Solid State Regulator for Lucas Generator

http://farmallcub.com/phpBB2/viewtopic.php?t=94792

Dynamo current and regulator circuits...

https://www.yesterdaystractors.com/TO20ALT12V_12-Volt-Conversion-Kit_25544.htm?gclid=Cj0KCQiAk-7jBRD9ARIsAEy8mh7fs6vn81AIxOgBETRnxzqUITH8ppY7v4goaO-JYYwAAJDHwGrWrVYaArYKEALw_wcB

https://www.yesterdaystractors.com/cgi-bin/store/model_parts.cgi?SearchArea=Ferguson&&md=TE20&cat=Electrical%20System&r=mcats

Thanks SE,I am aware of the alternator conversion.I have converted several old tractors to 1 wire alternators but I am looking to keep this one as original in appearance as possible.

The original mechanical voltage regulator controls voltage by varying the field current by constant on-off control of a relay.

Can I use an alternator voltage regulator to control the field current on the generator?

http://constructionmanuals.tpub.com/14273/css/Alternator-Output-Control-50.htm

..."An electronic voltage regulator performs the same operation as a contact point regulator, except that it uses transistors, diodes, resistors, and capacitors to regulate voltage in the system."...

The generator regulator has another (very important) function. A contact disconnects the battery from the generator when speed is to low (out put voltage too low) so that the generator will no be a motor and consume battery charge. The alternator uses semi conductor diodes but the generator rectifies by rotating. Sometimes (when cars had generators) this contact would weld and when ICE stopped generator would spin and sometimes burn belt (It could not turn over the V8). This could probably be solved by adding a diode in series which would not be needed for the alternator.

It's not an issue. The generator control box always incorporates a cut-out coil. The box is either a 3-bobbin one (cut-out + voltage reg + current reg) or, more likely with a tractor of this age, a 2-bobbin unit (cut-out + combined voltage and current reg). As you say it can give problems, or you can give yourself one if you accidentally close the cut-out contacts while the engine isn't running, but that's another story. I've never heard of the generator turning and burning the belt, usually the generator can't turn and things quickly get hot, resulting in a burn-out if you don't pull the contacts apart, likely getting a burnt thumb, but it's worth it.

Thank you for reminding me of proper name (cut-out). If fan belt is a little loose the generator will spin. It happened to me (about 1968 on 1956 pontiac) when it had been charging the battery adequately before.

No problem! I didn't mean to sound as if I were saying it couldn't happen, just that I'd never seen it.

If you retain the 6V generator, you will likely not be able to safely over-excite the generator to produce 12 volts for any length of time. Separate electronic regulators are a high volume commercial design that is over 30 years old for automotive purposes. Based on the size of the packages that are now located inside alternator cases, the field current for a 12v alternator is relatively low, much less than a 6 volt generator will require at half the voltage.

Many electronic regulators are designed to be able to cool off to a heat sink that is not isolated, so your next trick will be to find a positive ground regulator, or isolated ground regulator.

My guess is to keep the appearance of the restoration, you will find the old mechanical regulator will be easiest to apply, and also easiest for the next owner to troubleshoot and repair.

If you are able to source a high current solid state regulator, you will want to measure the field current required to produce a nominal 6 volt generator output while connected to a battery, to be sure the regulator ampere rating is sufficient. The drive for the generator is usually set so the speed at idle is low, and may not produce rated voltage. This reduces wear & tear on the brushes and commutator when the engine is at normal speeds, so you may need to keep the engine above idle when checking generator output voltage.

Thanks SE and JW for the valuable feedback.

After considering the implications of the modifications,I will forgo changing anything.

The old girl starts and runs just fine on 6 volts except in very cold weather and after starting up it runs great.

This model tractor was used by Scott to carry supplies in the Antarctic expedition,so cold weather is not normally an issue.

She's still going after 70+ years,a lot of them very neglectful.

It was locked up when I found it sitting in a field with a tree growing through the front axle.

It still had an original Ferguson oil filter on it when I got it.

There was about 1 inch of crud in the bottom of the oil pan,the oil bath air filter was dry so it was inhaling unfiltered air for a long time.

Surprisingly,the valve train was clean,but a valve was stuck, but even so,it still ran good,all things considered.

The starter fields were oil saturated so I had the fields re wrapped.The brushes and bushings are the same as used in the Land Rover starter of the period.

I cross referenced the spark plugs,and they were the same as used in the old Hudson automobile.19 MM diameter.

They used what I call "Gorilla engineering" back then,and everything was twice as strong as it had to be.

Maybe she will still be running in another 70 years or so.

My hats off to Henry Ferguson and the workers at the factory in Coventry, England.

I see you've decided to leave things as they are, but to answer your original question - no, you can't use a solid-state regulator (from an alternator) to control a generator. Or a trembling contact type regulator, as some early alternators used, mounted externally.

With a generator the field current is fed via the control box, which has two sets of trembling contacts in series, one limiting output current, the other voltage. (Yours is most likely an earlier type which has only one regulating coil, but it has both a voltage and a current winding, so the operation is similar). An alternator only has a voltage regulator (built-in these days), it is self-limiting for current. How it does it I don't know, in both cases the main coils consist of heavy copper wire, so it would seem an alternator would also overload on current if connected to a big enough load, but it doesn't.

I've asked various electrical engineers over the years, including on this forum, and none has given a convincing answer.

But thinking about it some more, maybe it's to do with the inductance of the stator coils. With a typical alternator rated output 55amp, to limit it to that would need impedance about 14/55 = 0.25 ohm. At an alternator speed say 5000rpm ~ 500rad/s the inductance = 0.25/500 = 0.5millihenry. But I don't have a feel for whether the stator coil would have that sort of inductance, I might try to estimate it sometime.

If you do decide to change to 12 volt, why not just fit a 12 volt generator and regulator? The appearance is the same, and probably easier to get hold of than 6 volt. Then you can polarise it -ve or +ve ground. You just need to turn the battery round, the starter will still go the right way.

Not the lowest tech or the cheapest option, but there are alternators available for classic cars built into Lucas dynamo look-a-like shells. that would give you 12volt, negative earth and more power than Harry Fergusson could have ever dreamt of.