Auto Air Conditioning Compressors...Why

[AlienCraft]

..Aren't they run by a separate electric motor, bypassing the old-school pulley and clutch from the internal combustion engine? By doing that wouldn't the IC engine re-gain the mileage relative to gasoline consumed by the loss when the A/C is used conventionally? I mean seriously couldn't there be an increase in effiency that would warrant making the change?

 

[Mandres]

How are you going to power an electric motor big enough to run an AC compressor?

 

[Doppel]

..Aren't they run by a separate electric motor, bypassing the old-school pulley and clutch from the internal combustion engine? By doing that wouldn't the IC engine re-gain the mileage relative to gasoline consumed by the loss when the A/C is used conventionally? I mean seriously couldn't there be an increase in effiency that would warrant making the change?

Yep, this is a great idea. In fact, it's exactly how the Prius does it--the car has zero belts, one of the few production cars without them.

This is how the AC in the Prius can continue to run on battery when the IC shuts off. It is also one of the very many reasons why Honda's hybrid technology sucks, as they still belt their AC to the IC so when the IC shuts off at the lights...no AC.

To Mandres' point, though, a typical 12V battery won't be enough to run it, so you do need a hybrid or electric car for this from what I can tell.

 

[justfrank]

On Hybrid cars, they're self contained electric compressors (at least on Toyota/Lexus vehicles) but on regular gas powered engines, it's far easier and less expensive to use the engines power. Modern day AC compressors don't use as much HP as those from say the 70s so it's not really a problem.

 

[Ferzerp]

So, what you're saying is that they should suffer the effeciency loss that happens with every energy conversion?

You would have to install a larger alternator, which would have to provide *more* mechanical power to in order to drive an electric motor than driving it directly with the mechanical energy.

Your options are

a) drive the compressor directly

b) drive the alternator, and create electricity, which you then use on an electric motor to get back to mechanical energy to drive the compressor.


Which do you think is more efficient? Here is a hint, there is always a power loss any time you convert between energy types, and doing it twice to go to another energy type and back to the one you started with is a little silly*.

*except in extremely limited scenarios that it allows you to keep the engine running at the most efficient state, and the efficiency gains in the engine are more than the loss of the mechanical-electrical-mechanical conversion, such as in diesel electric locomotives, etc. This would in no way apply to something as small and ancillary as an ac compressor.

 

[thomsbrain]

The thing with A/C is the compressor is clutched, so when not in use, it's just a free-spinning pulley. Obviously there's a little friction lost there, but not too much. What we're seeing instead is the introduction of clutched alternators so that they only sap engine power when needed to top up the battery. Should be standard issue on every car, IMO.

 

[alphatarget1]

I thought about this too but... Let's say the AC compressor takes 1 hp to power. Where is that power gonna come from? If you drive it with an electric motor, how much current will it draw?

http://www.amazon.com/1800RPM-Frame-Leeson-Electric-108047/dp/B000AL98W0

This sucker takes 39 amps at 12 VDC and only puts out 1/2 hp. That is a lot of amps. Let's say 1/2 hp is enough to power your car's AC compressor at full load. Will the DC power come from the alternator or the battery? The battery wouldn't last very long if the car is shut off. Now, I think a lot of alternators put out about 100 amps. You would essentially be converting the engine power to electricity, and then feed it to the AC compressor, or have the electricity from the alternator it go through the battery first. Either way the power will have to come from somewhere...

 

[Bartman39]

The thing with A/C is the compressor is clutched, so when not in use, it's just a free-spinning pulley. Obviously there's a little friction lost there, but not too much. What we're seeing instead is the introduction of clutched alternators so that they only sap engine power when needed to top up the battery. Should be standard issue on every car, IMO.

Just curious but where did you see a clutched alternator...? Also why would you even consider it...? Once a battery is fully charged the only drag induced by an alternator would be from keeping any other draws by various components working (AC, ignition, lights & other various electrical parts) which you would need or else your single 12 volt battery type system would die rather quickly...? Sorry this just does not make sense...? But hey show me if this coming...? (link or real reason of)

Only application I can even think of where this might be useful would be on a drag car so you can charge between rounds but not have the loss of HP in a run (have it switched by the driver)... The typical street car/truck needs the alternator to run full time with the demands of the electrical equipment of today...

