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MG Midget and Sprite Technical - Alarming overcharging

No I don't mean I paid too much, I mean the ammeter goes off the scale. The other day as I reached 70mph the needle went way past the 30A range of the ammeter. It dropped back to 15A or so when the speed dropped to 60. There was no obvious jump showing that the regulator had tripped. I have been worried about overcharging for a little while, as the meter doesn't always show the charge settling to a trickle. Whatever problem there is seems to be intermittent. The dynamo is one I rebuilt from various spare parts recently, and delivers lustily. Still charges with headlights, spots, and rear foglight on. I could not find anything very helpful in the archive. The control box was new about 10 years ago and I have never adjusted it. I'm afraid that I will fry the field windings if this goes on. I cleaned the control box contacts but will have to warm up the engine and rev to 4,500 to see if that made any difference - and it will annoy the neighbours. I'll probably have to do a lot of miles to be reasonably sure, as I don't see this effect consistently. Hence if I can get any clues as to the problem, that might expedite the process.

I suspect this is what damaged the electronic fuel pump recently.

Les
L B Rose

It would be interesting to know how many volts it’s charging at when it goes off the scale.
Dave O'Neill 2

As Dave says, measure voltage across battery at around 4500 revs. If above 14.5v or so, it is overcharging and must be the regulator not switching properly/ out of adjustment imv. Might be the field regulating contacts sticking.
Bill Bretherton

AES supplies regulators that have been set up correctly
Dominic Clancy

The plot thickens. Started up the car yesterday and no charge at all. In the past this has been because of over-lubrication of the rear bearing, contaminating the brushes with grease. So I stripped the dynamo and cleaned everything, all back together and still no charge. Tested the dynamo on the car and it's fine. Good steady rise in voltage. Tested the open circuit setting and it's way out. It should be 16.1 - 16.7v at that temperature and 3000rpm, but it struggles to reach 3.0v. It looks like the control box has failed. It's so far out that adjustment is unlikely to sort it out.

The rated output of the dynamo is 19A, so how was the 30A ammeter going off the scale? Yes I have checked it is working correctly.

Les
L B Rose

I'm guessing because that's its rating, not a limit. If something else is loading the circuit and demanding 30A the poor old dynamo will do its best unless the control system, which is external to the dynamo, steps in to limit the carnage.
It'll try to supply whatever load is presented to it, but it might not like it much.
Looks like the regulator is not playing the game.
Greybeard

I just found this article about repairing the control box:

https://www.mgexp.com/phile/3/191288/REPAIRING_THE_STANDARD_RB106.pdf

Fully reconditioned original ones are over £100, and the reproduction ones about £30. Of course I have the latter! I already had to repair it because one of the riveted contacts underneath corroded, so it's likely that there is more corrosion that can be addressed. I always like a challenge!

Les
L B Rose

How about -

"Advanced Dynamo Regulators is CDRC Ltd's own brand of electronic dynamo regulator.
We make them right here in the UK.
Why Advanced? Well, because our ADR range is by far the best and most reliable regulator available.

Our tried & trusted direct replacements for the original Lucas RB106 and RF95 regulators.
Outright purchase. No waiting.
Brand new and exactly the same as original units but ours have our trusted and proven electronic regulator inside.
Available in 6v or 12v negative earth and positive earth .
Fully fuse protected.
Forget cheap and nasty Indian made copies.
These units are entirely British. Made here in Lincolnshire using top quality components. You can even fit an original LUCAS lid to retain original looks from the outside if you prefer.
Please enquire for more details.
Trade enquiries welcome."

