YES! That type of discharge cycle is VERY hard on batteries. Most Type
27 deep cycle batteries are good for about 280-360 discharge/charge
cycles. You didn't indicate if your type 27s were deep cycle. If they
are standard auto starting batteries, the cycles will be less. You
should never discharge the batteries below 50% capacity. If you want to
run a 2300 watt inverter, get a pair of Trojan J305HC batteries (335 Amp
Hrs). a Balmar 100 Amp alternator, a three stage regulator for the
alternator,a Balmar Duo-charge, and keep the 27 for a starting battery.
krj

Stephen Trapani wrote:
Ken Heaton wrote:

Comments below:
"Stephen Trapani" wrote in message
news
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,


Okay, so my amp meter reads somewhere around 45 amps when it is charging
the battery, so I figure 45? X 14.6v? so I can expect, say 80%
efficiency just to be safe, 525 watts?

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.


I can tell by the amp hour rating of the batteries how long the two
group 27s will hold up in this over-use state, right? How do you figure
that? It will suck anything over 45 off the the batteries draining the
batteries faster the higher the charge?

And then if I keep running the over-use after the batteries run down,
the inverter overharge alarm will go on? No big deal I can just turn off
the large draw and charge up the batteries before I turn off the Yanmar?

Will the 12 volt Bible cover this? I just ordered it.

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...


One more question, is this sort of usage hard on the batteries at all?
Wear them out faster or anything?

Make sense?


Very helpful, thank you!

Stephen