Let's do the math!

To get 1000W from 12VDC, one needs to pull 1000/12 = 83 amps from the
battery. Since the inverter is not 100% efficient, and if it can indeed
deliver 1000W into your load, it will be pulling more than 83A from the
battery. So the mfgr's fuse rating is probably based on their experience
of what happens when a customer uses too small a fuse, and he tries to
light up a microwave oven along with some other loads at the same time,
and the fuse blows.

Use fat wire. When pulling that kind of current, the DC resistance of
the wire can significantly lower the voltage at the inverter. For
example, if a fellow has 4 feet of wire connected from the battery to
the + terminal of the inverter, and 4 feet connected from the - terminal
to chassis, he's got 8 feet altogether. According to the endless number
of web pages that list the resistance of copper wire, a fellow using 8
feet of, say, 10 gauge wire will have a total resistance in the run of
0.016 ohm. Voltage drop is current x resistance = 83 x .016 = 1.3 volts.
So while your battery might have 12.6 volts at its terminals, the
voltage across the inverter will be 11.3 volts.

Of course, it's not likely that you will be powering a 1000W load . . .
. or for very long from one Optima!

Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana")
KG6RCR

On 6/14/2006 1:59 PM Gilles Turmel wrote:
> Hi,
> I want to isntall a 1000W converter from my Optima yellow top.  In the
> instructions they say to put a 150ADC fuse between the converter an the
> battery.  I find this fuse to be very big.  Anyone on the list did that
> kind of installation?  If yes what size fuse did you use?
> Best regards.
> Gilles Turmel
>
>