Why do ppl think that more electrical current draw == more drain on engine? - Page 2 - PeachParts Mercedes-Benz Forum

winmutt · #16 08-11-2006, 03:49 PM

Quote:

Originally Posted by vstech

a generator/altanator uses electromagnets to convert mechanical energy into electrical energy.
the more electrical load on the altanator, the stronger the current passing through the windings, hence the stronger the magnet will be pulling against the iron stator. the stronger the magnetic field, the more hp is required to turn the winding.
directly proportional to power used. perhaps you are correct in that the altanator is designed for a specific power output, and that output will not change by rpm, but the regulator will drop in and out the field based on demand.
Hmm, perhaps you are confusing power with amperage... the same 14.4 volts will be produced no matter how much you turn the rpm's due to the VOLTAGE regulator bringing in and out the circuit.
imho
John

Yes and no. In a generator, natural magnets are used hence the same power is always generated, the regulator dissapates the energy. On an alternator that magnetic field is regulated by the regulator. So in reality an alternator is much more efficient than the generators of old.

pawoSD · #17 08-11-2006, 03:52 PM

Quote:

Originally Posted by winmutt

Yes and no. In a generator, natural magnets are used hence the same power is always generated, the regulator dissapates the energy. On an alternator that magnetic field is regulated by the regulator. So in reality an alternator is much more efficient than the generators of old.

Very true, imagine how much fuel/energy would be wasted if a car's alternator always put a multi-horsepower equivalent drag on the engine....good thing it doesn't most of the time!

Jeremy5848 · #18 08-11-2006, 03:54 PM

Quote:

Originally Posted by winmutt

... How is this more advantageous than a generator?

In a generator, the load current is supplied from the rotor, with rectification (turns AC into DC) by the commutator. All of the energy drawn by the various loads must pass through the commutator and the brushes. When generators are built larger to provide more current for option-loaded cars, brushes and commutator must be made larger and wear faster.

In an alternator, the current to the load comes from the stator, which does not turn. The rotor supplies the magnetic field, which requires much less current and goes through slip rings. The stator winding can be made larger and with heavier wire so that more current can be supplied.

Additionally (and I no longer remember the physics of WHY), an alternator supplies current sooner (at lower RPMs) than a generator. The disadvantage in an alternator is that the voltage produced is AC and must be converted to DC using diodes. Failure of one or more diodes is a common alternator failure mode. One of the reasons why alternators weren't around before (approximately) the 1960s was that reliable semiconductor rectifiers weren't available.

jrgslg · #19 08-11-2006, 03:57 PM

Also note when a huge load is on the alternator how hot it physically gets,and how it drags the engine rpm down trying to carry the load.

Jeremy5848 · #20 08-11-2006, 04:10 PM

Quote:

Originally Posted by winmutt

Yes and no. In a generator, natural magnets are used hence the same power is always generated, the regulator dissapates the energy. On an alternator that magnetic field is regulated by the regulator. So in reality an alternator is much more efficient than the generators of old.

In the 1970s, BSA/Triumph produced a motorcycle with such a generator. It had a huge zener diode on a unique and very recognizable sunburst-shaped heatsink that was mounted just under the steering head. The generator ran wide open and the zener was used to "throw away" any unnecessary current, i.e., turn it into heat. Modern generators (like the one in my wife's 1969 VW Beetle) have a regulator that controls the current to the stator and work very much like a more modern alternator.

Modern regulators, as has been said, whether mechanical or electronic, control the current to the alternator's rotor through the slip rings based on the load. When the electrical system "calls" for more current, the regulator increases the current to the rotor. That generates a stronger rotating magnetic field and hence more current is generated as the "lines of force" (a convenient fiction) are cut by the wires in the stator.

There are some losses (heat) involved due to friction and resistance but to at least a first approximation, a properly designed, built, and operating alternator-regulator system generates no more current that the load wants. No current is deliberately thrown away.

The load on the engine does indeed increase as the electrical load increases but it is hard to observe in normal every day operation. As has been mentioned in an earlier thread, one horsepower equals 746 Watts, so an alternator, even a big one operating at maximum output, does not present that much load. Nevertheless, an idling engine is in a balanced state and any load will cause it to slow down, as people here have noted. Large alternators are just one of the many accessories that our modern engines must power. All of it decreases available power to the wheels and increases fuel consumption, generates more heat, and gives us more to repair.

