Date:         Sun, 29 Jul 2007 22:30:34 -0400
Reply-To:     Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
Comments:     RFC822 error: <W> MESSAGE-ID field duplicated. Last occurrence
              was retained.
From:         Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject:      Re: Deep Cycle Batteries
Comments: To: Geza Polony <gezapolony@SBCGLOBAL.NET>
In-Reply-To:  <vanagon%2007072920395069@GERRY.VANAGON.COM>
Content-Type: text/plain; charset="us-ascii"

1200 watt inverters are sold because there is a need for them. My motor
home has a 2,500 factory installed. It also has 450 A/H of house battery
and the largest draw is the microwave. The problem is that you need the
battery and alternator power to back it up. In general, batteries should
be sized for a 5 hour discharge rate. So for an extended 80 amp load, you
need 400 amp hour of capacity. Yup, extreme. 5 minutes is really not an
extended load but a 40 amp hour battery is not going to cut it. Your load
is full discharge in 1/2 hour. 2 hours discharge rate is really a
practical limit.

Also 45 minutes is not charging a battery.

Your short 4 gauge wire to the inverter sounds perfect. Now since you only
need that coffee machine for a few minutes, a proper charge circuit again
sized for the load or at least your alternator output would have allowed
you start the engine and use the alternator to make your coffee and
maintain the charge and only have the battery support part of the load.
Again, my earlier suggestion, and for this use, fuse or circuit breaker
protection of that dedicated charge circuit is recommended to protect the
alternator. A smart relay like the sure power will automatically
disconnect if the alternator can not keep up with the load. This is why I
just use a really unless there is regular charging form solar or shore
power. Yes, the sure power can be forced on during this use.

Oh, so many choices. But you need the reserve in place to meet the demand
and power management is always an issue with batteries.

Oh, and most folks that use inverters for power tools know they need to
run the engine or expect a dead battery.

Dennis


-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Geza Polony
Sent: Sunday, July 29, 2007 8:32 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Deep Cycle Batteries

Dennis, Michael,

Thanks for replies.

Michael, I have a 4AWG wire feeding the 1250W inverter, and it's only
about
2 feet long, so it ought to be large enough. I charged the aux battery
with
no load on it (fridge and inverter are the only things wired to it) for
about 45 minutes to get to 12.30 volts. In an hour and a half of using the
fridge it dropped from 12.3 to 10.62 volts, about the lower limit for any
cooling. Seemed to bounce back some when I turned the fridge off.

Dennis, if 800 watts at 120 volts fried the battery--then what the h**l do
they sell 1200 watt inverters for? I thought you were supposed to be able
to
use Skilsaws etc. with the larger inverters. These are designed to go into
normal cars and trucks with normal batteries, no? Or was it the length of
time using it that whacked the Optima (maybe five minutes, no frothy milk
on
the coffee) ?

So what I'm hearing is that the aux battery isn't holding a charge, which
explains why the voltage during charging is lower than on the vehicle
battery.

Next time I get a degree, it's going to be electrical engineering.