Power from a battery bank is real easy to get these days. Of course,
boat power from a boat parts place costs three times as much for the
same technology.

The problem with DC power is the very limited SOURCE, the storage of
power in batteries. Deep cycle batteries, the kind you can discharge
down without eating holes in the plates like starting batteries will,
are rated in ampere-hours (AH) at some rate that makes the
manufacturer look good, like 10A or 20A...it's on the label, or is
supposed to be. 20A at 13V = 260 watts out power output. The
inverter is going to eat up about 5-10% of that, say 20 watts for fun,
because no inverter is 100% efficient, so you're left at that level
with 240 watts of AC power, a thousand watts short of the coffee maker
which draws 1200 watts for 10 minutes, then, if it's got a pot heater,
50w continuously.

The AH rating on the house batteries DROPS significantly as load
increases on them. The chemistry freeing up electrons and moving the
dissolved salt created when you discharge becomes much less efficient
the more electrons you use.

Let's look at the coffee pot load for a minute. If the coffee pot
uses 1200 watts and the inverter at this load level puts out 90% of
what it gets from the battery to the pot, 1200/.9=1333W from the
battery. Let's pretend the heavily loaded battery and the corroded
cables to the inverter put 12V on the inverter under load (it's
probably LESS at this current level). 1333W/12V= 111 amps of load at
12V. Make SURE the wiring from the inverter to the battery is LARGER
than the wires to the starter! Starters on gas engines draw about 80A
starting the beast. We're over that, just making coffee!

Question - How long can you run the starter before the battery is
dead? 3 minutes of CONTINUOUS cranking? 4? 5? It ain't gonna make
10, is it? At 111 amps, we're gonna need a powerful battery to make
that coffee, aren't we?! See the math working, here? Think the 12V
wires will get warm?..(c; They will. Small ones will melt....

Question - Armed with this information, how much current will a Heart
4000 watt inverter draw that's, say, 95% efficient?

4000W/.95=4210W/12V=THREE HUNDRED FIFTY AMPS! Wow! We're gonna need
some POWERFUL HEAVY WIRES to hook that baby up! #000 is 200A
service!

Now, let's be honest. Most boaters, even the rich ones, are
cheapskates. They're using the golf cart batteries from some discount
house rated at 225AH, 6V with two in series to get 12V. These
batteries are the most bang for the buck. My stepvan has 4 of them
for house batteries on a 500W inverter and they work just fine at an
80A load. They're probably only 160AH at 80A, but that's still 2
hours at FULL LOAD of all my DC and inverter loads...not bad. But,
350A is just gonna make them EXPLODE from internal heat generated way
beyond their capacity. You CAN add more banks, if you got the room,
in parallel. Four banks in parallel would reduce the load on each
battery to under 100A on that beast. See the problem?

1333W for 10 minutes on a carafe coffee maker that doesn't have a
heater IS doable. 111A for 10 minutes = 111x.16667hrs = 18AH.
That'll work on the golf cart batteries derated to 150AH at 111A.
It'll make about 9 pots of coffee, won't it? That works.

You can do the math approximations for your other loads. As you can
see, there really isn't many Watthours of electricity available from
225AH batteries.

I have a saying....."Nothing is funnier than watching a yachtsman with
a new 4KW Heart inverter carrying his electric heater down the dock
with a big smile on his face."......(c; Think about it....

He's gonna need those old WW2 diesel-electric submarine batteries we
used to service at Charleston Naval Shipyard's battery shop. EACH 2V
cell was about 7 ft tall, 4' x 3', weighed about half a ton and had
6,250AH rating at, I think I remember, 400A load. 6 of them will heat
the boat.....er, ah.....if it'll float.

Now, if you want some NEAT power, serious power, go to a Honda dealer
and look at the EU2000i tiny portable gas generator. It weighs about
35 pounds, makes very little noise, is amazingly easy on gas with its
OHV 4-stroke engine and the computer in it varies the engine speed
depending on your load, dropping it down really low at low loads under
800W because you always get 60 Hz filtered good enough for computers
out of it 2KW inverter! I use the EU1000i 1KW model in my service
truck. It'll pull my little 5000 Btu AC! MUCH more efficient, MUCH
less weight and you can load it to 1500 watts 24/7 for about 6 gallons
of gas! Before buying it locally, though, put EU2000i into google.com
and find the best price. Mine came from a sawmill supply company in
Oregon, on the other side of the country from Charleston. I can buy a
LOT of "service" for the $380 I saved....



Larry W4CSC

"No, NO, Mr Spock! I said beam me down a WRENCH,
not a WENCH! KIRK OUT!"