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Voltage Regulator RB106 problem


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Hi all, I seem to have a weird situation I cant fathom so looking for a voltage regulator expert!

My voltage regulator wont operate the cut out solenoid.

I've tried two different voltage regulators (both tested the cut out independently with 12v supply and the cutout worked fine)

I have also tested the C40 dynamo independently and is giving out plenty of voltage but when connected to the voltage regulator it wont go past 7-8 volts which is too low to trip the cut out. (as needs roughly 12v)

So I'm not sure which way to go here as both elements seem good separately but not when connected!

Where is the voltage drop occurring I wonder!!!

Anyone any ideas?

Thanks

Edited by DSJ666
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If the dynamo isn't giving much voltage when on the car but tests ok on the bench, it is possible it isn't getting enough field current.  I would start by checking the connection from the regulator F terminal to the small spade on the dynamo (yellow/green wire). 

How did you test the dynamo independently?  In case you don't have this, here is the Lucas test and adjustment instruction leaflet:

https://mgaguru.com/mgtech/books/pdf/Lucas_Generator_and_Control_Box_Tests.pdf

 

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1 hour ago, RobH said:

If the dynamo isn't giving much voltage when on the car but tests ok on the bench, it is possible it isn't getting enough field current.  I would start by checking the connection from the regulator F terminal to the small spade on the dynamo (yellow/green wire). 

How did you test the dynamo independently?  In case you don't have this, here is the Lucas test and adjustment instruction leaflet:

https://mgaguru.com/mgtech/books/pdf/Lucas_Generator_and_Control_Box_Tests.pdf

 

Thanks for the link...some really good info to absorb there!

I think I actually did what is stated on the instruction leaflet for in car dynamo testing. (Part 1 Test 4 Reading A)

I connected a short cable link between the field F cable from the dynamo with the D dynamo cable (both disconnected at the regulator end) then put my voltmeter between the link and earth. Started the engine and slowly increased the revs, it was giving increasing voltage up to ~20V.

So that seems OK so far and should mean the dynamo and F & D cables to the box are good.

I think I'll now work through the rest of the test leaflet and see what I can deduce.

 

Thanks very much for your input its spurred me on! :D

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7 hours ago, Z320 said:

Did you plug the earth cable to the regulator?

If yes, what about the other end of the cable?

I'm not sure what you mean? The dynamo test is total independent of the regulator, just disconnect the F & D cables from it and do the link etc.

Or do you mean is there a bad earth to the regulator? If so, it seems good from a continuity test.

As RobH suggested, I'm now thinking its somehow related to the field current being reduced through the regulator and thus limiting the dynamo output voltage. I'm going to give some attention to the voltage regulator side of the control box.

I was previously focusing on the cut out relay as it was that which wasn't functioning but I now think that's a symptom and not the cause. 

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This is my own sketch of the RB 106 from an article I wrote some years ago for the German TR IG magazin

7KstOkYCORRtutRYyBcCSd7N8OwcJYGbDNmIFTSJ

You see, the coil of the cut out (right side) and the coil of the regulator (left side) are connected inside to terminal "E",

and E needs a proper connection to the frame / ground.

Edited by Z320
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Thanks Z320 for that diagram, do you have the key for the numbers? (I appreciate it'll probably be in German!)

Anyway, I've made a great leap forward!

Bob you are quite correct, the regulator contacts are the crux of the issue. I didn't realise that the cut-out relay function is dependent on the regulator even when they (allegedly!) closed and are not operating i.e. before the cut-out operates.

It would appear with mine that the regulator contacts when closed could not pass the correct field current to allow the generator to create the ~12.5V necessary to operate the cut-out relay. This makes total sense to me now as the function of the regulator is to control the field current and limit the output of the generator. Except in my case it was over limited due to pitting/oxide etc. so couldn't get past stage 1 (operating the cut-out)!

I worked all this out with the help of the Lucas Test Leaflet (linked above), so thanks to RobH for that. Bridging the regulator contacts with a screwdriver miraculously allowed the cut-out to operate!

Having now established it was the regulator contacts I decided to bite the bullet and follow these very comprehensive repair instructions https://www.mgexp.com/phile/3/191288/REPAIRING_THE_STANDARD_RB106.pdf and refinish the contacts using a small dremel disc mounted in a pillar drill to ensure a flat and square surface. The contact surface was massively pitted to start with but ended up blemish free, see photo.

So after reassembly I'm now back in business, just need to spend a bit of time setting it up correctly as it seems a bit off the specified values. But I suppose its done alright for the last 50 odd years, just hope now it'll last a few more!

I think I'll also go the extra mile and as suggested in the repair instructions add a snubber diode across the field coil connection and earth to further preserve the contacts.

Thanks to all above for your assistance and the power of the forum!

Plus I've solved my lifelong mystery of figuring out how a control box actually works! :D

20210616_202313.jpg

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Glad you've sorted it. If that is a Lucas original you're all set for another half - century. Not necessarily the case with modern copies as they often don't have the correct contact materials. 

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Hi DSJ666,

of course I can expain the numbers, but I could be wrong with by translation of some technical terms.

The arrows in the current lines are the directions the current can flow

1) the cut out (relais), contact only closes when voltage is higher than the battery voltage

2) frame / body of the RB 106

3) "anchor" of the cut out relais with a "to close" contact

4) current coil of the cut out (relais), helps to hold the relais close when closed, more urgend: will delete the remaining field and helps to opens the conatct fast again when the current flow reverse!

5) voltage coil of the cut out(relais), will close the contact when voltage is high enough - without 4) it gives the contact only free by spring load when the battery is discharged down to about 11 - 8V, 9V on my RB106

6) the regulator (relais), always closed, opens to reduce the current to the field coil when when the voltage is too hight or / and the current is too high

7) "anchor" of the regulator relais with "a to open" contact

8) current coil(s) of the regulator (relais), open the contact and reduces the current to the field coil when the current to high

9) voltage coil of the regulator (relais), as 7) when the voltage is too high

10) resistor, commonly known for a reduced current from D to F when the regulator contact has opened, in my opinion to reduce the spark on the contact

11) "12V" DC generator, indeed it can supply much more voltage, if not regulated

12) current gauge in the dashboard

13) battery 12V

14) consumers without ignition

15) ignition switch

16) consumers over ignition

17) charging control lamp in the dashboard

If you have any question please ask.

The atricle in 3 parts you find here, sadly I wrote it in German:

- basics for beginners

- for those who want know more

- for the workshop

Ciao, Marco 

Edited by Z320
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DSJ666,

Over the years I have accumulated various documents that address Lucas devices, including course manuals on the generators and regulators. I have attached the course manual that addresses the operation for the RB106 regulator. Hopefully this will help you to get a full understanding of the beast.

Kind regards

TT

Session5_GeneratorControl.pdf

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