I might be off track but I think an ordinary diode-type "battery isolator" might be the thing. The isolator is connected to your charging source and both batteries, but it will prevent current from going from one to the other. When charging it sends the bulk of the charge to the lower battery. I don't think battery isolators are particular as to voltage, as long as both batteries are the same.
There is also a "battery combiner" or charge relay which works a bit differently, it automatically connects the batteries when either battery bank exceeds normal voltage (such as when under charge) and will charge the other battery. When the charging source stops, the relay automatically opens. The only ones I'm familiar with are 12v specific, though.
The "isolator" and the "combiner" are NOT the same and they work differently, but one or both of them may work for you.
Willie
--- In electricboats@yahoogroups.com, dan walker <dsailormon@...> wrote:
>
> yes exactly. interesting thoughts. seems I always read u have one house batt and one starter batt. after starting engine switch to both and charge both. so if I understand u it would be better to stat the engine, let the starter battery br e topped off, then switch to the house battery and bring it back up. assuming you have really drained the house battery.
> thanks for the feed back
>
>
> ________________________________
> From: Roger L <rogerlov@...>
> To: electricboats@yahoogroups.com
> Sent: Monday, August 19, 2013 11:54 AM
> Subject: Re: [Electric Boats] perkos switch and battery charger
>
> Â
>
> I believe I have that same switch on
> my boat. Two large 12 volt batteries with the negatives connected to a
> common rail and a Perko that allows Off/batt1/batt2/both. Is that what you
> have?
> Â
> Yes, the trickle charger will charge both when
> the switch is on "both". Both batteries will interact with the charger OK,
> but you have to think what else might happen because the batteries can
> also interact with each other. Best to read on a bit farther before doing
> much of that. Â
> Â
> There's an odd problem that can happen when
> the Perko switch is set to "both" unless steps have been taken
> to limit how the batteries interact with each other.Â
> Â
> All the Perko switch does is the simplest thing
> possible - it hooks the like terminals of both batteries together (usually
> the +), and depending how the rest of the boat is wired there's
> apossible problem when the like
> terminals of two batteries with different charges are hooked together. Of course
> the problem only happens if the other terminals (the - in this case) of both of
> those batteries are also hooked together into a common rail or common floating
> ground - but that is usually how most boats are wired and chances are yours is
> too.
> Â
> So suppose the batteries are both hooked up
> that common way and you have been using battery number one to power reading
> lights last night and sort of saving battery number two...just like I often
> do and the result is that now one battery is at a lower charge (and also a
> lower voltage than the other).Â
> And now you want to switch the Perko
> onto "both" because you want to charge both at the same time....but you
> wonder if this is a good idea. Is that right?Â
> Â
> Assuming the common rail system, switching
> the Perko to "both" will put those two batteries into
> parallel. Now the battery with the most charge - which will also have the
> higher voltage - will promptly attempt to charge the other battery. If
> the voltages aren't all that different then not much will happen,
> but make sure that both your wiring between the batteries and the Perko
> switch itself is up to handling that many potential amps without
> overheating.Â
> I do this and haven't had a problem yet, but
> first I check the battery voltages and don't do it if the voltages are much
> different. What I'll do instead is switch over to the higher battery and drain
> it down a bit first.Â
> Still, that "both" setting is tempting and would be useful for
> equalizing batteries as well as charging them from a single source. And
> there is one other thing that you can do and that is to add a few items to the
> circuit to limit the interaction of batteries when they are put in parallel.
> That's the best of all worlds and it's the tack I'd recommend - although I
> admit I haven't done it in my own boat....
> With a little thought it ought to be possible to limit
> the interaction of multiple batteries with some diodes and possibly some
> resistors so that I could use the "both" feature without concern. Or maybe there
> is a commercial unit that someone can recommend...? I've been meaning to do this
> but haven't yet.
>
> Â Â Â Roger L.
> .....
> ...............
>
> ----- Original Message -----
> From: dsailormon
> >To: electricboats@yahoogroups.com
> >Sent: Monday, August 19, 2013 6:57 AM
> >Subject: [Electric Boats] perkos switch and battery charger
> >
> >i am not an electrical person. i did install a thoosa on my 30 ft alberg. but i have another boat with a two battery setup and a perko switch. the question for all u electrical folk----if i have a trickle charger on one battery and the perko switch on both will both batteries be charged. probably a simple question for ya'll but would appreciate knowing. thanks in advance
> >dan
> >
> >
> >
> >------------------------------------
> >
> >Yahoo!
> Groups Links
> >
> >
> Traditional
> >
> >Â Â Â
> (Yahoo! ID required)
> >
> >Â Â Â electricboats-fullfeatured@yahoogroups.com
> >
> >
> >
> >
>
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