Electricity


#1

why did auto maker replace the generator with the alternator back in the early 1960.


#2

The alternator is much more efficient.


#3

Alternators are smaller, lighter, have a higher electrical output, and will charge at low speeds like when the car is idling. I also think they’re not quite as durable, but that is open for debate.


#4

The main reason given at the time was that in city traffic a generator did not deliver enough power to keep the battery charged, especially with all the modern accessories such as rear window defroster. Alternators were much faster in output at low speed. A generator with equivalent low speed output would be very large and heavy, and more expensive.

P.S. Tom McCahill of Mechanix Illustrated tested a mid fifties Lincoln with with a large number of accessories, and remarked that “the generator on this rig looked like it was stolen from Consolidated Edison”!


#5

Alternators are easier to regulate voltage and current over a wide range of RPM than generators. They last longer too.


#6

And they are much cheaper to manufacture. No high-amperage brushes to burn out or wear out.


#7

I believe Chrysler was the first to come up with this. They used to have a lot of engineering advances.


#8

@dripper…if you ever drove a vehicle with a generator you would know that an alternator is a vast improvement. It’s like going from a broom to a vacuum cleaner.


#9

There is no such thing as an alternator, there are only generators. alternator was a marketing term dreamed up at Chrysler, but it is a 3 phase AC generator with a rectifier pack, where the older generators were DC generators.

Now ask me why three phase.


#10

Why three phase, @keith?


#11

Because the cosine of 60° is 0.5.


#12

The rotor of an alternator can turn much faster than a generator’s before it will be destroyed by centrifugal force enabling an alternator to be geared to run faster at idle and therefore charge at idle yet not be destroyed at high engine speeds. Generator brushes typically wore out before 100,000 miles. It’s unusual for the slip ring followers of an alternator to fail before 100k miles. Alternators have smooth slip rings while generators have segmented commutators enabling the alternator slip ring followers (not called brushes} to last longer. Three phase does two things: It permits more efficient use of a given weight of copper and iron components and when full wave rectified provides a smoother output wave form which would tend to make less electrical noise that might interfere with a radio.

A generator produces ac current in the rotor but the current is taken via the commutator and brushes at appropriate timing so the output is seen as dc.

The availability of relatively inexpensive and durable solid state half wave rectifiers (diodes) made the use of alternators in autos possible. An alternator also permitted a cost reduction in the regulator as a maximum current limiting relay was no longer needed, reducing the number of relays needed from three to two. Magnetic saturation in the alternator did the job of maximum current regulation.


#13

@Keith
I see you are " trigging" around now with your explanations…


#14

Have heard that a malfunctioning alternator can put out 110 volts,true?-Kevin


#15

I’ve seen 30 volts at the battery lug of an alternator.


#16

I was told by a ricky racer that under drive pulleys will lower the horse power used by the alternator when racing. Well we argued since this isn’t true. It may reduce the alternators drag at low speeds or idle, but at high speeds the alternator will take as much horsepower to turn it since the alternator load will increase even if the shaft speed is lower with underdrive pulleys.


#17

Quote from WheresRick: “I was told by a ricky racer that under drive pulleys will lower the horse power used by the alternator when racing. Well we argued since this isn’t true. It may reduce the alternators drag at low speeds or idle, but at high speeds the alternator will take as much horsepower to turn it since the alternator load will increase even if the shaft speed is lower with underdrive pulleys.” Unquote

True but there will be a very small reduction in drag due to the alternator’s cooling fan not being run as fast plus a small reduction in rotor windage loss. Also, wrapping the drive belt around a larger diameter pulley should result in a tiny reduction in friction due to less belt flexing.


#18

Ok but if you are idling any amount of time and the alternator is not putting anything out and the electrical load is discharging the battery, as soon as you start “racing” the alternator will start charging causing loss of overall horsepower.

Slowing the alternator reduces horsepower demand at very low speeds and idle, but only if it also stops the battery from charging or if the alternator stops running the vehicle electrical load. Do you really care if you have more available horsepower at idle, or would you rather have the battery charging?

Why would anyone want to not charge a battery, and actually discharge the battery at slower engine speeds, and then take horsepower away at high engine speeds to charge the battery?

The only way to ensure that the alternator is not robbing power, is to take the belt off or you can get rid of the generating losses by killing the field current. Many true drag cars have no charging system. Some hyper-milers run without an alternator hooked up.


#19

Actually Ricky Racer is kinda right. You are mostly correct about the electrical load, except that an alternator will still have an output if it is underdriven. Since most race cars have very few electrical loads, like a blower for the AC or a high powered stereo system, a little underdrive probably doesn’t even cause the battery to discharge.

Some race cars achieve the under drive by using a smaller pulley on the crankshaft, so everything is under driven, alternator and water pump. The biggest savings is with the water pump, but the same principle applies to both, when the engine changes speed, the mass of the accessories must also change speed and accelerating any mass is going to rob horsepower from the engine when it needs it the most.

The water pump is the worse offender because the coolant acts like a dynamo, it does not like to change the speed of its flow. This affects normally driven street cars as well, reducing gas mileage. I don’t know why the manufacturers don’t use electrically powered coolant pumps and just overdrive the alternator should result is better fuel economy. They gotta do something to meet the new CAFE requirements.


#20

@keith

I see your point, I am talking about a 5 liter mustang, I just call it a race car. Its a daily driven car, driven at night with the headlights, driven in the cold winter. The kid that owns it races it at a dragstrip from time to time, and street races it.

2013 Toyota Prius, has no drive belt, water pump is electric, AC is electric, PS is electric and the battery is charged from the inverter.

I believe its the first production car that has no belt.