James,
I purchased a $40 750 watt inverter from Wal-Mart, and it is rated at 85%
efficient. I have tested the inverter and group 27 batteries through 3 full
cycles, and I am getting better than 85% efficiency on the inverter or more
amp hours out of the batteries by about 12% longer output. This inverter
does not get hot, and has a digital display to show the DC voltage and
current draw.
With one group 27 battery and a 350 watt load, you should get 1.7 hours of
use at 85% efficiency. So 90 minutes sounds about right for the capacity of
the battery. If your wires or inverter is hot you are losing output
producing heat. Either your cables are too small, or your inverter is under
sized or defective. Never run a deep cycle battery below 50% charge, which
is about 12.1 volts with no load. Many years ago I learned the hard way
that if you run a deep cycle battery way down only a few times, it will lose
up to 50% of its capacity. If you never go below 50%, the batteries will
give you full, or close to full, output for many years. A DC volt meter is
a must when running deep cycle batteries.
Dan Mohr
From: artshow_photo@yahoogroups.com [mailto:artshow_photo@yahoogroups.com]
On Behalf Of James Dunn
Sent: Monday, May 09, 2011 3:38 PM
To: artshow_photo@yahoogroups.com
Subject: Re: [artshow_photo] Re: Battery Operated Lighting System for
Outdoor Show
There is a good reason to eliminate the inverter. I know that
some manufacturers claim high efficiency, some as much as 90%,
but in my experience those inverters are always very expensive.
The cheap inverters are terrible at efficiency. I bought a $90 Coleman
inverter and ran a 350 watt halogen system and never got over 90
minutes on my boats group 27 deep cycle battery. The inverter got
so hot I could not touch it. Not the wires, the inverter. I'd bet the
efficiency was less that 50% with all that waste heat.
--
James Dunn
www.ImagesByJamesDunn.com
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