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How come A/C compressors aren't driven by electric motors?

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  • spokanespokane Member Posts: 514
    I fully concur with the advantages you cite for 3-phase motors and voltages greater than 42V. For vehicles having the new 42V electric, but retaining conventional mechanical vehicle propulsion, I understand the automotive industry has agreed not exceed 60 Volts in any circuit. Because of this, please do let us know if you hear anything specific regarding plans to use inverters.

    We should note that if a DC motor is used for the A/C compressor, the motor and compressor will need to be connected by a coupling and a mechanical seal used (like existing compressors) to retain the refrigerant. This, as you know, is because the commutator and brushes of the DC motor need periodic service and cannot be immersed in the refrigerant. The A/C motor, of course, would be integral with the compressor like a refrigerator or home air conditioner, and would thus be a sealed system. The same reasoning applies to the water pump. So ... there's a strong argument for use of inverters.
  • 79377937 Member Posts: 390
    Well, there are brushless direct current motors and it's quite possible they could be used too. I do not have much experience with them though. I know they were used in certain video recorders. Another type of motor is a digital motor. We use them on certain of our test jigs for positioning probes. They are driven by a computor. The computer sends pulses to a controller. The contoller then pulses the motor a certain amount of pulses and postions the rotor. If you send 360 pulses the motor will turn one revolution and lock. A stepping motor in other words.

    About the voltage being agreed upon by the automotive industry - new developments will have to be taken into account. At one time they all agreed on 6 volts. Time marches on.......we will see.
  • kabbalahkabbalah Member Posts: 58
    Take a look at the following website.
    www.aurasystems.com

    Aura Systems manufactures an under the hood power generating system that can power up compressors or other electrical stuff at engine idle. I work for the company.
  • tboner1965tboner1965 Member Posts: 647
    You just take the AC directly from the generator for accessories.

    The only reason to convert to DC is to store in a battery. If we are not talking about a gas/electric hybrid, why would we need a large storage battery? A small inverter to convert DC to AC to run accessories while the engine is off, and everything is AC powered except the starter motor.

    TB
  • 79377937 Member Posts: 390
    You need a battery because you need a constant voltage for a motor driven A/C for example. The alternating current coming off the alternator changes in voltage and frequency dependant on engine speed. It would be the same as trying to run household appliances such as a refrigerator with a varying voltage and frequency. The alternator output is rectified to direct current and only serves to keep the battery charged. The battery acts as a sort of buffer between the alternator and alternating current drive motors.

    And yes, we are of course talking about hybrids. The difference being that in the examples I am talking about, a greater step forward has been taken. You must concede that a World War 1 submarine drive system is no different in concept to a modern hybrid vehicle such as a Toyota Prius.

    What we have in both is exactly the same. An internal combustion engine (diesel in this case), driving a generator which drives a motor and at the same time charges banks of batteries for underwater travel. The batteries will drive the motors underwater and on the surface if needed. The concept is hardly new.

    What IS new however, is the electronics available today to make everything more effient. This is why so much interest is being shown again in an old concept.
  • andre1969andre1969 Member Posts: 26,023
    ...like what you see on the roofs of motorhomes and other RV's? How are those things powered? I know when they're at the campsite, they're either running a generator or hooked into an electrical outlet, but what about going down the road? Of course, nobody's going to want one of those things mounted to the roof of their car, but maybe something could be done with the technology to apply it to a car.
  • tboner1965tboner1965 Member Posts: 647
    you can run the engine at one constant speed. The engine can be designed for maximum efficiency at a certain RPM range and the computer controls and regulates the RPMs so you have a reasonably consistent alternating current.

    The throttle would just control the speed of the electric drive motors. Heck, you could put a small drive motor on each wheel (I think that was mentioned here) and some of 'dem newfangled 'lectronics could act as the differential, traction control, etc.

    I like the idea of the redundancy too. The engine drives two smaller generators, and there are four drive motors. The only powertrain failure that would sideline the vehicle is an engine failure.

    Of course, for the ultimate in redundancy, you could have the batteries as well.

    It is just that batteries are so heavy and will take up so much space, I'm not sure we would want to have a skid full of 'em. Not to mention all of the nice toxic goo found inside.

    TB
  • 79377937 Member Posts: 390
    Running the engine at one constant speed would hardly be good for fuel consumption. At a stop light and stalled traffic for example who wants their engine racing? No, the computer will decide what the engine speed must be to conserve fuel. That is after all the object of the whole exercise. More on the great hybrid debate later I'm tied up for the moment.
  • tboner1965tboner1965 Member Posts: 647
    Just because an engine runs at a constant
    speed doesn't mean it is running at a high speed. Additional power can be produced by adding more air and fuel, even at low engine speeds.

