Best Answer gaspen , 23 October 2025 - 08:03 AM
I've contacted the manufacturer. I have to install a resistor btween D and F :
This provides a path for the initial current to feed into the field winding and get the electromagnetic process started (positive feedback loop) once it get above 3 volts the regulator kicks in and then it takes over, the resistor will have no effect on regulation but burns about 0.6 amps of current which is not an issue on a 22 amp dynamo
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Posted 07 May 2026 - 06:10 AM
he A and E connections should of course be tested first.
I assume I should register charging voltage there, right ?
****
I am a little bit confused. Some manual says that I have to measure 14V on the disconnected dynamo D terminal, others says 2-4V is enough
Testing a dynamo and checking output | How a Car Works
What's the truth ?
Edited by gaspen, 07 May 2026 - 06:11 AM.
One Carb Or Two?
Posted 07 May 2026 - 06:19 AM
he A and E connections should of course be tested first.
I assume I should register charging voltage there, right ?
****
I am a little bit confused. Some manual says that I have to measure 14V on the disconnected dynamo D terminal, others says 2-4V is enough
Testing a dynamo and checking output | How a Car Works
What's the truth ?
Yes, charging/battery voltage.
The first step in the Lucas instructions is to disconnect both leads to the generator. With a meter connected to the D terminal and earth, you should see between 2 and 4 volts. lower is no good and higher is no good. This test has nothing connected to the F terminal.
The second step is to leave the meter connected and now join the D and F terminals. You should see above say 12v as the rpm is increased. Lower than this is bad.
The tests are then repeated but doing it at the regulator end to ensure the wiring is good.
https://www.mg-cars....r/pdf/lucas.pdf
One reason I prefer the Crypton books is that they give diagrams. The Lucas books seem to assume that you have done it all before and already know where everything is.
Also don't get confused with instructions for American types of regulators as they are tested differently.
Edited by 68+86auto, 07 May 2026 - 06:21 AM.
One Carb Or Two?
Posted 07 May 2026 - 06:56 AM
he A and E connections should of course be tested first.
I assume I should register charging voltage there, right ?
****
I am a little bit confused. Some manual says that I have to measure 14V on the disconnected dynamo D terminal, others says 2-4V is enough
Testing a dynamo and checking output | How a Car Works
What's the truth ?
Yes, charging/battery voltage.
The first step in the Lucas instructions is to disconnect both leads to the generator. With a meter connected to the D terminal and earth, you should see between 2 and 4 volts. lower is no good and higher is no good. This test has nothing connected to the F terminal.
The second step is to leave the meter connected and now join the D and F terminals. You should see above say 12v as the rpm is increased. Lower than this is bad.
The tests are then repeated but doing it at the regulator end to ensure the wiring is good.
https://www.mg-cars....r/pdf/lucas.pdf
One reason I prefer the Crypton books is that they give diagrams. The Lucas books seem to assume that you have done it all before and already know where everything is.
Also don't get confused with instructions for American types of regulators as they are tested differently.
Yesterday I found this same manual that you linked here and now I follow its instructions
Now I removed the dynamo from the car, put it in the bench and turn it with a drill
TEST 1 : 2 Volts OK
TEST 2 : voltage rising with rpm OK
TEST 3 and 4 are also OK
The dynamo is in good working order
To be continued....
One Carb Or Two?
Posted 07 May 2026 - 07:28 AM
I noticed that there is a short-circuit between the D terminal and Earth on the DVR3 unit
I assume it is the fault ?
One Carb Or Two?
Posted 07 May 2026 - 09:35 AM
Probably but I have no experience with the DVR3. Is it actually a short or is there a resistance?
Edited by 68+86auto, 07 May 2026 - 09:36 AM.
One Carb Or Two?
Posted 07 May 2026 - 10:00 AM
Probably but I have no experience with the DVR3. Is it actually a short or is there a resistance?
I switched the multimeter to continuity test and it beeps.
I put together a test environment on the bench with the regulator and battery but still no charge. I am sure that the DVR3 is dead 
After that I disconnected everything from the dynamo and tested it again. Both TEST 1 and TEST 2 failed.
Then I re-polarized it to -ve earth and it became good again 
Next I will borrow an old RB106 and see how it works.
One Carb Or Two?
Posted 07 May 2026 - 11:36 AM
Out it into resistance mode and see the resistance but it does sound like the DVR3 is bad.
I think you had ignition issues recently? Did you have the plug leads off at all to check for output? If the HT circuit doesn't have an "easy" path to ground like through the plugs, it can damage electronics. So many people seem to not realise this.
One Carb Or Two?
Posted 07 May 2026 - 01:40 PM
Out it into resistance mode and see the resistance but it does sound like the DVR3 is bad.
I think you had ignition issues recently? Did you have the plug leads off at all to check for output? If the HT circuit doesn't have an "easy" path to ground like through the plugs, it can damage electronics. So many people seem to not realise this.
I never plugged off a HT lead but somehow I burned a coil recently Coil Burn - Problems, Questions and Technical - The Mini Forum
I guess there is connection between the two events.
Lesson learnt at least 
One Carb Or Two?
Posted 07 May 2026 - 03:59 PM
I've been running DVR3s for over 10 years. I bought a spare after 8 years but the original is still working well.
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