Desoto s-11 generator upgrade

[tom61]

When the generator of my s-11 Desoto would not spin anymore (spin test), I bought an untested original chrysler generator.It looked almost the same as the one that came on the car when I bought it. The only difference being that the 'new' one is much larger and is rated at 50amps, while the previous one was only 35 amps.

I tested the generator and I am certain that it works good. I also cleaned it very well.

The new generator is larger, but it fits perfectly into the mounting screws and the pulley is the same width though larger diameter than the old one( perhaps this was an upgrade generator????)It is also in-line with the belt.

 

My question is, should the ammeter show a larger charge rate?(i.e. Should the ammeter needle move to over the 0 mark to the charging side, 10amp for example?)

 

From what I know( please correct me if I'm wrong) these old generators would not charge when engine is at low rpm (at idling for example).

But now that I installed a higher amp generator, should this change?I'm also curious to know how does this change the voltage regulator, as I installed a brand new one that doesn't have a amperage rating on it.

 

 

Thanks for any help and advise.

[TerryB]

The new generator is capable of supplying more amps, 50 vs 35 than the old one.  It will only supply the amount needed to keep the car up and running as determined by the voltage regulator.  If you had lots of accessories that took a lot of power, your new generator is easily able to supply it.  I'm not sure if the regulator has to be matched to the gen output.  Police cars and ambulances would be common uses for higher output generators.

[tom61]

But if it is able to supply 50 amps, why does the ammeter not show 'charge' when idling? Is it because It is able to output 50amp only at high rpm?

Or maybe the new regulator needs to be adjusted?

[TerryB]

Yes, regardless of rated output, it's the spinning action of the generator that produces the output power.  The generator is XX output at a certain rpm.  The advantage of an alternator is it takes less rpms to make current output.

[Rusty_OToole]

The generator output depends on how fast it is turning. Turn it twice as fast, get twice as much electricity. To control this they put on a voltage regulator. It caps voltage, and controls amperage to match the needs of your battery and electrical system.

 

In normal circumstances the car can easily run off the battery for a few minutes then charge up once you get rolling.When the engine is idling the generator is not turning fast enough to make much electricity. This is not a problem unless you do a lot of driving in city traffic, in winter, with the headlights, heater, windshield wipers and radio all on at the same time.

 

They made different generators for different uses. It is possible a Chrysler got a bigger generator because it had more power using accessories.

 

You should not notice any difference on the ammeter. The regulator will control the output and keep it in the correct range.

[Bloo]

Yes, exactly.

 

The generator current rating is how much it can stand without burning up. The actual limit is set inside the regulator. If it is a regulator that was for the original generator, the maximum current you will get is likely 35 amps. This is an adjustment.

 

If the regulator is new, it probably is riveted shut. If you need more than 35 amps, consider going back to your old regulator,, and learning how to set it up from the manual.

 

The generator will only generate enough current to maintain the system voltage. The system voltage is another setting inside the regulator. If the car only needs 5 amps to maintain the system voltage, then you only get 5 amps. This is just as true with a 200 amp alternator.

 

Since the generator only charges as hard as it needs to,  the big one will not put out any more than the smaller one, unless the smaller one was loaded to the limit. Even then, you would have to change the current limit in the regulator before you would get any more.

 

Ammeters typically are wired so they only show the current charging (or discharging) the battery. You usually wont see any difference on the ammeter (from a bigger generator) unless you have exceeded the current output the system is set for.  If you set current limit higher, a dead battery will swing the ammeter higher while it recharges.

 

Generator cars don't keep up at idle, and dim at stoplights with the lights on. Alternator cars may have about 1/2 their output available at idle and usually do not. In normal use, this really doesn't make any difference.

 

All the above applies to post-1939 generator systems with 3 relays inside the voltage regulator. Old prewar third brush systems are whole different can of worms.

 

 

[tom61]

Thanks for all the help. Although I have not had a 'dim lights at idle problem' , and the system seems to be charging correctly, I would really like to prevent this.

 

Would it be good to replace the generator pulley by one with a smaller diameter(old one for example) so that the larger generator spins faster at idle and thus has a higher output?

 

 

 

[Bloo]

Maybe. If you spin it too fast though, the centripetal force makes the armature explode (windings come off). There is a reason they set generators up the way they do. Nevertheless, some calculation might be in order. You might not have the same pulley size as you did before. Something close to the old one is probably a good guess. If it were me, I would leave it alone, doubly so because you don't notice it dimming.

 

This is always a game, trying to spin it enough without spinning it too fast. It is true with alternators, too. Alternators have more range due to the rotor construction (it's tougher), and also the fact that they can start charging earlier. It is still a game. The MoPar 340 engines had a great big pulley on the alternator. This was for 2 reasons, minimizing the horsepower load on the engine, and also not overspinning the alternator on a car that was going to be revved high a lot. Those cars dimmed at stoplights just like car with a generator.

 

I once had a car (modern)  that ran over a pretty wide RPM range, and had standard shielded metric bearings in the alternator. It hung down low where the alternator fan sucked in road dirt, water, snow, bugs, rocks, and anything else that happened to be flying low. The bearings were of course bad. I remember thinking how insane the maker had been to put shielded bearings in when sealed ones are readily available in the same standard metric sizes. I put in sealed bearings. The next time I had it apart, the seals looked kind of funny. They were melted. A little math revealed that at redline, I had exceeded the RPM rating of the seals by quite a bit. Even melted, the sealed bearings kept dirt out a lot better than the shielded bearings did, so I continued to use them.

I guess it boils down to what you think you can get away with.

 

Edited October 11, 2017 by Bloo (see edit history)