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

Mark Magee edjonesbrady at gmail.com
Wed Jul 11 15:10:59 CDT 2012


Sid,
Here is the specs on the unit I discussed. I have run it on a 500w sine wave inverter (1000w surge).
I pulled it apart and the critical parts weigh about 7 lbs.

http://www.toyotomiusa.com/products/portableairconditioners/TID-1200.mv

Can you tell me from this data that it requires 100amps VDC via 92% efficient sine wave inverter?
My calculations are I/2 that, yet I don't claim to be an EE.

Mark B. Magee
Sent from IPhone 4

On Jul 11, 2012, at 1:45 PM, "sbjknox" <sbjknox at earthlink.net> wrote:

> 
> ----- 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
> 
> Velocity  173 RG  N199RS
> Starduster  N666SK
> KR2         N24TC
> W7QJQ
> 
> 
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