RB106 control box and gremlins

[biomed32uk]

So having finished my front suspension rebuild it was time to get the car off the stand and ramps, she has not been started for 3 months. It seems while I have been hard at work underneath, the electrical gremlins have also been busy

When I last ran her the charging circuit was fine, never had a problem with it, but yesterday the ignition light was firmly on.

The dynamo is perfect, and will run as a motor fine. The wiring is all good with no problems, the earth strap is all fine, infact that's the only bit of the electrics I have actually touched as I welded some new cage nuts into the legs.

I have cleaned the contacts in the control box, the cutout tries to close when reving the engine but dosen't make it, and the finger of suspicion is leaning towards the control box. I have found the guide below just for some resistance measurements, the guy reckons I should get 5 ohms or so between D and E, which is measuring the shunt windings - I get 56 ohms. I don't have another control box to test, does someone have a control box and an ohmmeter that would be willing to verify this resistance for me please, all the others measurements check out fine.

Are the pattern control boxes any good?, or am I best off searching for a decent original one.

http://mgaguru.com/mgtech/electric/et121.htm

[myoldjalopy]

Not sure I would trust an old control box unless it had been stored in very dry conditions.
'Modern' control boxes are not expensive (aroun d £20, I seem to recall). But neither are they infallable........One I fitted lasted about 15 years, another only around one year. A third has lasted about 2 years so far and still good.........

[RobThomas]

Hold a compass near the coils of the regulator. If the coils have burnt out internally you won't get a change in field when you should have. That is the best test.

Modern non lucas branded regs are awful in their quality of construction, although, they may work alright.

[Sandun]

Ok - I can help you - Look at the Points of the regulator side clean it ( it is the main gateway that dynamo contact with the circuit) Remove the 2 screw ( control box fix to the car ) and look back side of the control box If you can see rust - try to clean it - check the the A1 A F D E screws and clean them - remove the wire terminal of the dynamo ( dont change F and D wires ) take new two wires and joint them Dynamo F and D terminals and end of the new two wires joint them together - start your car and quickly short the wire with body - if it make good spark ur dynamo is ok - remove the test wires reset F and D terminal to the dynamo - inform me what are the results - u can use PM also

Regards
Sandun

[biomed32uk]

Thanks everyone for the help, being an electrical/electronics engineer a simple regulator and dynamo should be sortable, I spent many hours learning rotating electrical machinery as an apprentice in industry.

Well I whipped the Dynamo off, thinking it was a stuck brush or something through lack of use, that all checked out fine, and putting the dynamo across a battery had it running as a motor so as far as I am concerned is OK.

Took the control box out, which looks fine, no corrosion anywhere. Did the measurements according to the Lucas manual of the cut out with feeler gauges and it seems the bend fairy has been there. The armature was also not sitting square to the core when pressed closed, so squared that up, reset the gaps where needed to spec.

Put E and D across the bench power supply and gradually increased the voltage, closing at approx 11 volts which is too low. So adjusted the closing point to be 13 volts, all working fine. The regulator armature will also close like this if pressed down. So both coils are fine, I don't believe there should be 5 ohms across E and D, considering they are two relay coils in parallel 50 odd ohms is much more reasonable for this arrangement.

Cleaned all the terminal blades, inspected and nipped up the connectors on the loom, refitted, tested and all fine. So I don't actaully know what was up, but some TLC has sorted the problem out.

[Fingolfin]

When I first bought my Minor in 2008, the original dynamo/control box system charged perfectly, but after the restoration (so getting into 2011-2012) I couldn't get the ignition warning light to go out. The dynamo checked out as in good health. I went through three NOS control boxes and had no luck whatsoever. Switched to an MGB alternator - cured! And never a problem since.

Since then I'm convinced these control boxes are just asking for trouble. You have my admiration for solving your problem!

[biomed32uk]

I agree the alternator is the more reliable way to go, and if she was a daily drive then it would be that way.

I just like the quaint charm of the dynamo on what is a fun car, and I am very used to sorting out and calibrating electrical / electronic devices, and it's only an overgrown relay really. I've set up and adjusted far more awkward devices than that. I have no idea what the gremlins were messing around with though, wierd !.