After reading a article in this months C&D, I was wondering how much of a power/ mileage gain we would get if the A/C wasn't driven off the engine, but off a electric motor. I know the alternator is still driven off the engine, but I thought it might be interesting to bounce the idea around, and see what if any thing could be done to make this happen. With all the other engine mods people do, installing an electric motor powered of the alternator seems like a straitforward mod, but it may be that the alternator doesn't have the power to run the other car systems and the A/C at the same time...I don't know. This could necessitate needing a larger alternator which could end up sucking as much power away as the A/C.

Just curious what peoples thoughts on this are.

 

You'd be converting mechanical energy to electrical energy and then back again with losses both times, before even turning the compressor. Perhaps you could make it up by taking advantage of being able to run the thing at an optimal RPM...

A/C compressors consume a LOT of power, though I don't know what the wattage would work out to...

 

stay at over 65% throttle and it will be off all the time

 

Well the main difference wouldn't be "while" the AC was running, but when the AC was completely shut off. Some individuals (like myself) don't use the AC very often, if ever, and this would reduce the parasitic loss from the additional belt/pulley to nil....AC off = no current drain.

On some car's you could end up with everything but the generator run electrically....eliminating all but 1 belt and 2 pulleys.

 

In the upcoming GM truck line-up the alternator doubles as the starter....I can't wait to see how that turns out.

I'm not sure what the draw of the clutch is anyway..

 

The A/C compressor in our RX-8 draws between 1/2 to 3 hp when it is engaged.
The power required varies with the engine rpm and outside air temp. Higher
ambient temp means higher refrigerant pressure and more required power to turn the compressor. Several of todays hybrid cars have compressors driven by electric motors. You would need a minium of an 1500 watt motor to due a decent job of cooling our car. This equates to about 125 amps of 12 volt current. This is quite a bit more than our alternator is capable of. With the advent of more and more vehicle accessories being electricaly powered (our power steering) auto makers have decieded that there needs to be a new standard. As Snap-on has indicated above both Ford and GM will soon be introducing us to the world of
42 volt automotive electrical systems. These new autos will have an alternator built into the flywheel near the transmission. Due to the size of the rotor able to fit into this area they can produce lots of electrical power. This flywheel generator
can be used to start the vehicle as well as power all the accesories steering, water pump, brakes and A/C. This would also eliminate the need for a belt and its maintence on the engine as well as a front crankshaft seal to possibly leak oil. Ford and GM sa to look for the first of these new 42 volt charging systems to come out in model year 2007.

 

The AC compressor has a magnetic clutch - when it's off, the magnet disengages and the clutch free-wheels. Power loss with the AC off is negligible - very little horsepower is required to turn a free-spinning pulley, if any at all.

Dale

 

we only lose 0.5-3.0whp when the A/C is going? I have a hard time believing that, given the difference I feel

 

Well with all the threads on lightened and underdrived pulley's, one would imagine the superior solution would be just abandoning those pulley driven devices completely and replacing them with electrically driven ones.

I do understand that actually driving the AC would take a considerable amount of power (which would probably negate any gains by requiring a larger alternator), but if I could just reduce the strain on the rotational mass by replacing it with something I'd almost never use (maybe 4 times per year), I'd still consider it a benefit. No belt = good.

 

Step 1: Remove AC system
Step 2: Replace AC system with the following electrically driven cooling system



Sorry about being a smart **** :D

 

I'd do that...cept everyonce in a long time females actually ride in my car...and for some reason they don't like things called humidity and heat.

 

Get a tougher female. Maybe get someone from Georgia or the Amazon?! Nothing should stand in your way of pursuing ultimate HP.

 

Our A/C compressors are also used in industrial vehicle applications for truck refrigeration and motor coach A/C. It is common for them to be belt driven by a
1 hp electric motor. At crusing rpm in our 8's, a 3hp draw can be almost 5% of our engines power output. I can post a power consumption chart for our compressor if you are interested. Also our compressors cut when accelerating at over 65% throttle opening for more Zoom Zoom :D

 

Magic8,

I'm working on that . I guess you can eliminate them pretty quick if you tell all the potential canidates "oh sorry baby, this car doesn't have AC".