REFLECTOR: A/C (was Re: GRT Displays overheating - Anyoneelseseethis?)

[sbjknox]

----- Original Message ----- 
From: "Mark Magee" <edjonesbrady at gmail.com>

Subject: Re: REFLECTOR: A/C (was Re: GRT Displays overheating - 
Anyoneelseseethis?)


[snip]
> I pulled apart a small roll around 4,000 BTU A/C that pulls 4 amps on the 
> AC
> I Used camping with the kids. I think 4000 BTU's of A/C would marginally 
> cool
> an XL cabin on a 100F OAT day. The good part is the whole unit can be run
> on an inexpensive 1000W sine wave inverter that factoring in 8% efficiency
> loss it would still only pull about 50 amps on the 12V. I'm hoping a 
> second
> alternator, possibly a  supplenator would fit the bill and double as a 
> back
> up alternator. As well I might install some 110V outlets for use in flight
> after the A/C was shut down in the cool air.


Some rather creative math going on here...
Strictly speaking, you can't equate BTU and Watts but common useage of BTU 
when refering to air conditioning actually is BTU/hour so that 1000 Watts = 
3415 BTU/hr and 4000 BTU/hr equates to about 1171 W.
But the real issue is with the current at 12Volts.  Even if you had a sine 
wave inverter with 92% efficiency (which I believe is overly optomistic) the 
current at 12V is
(1171W)  /  (12V) / (.92)  =  106 AMPs!

> I think the whole arrangement with alternator might add 12 lbs.

For 4000 BTU/hr, not likely...

However,  your 4000 BTU roll-around unit could not have produced anywhere 
near 4000BTU/hr if it was only pulling 4A from the 115VAC line.  (4A)  x 
(115V) = 460 W.
(460W)  x  (3.415BTU/hr/W)  =  1571 BTU/hr  at 100% efficiency.

So, IF your roll-around unit would   "...marginally cool an XL cabin on a 
100F OAT day.", then a much smaller (than 4000 BTU/hr) A/C might work and 
your current draw at 12V would perhaps be acceptable.

Sid Knox
Oklahoma

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