Generator question

[bnam]

I was helping a friend with his car (a 71 bus actually) which has a 1600DP engine with a generator.

Engine was not running well and the existing harness was pretty hacked up and rat bitten. The generator was connected to a local Lucas type electromechanical voltage regulator that did not appear to be regulating well as it would show 15V when revved up.

I built new harness for the engine back to stock spec down to wire size and colors and installed a new Bosch electronic voltage regulator. Engine started up and ran well and the poor running problems were solved.

But, I discovered that the generator was no longer charging. At idle it put out 0.5V which got to 1.5V at about 2000rpm.

I rechecked all wiring. I thought I may have damaged the generator as the D+ stud did turn when I unscrewed the nut to remove the wiring. I suggested he get the electrician who had originally repaired/rebuilt the generator to have a look.

Today the guy came over and he cryptically said that the Bosch VR was not a match for the generator. He refitted the old VR and voila, there is voltage output again.

Since VW aircooled parts were not available in India until a few years ago, many cars run with locally rebuilt generators with locally sourced VRs.

My question is, when a generator is rebuilt, is it possible that it was rebuilt in such a way that it no longer works with a Bosch regulator (or more specifically) with an electronic voltage regulator, but works with an electromechanical regulator? Or should all 12V regulators and generators be interchangeable?

The resistances I measured D+ to DF was in the range of 25ohms -- is there a Bosch spec I could compare against. D+ to D1 was about 4ohms

While it is possible that the electronic VR was a dud, this is the second such instance of a Bosch VR not working on a locally rebuilt generator that I've come across. I feel personally involved as in both cases I had recommended that they get the electronic Bosch VR as I'd had great experience with it.

I will check the new Bosch VR in my car to see if it is a VR issue or not. But, if it is ok as I expect it to be, what could be the explanation for why it does not work?
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1971 1302LS Convertible (RHD) owned since '74
Click to view image
1965 Karmann Ghia Coupe - under restoration
1966 Fiat 1500 Cabrio (with 1600 Twin cam)
1952 Citroen TA 11BL

[bnam]

I think I may have found the answer.

https://mgaguru.com/mgtech/electric/et231.htm

Apparently Lucas generators are wired differently (internally) than Bosch generators. And when the Bosch generators are rebuilt here, some/all of them may have been rewired in the Lucas style since old school electricians seem to be more familiar with Lucas electricals (which are also manufactured in India).

Apparently, Bosch VRs don't work with the Lucas style wired generators. But, Bosch generators seem to work with the local Lucas style VRs without any changes. Don't have an explanation for that yet.[/url]
_________________
1971 1302LS Convertible (RHD) owned since '74
Click to view image
1965 Karmann Ghia Coupe - under restoration
1966 Fiat 1500 Cabrio (with 1600 Twin cam)
1952 Citroen TA 11BL

[busdaddy]

Could be, early Lucas dynamos use a positive field, VW uses a grounded field, if it's been rewound it could happen.
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[bnam]

Doesn’t need to even be rewound per my understanding of the article. Just the field needs tobe rewired. The end that was connected to D+ is connected to the DF stud which now becomes F, and the end that was connected to DF is now grounded to the body or the ground brush. Theoretically, should be easy to undo that change.
_________________
1971 1302LS Convertible (RHD) owned since '74
Click to view image
1965 Karmann Ghia Coupe - under restoration
1966 Fiat 1500 Cabrio (with 1600 Twin cam)
1952 Citroen TA 11BL