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2-4% extra car power, for free

Disconnect the altenator when it is not necessary
  (+5, -7)
(+5, -7)
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against]

A road-car's battery is constantly topped up by a device connected to the engine called an 'Alternator'. Basically transfers movement within your engine to electrical power in the battery. This costs you about 2-4% of your total engine power. On current cars it is always connected. Your car is constantly recharging or trying the recharge the battery no matter what its state, even if it's full.

When the engine is on, the alternator charges the battery FASTER then your car can use that power.

My idea is simple. A small electronic sensor and motor, that disconnects the alternator when the battery is 90% full or more, and doesn't reconnect until it's down to 30% .

Enjoy the 2-4% extra power as you drive for a while (a few hours) .. It's costing you no extra petrol .. its free. Your battery will be 100% fine without being recharged for a while. The car will feel like its got an extra 40BHP, without drinking more petrol! (trust me!). This power constantly drained by the alternator is precisely why formula 1 cars do not have them!

I honestly have no idea why the alternator is currently connected 100% of the time .. probably cheaper manufacturing or some lame excuse.

britboy, Feb 23 2004

(?) A bit about the alternator's functionality http://www.curricst...harginginfopage.htm
"The alternator does not constantly produce electricity, rather it cycles on and off as the system demand goes up and down..." [half, Oct 05 2004, last modified Oct 17 2004]

[link]






       once again, I don't feel qualified to confirm or deny this [britboy] idea, but if true then +.
jonthegeologist, Feb 23 2004
  

       The alternator generally provides the power for the sparks as well. You'd get a better power saving by disconnecting the air-con compressor (in the UK). Formula 1 cars don't have starter motors - they do have alternators.
Frankx, Feb 23 2004
  

       I stand corrected with regards to Formula 1 cars...
britboy, Feb 23 2004
  

       The voltage regulator effectively turns the alternator "on" and "off" (actually, some levels in between as well) in terms of generating electrical energy by varying the current applied to the rotor. (If it didn't work this way, your battery would be toast in no time at all.)   

       However, when there is no demand, you are still driving the belt and spinning the rotor.   

       The way I read your idea, it is much like the clutch on an automotive air-conditioner compressor.   

       I don't know exactly how much power it takes to spin an alternator that isn't producing electricity, but it isn't much. They will spin fairly freely when spun by hand. Most of the drag in non-charging mode must be caused by the belt/pulleys. Do you propose to somehow disengage the belt? This is a tricky task as it will likely result in fried belts when attempting to mechanically disengage and reengage at as frequently as an alternator would need to do.
half, Feb 23 2004
  

       First off, why is 2-4% result in 40 BHP. How many street cars have 1,000 or more HP?   

       Second, the voltage regulator will decrease the streagth of the field windings when less electrical power is needed. This decreases the force that the alternator requires.
GenYus, Feb 23 2004
  

       Oh bugger.   

       May I officially take this opportunity to hang my head in shame .. and quietly scuttle back to the drawing board!!
britboy, Feb 23 2004
  

       Not a silly idea at all britboy, although as mentioned an alternator is easy to spin with you fingers it would suck considerable horsepower to spin at the 10 thousand rpm or so that it does when then engine is at cruise speed, the aerodynamic drag must be quite considerable.   

       If you idea was a mechanical clutch then you would see a reasonable saving but this depends on the initial assumption that generally the alternator is not charging. I think if you were to monitor most alternators they are always putting out something, the headlights, heater/air con internal fan(s), heated seats, heated rear windows, windscreen wipers, mega watt stereo are all sucking from the electrical system.   

       However, if I may be so bold as to modify your suggestion and suggest a simple baffle that cut the air flow off to the alternator while it was not charging that would be easy to do and would reduce the drag.
KiwiJohn, Feb 23 2004
  

       [britboy] Your question is a good one though - "why the alternator always connected?"   

       I believe some manufacturers are looking to combine the flywheel- starter-alternator as some motorbikes already do. This would remove one belt and the weight of both items (almost).   

       The fact that car makers do not do this already is an example of the hide- bound narrow to closed-mindedness of the automobile industry.
timbeau, Feb 23 2004
  

       //The fact that car makers do not do this already is an example of the hide- bound narrow to closed-mindedness of the automobile industry.//   

       Or it might be due to the fact that a constantly running alternator needs airflow to cool it and under the engine (where it might get oil in it) is no place for an electrical device with lots of gaps in the case. Ever noticed that a starter motor is sealed with no air gaps? Or, it could be so that when the alternator bearings seize, it doesn't destroy the flywheel and tear the engine apart?   

       Also, are you sure that the motorbikes don't have a starter-generator? AFAIK, an alternator cannot be used as a DC motor. For one thing, there is no way to supply alternating current to the windings. Don't forget that an electrical motor needs to have the current alternate in order for it to spin. There would have to be a commutator and brushes in the alternator-starter in order for it to be used as a motor. And in order to get enough torque to start an engine, the windings would have to be made much heavier.   