As for an electric motor driven AC compressor it may come but the 12 volt motors of today do not put out enough HP to run even the newest low drag AC compressors unless they are huge and really expensive... Possibly if we went to 24 volt or 36 volts systems but then everything would get real expensive... Sometimes simple is better until tech can catch up...

 

[LTC8K6]

Seems to be about 5-10hp for conventional modern a/c compressors. The ones on the hybrids are probably special higher efficiency units that use a bit less hp.

 

[LTC8K6]

Just curious but where did you see a clutched alternator...? Also why would you even consider it...? Once a battery is fully charged the only drag induced by an alternator would be from keeping any other draws by various components working (AC, ignition, lights & other various electrical parts) which you would need or else your single 12 volt battery type system would die rather quickly...? Sorry this just does not make sense...? But hey show me if this coming...? (link or real reason of)

Only application I can even think of where this might be useful would be on a drag car so you can charge between rounds but not have the loss of HP in a run (have it switched by the driver)... The typical street car/truck needs the alternator to run full time with the demands of the electrical equipment of today...

IIRC, several modern cars can "turn off" the alternator at times for efficiency. Whether they are clutched or not, I don't know.

 

[LTC8K6]

http://www.metronews.ca/toronto/life/article/485277--hyundai-has-a-smart-way-to-save-fuel

New smart alternators charge the battery during deceleration when the fuel is cut off.

 

[PottedMeat]

http://www.metronews.ca/toronto/life/article/485277--hyundai-has-a-smart-way-to-save-fuel

New smart alternators charge the battery during deceleration when the fuel is cut off.

makes sense. most automakers could implement this easily by controlling the voltage regulation through the ECU. i think chrysler controls the field strength through the ecu already, maybe they already do it.

i guess a clutched alternator could save gas since you're keeping a fairly big chunk of rotor spinning, but it may not be worth the price of an extra electronic clutch.

 

[Bartman39]

I still do not see the value of it...? It cannot affect fuel economy that much and like I said with the demands of the electrical systems in modern cars for it to turn off means the battery discharges so the alternator would have labor even more to catch up...? The regulator in an alternator reduces the rate of output as the load drops so once the battery if fully charged its only producing for the other load draws in the car... Also I would not want my electrical system to drop to just battery voltage from time to time and then power back up to charging voltage (this could be rough on certain electrical items)...

May be practical in some applications but to me it seems like an expense that is not worth the additional cost and makes for another system to possibly fail...? Uh also how often do you decelerate really...?

Bet it wont go over very well with the high power stereo people...?

 

[LTC8K6]

IIRC, BMW was doing something similar with the alternator. GM is also, I believe.

 

[LTC8K6]

Brake Energy Regeneration.
Make use of every watt: by charging the battery only when your BMW is braking, coasting or decelerating, Brake Energy Regeneration improves fuel efficiency by up to three percent and ensures that the full power of your engine is available for acceleration.

Today's vehicles require much more electrical energy than older models, due to the much wider array of electric and electronic on-board comfort and safety systems. This energy is created by the generator (also known as the alternator) which converts the engine's power output into electricity. In conventional systems, the generator is permanently driven by a belt connected to the engine.
BMW's Brake Energy Regeneration operates differently: the generator is activated only when you take your foot from the accelerator or apply the brake. The kinetic energy that would otherwise go to waste is now used efficiently, converted into electricity by the generator and stored in the battery.
Producing electricity in this highly efficient way delivers an additional advantage: when you apply the accelerator, the generator is deactivated - so the full power of the engine can be directed to the drive wheels. Brake Energy Regeneration thus increases fuel efficiency while simultaneously enhancing driving dynamics. As a safety precaution, the Brake Energy Regeneration system monitors the level of battery charge and will, if necessary, continue to charge the battery even during acceleration to prevent a complete discharging of the battery.

