<VV> Gens and Alts

[Frank DuVal]

Lon,

I don't know where you hear these old wives' tales, but there is so much 
wrong with your explanation from an EE standpoint....

The regulator controls the output of both an alternator and a generator 
as found on our cars.

If the regulator is disconnected from the generator or alternator, they 
both stop producing electricity, so where is this mystery "burns itself 
up" you speak of?

Now, the generator will try to self excite, due to residual magnetism, 
but without a complete circuit from the field terminal, it will not 
excite to full output.

The big difference in circuitry (on GM cars of our period) between the 
generator and alternator systems, is the field of the generator is 
internally connected to the armature terminal, so one (person or 
regulator) grounds the field terminal to get output. If the field wire 
shorts to ground, the generator will full output, and that can burn 
stuff up. The field of the alternator needs to get +12 to make power 
output, so if the field wire to the alternator shorts to ground, the 
wire burns up, but the alternator does not.

If the brushes wear out in a generator, the red light comes on, telling 
you there is a problem, but nothing "burns itself up". Just the battery 
stops charging and slowly goes dead (depending on # of accessories on). 
You can drive forever, just stopping to charge the battery. Known 
several people who did that until they could get to or afford a repair 
shop. If one is worried about burning their armature up, just disconnect 
the field wire (F on the generator) and motor on.

Both a generator and regulator limit the charge to the maximum output of 
the object during normal operation. However, if either a generator or 
alternator regulator go bad, it will drive the protected object to 
failure! There is no extra safety in an alternator regulator vs a 
generator regulator! What part of an alternator circuit" just cycles 
(stops charging)" ? Some magic brain ECU?

About the only difference I can see here is an alternator is typically 
not as stressed as a generator, since the early generators were rated at 
30 amps, and the lowest alternator rating back then was 37 amps. So for 
the same electrical loads, the alternator would be "less loaded" by the 
loads.

Now, I can agree that alternators are less trouble prone, as in these 
three reasons:

There are only two coils (relay type regulators) in a typical GM 
alternator regulator vs three coils (relay type regulators) in a 
generator regulator, so that's 1/3 less contact points, etc, to go bad,  
so the alternator regulator could be less prone to failure in actual 
use. I think repair data from back then would agree with this.

Another MTBF (mean time between failure) difference between alternators 
and generators is the brushes. Again, not something that "burns itself 
up" or causes other damage to the system, just stops charging the 
battery. The reason for more brush failure is the generator charging 
current (0 to 30 amps) flows through the two brushes. This heats them 
up, there is always some arcing, etc so they wear at an accelerated rate 
compared to alternators. Before we had alternators to compare to, this 
wear was considered normal.  An alternator just has brushes in the field 
circuit, a much less current flowing circuit (0 to maybe 5 amps). These 
brushes are much smaller, but still last a long time.

And of course the big one  for us early drivers, the weight. Not of the 
whole unit, like others who want to lose some rear pounds, but armature, 
or turning weight. Like the heavy steel fan, the combined weight of the 
armature and steel fan did cause people to throw belts when shifting 
spiritedly. But this is fan belt MTBF, not generator.

An old time rebuilder told me years ago, to make a generator last in any 
car, remember to drop a drop of oil in each oil cup when checking your 
oil. You already have the dipstick in your hand, just open the flip lids 
on the generator endbells.

Frank DuVal

ps you said rebuilt by the side of the road, you mean just two brushes, 
or changing bearings and bushings? Had a growler to check the armature?

On 4/10/2012 5:27 PM, lonwall at corvairunderground.com wrote:
> Bob - You're not as crazy as you come across in person - I too have only
> earlies (right now) and they are all converted to alternators. The
> weight issue is a good reason but more compelling is the basic theory of
> charging philosophies between a generator and an alternator.
>
> When a generator suffers from a "break" in it's charging circuit it
> shortly burns itself up. That problem can be a battery with a defective
> plate, an overtaxing of the system itself, a broken or disconnected
> wire, a malfunctioning regulator etc etc.
>
> When similar things happen to an alternator is just cycles (stops
> charging) so no damage is done.
>
> I suffer a similar fate as you did. Around 1991 I was in a caravan in my
> still generator equipped Greenbriar headed down to the Fan Belt Toss
> (Palm Springs). I told my passenger (and friend) Gary Baldwin that the
> only thing I feared on the trip was losing the generator.  Sure enough
> it was about 11 pm (In November) just out of Grants Pass and the
> generator light came on.
>
> We had a crew with us and had to rebuild the generator by the side of
> the road. It was NOT fun. I didn't have a choice.  With an alternator i
> could have kept going until at least it was convenient. With the
> generator is was SHUT DOWN NOW or burn up the armature.
>
> Lon
> www.corvairunderground.com
>