quote:
Originally posted by Rusty
Anachronus, I dont know about this but couldnt you use two 6 volt batterys hooked up to get the 12 volts? Would two 6 volt batterys be smaller than one single 12 volt or would the 12volt be smaller of the two?
Personally I think 6 volt would be enough but after reading about how you can get more time on the water with 12 volts I might have to consider that.
With 2 @ 6V batteries, you can wire them in series to get 12V or parallel to get 6V (with double the AH, which means double the runtime - except that the current draw increases as voltage drops, for the same load). It's nice to have the flexibility of choice.
Example: 2 @ 6V/12AH batteries. In series, you'll get 12AH on 12V; in parallel, you'll get 24AH on 6V. If your current draw @ 12V is 1/2 or less of the current draw @ 6V, then you'll get more runtime on 12V than on 6V (all figures approximate - YMMV). Example: Ship draws 4A running 6V, 1.8A running 12V. 2 @ 6V/12AH batteries will give you 12AH wired for 12V while the same batteries in parallel @ 6V will give you 24AH. 12AH/1.8A = 6hrs 40 minutes runtime. (12AH * 2)/4A = 6hrs 0 minutes runtime. Of course, it never works out exactly that simple, but that's the general idea.
What you really want to do is achieve balance among all the factors involved: Speed, acceleration, endurance, power, weight, space, operating range of components. All need to work in harmony & cooperation with one another.
A lot depends on what will fit into the ship, within the space & weight constraints. I put 2 @ 6V 12AH gel cells into a battleship, but that won't fit into a cruiser, where I use a pair of 5-cell packs of NiMH C cells). BB-34 may be somewhere in between, not quite being big enough for a pair of large gel cells. That's what you'll have to figure out, especially if you intend to arm the #3 turret (which I wouldn't do, since that's exactly where you'll need whatever battery you choose to sit (among other reasons)).
Here's the basic setup that I use for everything from a 25kt HMS Nelson to a 33kt USS Pittsburgh: 6V power, MTronics speed control, 2 Mabuchi RS-550 motors, direct or reduction drive (chain) of 2 shafts (even if 4 are available). I like 6V because I get enough power (this isn't racing, after all; all-out speed isn't the objective. Sometimes it's a challenge to get SLOW enough, which is where the reduction drive comes in, where needed) & I can run all ships' systems on 6V (receivers & servos cook on 12V, so they'd need some additional power source that they're happy with). As for runtime, I have no earthly idea. I've never run out of power before running out of day (with 2 @ 6V 12AH fully-charged gel cell batteries, usually 1 running the screws & the other running everything else).
For a 1:144 Big Gun BB-34 at 25kts, 12V will be way too much power, unless you use a very steep reduction gear and/or very shallow prop pitch (another consideration). You'd be working with a very small portion of the speed control's available power band instead of having the whole range to work with. Of course, 99.5% of the time you'll be at either full speed or stopped, so in-between isn't so important. However, fine-tuning of speed is easiest if you have a lot of speed control range to work with.
JM