Even more intensive is the use of freed-up kinetic energy in vehicles with electric motors, like the BMW ActiveHybrid models or the BMW ActiveE with fully-electric drive system. In this case, the motor serves as a generator and produces electricity as soon as the driver takes his foot off the accelerator. This principle increases the range of the BMW ActiveE by up to 20 percent.

 

[Bartman39]

Thats all cool but glad I do not work in the automotive industry any more... I feel for these hybrid owners and what will happen when they are out of warranty but still have to take them to the dealer as many shops wont want to mess with them... This will also be true with some of these types of newer idea's like this... Reg shops for the most part will not want to get involved so it will cost even more at the dealer because they would be the only place that can work on them...

Just like in the type of construction equipment I work on (Komatsu) we have to go to all kinds of schools to learn about all the new stuff they keep coming out with like tier 4 engines... To me its really crazy to put that stuff on construction equipment engines...

Sorry also a little off topic but as a mechanic some of this stuff just seems like someone needed to come up with some BS to keep their job...? There are many other areas to focus on to improve fuel economy but its like they do not want to do it but rather worry about emissions to the point it will be so complicated and expensive no one can afford it... Just seems like a sad future for the auto industry...?

 

[Eli]

Can't have your cake and eat it too.

The main reason the Prius uses an electric A/C compressor is because of EV mode. Nobody would be very happy if the A/C didn't work below 30MPH when cruising around in the city.

The Insight uses a traditional ICE driven compressor, and you lose A/C when stopped at a light in auto-stop. It doesn't really bother me considering I use the A/C about once or twice a year, lol. But I've seen people complain about it, especially if they're used to a Prius.

 

[Ferzerp]

Can't have your cake and eat it too.

The main reason the Prius uses an electric A/C compressor is because of EV mode. Nobody would be very happy if the A/C didn't work below 30MPH when cruising around in the city.

The Insight uses a traditional ICE driven compressor, and you lose A/C when stopped at a light in auto-stop. It doesn't really bother me considering I use the A/C about once or twice a year, lol. But I've seen people complain about it, especially if they're used to a Prius.

Of course, then you have cars on the other end of the spectrum that kick the A/C compressor off during WOT because we don't want to lose any HP at all if we're being silly.


But I say again, the most efficient way (without creating a system that adds a ton of complexity to your car) to run that compressor is to pull the mechanical energy off the engine.

 

[Bartman39]

Never mind am posting this in OT
http://pubs.acs.org/doi/abs/10.1021/nl203806q

 

[SpatiallyAware]

Thats all cool but glad I do not work in the automotive industry any more... I feel for these hybrid owners and what will happen when they are out of warranty but still have to take them to the dealer as many shops wont want to mess with them... This will also be true with some of these types of newer idea's like this... Reg shops for the most part will not want to get involved so it will cost even more at the dealer because they would be the only place that can work on them...

Just like in the type of construction equipment I work on (Komatsu) we have to go to all kinds of schools to learn about all the new stuff they keep coming out with like tier 4 engines... To me its really crazy to put that stuff on construction equipment engines...

Sorry also a little off topic but as a mechanic some of this stuff just seems like someone needed to come up with some BS to keep their job...? There are many other areas to focus on to improve fuel economy but its like they do not want to do it but rather worry about emissions to the point it will be so complicated and expensive no one can afford it... Just seems like a sad future for the auto industry...?

I agree sooo much with this. There is no consideration for return on investment when dealing with these things past 5 years out.

Modern cars are designed for the american masses, which lease or buy and keep 3 years before reselling. In this sense ALL that matters to the original buyer is MPG, emissions, safety ratings and manufacturers are catching on to this.

It's already gotten to where you can't just find a 'mechanic'. You have to find someone that specializes in whatever crazy modern mpg-savings setup the manufacturer decided to use for 2 years before scrapping and moving on to something else.


This is something I REALLY like about BMW... they come out with an engine design and stick with it for at least 4-5 years. Ford is ok with it as well. The worst, imo, is GM with all their different 'series' and engine changes within a single body style. Years ago I had a grand am which had something like 6 different engines types within a two year model run..

 

[Hulk]

Everyone posting here is kind of getting to it but not really.

