Hi all-
I was under the recent impression that the AC on the MCS's were electric,-bascically, on or off it drew no additional power(other than voltage) from the motor. I guess I was given false information or just never really researched it enough. :impatient

Anyway- Im posting mainly because I am wondering if anyone here has ever done or has seen done, an electic AC system switch over. I know MiniMania supplies an AC Idler Pulley that enables the Serpentine Belt to stay in Stock Routing Configuration, while removing the AC Unit, but that leaves me to wonder, if anyone has maybe installed that part and relocated the AC compressor and lines somewhere else with an electric motor hookup??

Im also wondering, if no-one has seen or done it out there, does everyone think its doable?? Give me some Feedback!! Thanks!!

 

Even if you could do this (and I believe the Toyota Prius and maybe other hybrids do it - you want AC to keep going when the engine is stopped), there would not be much net gain in saving engine hp.
When the motor was running to drive the AC compressor, it draws a lot of current which is pulled from the alternator - this in turn causes the alternator to load the engine, and sucks some hp.

You find a similar effect on (older) cars where turning the lights on causes the engine idle speed to drop a little.

HOWEVER: if you had a smart system, you might be able to vary the motor speed to run the AC at part speeds, so that it only made the air as cool as needed - this would be more efficient than the current way of running the AC at max always, and mixing heated air in to bring the temperature back up.
You could then have a system which only loaded the engine as much as was needed for the required cooling.

 

Now by part speeds, you mean run the AC electric motor only depending how hot the cabin is?? Im primarily not so much worried about Voltage draw at idle, as I am with it from 1500-3000 rpm- as well as impoved gas mileage.

I would think that the AC compressor wouldnt need to be spun at much more than 1800-2000 RPM to produce enough BTU. Even if I use an 1/8 hp electric motor that draws 10-15 amps at 1800 rpm, thats less than most car audio amps correct? I guess Im just pickin the details on this one.. Thanks!!

 

Yes. That would require some sophisticated control.

Ah! That is something I had forgotten.
You have a similar benefit already with the power steering on the MINI.
Normal hydraulic power steering has to be "geared" (belts/pulleys) to draw sufficient force at idle to allow the steering - this means at high revs it draws much too much and just wastes it.
The electric power steering of the MINI spins at the same speed so draws the same load from the engine at any revs.
If you did the same with the AC, it would be the same load no matter what revs the engine are at. But what I don't know is how the AC on the MINI handles this now - is there just not enough cooling at idle revs? In my MINIs at least, there is never too much cooling at high or any revs, so where does the extra go when the engine spins fast?

I really have no idea how much energy the AC compressor needs.

...
Reading MINI Complete ...
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Not much help, but it does say that the AC compressor varies itself - "the more cooling required in the passenger compartment, the higher the flow rate". I think this variation also is what solves the issue of varying the compression with engine revs.


As a general principle, the same WORK requires the same ENERGY. For the AC compressor, the work is that needed to do the compressing of the refrigerant.
Currently the enegy to do that work comes direct from the pulley/belt attached to the engine, via the electric clutch.
If you instead drive the AC compressor from an electric motor, you should be able to eliminate the clutch and any slippage losses from it, but you now need to get the same energy via the alternator & electric motor.
Neither of those are 100% efficient, and I don't imagine they are as efficient as a direct coupled belt/pulley, so to get the same work done you theoretically need MORE overall energy from the engine, to compensate for the increased inefficiencies.

 

I think your'e wasting grey matter on this one. Nice thought though. Variable speed pulley would be your best bet. Ofcourse it would be huge Dang no room.

 

Peter [M7] and I spoke about this. He did runs with and without AC for kicks and saw about 8hp loss. Not sure if wheel hp or not. That really isn't much, is it?

 

Ingsoc, your correct. The A/C in the MINI should draw about 8 hp from the engine. Any A/C unit should be near this figure. I also drive a Honda Insight so I know the effects of the A/C cycling on and off (you can actually feel the jolt). The Insight uses a different type of A/C that only draws about 4 hp. That said, I'm not sure your going to get any more power from an electric motor as your just adding another step to getting power to the A/C.

 

I wonder- I guess we shall see when I actually start doin the under bonnet mods! It was just some food for thought. I always liked the electro-hydraulic steering on the MCS and was curious about its positive effects elsewhere. HMMMM... Thanks all!!

 

8hp is like adding an exhaust and can surely be felt. Also on a MCS the A/C hinders the engine from gaining speed from a start.

Just my 02.