       Another problem is that the gear ratio between a starter and the engine is much higher than the belt ratio between the alternator and the engine. (Take a look at a flywheel diameter vs the crankshaft pully sometime.) So now the starter/alternator is spinning even faster. Faster spinning means even more drag on the engine and more likelyhood of bearing failure. Motorcycles can probably get away with this because the torque requirements for motorcycles are much less than car engines.
GenYus, Feb 23 2004
  

       Perhaps if you took the alternator out of the belt loop completely and powered it with an electric motor...
RayfordSteele, Feb 23 2004
  

       Perhaps if you just stayed home...
Ander, Feb 24 2004
  

       Why not use waste engine heat to power the alternator. 50% of fuel is lost as heat. Recover it and power as many items as possible with electricity.
zonedance, Apr 12 2004
  

       Someone (an individual, not a company) once built an engine that recycled waste heat - I think it was ceramic. In any case, it got something like 300HP and 45 mpg. It's still sitting in his garage on the bench, because none of the car companies will buy it. They're all pork-barreling with the oil companies, I know it.
Macwarrior, May 03 2004
  

       That sounds like an urban legend to me...
david_scothern, May 04 2004
  

       Combined alternator Starter motor setups are or atleast where in production. They will probably be part of the switch to 48V car electrics rather than th eusual 12V.
engineer1, May 04 2004
  

       Guys, drag racers and hot rodders alike have been doing this since before I was born. Putting the alternator on a switch is a good way to shave .01 of a second off your quarter mile time, doesent sound like much, but in drag racing that's an eternity.   

       I won't say all, but most gm alternators (and most other manufacturers) from say 1960 to 1985 had an energize point to start charging. This means the alternator would have to be excited, which meant revving the engine over 1800-2000 rpm. If the aternator wasn't excited (engine started and left idleing for an hour) the battery would die and the engine would shut off. No one would leave there engine idleing for that long so it wasn't a problem. The thing is, once the alternator was excited, it would continue to charge 12 volts even if the rpm fell under the energize point. The voltage regulator is a series of switches that keeps the alternator producing voltage in a range of +12 - +14.4 volts. If the alternator "switched off" under normal driving conditions the voltage from the battery would drop to 10v or less, most likley killing the radio and dimming the head lights pretty bad (<good way to tell that your aternator is bad). Another thing is that would happen is the battery would go dead after about 30-45 minutes, unless it was a deep cycle marine battery which has a reserve of a couple of hours. Normal batteries only have about 30 minutes of reserve capacity. Meaning if there's a load of more than 6 volts it will only last for 30 minutes.   

       One more thing, alternators DO have brushes, and make very good electric motors with very little modification. Starters are sealed for two reasons one they do not spin 100% of the time and dont need the extra cooling, and 2, Most starters sit low on the engine, closer to water puddles and road debris, both of which are bad on the brushes and windings. A good example of a sarter/alternator combo setup is gasoline golf carts, like the older harley davidson and kawasaki 2 strokes. They use a belt driven electric motor to start the engine and keep the battery charged when it's running.   

       Good idea britboy, but it pretty much only works for drag racing where every thing happens at a few seconds at a time.
anobii, May 23 2004
  

       Great idea!   

       NOTE: Car batteries will be destroyed if regularly discharged 30% (70% remaining). However, there would still be a good power savings if the clutch kicked off at 85% or more of full charge.   

       A simple electromagnetic clutch similar to the air conditioner compressor clutch would work great.   

       At 55M PH, I can see a 2% savings in HP, and probably 2-3 MPG fuel savings. At current fuel prices, that's not trivial.
bobad, May 23 2004
  

       This is one of those ideas where the fishbones are out of proportion to the annotations. Is there something sinister in this?
KiwiJohn, May 23 2004
  

       This already exists. New cars disengange the alternator (the belt runs more or less freely) at full throttle.
Globi, Jun 09 2004
  

       How about control the alternator so that it only charges when breaks or when the battery is too low?
John_sea, Jun 09 2004
  

       An alternator essentially converts mechanical energy into electrical. When you use the lights, or the fan, they get its energy from the battery and the voltage drops. The alternator then produces the energy that's been used AND NO MORE. That's what the regulators are for. Try turning the lights on and off with the engine at idle, you'll see how the revs go down when you turn them on and only then, because when the alternator is working its drag slows slightly the engine. What happens when you switch off the alternator when drag racing is that the little power needed for vital functions like the spark is then draw from the battery, not from the engine, but you can't do that all the time without sucking the battery dry. Resuming : no.
finflazo, Aug 22 2004
  

       I read somewhere that water cooled alternators are the coming thing. Seems to me that this would eliminate most of mechanical energy consumed in cooling the alternator. Kiwijohn's idea of a baffle is good if it were done right. Disengaging the alternator is not worth the trouble IMHO.
hangingchad, Oct 27 2004
  

       lots of energy ideas lately. i wonder why
benfrost, Oct 27 2004
  

       There is a way to use the electricity from the alternator continuously to provide more fuel - namely hydrogen from water. Connect the battery to an electrolysis device which separates water into hydrogen and oxygen, and introduce them both into the cylinders along with the fuel-air mixture. When the spark ignites, the hydrogen will recombine with the oxygen, thus giving more of a "bang" in the cylinder than if the hydrogen-oxygen mixture had not been introduced into the cylinder along with the fuel-air mixture. This will give greater fuel economy for the same speed or greater speed for the same fuel consumption.
ardeshirmehta, Jul 15 2008
  

       I think hybrid cars like the Prius use the engine/battery system in such a way as to save battery power when it's not charged and then save petrol by using the battery to assist the engine. I don't know if this means the alternator becomes a motor at some point in the process, but it seems like more of a 'solution' than this idea. I think battery/engine hybrid systems will get more popular now.
mecotterill, Jul 15 2008
  

       'better to leave the car in the Sun, light providing Electrons, from Body, in say Panels, x 32 x 54 cm's to topple of, and off.-set 'losses0' pending next drive.
sirau, Jul 07 2011
  

       [sirau], that was almost understandable. Have you been drinking?
MaxwellBuchanan, Jul 07 2011
  
      
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