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**G'day
folks, lets see if we can make these muddy waters a little
less muddy.**

So let's start with finding out what the difference is
between **Amps, and**** ****Amp-hours!**

**I
think it's easier to understand if I give you some easy examples to
work through.**

**For
the sake of this explanation lets say you have a 12 volt ****fridge with a ****compressor
motor, and this fridge draws 5 amps while it's compressor motor
is actually running, now if the compressor motor ran continuously for
the whole hour, the fridge will have drawn 5 amps in total for that
hour, and we express this as 5 Amp-Hours
(5Ah), and so if it ran
like this ****continuously
****for
24 hours, it would have drawn and consumed a total of
120 Amp-Hours
(5Ah
x 24h = 120Ah). **

**However
the fact is the compressor motor should not ever be running
continuously for
the whole 24 hours, it should cycle on and off as required to keep
the fridge at a constant ****temperature, ****to whatever you have
set it to in the fridge, so now if it was running on say a
50% duty cycle, i.e. running on and off for a total of only 1/2 an hour
running in
total within that hour, it would still be drawing 5A while it's
running, but seeing it's running for only
half of the hour, it's total power consumption for the hour would now
be just 2.5Ah, and just
60Ah
over a 24 hour period ****(2.5Ah
x 24h = 60Ah)****.**

**So
along these lines lets look at say an electric 12 volt water pump,
while it
may draw 10A
when it's running, **

but if it only runs for a total of 15
minutes each day, it's total draw for the whole day
(24h) would be just 2.5Ah,
so not much at all.

Really, given the very limited amount of
water that can be carried on-board by most folks,

we can
expect that in most cases water pumps get used for less than 5 **minutes a day****,**

so hardly
worth worrying about what **water pumps**** consume power wise at
all! **

**
Watts
that you say?
**

**Ok
some electrical appliances are rated in Watts
rather than Amps, but that's ok, it's easy to convert these Watts
to Amps.**

**You
simply take the stated Watts,
and divide that by the Voltage
and this gives you the Amps
that the item will draw**

So lets say for example
you have a 120 Watt light
globe (like
the
type you find in some car spot lights) and divide this 120W
by the 12V that is used to power it and you end up with 10A at 12V (120W ÷ 12V = 10A).

**This
also works the other way around, if you have the amps and the voltage
of an item and you want to know the Watts,
simply multiply the amps by the voltage and you have the Watts.**

**So
for example remember that water pump that was drawing 10A at 12V, well
10A x 12V = 120Watts**

Now this works for any
Voltage, Watts
and Amps combination.

Like a 100W
household light globe at 240V
= 0.41A.

**So if you had a
2400W
room heater, at 240V
= 10A,
and this just happens to be the most you can
draw out of a standard household power point, 10A or 2400W.**

**Inverters**

**When
trying to work out how much power will be drawn from your batteries by
an inverter, a very rough but easy calculation is for every 100W
at **__240V__,
you can expect the inverter will draw about 10A at __12V__
from your batteries, it really works out a bit
less than this but it's close enough for doing quick calculations.

** ****
**

**
**

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****
**
**Val
Rigoli ****Copyright ©**

** **

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