[TheForge] OT Anyone out there knowledgeable about automobile air conditioners and/or 12VDC motors?

[Richardson, Grover]

Find an ac mechanic and see how much btu of cooling an average vehicle unit produces.  A phone call will likely do.  Then the easiest thing to do is to visit Home Depot and see the current ratings required for the 110V air conditioners there, that are of similar btu output.  That will get you ball park on power requirements, including some inefficiency.  A rather large amount of power.  Yes, there is a difference in the ac and dc power levels, but that can be calculated out.  

Possible yes.   Feasible, I would not consider it so.
Reasons:
1.	You need,,, say a 3 horsepower motor at 12 Volts.  746 Watts per horsepower, that is 2238 Watts.  At 12 Volts (nominal), that is 186.5 Amps.  That is a whole bunch of amps.  A power supply that regulates that amount of power will be expensive and hard to find.  
2.	Then you will need large wire, say 00 or so (depending upon distance).
3.	The power supply, if linear will be about 50% efficient (no kidding).  So double the power that you are using, to figure out what you are paying for, that is coming out of the wall.
4.	You need an expensive relay that will turn that power on and off.

All of the above needs are not standard for anyone who does not work in the high power electronics field.  Finding someone qualified, and willing, to take on the task can be a challenge itself<G>.

All the best.



-----Original Message-----
From: theforge-bounces at mailman.qth.net [mailto:theforge-bounces at mailman.qth.net] On Behalf Of CGRAF
Sent: Wednesday, September 05, 2012 3:31 PM
To: Blacksmithing List Sponsored by ABANA
Subject: Re: [TheForge] OT Anyone out there knowledgeable about automobile air conditioners and/or 12VDC motors?

Add another question.
The car AC compressor is designed to be run by the engine, which has a lot of power. Just how big would the electric motor need to be to overcome the internal resistance of the compressor?

Mike Graf

On 9/5/2012 6:39 AM, Bruce . wrote:
> I'm asking this here because of the diversity of knowledge of the 
> participants in this forum.We can take this discussion off-line.
> Please respond to me directly at freemab222 at gmail.com .
>
> Did you see this:
> http://www.nypost.com/p/news/local/hizzoner_cold_feat_lYxDIMuat7x4PL7n
> UbdBEM
> ?
>
> Well, that just struck me as dumb -- attaching a 120VAC window A/C to 
> pre-cool a car.  But then I noticed that some (or maybe ALL?) RV's 
> have "window-style" 120VAC A/C's mounted on them and I got to 
> wondering about it.  Of course, these RV's typically are parked at a 
> 120VAC electrical hookup when not being driven, so the 120VAC A/C is 
> the simplest solution.  But what about for remote use?  Say, a person 
> who works out of his car in hot weather and finds he only has the 
> choice of running the engine or sweltering?
>
> It seems to me that one could use the engine-driven A/C unit of a 
> vehicle to cool the vehicle without running the engine.  You'd need an 
> extra (12V?) motor to drive the compressor and you'd need a fan -- the 
> electric radiator fan might work -- to blow air over the A/C heat 
> exchanger.  You'd have to use the motor to drive the compressor.
>
> As I understand it, a car A/C already has a slip-clutch on its 
> compressor pulley so that the compressor only runs when called upon to 
> do so.  Maybe the motor could be mounted directly to the compressor 
> shaft.  Or perhaps there's a better way, maybe involving a double 
> pulley or something..
>
> Does this sound feasible?
>
> Ignore for the moment space constraints -- like where could you FIT 
> the electric motor.  Also ignore power constraints -- like, how 
> quickly would the electric motor driving the compressor run the 
> battery down.  Those obviously are issues, but they're secondary to 
> the question.
>
> Anyone?
>
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