Fatal Error.
The heating element is resistive. 120V 2KW element is approx 7 ohms. Reduce
voltage to 24 v and current draw drops to 3.5 amps. Power is not a constant.
"Larry W4CSC" wrote in message
...
Wouldn't actually make much of a difference. If the 2KW water heater
were running on 12V, it would draw 167A. On 24V it would still draw
83.3A, draining the batteries in a matter of minutes, not hours......

Then, comes the problem of battery real estate. in the same space it
takes to put 500 amp-hours of 12V batteries, you get 250 amp-hours of
24V batteries.....the same exact kilowatt-hour rating. If you
parallel two 130AH 12V deep cycles, you get 260AH at 12V. If you
series them, you get 130AH at 24V......the same exact power output in
KwH. You can use smaller wire, though....(c;

Running large electrical loads of batteries is a pipe dream on these
boats at any voltage. There just isn't room for a proper battery
bank, like you'd need. A 350AH large golf cart battery, which is only
6 volts, is only 2.1Kwh but at a very low rate like 20A, not 200A. We
run 4 of these monsters in 2 banks in series-parallel to get 12V at
700AH in Lionheart's engine room. You can't use all 700AH because
that would really shorten their life, so you only discharge them about
400-500AH before charging, and that's stretching it. Then, it's so
hard to get that last 15% to full charge, there's no point running the
charging engine for hours more so you lose 15% more capacity charging
them only up to 85% of full specific gravity. This battery bank of 4
is about 4' x 20" x 24" tall and 400 pounds of ballast. In
comparison, each CELL of 126 cells in a WW2 submarine is about 7' high
by 4' by 3' and puts out 2V at 6,250AH to drive the sub 48 hours at
only 2 knots on TWO 126 cell banks...one forward, one aft. WW2 subs
carried nearly 1000 TONS of batteries to accomplish this level of
power. No wonder they sank a perfectly good boat!

With an 80A alternator running flat out, you can recharge Lionhearts
400AH "standard discharge" in about 5.5 hours. Charging too fast, and
this is almost too fast, makes charging more dangerous (heat) and
boils off the electrolyte (hydrogen). With a tapering charge, it
takes longer...6-7 hours. At 80A, the fanbelt better be TIGHT!
Charging monster battery banks is another problem altogether.....

Nothing is funnier than a boater with a new 4KW inverter carrying his
electric heater down the dock with a big smile on his face.......

The real answer is a super quiet insulated diesel genset with a small
starting battery and a hundred gallons of #2 fuel oil.....an immense
pool of liquid power...(c; The Navy prefers nuclear power but the
refueling is messy.



On Sat, 10 Jan 2004 22:20:53 GMT, misia
wrote:

On my new boat I will have a powerfull 24VDC battery bank charged by a
diesel generator and auxiliary sources.

I did a bit of search but couldn't find much- are there any 24 VDC
appliances such as cooker/oven, fridge, AC and water heater you could
recommend?

I know I can run standard items through power inverter but I would
prefer not to do it for the sake of reliability/efficiency/cost. I want
to go totally electric (no gas)

Regards Mi