I usually like this kind of "old school" solution, especially where it can simplify things. Not sure about this one though. It sounds like it would add quite a bit of complexity instead. You'd need a lot of wiring to the batteries (and don't forget to fuse all the legs) plus some electronics to sequence the relay.
Seems to me that one of the simplest setups would be to have a converter/charger that takes 48V from the propulsion bank and charges a 12V house battery. I didn't go back and read the older posts but I think that's what Eric was talking about. Modern power conversion electronics are pretty damn reliable, and you can always carry a set of jumper cables for emergencies.
Lot's of ways to skin a cat though. That's just my $.02 for the moment.
Cheers,
Jim
--- In electricboats@yahoogroups.com, Ben Okopnik <ben@...> wrote:
>
> On Mon, Aug 01, 2011 at 02:15:29AM +0000, Capt. Mike wrote:
> >
> > I went with separate 12 volt house and 48 volt propulsion bank. I personally
> > did not want all the eggs in one basket.
>
> I wasn't thinking about it quite like that when I decided to go this
> way, but - yeah, looking at it from that perspective, that was a pretty
> major decision factor in my own thought process. Although Eric's
> approach, which involves a "buffer" battery - that's a good bit of
> thinking, there! - sounds pretty good, a pair of AGM 4Ds beats a box of
> electronics in the reliability department any day. :)
>
> Incidentally, does anyone know where I can buy 4D AGMs in the NYC area?
> Universal Power UB-4Ds tend to run ~$310 each, which is fine, but the
> shipping charges are pure murder. I'd like to find them locally, if I
> can, so I can pick them up (at 130 lbs apiece, they're still manageable.)
>
> > I will use the 48 volt bank to power
> > some 12 volt items like my laptop but, find the sevcon converter gets rather
> > warm with extended use and is only about 85% efficient. Not a problem if you
> > are at a dock with AC available but, out at anchor it can eat a lot of amps if
> > you are feeding the 12 house wiring with it for an extend stay away from the
> > dock. Something you might want to consider.
>
> Well, the upside - of course - is that I'd be saving weight if I went
> with a converter. On the other hand - ooh, just had an idea. Whenever I
> do get around to the full conversion, have a rotary relay that feeds a
> small buffer battery, /a la/ Eric, from each 12V set/battery in the
> drive bank, and trips (i.e., switches to the next set/battery in the
> chain) at regular intervals (say, once an hour.) Seems like it should be
> 100% efficient - no conversion losses - and there wouldn't be much of a
> switching load, since the buffer battery would handle that end. I've
> seen relays like that in military equipment; should be easy enough to
> find them in surplus stores.
>
> Can anybody see a problem with that?
>
>
> --
> Ben Okopnik
> -=-=-=-=-=-
>
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