    Perhaps a turbo with electronically controlled boost.

    Just thinking out loud.
  • 79377937 Member Posts: 390
    Sure, but engines have an optimum speed at which they are at their most efficient. That might be in the region of 3000rpm or so. Also, engines are at their most noxious while idling with no load. If we look at the Toyota Prius we see that the engine gets switched off at standstill and only starts up again when the battery requires charging. Any engine idling is regarded as a waste. Idling engines in stalled traffic are one of the biggest pollution generators. It is exactley because of this, (engine switch-off at idle and fine tuning by the computer when running) that the high mileage per gallon is achieved on the Prius. The engine only kicks in when needed. In fact, when you drive off in a Prius you might go quite a distance on battery only power before the engine starts up and charges the battery again.
  • 0patience0patience Member Posts: 1,712
    One of the biggest reasons the automotive industry went with DC electricity was to prevent death. If a DC system spikes on a dc voltage system (less than 100volt DC)than the harm to a person would not usually be life threatening.
    While an AC system, the potential for harm to a person is much greater.
  • 79377937 Member Posts: 390
    Well we live with death all around us then. Every househod is a potential death trap with its 120 volt ac supply. In Europe the voltage is 220 volt ac household supply and in the case of a 3 phase supply, it is 380 volts ac between phases. And in the context of mechanics repairing "high" voltage motor cars and exposing themselves to danger, everyday electricians are working on much higher voltages in the course of their work. Mechanics of the future will just have to be trained in the new technology. The high energy ignition systems used today on vehicles have a great potential to cause cardiac arrest should a person accidentally be zapped by it.

    In any case, such high voltage circuits would be very well insulated and clearly marked "Danger High Voltage." In the case of an accident, fail safe design will allow all high voltage circuits to switch off.

    I've been looking through my automotive books and have come up with something interesting. As far back as 1916 the Woods Dual Power motorcar was on the market. It was a hybrid motorcar using a 4 cylinder gasoline engine driving a generator which charged batteries which powered the electric motor. It wasn't a success because the power to weight ratio was bad. Not surprising for those times but the idea was there.

    Then there was the motorcar design that coupled the engine to the drive wheels with a magnetic coupling. The dynamo as they liked to call them those days was directly coupled to the drive motor. No controls in between. Just rev up the engine, the dynamo gives more output to the motor and the car moves off. No clutch, no gearbox. The car was called the Crown Magnetic and was built in 1920. None of these cars were a success then but given modern materials I'm sure they would have all worked better. My point is, the concept of hybrids is not new.

    Well, I've spent a lot of time here and feel I should move on. Maybe I should join the great "engine sludge debate" on the other board. Its been good fielding arguments and I hope I've given you all food for thought. Don't let the naysayers tell you it can't be done. They said the same about putting a man on the moon. In 20 years from now just maybe something of what I have said will have come true.

    And Opatience, 20 years from now, don't forget to put your electricians safety gloves on when when you tune up that hybrid vehicle. Only kidding only kidding............
  • 0patience0patience Member Posts: 1,712
    Look, I didn't say I agreed with it or whatever or that is would be a problem today or any of that.
    I was merely stating a fact. Whether you like it or not.

    And yes, the new Hybrids are much higher voltage than the concept cars of years past. And mechanics of the future will be more of a cross between a mechanic, electrician and computer technician.

    The concept cars or hybrids are not new, the only difference is that this is the first time they have been even remotely accepted.
    In the 70s Europe made an attempt at a few all electric cars, had they had more power and range, they might have been accepted.
    The hybrids still have along way to go to be competetive with the IC engine vehicles, mostly because most people prefer the power of a real engine.
    It took almost 20 years for the diesel to be accepted as a power plant for cars or pickups and be popular.
  • 79377937 Member Posts: 390
    No offence was intended Opatience. I'm afraid though that in the future it's not what people will accept or not but rather, what the needs of the day will be. And the need will be to conserve energy. Because petroleum products have been so relatively cheap not much effort has been given to developing more effient vehicles. That will have to change. The day of the "real" engine has passed.

    Today I heard that Opec will be reducing oil production and once more hold the USA to ransom with high oil prices. They cannot be allowed to do that and the only way to prevent being held to ransom is to use less of their products.
This discussion has been closed.