt, 100ah battery banks with a common negative. If I switched both on at the same time would I get one bank at 200ah? There is a diagram here; http://groups.yahoo.com/group/electricboats/photos/album/237790029/pic/72846009/view?picmode=large&mode=tn&order=ordinal&start=1&dir=asc
>
> I've always figured I would fry something if I turned both on but someone mentioned that it would just act as one 48 volt bank with both switches on.
>
> Thanks,
>
> Mark
> Santa Cruz
>
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