1. There are relatively large electrical demands required for the size of a motor needed to run the AC compressor. The battery, alternator, and electrical system of a 12V non-hybrid vehicle aren't up to the task.

2. It is more efficient to run the compressor off the engine using a clutch/pulley arrangement than using an electrical motor. As one poster stated there are losses going from mechanical energy>electrical energy>mechanical energy. UNLESS #3 below.

3. If you have a hybrid vehicle where energy gained from braking can be stored and used to power the AC compressor and shut off the IC engine while still running the AC then efficiency is increased over the traditional system. In addition the electrical system in a hybrid vehicle is up to the task (higher voltage and higher energy storage capability).

 

[skyking]

Everyone posting here is kind of getting to it but not really.

1. There are relatively large electrical demands required for the size of a motor needed to run the AC compressor. The battery, alternator, and electrical system of a 12V non-hybrid vehicle aren't up to the task.

2. It is more efficient to run the compressor off the engine using a clutch/pulley arrangement than using an electrical motor. As one poster stated there are losses going from mechanical energy>electrical energy>mechanical energy. UNLESS #3 below.

3. If you have a hybrid vehicle where energy gained from braking can be stored and used to power the AC compressor and shut off the IC engine while still running the AC then efficiency is increased over the traditional system. In addition the electrical system in a hybrid vehicle is up to the task (higher voltage and higher energy storage capability).

Very much agree :thumbsup:
I am converting my truck to a pair of electric Ford taurus fans from the mechanical fan and taking on that electrical load for a very specific reason.
I have a viscus clutched fan that always spins. Always takes power.
If I had an electrically clutched fan I'd be very happy, but the diesel is so cool running, I have driven it two months without any fan. It only got hot sitting idling in really bad stop and go.
I designed a progressive circuit that fires one fan at low, then the other, then both on high. I'll never hit my electrical system with start loads on high.
I also have one fan come on low at the command of the air conditioning compressor circuit.

 

[speedy2]

The worst, imo, is GM with all their different 'series' and engine changes within a single body style. Years ago I had a grand am which had something like 6 different engines types within a two year model run..

Take a BMW to get it fixed. And then take a Grand Am(Any "series') to get it fixed.

I had an L32 In my Grand Prix GTP. It was a "Series III." It added an electronic throttle body, different head design, and a more efficient Supercharger. I'll gladly take that upgrade, even in a two year spread. It's not really that big of a deal. I'm no mechanic and I know all the differences and working on that engine was easy as pie too.

 

[PandaBear]

IIRC, several modern cars can "turn off" the alternator at times for efficiency. Whether they are clutched or not, I don't know.

You do not need to clutch off the alternator. As soon as you disconnect the diodes from the circuit it will not draw much mechanical energy.

Simple high school physics experiment: connect an electric motor to a light bulb and try to spin the motor, and disconnect the light bulb and try to spin the motor. See the difference in resistance? That's the amount of energy used by the light bulb.

 

[LTC8K6]

You do not need to clutch off the alternator. As soon as you disconnect the diodes from the circuit it will not draw much mechanical energy.

Simple high school physics experiment: connect an electric motor to a light bulb and try to spin the motor, and disconnect the light bulb and try to spin the motor. See the difference in resistance? That's the amount of energy used by the light bulb.

You might not need to, but...quite a few cars have them.

http://www.americanenginesco.com/servlet/the-49/nissan-altima-Sentra-2.5L/Detail

http://metalmanparts.com/product.sc?productId=317&categoryId=38

http://www.ebay.co.uk/itm/VAUXHALL-ASTRA-H-1-7-CDTI-NEW-CLUTCHED-ALTERNATOR-05on-/280643186703

IIRC, the police package Crown Vic had an alternator clutch on the 200A alternator.

http://en.wikipedia.org/wiki/Overrunning_alternator_pulley

It's not always obvious that there is a clutch there, but they generally have this cover on the end of the pulley. This is a Ford Mustang clutched alternator.

http://www.cvpi.org/archives/p71interceptor/alternator/modelnumbers/8436/wsdindex.html