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Re: [PSUBS-MAILIST] 36V verses 24V



The difference in size of a K250 versus a K350 isn't that great, is it ?
I'm not building a K boat so shouldn't even pipe in on this, but here I go anyway........( big mouth )
Wire size is related mostly to amperage capacity. A higher voltage with lower amperage will mean smaller wire size, and other electrical components. Most individual components are rated at 600 volts. Look at toggle switches and stuff like that. They mostly say 600 volts. High voltage will "jump" even if the amperage is fairly low. Components are designed for high voltages so they don't allow sparks to "jump" across and start fires.
A component that carries a lot of amps on the other hand, is made real beefy because there's more power there, which will create heat at any point of resistance, including resistance in just the wire itself. Hence, high amperage wire and components are bigger than low amperage stuff.
On the thru-hulls, again I don't have a set of K boat plans but it would seem to me that the pods carrying the battery banks are for the motor batteries. A single 12 volt battery for lights and whatever controls would be most useful inside the sub so you could monitor it's electrical status more easily. It's really a completely separate electrical system. Carrying a spare inside for back-up would be a logical choice too. If there was a short and it blew the battery, you can still disconnect the bad component and plug into the back-up battery after affecting repairs.
As for charging.......ya, a 36 volt charger is needed. Maybe two of them. That means a 220 volt AC source for the chargers unless you want to wait three days to get a full charge. The single 12 volt instrument battery gets it's own little charger. Probably just throw it up on the dock and/or switch it out with a spare. These won't draw a lot of power so maybe won't need a full new charge every night. Depends on what's hooked into it.
As for cost ?  There's a lot of parts in the system. The difference in cost between a 12 volt motor and a 36 volt motor ( talkin' Minnkota's here ) isn't that much when buying it new. Running a 12 volt motor "hard" to get the thrust you want versus running a 36 volt motor "easy" and having that extra "boost" if you actually needed it.....well, that's your call.
Complexity, extra work ?.....I don't really see any difference here. The schematic would be the same, the number of wires, connections, parts and pieces is all the same. You just group the batteries in series rather than parallel. OK....you need a separate 12 volt system for lights/instruments but that system should be separate even if the whole sub is 12 volt. If the shit hits the fan you still want the lights to work.
Well, as I said, I probably shoulda stayed outa this one.......just my thoughts.
Frank D.