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not really noticeable on a diesel car as there is more low down torque.
Probably why things like light bulbs last longer on a diesel car (compared to petrol)as the voltage does not sway by much once the engine is running
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one of the tricks of systems like efficientdynamics and simuliar systems is to disconect or turn off systems when not needed. So if the battery is fully charged the alternator is disengaged.
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one of the tricks of systems like efficientdynamics and simuliar systems is to disconect or turn off systems when not needed. So if the battery is fully charged the alternator is disengaged.
To my knowledge, Ford and Hyundai have been like that for many years.
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not really noticeable on a diesel car as there is more low down torque.
Probably why things like light bulbs last longer on a diesel car (compared to petrol)as the voltage does not sway by much once the engine is running
Cars have had voltage stabilisers for many decades
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My last carbrettuer car (Ford Escort) obviously had a voltage regulator on the alternator but on tickover the lights were quite dim.
The engine idled just low enough for the battery to charge.
raising the revs up by as little as 100 rpm made the lights glow correctly.
That car used to get through light bulbs quite often.
hence I suspect less of an issue these days with fuel injected engines
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The effects of alternator drag are not that noticeable on modern fuel injected cars as the ECU can make adjustments to maintain a stable engine speed. The most you might see is the rev counter needed drops a little before springing back up to the normal idle speed when you switch on the headlamps.
You would be surprised just how many HP it can take to turn an alternator under full load conditions.
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The effects of alternator drag are not that noticeable on modern fuel injected cars as the ECU can make adjustments to maintain a stable engine speed. The most you might see is the rev counter needed drops a little before springing back up to the normal idle speed when you switch on the headlamps. You would be surprised just how many HP it can take to turn an alternator under full load conditions.
Around 6 hp.
A hp is 748 watts - at 50% efficiency, that's 160 amps at 14 volts.
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160amps x 14v = 2240watts.
Car alternators seem to go from around 90 (our Focus) to 190amp (water cooled in my A8!). Lights on only consume around 150watts. The really big effect on petrol consumption is of course the aircon - around 3kw (approx 4hp) at full chat. I remember switching it on in a tiny hire car in California - it was as though someone had pulled on the handbrake.
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160amps x 14v = 2240watts.
Car alternators seem to go from around 90 (our Focus) to 190amp (water cooled in my A8!). Lights on only consume around 150watts. The really big effect on petrol consumption is of course the aircon - around 3kw (approx 4hp) at full chat. I remember switching it on in a tiny hire car in California - it was as though someone had pulled on the handbrake.
A number of small cars automatically turn off A/C when full throttle is used.
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Sit with the car stationary and then switch on electrical equipment such as fans, heated windows, lights etc. You will hear the engine note change as the alternator load increases. That will use slightly more fuel.
Probably not a lot more fuel but it all adds up.
I will try that test. Thanks.
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Conservation of Energy laws state you cannot get something for nothing: if you add electrical load for lamps/heater blower etc, the power has to come from somewhere. If the engine is off, it comes from the battery, if the alternator is running and provides this extra current, the load on it is higher and more torque is needed to drive the alternator belt, so fractionally more fuel will be used.
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As someone once said "ye canny change the laws of physics". However, these extra loads will only soak up a fraction of a horsepower so MPG should not suffer dramatically.
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In egypt taxis drive with their head light off at night to save fuel!!!
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Cars used to have very little electrical consumption and used dynamo's.
When alternators became the norm they were 35 amp on cars like Mini's and Escorts.
Now you never see an alternator with an output of much under 60 amps, diesels are higher.
As was said above, you don't get owt for nowt and the electrickery has to be supplied.
When I raced we used batteries that had enough power to supply the fuel pump and ECU but not enough the start the car, had a beautiful assistant with a battery on a trolley for that. No alternator on the car to sap power. You paid £££'s for each extra horsepower and did not want to waste it.
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Cars used to have very little electrical consumption and used dynamo's.
When alternators became the norm they were 35 amp on cars like Mini's and Escorts.
The original poverty-spec Fiesta had a 28 amp alternator, with the bigger engined models getting 35 amps
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Conservation of Energy laws state you cannot get something for nothing: if you add electrical load for lamps/heater blower etc, the power has to come from somewhere. If the engine is off, it comes from the battery, if the alternator is running and provides this extra current, the load on it is higher and more torque is needed to drive the alternator belt, so fractionally more fuel will be used.
I'm not argueing - so easily assumed on message boards - I just want to know. How does the electrical demand on an alternator cause a drag on it? There is no physical component that applies counter force like a brake on the rotor.
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" How does the electrical demand on an alternator cause a drag on it? There is no physical component that applies counter force like a brake on the rotor."
Magnetic fields.
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Dynamos in the old days used to put out 20-22 amps(C40);now 100(and higher) amp alternators are common.
Edited by jc2 on 03/02/2016 at 15:08
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On modern cars the alternator will load up the engine depending on the current put through the alternators variable field. The ECU calculates what current is required.
Fuel savings are made with smart systems by allowing the alternator to load up on the overrun or when braking. Along with other systems such as capacitors in a E-loop system.
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" How does the electrical demand on an alternator cause a drag on it? There is no physical component that applies counter force like a brake on the rotor."
Magnetic fields.
That must be one hell of a field.
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Its simple.
This applies to all engines. As an example, in a petrol engine to get more power out you put more air and petrol in.
