Modern auto alternators -vs (old) auto generators?

[Ed_Flecko]

I was chatting with someone this weekend who made a statement that's different than how I understood car alternators -vs the old generators that cars were equipped with function.

He said that the alternators of today shouldn't be thought if as "battery chargers"; he said alternators are really only intended to power the cars' electrical system, and even then only at higher than idle RPMs. He said that it's very likely, especially if a car is driving at low RPM as in stop and go traffic, that the battery is actually subsidizing the output of the alternator to keep the car running and is, therefore, slowly discharging your battery! He said the typical alternator *can* keep a healthy battery charged, but only at higher than idle RPMs.

I've always thought that was the major advantage of alternators -vs the old generators (remembering my old, VW bug) in that alternators produced full output, even at idle, but generators DO produce more power as the RPMs climb.

Am I wrong?

Thank you,
Ed

 

[Rand]

its easy to tell if the alternator is being overpowered at idle.. check your voltage.. if its over 13v its the alternator.. if its 12.x its the battery helping out. this would normally happen from a large aftermarket audio system with headlights, blower etc all running.

in my experience it takes around 1500-2000rpm to produce full output from an alternator.. (might not be all alternators)

so yes you are incorrect?.. but the other guy isnt right either.

 

[bdcardinal]

With the battery management systems alternators can be "turned off" when needed. The Police Interceptor Crown Vics and Mustangs of certain model years had a clutch on the alternator pulley.

 

[emmett442]

Generator vs Alternator = DC vs AC conversion

 

[Ed_Flecko]

Originally Posted by Rand
yes you are wrong.. but the other guy isnt right either.

O.K., do you want to correct us?

Ed

 

[Rand]

Originally Posted by Ed_Flecko
Originally Posted by Rand
yes you are wrong.. but the other guy isnt right either.

O.K., do you want to correct us?

Ed


already edited in my post didnt mean to post that fast.

and I would like to say what I said may not apply to all models and I dont know much about the difference between generators except alternators produce AC which is then rectified to DC.

 

[Ed_Flecko]

Originally Posted by Rand
its easy to tell if the alternator is being overpowered at idle.. check your voltage.. if its over 13v its the alternator.. if its 12.x its the battery helping out. this would normally happen from a large aftermarket audio system with headlights, blower etc all running.

in my experience it takes around 1500-2000rpm to produce full output from an alternator.. (might not be all alternators)

so yes you are incorrect?.. but the other guy isnt right either.


Thank you.

Can you tell me how to safely check the outputs as you suggest?

Ed

 

[Quattro Pete]

Originally Posted by Ed_Flecko
Can you tell me how to safely check the outputs as you suggest?

Connect your DMM (volt meter) to the battery?

 

[WyrTwister]

Yes , connect volt meter to battery posts . If the reading is " low " , then check it at the large positive terminal on the alternator and the frame of the alternator . Any significant difference would indicate voltage drop between the alternator and battery positive and battery / frane negative ( ground ) .

If the alternator is doing full charge , expect a high 13 to low / mid 14 volts .

I read newer cars play " tricks " with charging , to get better MPG numbers for " CAFE " regulations ? I think older alternators made system performance / reliability the priority ?

 

[Yah-Tah-Hey]

My understanding is that the alternator light will illuminate if the battery is powering the system. If not, the alternator is supplying the current.

 

[CR94]

Originally Posted by Yah-Tah-Hey
My understanding is that the alternator light will illuminate if the battery is powering the system. If not, the alternator is supplying the current.
If current demand exceeds available alternator output (typically with heavy electrical load while engine is idling), then the battery is contributing some current to make up the shortfall, but the alternator is contributing too (assuming a healthy system). The idiot light probably would not come on in that circumstance. The light came on in my Mazda only if the alternator speed was lower than at normal idle speed (including stopped), but unfortunately not when the alternator ceased functioning because the brushes in the alternator wore out.

Generators had low output at low speed, too, despite what Ed_Flecko's friend claims.

 

[Oily_Thing]

Another difference: generators need to be polarized before being installed.

 

[Yah-Tah-Hey]

Another difference: generators need to be polarized before being installed. [/quote I had forgotten about that. Isn't that what they used to refer to as "flashing the field?" If I remember correctly, it was done with the battery, but I can't remember the procedure. Was it done using the current relay terminal on the voltage regulator? (Three Unit control) The old voltage regulators had three separate components, voltage regulator, current regulator and reverse current relay. The battery would discharge back through the generator if the reverse current relay failed to open on shutdown.

 

[CT8]

An alternator is a generator. I have worked on both and the alternator is a far superior generator.

 

[CT8]

An alternator is a generator. I have worked on both and the alternator is a far superior generator.
Originally Posted by Yah-Tah-Hey

Another difference: generators need to be polarized before being installed. [/quote I had forgotten about that. Isn't that what they used to refer to as "flashing the field?" If I remember correctly, it was done with the battery, but I can't remember the procedure. Was it done using the current relay terminal on the voltage regulator? (Three Unit control) The old voltage regulators had three separate components, voltage regulator, current regulator and reverse current relay. The battery would discharge back through the generator if the reverse current relay failed to open on shutdown.

The battery can discharge the same way if a diode fails as well.

 

[cwilliamsws6]

I have a custom wound 3-phase 250-amp alternator on my CR-V because I have a competition audio build. My car idles around 800RPM and at that speed my voltage is 14.4, when driving it'll bounce around between 15 even and 14.2 depending on how much current I'm pulling from it.

 

[andyd]

The neatest thing about generators is that you could start a car without a battery. You had to get it going fast enough to spin the engine in gear until enough spark was generated to fire the coil.

 

[eljefino]

When Mopar came out with the alternator in 1960 they advertised it as being able to charge at idle, which is something that was more challenging before. That car needed a few amps for the ignition coil and the fuel gauge, and that's about it, unless they turned on some lights!

Your typical alternator makes 40 amps at idle and 100 driving down the road. You need at least 20-25 to run now, including the heated o2 sensors and high pressure fuel pumps. If your rad fan kicks in, you might indeed go over what's supplied.

The human ear is very good at noticing changes in pitch. If you have the HVAC fan running, you'll hear it slow down if there's a voltage drop. Rare. Most likely in traffic with the AC blasting.

There's a "dead zone" in battery chemistry that neither charges nor discharges. If you draw too much, you'll dip through this zone pretty quickly, and your system voltage will sag from the low 14s to the mid-12s. This is why cop cars have heavy duty batteries-- dumb if they never turn them off, but they idle a lot and can start losing power, which comes back when they hit the road again.

Generators put 100% of their current through field brushes. This wears them out faster. They also pretty universally came with vibrating-points type regulators, which were awful, but better than the manual wild-s-guess type you'd see in the 1920s- early 30s.

 

[clinebarger]

Most so called custom 250 Amp alternators couldn't output 250 Amps if it they were struck by lightning. A lot of Competition Audiophiles around here run two 170/200 Amp alternators, Each having dual Bridge Rectifiers......For a total of 24 Diodes.

Of course there are real 250 Amp alternators with 12 Diode Rectifiers. They run $450 & up.

 

[Dinoburner]

Both alternators and generators produce more amps as rpm increases, alternators start out at a higher output due to superior design.
Generators at idle put out very little power and required more maintenance.