Comments below:
"Stephen Trapani" wrote in message
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So, say I've got a measley 2 group 27s and my old Yanmar 2GM15 and I
want to by a 2300watt continuous inverter. BUT...

I'm willing to run the Yanmar while I'm using any heavy loads like a
power tool, microwave, or electric heat and I only use the inverter
*without* running the Yanmar/alternator for small loads like a TV/VCR or
a boombox.

Any problem with that?

Stephen

Simple math. Watts = Amps x Volts

So, lets say the alternator attached to your Yanmar is capable of putting
out a sustained 65 amps at 14.6 volts with the engine running at, say, 2000
RPM without overheating or burning up the belt or whatever. And it can do
this for as long as you want to support a heavy load on your inverter.

So: 14.6 volts x 65 amps = 949 watts x 85 % efficiency = 800 watts or so.

This means, if your inverter is 85 % efficient at converting 14.6 volts to
115 volts you will only be able to get enough power from your alternator
through to your inverter to deliver a sustained 800 watts to whatever it is
you want to run. In other words, if you run a 1000 watt electric heater
(and most are 1500 watts or more) off your inverter with your engine running
you will still be slowly running your batteries down. Any sustained load
below 800 watts or so will run off the alternator, with perhaps a little
left to trickle charge the batteries.

On the other hand, if your load is intermittent, like a power tool, or
microwave, it depends on how much of the time the tool/whatever is running.
If it causes the inverter to draw more than your charging system can deliver
it will draw the extra from the batteries but when the tool is off the
alternator will charge the batteries back up. Expect more inefficiency in
charging the batteries so it wont be a 1 to 1 relationship of run time to
recovery time, more like 1 to 2 or worse.

But it can be done and is. You should probably forget about the heater
though...

Make sense?
--
Ken Heaton, Cape Breton Island, Canada
kenheaton AT ess wye dee DOT eastlink DOT ca