An alternator produces power, electrical power. To get more power out you have to put more fuel in which in a car is delivered from the car engine via the auxilliary drive belt.
If you could invent an engine that produced more power without increasing the amount of fuel required you would save the world.
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Its simple.
This applies to all engines. As an example, in a petrol engine to get more power out you put more air and petrol in.
An alternator produces power, electrical power. To get more power out you have to put more fuel in which in a car is delivered from the car engine via the auxilliary drive belt.
If you could invent an engine that produced more power without increasing the amount of fuel required you would save the world.
What would happen if the alternator was at maximan capacity all the time but was regulated down if no electrics were being used? This is how i imagined they worked in the first place but obviously I was wrong.
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What would happen if the alternator was at maximan capacity all the time but was regulated down if no electrics were being used? This is how i imagined they worked in the first place but obviously I was wrong.
I know very liittle about how car electrics but I do know that an alternator responds to demand. As others have said modern cars have smart alternators that put as much charge into the battery as they can on the overrun when no fuel is being used thus maximising fuel consumption.
Old Lucas ACR alternators used to charge at about 13.7 volts.
More modern alternators such as Motorola, Valeo and Denso charge at about 14.3 volts.
I stuck a volt meter in the ciggy socket of the BMW and was astonished at the variation in voltage. Anywhere from just over 13 volts to almost 15 volts. That is why modern cars used AGM batteries instead of the old lead acid ones, they could not take the voltage being pumped in.
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Pulgees, try and find yourself a little permanent magnet electric motor and turn the spindle with your fingers, then join both supply wires together and try turning the spindle. Then you'll understand how much difference it makes turning a loaded alternator.
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Pulgees is correct that old style alternators work in the way. The voltage is regulated to a max of 15.4volts (depending on system).
Issue is that the alternator produces back EMF which causes a load to be put on the engine. So when the alternator is not required it's detached
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Pulgees, try and find yourself a little permanent magnet electric motor and turn the spindle with your fingers, then join both supply wires together and try turning the spindle. Then you'll understand how much difference it makes turning a loaded alternator.
I will try that. I've got an old Flymo motor I'll dig out and see.
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This thread got me thinking. On a cold winters morning after the glow plugs have taken their tole and the starter motor has pulled huge amps from the battery. Is it wise to stick on the heated seats heated rear window and mirrors straight away?
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"On a cold winters morning after the glow plugs have taken their tole and the starter motor has pulled huge amps from the battery. Is it wise to stick on the heated seats heated rear window and mirrors straight away?"
I'm pretty certain the designers have taken all that into consideration and that the battery and the alternator's output will cope, provided the car gets driven for a reasonable time/distance afterwards.
But, as the rest of this thread shows, the energy has to come from somewhere, and that means increased petrol consumption.
Overnight I'm able to keep my car in the garage, which is integral to the house and thus not as cold as outside and not subject to frost or condensation, which means I don't often use the heated screens and usually don't bother with the heater at all. It must save me some money, but perhaps not all that much.
Edited by FP on 04/02/2016 at 08:23
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I still retain the results of nurturing during the age of dynamos. As a result, even on a brand new car, I get the engine started and then wait a few seconds before switching anything on, and even then I do them little by little.
SWMBO, in comparison, gets in the car, clears the windows with the wipers, uses the electric windows, turns on the heater blower, turns on the headlights, and then tries to start the engine. Fortunately, she mostly gets away with it, but boy that starter motor sounds sluggish sometimes.
As various roller-blind cords, irons, ovens, appliance doors and knobs can attest, she has no concept of mechanical sympathy. Drives me nuts.
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HandCart,
You've hit the nail on the head with your last few words alright. I'm amazed at how rough some people are.
When my old fella was teaching me the art of handling a set of spanners when I was maybe 9 or 10, he always used to say something along the lines of "be gentle, you're not tightning-up the nut that holds the propeller on the Queen Mary...."
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Exactly,after 40+ years in the motor industry,our firm came up with the severest tests for components we could think of,but our engineers and test drivers were mechanically sympathetic and could not simulate the stresses caused by the "little old lady" in her new car.
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This thread got me thinking. On a cold winters morning after the glow plugs have taken their tole and the starter motor has pulled huge amps from the battery. Is it wise to stick on the heated seats heated rear window and mirrors straight away?
Along those lines, seem to remember HJ mentioned in a Q&A that some cars now do not begin to charge the battery until the engine has reached operating temperature (done to keep emmissions down, IIRC). The upshot is that a life of short journeys and electric power consumers can flatten the battery.
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Under this circumstance, the alternator will be able to provide more than enough power. the problem is the battery. As the temp drops below 5C the battery is progressively less able to accept charge untill about -2C when it will not accept any charge. It is therefore necessary for the battery to warm up a little as the car drives before it will accept charge. this is the main reson why batteries die after a series of short journeys in a cold spell.
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But there is a physical counter force, it is electrical and its explained by Lenz`s law.
https://en.wikipedia.org/wiki/Lenz%27s_law
Note the following..... "Lenz's law states that the current induced in a circuit due to a change or a motion in a magnetic field is so directed as to oppose the change in flux and to exert a mechanical force opposing the motion."
Basically its saying to get something out you have to put something in.
Same reason why those massive alternators you see in power stations have an equaly massive steam turbine powering them......and not a donkey on treadmill!
Edited by TedCrilly on 06/02/2016 at 11:53
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