DC Generator in older cars 1

[Paulista]

Does anyone know what type of DC Generator was standard issue on cars, prior to the adoption of the Alternator cum 3-phase (full-wave) rectifier pack ?

Was it a compound-type of DC Generator - shunt + series field winding - or was the field winding excited independently ?

What type of Voltage regulator was supplied on these DC Generators ?

 

[Warpspeed]

From memory the actual generator design varied a bit from manufacturer to manufacturer, but basically they all had a separate main (shunt) field winding that was externally controlled from the voltage regulator.

The voltage regulator box was entirely electromechanical, no diodes anywhere. As I remember it, there were usually two or three relay looking things that controlled the charging voltage, maximum current, and a cut out to prevent the battery from feeding back into the armature if the engine stalled or idle Rpm was too low.

All the voltage and current regulation was done by making or breaking a mechanical contact in series with the field winding. An ancient form of mechanical pulse width modulation. They actually worked pretty darned well when set up properly.

Some old books and original workshop manuals might give more details.

 

[Paulista]

Many thanks Warpspeed.

I suppose one could retro-fit a standard, low-cost, solid-state DC Motor field-current controller to successfully replace one of these earlier electro-mechanical regulators, which are probably not available anyway.

Or a switching voltage regulator IC as used on power supplies, adequately doctored ?

Th reason I am asking is that a chap has one of these DC Gens on his vintage boat and needs a new regulator.

Actually, I have a pair of these all-electro-mechanical regulators that were used on early 60´s Alternators. No solid-state devices but an assortment of relays that made for electro-mechanical PWM of field current, how efective I do not know.

I presume the respective Alternators were equipped with selenium diode rectifiers, as silicon hybrid (discrete + IC) and/or power devices were probably still not out there in the market.

 

[Warpspeed]

I think you probably have two alternatives. Either replace the whole generator with a modern internally regulated alternator, or replace the electromechanical regulator box with something completely electronic.

If the generator itself is in reasonable condition, how about stripping out the internals of the electromechanical regulator box and fitting an electronic regulator inside? It could all then appear "original" on the outside so as not to offend the purists.

I have never attempted anything like this myself, but I can speculate on how it could be done.

The first step might be to fit a single large silicon alternator rectifier diode in series with the main generator output lead. That will prevent current back-flow through the armature when the engine is stopped or below generator cut in voltage. The diode will obviously require a suitably sized heat-sink.

A standard alternator regulator module should probably be able to regulate the generator field current, just as it did in the original alternator.

Power for the electronic regulator module should come from the armature through a second smaller silicon diode, and also from the original dash warning lamp.

Basically you just duplicate a standard original alternator circuit, but now the generator armature uses the commutator to create dc, whereas an alternator uses three phases and six diodes to do exactly the same thing.

I am sure it should work. Just check the generator field winding current is not significantly higher than the alternator field winding current, or at least not high enough to fry the regulator module. That should give you a pretty good temperature compensated charging voltage, and it should be a lot more reliable.

 

[Paulista]

Warpspeed,

Now that was very clever of you !

I am nearly sure it should work, as I have found no reason to the contrary, provided the field current requirements are not disparate.

In the worst case, use an Alternator VR of higher field-current rating.

Thanks

 

[evelrod]

You guys are 're-inventing the wheel'. All this is available over the counter from several vintage auto emporiums, world wide. I have been using solid state regulators with OEM DC gens on Model A Fords for 15 years, cheap, too.
I also converted an early AC Delco OEM DC regulator from a 1937 Buick Roadmaster to solid state...with parts from Radio Shack...< $10!!!(That particular conversion also required a new mechanical starter motor circuit as well).
This is one 'do-it-yourself' project that works very well, but all the mechanical regulators are still available. How expensive and reliable these repro units are, I do not know. I seldom get repro items that don't need some "tweeking".

Rod

 

[TChronos]

Relay type generator regulators are still made by a current incarnation of Lucas. Try any place that specializes in British cars.