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delbertinie

Member
Here is my twisted question.

I am running a vw motor so I don't want to rob the motor of precious hp
So I have been toying with the idea of using a 12 volt dc motor that runs at 2000 rpm.
How much horsepower would I need to run the compressor?
I planned on running two batteries in series so it remains 12 volt.
I have a custom built alternator that is wound for 120 amps internally regulated.
I am planning to use on of the really small compressor like the one on my mazda .
The stem only has 1 lb of freon.
 

Peter

Active member
Thinking the same way here, I don't need heating as minimum temp is about 8c in winter, if you can call it that.
Looking at stand alone 12v A/C units for boats and RVs too. bit pricy but a lot less work.

'They' say it takes about 10% to drive the A/C so on a VW 1600 about 5 hp and that is not a big electric motor, can be mounted parallel with the compressor on a short ribbed belt as usual.
I was also thinking of using the guts from a domestic freezer as the pump is transformed down from AC to 12vDC in many units and using car evaporator and condensers might work.

Google is a wonderful thing, just search 12v air/con images


.A kit made to run on 12v with controls.
$_12.JPG

Self contained unit
5_200_btu_cabin_air_conditioner.jpg
 

letterman7

Honorary Admin
If you figure it out, let me know. Peter is about right - 5hp or so. Problem then becomes a space requirement, then the electrical requirement. I have yet to see a compact electric motor at that hp rating that's 12 volts.. or even 120 volts.

I looked into all those options years ago, and the closest thing I found were the 12v self contained electric compressors from Masterflux (MasterFlux - Makers of AC and DC Variable Speed Compressors and Specialized Thermal Systems). The Sierra line has the widest range of options for 12v output, but even at the highest btu rating still falls short of what a car cabin typically uses... and is a high amperage user at that.

I had even toyed with in-line Peltier units ducted with fans on either side. Might have worked if it weren't for the power draw. Funny thing... Mercedes is using Peltier units for their in-seat "air scarf" heat/cool option.

It all came down ultimately to cost versus efficiency versus space.. and an engine mounted compressor always won out. With the new style compressors there is far less drag on the engine than you would think. Purchase a compressor off a mini car, like a Smart, and you'd be ahead of the game. I doubt you would even feel the difference when it kicked on. Remember, your car is a little lighter than the Beetle it was born from.
 

delbertinie

Member
. I was planning on using a automotive compressor and a 12 volt motor via a belt. I have found a 2.5 he that runs at 2200 rpm.
Dc motors have 100 of their torque at start up once it is spinning I wonder if it would take as much hp
to turn the compressor
 
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letterman7

Honorary Admin
Probably not, once the compressor has started turning. You'll have to build in a little leeway for the compressor start/stop cycle.. and overdrive pulley on the motor side might help that. Personally, I'd bench test a system before putting it in the car. A little more trouble initially, but it would root out any potential issues and you could find what kind of draw the motor actually pulls from a battery. If you have portable generator with a 12 volt charging system and battery, that would be a perfect substitute as a test bed.
 

delbertinie

Member
one thing that has led me to this idea is the lack of brackets for the vw's to add an a a/c compressor.

Does anyone have any sources for brackets?
 

ratrog64

Well-known member
HP

The new compressors we have available today only require about 1.5hp or less to drive them (per the mfg of the compressor I just bought), Not like the old days when a compressor needed 4 to 6 hp to drive it.
The 120amp alternator you have more then likely requires about the same hp to make it work.

I have recently ordered 2 different compressor brackets and should have both next week (I hope).

One is coming from Gilmore Ent (I know it will be perfect). Ed has had some recent surgery so not sure how soon I will get it. But he said a few weeks.
HOME

And the other is the one from Vintage Speed (Taiwan).
Vintage Speed Air Conditioner Compressor Mounting Kit, 1968-77 Beetle, for Sanden 505, 507, and 508, 155-291-11203 - Aircooled.Net VW Parts

I will post to my builders journal both brackets when I get them.

Ed's bracket will come unwelded since I am using a slightly different compressor (Sanden 505) then what he commonly uses. So I will be mocking it up and doing my own welding.

Ed said it would run about $210 for his bracket. Vintage speed was $169.
 

Peter

Active member
OR
A/C Conversion

Been looking at many options and it seems although the traditional belt driven compressor (SAAB 1999>04 is very small) there are many alternative options.

I'm looking at passive Peltier electronic systems but using the device(s) to cool fluid in a liquid system as well as the one above.
 
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