cookie Posted May 3, 2022 Report Share Posted May 3, 2022 Hi, A friend has an issue with charging on his 3a. Disconnected the dynamo wiring and ran the car. Output from the D terminal was only around 2.5 volts. When connecting the D and F terminals together the voltage was very high, around 30v We would be very grateful for any ideas. thanks Dave Quote Link to post Share on other sites
RobH Posted May 3, 2022 Report Share Posted May 3, 2022 (edited) Looks as though the dynamo itself is OK - with no field current you get little output 30V is in the right ball-park for for full field excitation. That could mean the control box is not supplying sufficient field current to the dynamo. As a quick first check , look at the continuity of the yellow/green wire from F on the control box to the dynamo field terminal, in case the wire has broken internally. Also check all of the other connections to the box including the earth. If those checks are OK it must be the control box itself. What are the symptoms he is seeing? Does the ignition lamp go out or remain on? After starting, can you see a large charging current on the ammeter which decays towards zero after some time? The control unit is not easy to fix or adjust - about the only thing you can do is to clean the regulator contacts very carefully using very fine emery-paper, taking care not to bend anything or change adjustments. That might fix things temporarily at least. Doing a proper repair and recalibration is not really a DIY thing and is best left to an automotive electrician unless you are brave https://www.mgexp.com/phile/3/191288/REPAIRING_THE_STANDARD_RB106.pdf. https://mgaguru.com/mgtech/books/pdf/Lucas_Generator_and_Control_Box_Tests.pdf A common problem with some modern far-eastern replacement control boxes is poor materials used for the contacts which means they don't last long. If this is an original Lucas unit it is probably worth getting it repaired. As an alternative, there are replacement electronic units available housed in the same case so it still looks right. Edited May 3, 2022 by RobH Quote Link to post Share on other sites
cookie Posted May 4, 2022 Author Report Share Posted May 4, 2022 16 hours ago, RobH said: Looks as though the dynamo itself is OK - with no field current you get little output 30V is in the right ball-park for for full field excitation. That could mean the control box is not supplying sufficient field current to the dynamo. As a quick first check , look at the continuity of the yellow/green wire from F on the control box to the dynamo field terminal, in case the wire has broken internally. Also check all of the other connections to the box including the earth. If those checks are OK it must be the control box itself. What are the symptoms he is seeing? Does the ignition lamp go out or remain on? After starting, can you see a large charging current on the ammeter which decays towards zero after some time? The control unit is not easy to fix or adjust - about the only thing you can do is to clean the regulator contacts very carefully using very fine emery-paper, taking care not to bend anything or change adjustments. That might fix things temporarily at least. Doing a proper repair and recalibration is not really a DIY thing and is best left to an automotive electrician unless you are brave https://www.mgexp.com/phile/3/191288/REPAIRING_THE_STANDARD_RB106.pdf. https://mgaguru.com/mgtech/books/pdf/Lucas_Generator_and_Control_Box_Tests.pdf A common problem with some modern far-eastern replacement control boxes is poor materials used for the contacts which means they don't last long. If this is an original Lucas unit it is probably worth getting it repaired. As an alternative, there are replacement electronic units available housed in the same case so it still looks right. Hi, Thanks that’s very useful. Not sure about the ignition lamp but the ammeter doesn’t move when engine revs up. Wiring continuity checked ok. Have concerns about the 2.5v from the single D terminal as this should be about 14v. Brushes look ok too. thanks Dave Quote Link to post Share on other sites
RobH Posted May 4, 2022 Report Share Posted May 4, 2022 17 minutes ago, cookie said: Have concerns about the 2.5v from the single D terminal as this should be about 14v. If there is no current being supplied to the field terminal you won't get 14V out of D. With no field current supply, there is only some small residual magnetism left in the field, not enough to generate anything much which is what you are reading. When you connected F direct to D the machine "bootstraps" and supplies its own field current to boost the field and so gives full output. The initial 2.5v is enough to increase the field a bit , the stronger field generates more output volts which increases the field current further which raises the output further and so on until you got to 30V. In effect the control box should make that same connection but regulate the current it by switching on and off rapidly to give the (approx) 14V constant output you want. Quote Link to post Share on other sites
mikej Posted May 4, 2022 Report Share Posted May 4, 2022 We have an article on electronic regulators in the next TR Action, as Rob implies, adjusting the voltage regulator (control box) is not for the faint hearted and needs some specific types of test equipment. It is all in the workshop manual split in two places. My experience with new ones is all bad and I would suggest scrounging a used one from someone who has changed to an Alternator. MikeJ Quote Link to post Share on other sites
Mr Blue Sky Posted May 6, 2022 Report Share Posted May 6, 2022 I have a regulator (Lucar type) spare - don't know whether it works as I need the screw type fir my car. Quote Link to post Share on other sites
ianc Posted May 7, 2022 Report Share Posted May 7, 2022 From postings on the Forum, the electronic version of the regulator seems to be very reliable (as it ought to be), and looks much like the original. I have no experience, as my car has had an alternator since 1993. However, along with the other three Works' Rally cars, it was equipped in 1962 with the RB340 regulator unit, which has separate voltage and current coils (so 3 coils in all), and I concur with MikeJ that adjusting the regulator unit requires the correct measuring kit (including ammeter capable of handling about 30 amps) and needs to be undertaken very rapidly - or not at all. Ian Cornish Quote Link to post Share on other sites
cookie Posted May 7, 2022 Author Report Share Posted May 7, 2022 14 hours ago, Mr Blue Sky said: I have a regulator (Lucar type) spare - don't know whether it works as I need the screw type fir my car. Thank you, I will ask my friend (also a TR Register member) to contact you. Dave Quote Link to post Share on other sites
cookie Posted May 7, 2022 Author Report Share Posted May 7, 2022 Thanks all for your comments, all very helpful. My friend who owns the TR3a is now away so work currently stopped. Will update on his return. Dave Quote Link to post Share on other sites
Richardtr3a Posted May 7, 2022 Report Share Posted May 7, 2022 I had problems with the control unit. New ones used low grade materials. I collected old ones and had them serviced by a specialist. Then I had a solid state one made that fits inside the original housing I never had another problem in the electric department Good luck Richard & B . Quote Link to post Share on other sites
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