Date:         Fri, 3 Aug 2001 11:25:45 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: insane AC idea
Comments: To: Joe Reed <joe.reed@MINDSPRING.COM>
In-Reply-To:  <018701c11c2a$0f2a0220$6401a8c0@nc.rr.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 10:38 AM 8/3/2001, Joe Reed wrote:
>We're using a second, deep-cycle 72-amp hour battery (dedicated to the
>a/c -- we're not using the Vanagon car battery) which at 100 amps provides a
>cycle of 7.2 hours of continuous draw before requiring charging.

Erm...70 AH at 20-hour rate.  Practical capacity say 45-50 AH.  100 amps
would give a nominal capacity of half an hour (you did say 72 AH, not 720,
right?) but at that discharge rate you'd be actually getting much
less.   Based on some quick fiddling with a Peukert's equation calculator
http://www.geocities.com/CapeCanaveral/Lab/8679/battery.html I would
estimate that you'd get less than 20 minutes practical use from the battery
at 100 amps.


>The a/c doesn't pull 10 amps -- at PEAK compressor activity it draws 6
>amps/690 watts.

At what temps?  IIRC the actual draw can rise well above the nameplate draw
as ambient temps rise, and the rating is made at a temp which gives
attractive numbers...

Another point to bear in mind -- no way will the Volt-amperes be equal to
watts in this application.  If you are measuring six amps then the actual
wattage will be less; conversely if you have a rating of 690 watts the
amperage will be more than 6.  Take a look at the inverter rating -- 15
amps at 110vac would be 1650 watts, but you notice the device is actually
rated to supply 800.

>  As I said before, the inverter we borrowed for the initial
>testing supplies 15 amps and 800 watts, which so far has proved to be more
>than adequate. Also, the efficiency on the solid-state inverter was rated at
>90% and so far we don't see anything to dispute that.

It probably is pretty close to that at some specific draw like 85% load --
probably moderately less at light and maybe very heavy loads.

Good luck, but watch those numbers...and don't forget that you're still
working with a unit that has maybe one-third or less of the capacity of an
automotive A/C.

david

David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"