Made a boob!

[Grumpy21]

Chasing an electrical fault that turned out to be a bad earth I’ve messed up the regulator, or dynamo or both.

So, I have a voltmeter fitted which fluctuates between 12.4 and 17.7v when driving. Steady 12.7v at idle. When the voltage drops the ignition glows brightly but the car drives fine then for no obvious reason the light goes out, voltage increases and off we go again.

So have I knackered the dynamo or regulator. Do I need to adjust (again) the regulator (not too sure yet how to do that correctly)

Should I just hasten the conversion to alternator and be done with it?

[oliver90owner]

The dynamo can produce higher voltage than required, depending on speed. As it can make 17V, it is OK. However, your battery will not last long if charged at 17V! That is why a regulator is required between the dynamo and battery.

It might appear that something is wrong with the regulator. Either the actual regulator or the wiring.

[svenedin]

How could you have messed up the regulator or dynamo? The most likely issue is a bad connection or dirty contacts in the regulator. The fact the ignition light goes out "for no obvious reason" suggests a bad electrical contact.

Check the electrical connections at the back of the dynamo are clean and tight. Then check the connections at the regulator end at "F" (field) and "D" dynamo. Open the regulator box and you will see two bobbins which have contacts ("points") at the top. With a piece of fine emery paper inserted in between the contacts, carefully clean the points. If you double the paper over you can clean both points at once. If the paper won't fit doubled over, use one side and turn the paper over. Now try running the engine.

When you say adjust (again) the regulator does that mean you have fiddled with its settings?

Don't panic! It's probably something easy.

Stephen

[Grumpy21]

Yes, I should have made that clearer.

In an effort to trace a different issue I adjusted both screws on the regulator. This had no effect as it turned out to be an earthing issue but in the process I ‘lost’ the original regulator settings. My attempts at re-finding the original settings haven’t gone well as I now get the fluctuating readings and sporadic ignition light. It’s the light that makes me wonder if I’ve overcooked something.

The manual says to adjust with a moving coil meter which I don’t possess. (Just 3 dvms which lack the latency of mc)

[geoberni]

I see your problem... cheaper Digital meters can have that instant fluctuation. I have a 'quality' instrument that cost me £20 at an autojumble, but used on the car gives me a slowly varying display of 13.90 to 14.10v.

What might help is to ignore the rather complex instructions in the Minor WS manual and look for a booklet online called "Lucas Generator and Control Box Tests"... actually here's a link: https://www.mg-cars.org.uk/imgytr/pdf/lucas.pdf
It's intended for the small operator/mechanic who isn't really experienced with auto electrics and it's layout makes it really easy to follow compared to the somewhat 1950s textbook style of the WS manual.

[Grumpy21]

I’ve done a few basic tests and the dynamo output is zero

The control box terminals are very pitted and covered in black dust. Cleaning has no impact. The two screws make no difference to any voltage reading with my DVM, found a mc meter on an old Gunsens multi tester.

As I suspected I think I’ve fried the dynamo but I was considering an alternator conversion anyway so I’ve gone ahead and ordered one. Cheaper than a new dynamo and control box too.

Thanks all

[svenedin]

OK. Thanks for clarifying. Fiddling with the screws in the regulator is not recommended but it isn't the end of the world.

Over the years I have read a lot about the RB106 regulator, how it works and its flaws. It is a clever piece of electromechanical kit for its era. Most of what I read I have forgotten but it is important to understand the basics of what the regulator does and how it does it.

The regulator basically does two things. The first is the "cut-out" controlled by the points of right hand bobbin. This connects and disconnects the dynamo from the battery. So with the cut-out points open the dynamo is not electrically connected to the battery. The left-hand bobbin is the actual voltage regulation. The points of the voltage regulator bobbin very rapidly open and close to limit the voltage going from the dynamo to the battery. This prevents the dynamo from charging the battery too fast when the engine revs are high.

Here are some videos that may help with an explanation of how things work. I don't have time to find all of the videos in the sequence for you but they are all by Moss Motors. Here are some of them to get you started.

I have one of these fairly cheap analogue multimeters: https://www.amazon.co.uk/Schneider-Elec ... B07B7PSYM7

Good luck!

Stephen

https://www.youtube.com/watch?v=zXLGsa6jRcY
https://www.youtube.com/watch?v=N8r40QB5WfA
https://www.youtube.com/watch?v=VwMn-5NV5eM

[Bill_qaz]

viewtopic.php?t=59496

Previous post with useful info for alternator fitting.

[svenedin]

I think it's a shame to have given up so easily and to move to an alternator which is no doubt a piece of nasty cheap Chinese stuff.

It's easy to test if the dynamo is knackered. All you have to do is test if it will behave as a motor. If the cut-out points in the RB106 are not closing properly or not making electrical contact when the engine is running the dynamo is not electrically connected and it will generate no electricity.

Stephen

[Bill_qaz]

Don't forget to swap to negative earth if its not already, as your alternator will most likely be a negative earth unit.
Also check other components are ok if earth swapped.
Fuel pump for example, electronic ignition if fitted.
Don't just fit without checking dont want to fry anything else

[Grumpy21]

Thanks for the above, the alternator swap was on the list of things to do anyway the impact of my fiddling has just brought the decision forward.

I’ve three events planned in the next week and I need a fairly quick solution and having tested the regulator and dynamo as best I can I’m fairly sure I’ve done some damage to one, the other or both