Wes Bender · #21 08-11-2006, 04:25 PM

No such thing as a free lunch. If you draw more amperage (generator OR alternator), you will need more horsepower to turn it. Try this test: Loosen the alternator belts just a bit. Start the engine and then rev it. Shouldn't be any belt squeel. Now turn on the lights and rev it again. Probably get some belt squeel this time. End of test. Readjust the belts and drive on enlightened.

fastpakr · #22 08-11-2006, 04:35 PM

As another illustration - this is the reason that alternator warranty's are typically voided automatically if the battery is not fully charged prior to installation of the alternator. The load on the alternator of fully charging a depleted battery can generate enough heat to burn up a brand new unit in some cases.

janko · #23 08-11-2006, 04:46 PM

wilmutt(?) should enroll in a junior college that offers a course in remedial physics for high schoolers. jmo.

winmutt · #24 08-11-2006, 04:51 PM

Quote:

Originally Posted by Jeremy5848

In the 1970s, BSA/Triumph produced a motorcycle with such a generator. It had a huge zener diode on a unique and very recognizable sunburst-shaped heatsink that was mounted just under the steering head. The generator ran wide open and the zener was used to "throw away" any unnecessary current, i.e., turn it into heat. Modern generators (like the one in my wife's 1969 VW Beetle) have a regulator that controls the current to the stator and work very much like a more modern alternator.

I have a '69 Kawaksaki A7 Avenger that has the heatsink.

You have the BSA?

winmutt · #25 08-11-2006, 04:52 PM

Quote:

Originally Posted by janko

wilmutt(?) should enroll in a junior college that offers a course in remedial physics for high schoolers. jmo.

Thanks. I was unaware of the fact that the alternator had a electromagnet that was generating the field. Hardly a need to go to remedial physics.

Brian Carlton · #26 08-11-2006, 04:57 PM

Quote:

Originally Posted by winmutt

Thanks. I was unaware of the fact that the alternator had a electromagnet that was generating the field. Hardly a need to go to remedial physics.

In reality, it's far simpler than all of the aforementioned discussions.

If the alternator took the same load from the engine, under all conditions, you'd be getting energy for free at some point..........and that's impossible.

Jeremy5848 · #27 08-11-2006, 05:31 PM

Quote:

Originally Posted by winmutt

I have a '69 Kawaksaki A7 Avenger that has the heatsink.

You have the BSA?

No, just remember seeing them as I rode past on my alternator-equipped BMW.

The heatsink was very distinctive and I was jealous until I discovered what it was.

winmutt · #28 08-11-2006, 05:39 PM

Quote:

Originally Posted by Brian Carlton

In reality, it's far simpler than all of the aforementioned discussions.

If the alternator took the same load from the engine, under all conditions, you'd be getting energy for free at some point..........and that's impossible.

If the electro magnet did not adjust it would be the same load. Youd just have to get rid of the extra power, eg the heatsink.

winmutt · #29 08-11-2006, 05:40 PM

Quote:

Originally Posted by Jeremy5848

No, just remember seeing them as I rode past on my alternator-equipped BMW.

The heatsink was very distinctive and I was jealous until I discovered what it was.

Its my winter project. I hope mine comes out looking somewhere near as nice as this one. Currently its just the frame and some wheels

.

OMEGAMAN · #30 08-12-2006, 01:20 AM

Quote:

Originally Posted by Jeremy5848

In the 1970s, BSA/Triumph produced a motorcycle with such a generator. It had a huge zener diode on a unique and very recognizable sunburst-shaped heatsink that was mounted just under the steering head. The generator ran wide open and the zener was used to "throw away" any unnecessary current, i.e., turn it into heat. Modern generators (like the one in my wife's 1969 VW Beetle) have a regulator that controls the current to the stator and work very much like a more modern alternator.

Modern regulators, as has been said, whether mechanical or electronic, control the current to the alternator's rotor through the slip rings based on the load. When the electrical system "calls" for more current, the regulator increases the current to the rotor. That generates a stronger rotating magnetic field and hence more current is generated as the "lines of force" (a convenient fiction) are cut by the wires in the stator.

There are some losses (heat) involved due to friction and resistance but to at least a first approximation, a properly designed, built, and operating alternator-regulator system generates no more current that the load wants. No current is deliberately thrown away.

The load on the engine does indeed increase as the electrical load increases but it is hard to observe in normal every day operation. As has been mentioned in an earlier thread, one horsepower equals 746 Watts, so an alternator, even a big one operating at maximum output, does not present that much load. Nevertheless, an idling engine is in a balanced state and any load will cause it to slow down, as people here have noted. Large alternators are just one of the many accessories that our modern engines must power. All of it decreases available power to the wheels and increases fuel consumption, generates more heat, and gives us more to repair.

What are the chances of that! Last night at work we were looking at an old BSA and that zener diode and heat sink was the first thing I noticed about the bike. Neither of the guys I was with could tell me what that was. Now I know. Cool.