Scott, if you want to use a 36 (or greater) volt system, it is simply a
matter of series-connecting batteries or individual cells until you get
the desired system voltage. Your charger would work across the whole
bank, charging at 36V. There are a few ways to take 12V off of this
without requiring a completely isolated 12V battery bank. The simplest,
which is not recommended, is simply to draw 12V off of an appropriate
number of batteries or cells in your bank. In that case, you would
simply tap off the bank negative and an appropriate intermediate
positive terminal. The reason this is not recommended is that this
unequally drains the batteries, making them more difficult to charge,
and over repeated charging cycles, reducing their performance. Another
possible method, which is useful if you know all of your 12V loads with
reasonable accuracy, is to split them among all of the batteries in your
bank, similar to the method above, but split according to load in order
to drain all of the batteries equally. Even if you get this right,
however, this method has the disadvantage of having all of your 12V
circuits at different potentials, which may complicate wiring and limit
your expansion options - it's easy to make an expensive mistake when
playing around with electrical connections at different potentials. The
third, and best solution for simplifying charging and increasing battery
longevity, is to use a DC to DC converter which takes the bank's 36V as
an input and provides 12V at the output. By spanning the whole bank,
this ensures that the batteries are equally drained. The disadvantage
of such a converter is that it is inefficient, requiring greater
capacity in the bank, and it is expensive. Depending on the scope and
complexity of your electrical system, however, that may still be a
better option than a completely isolated 12V bank. Note that an
isolated emergency backup power system is not a bad idea and is
advocated by ABS, so that is a consideration.
-Sean
Scott Waters wrote:
Ok. So I want to make sure I got all the facts straight. (This is for
my K-350)
36volt:
Advantage - More effecient power
Advantage - Has ability to provide more thrust (good in current or
dangerious situations)
Advantage - Last longer and won't overheat as likely
Disadvantage - Need second tru-hull (from pod to hull) because of
gauge of wire
Disadvantage - difficult to charge because of 12V and 36V both in pod
Disadvantage - more money for wire and parts
12volt:
Advantage - Easyier to wire (no need for extra tru-hull
Advantage - Easy to charge
Advantage - Costs less
Disadvantage - Less effecient power
Disadvantage - Less thrust (not 100% sure will have enough power,
snoopy is 12V and works, but it is smaller sub)
Disadvantage - Won't last as long, possible overheating in extreme
situations
I am stuck in between a rock and a hard place as what to do. I want to
do the 12volt, but am worried it won't have the power I need. I don't
understand the K-350 plans as how to get the power from the pods to
the hull. I assume you run it through the aft battery vent and
actually vent with the forward vent. The blueprint only showes 2 vents
per pod, yet I noticed on Persistance there is a 3rd tru-hull. That is
one of the 3 main issues. The second is how in the world does the
charging work with a 36V and a 12V in the sub. I can only think the
way to do this is either have a 36V charger and a 12V charger or take
all the batteries out and charge them separately. The 3rd issue is
will a 12V system have enough power to run the motors with enough
thrust for a K-350? I heard that Snoopy is all 12V and manuvers fine,
but Snoopy is a K-250. I am pretty much at a stand still till I get
this problem solved. The next step is attaching the battery pods, but
I don't want to do that if I need a 3rd tru-hull.
Any help is greatly appriciated.
Thanks,
Scott Waters
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