Loads of details about them here- http://www.dynamoregulatorconversions.com/reproduction-rb106-and-rf95-regulators.php
Nigel Atkins

Les
When you say the dynamo is fine on the car, what is the voltage at the battery? I assume "open circuit" means with dynamo disconnected?
Bill Bretherton

If considering a new electronic regulator why not just fit a Dynamator from the likes of Bad Boy Classics and either do away with the regulator or for the sake of originality gut it and use it as a junction box.
The Dynamator is available in C39 pattern with the rencounter take off at the rear. I have been running one for a couple of years. An (original) T Series MG owner stripped one and commended the quality of internal parts. A search of the internet will find his report.
Alan Anstead

I fitted an alternator from a Mini to mine years ago, removed the regulator and cut some bits of copper to bridge the necessary connections at the bulkhead. No wiring loom changes needed, bit of a bodge perhaps but worked fine and kept the driving lamps nice and bright for night rallies in my younger days.
AdrianR

Les

Dr John E Davies did a superb job of checking and refurbishing my voltage regulator, dynamo and rev counter gearbox for my 948cc MkII Sprite. And all at a very reasonable cost (you could just get the voltage regulator refurbed)

If you are a MASC member he often publishes articles in MASCOT and sometimes has such refurbished items for outright sale as well as repairing people’s own. I can ask him if he is still doing refurbs if you like?

An alternative to Alan’s great option of the alternator that looks like a dynamo and can still drive the mechanical rev counter on 948cc Sprites.

Cheers
Mike





M Wood

Bill, I meant testing as per the workshop manual, which means disconnected from the control box and with both terminals bridged. I have just serviced the box and found that the regulator contacts were quite badly burnt. All back together, and I find that the cutout is not working. The battery discharges through the dynamo. I could not find any bad connections in the control box, and I have not touched the adjustments. This looks like an expensive episode.

Les
L B Rose

The Dynamator is currently not available from Bad Boy Classics with tacho drive (C39T). Are there any other suppliers?

BTW the CRDC website is one of the worst I have ever seen. Chaotic, horrible to read. You can tell I'm in a bad mood.

Les
L B Rose

Les
Sounds like the cut-out armature is stuck on, in addition to the regulator armature points maybe sticking. I have an alternator on the Frogeye rebuild so have no recent practical mechanical regulator experience but I know how they work.

If you look at the cut-out (charging) electrical contacts (RH coil looking from the terminals side) they might be stuck together - that would drain the battery through the dynamo. If stuck, see if they'll separate and clean up assuming they're not completely burned out. Same with the field regulation contacts - they have a hard time as they're opening and closing continuously. Effectively, they switch the dynamo field on and off to set dynamo output voltage at around 14v. The regulator is quite a simple device really and should be fixable.
Bill Bretherton

Bill, I have cleaned the contacts and they are not stuck. I can see that at rest the cutout contacts are open, and the regulator contacts are closed. Is this correct? As I said before, I have not touched the adjusters.

Les
L B Rose

Les,
how about an alternative - https://www.ebay.co.uk/itm/124189316715

Info - https://www.powerlite-units.com/about-dynalites.html
Nigel Atkins

Yes I looked at the Dynalite, but £450 is a bit steep when the out of stock Dynamator was £159. I am thinking about using an ordinary alternator and converting the tacho to electronic. I have rebuilt those tacho gearboxes for a pastime...

Les
L B Rose

Sorry Les I had no idea of price, and didn't think you'd really even consider electronic replacements.

How about this then - https://www.youtube.com/watch?v=KL5ioH8idFI
Nigel Atkins

Les
Yes, contacts at rest are correct. When engine revs, cutout contacts should close (charging) and when at tickover contacts should open. The regulator (LH) contacts should be continuously switching whilst engine is running.
Bill Bretherton

There are some really useful articles in Mascot by DrJ E Davies about control boxes, what faults are likely and how best to deal with them. He is very scathing about some poor aftermarket replacement regulators which cut costs with design alterations which really mess up the operation of the device. It's worth reading up on them before you start to make any random adjustments!
GuyW

How about this for a project an article about converting the RB106 to use a commercially available Bosch dynamo regulator.
David Billington

Accuspark also stock the dynamator.
Alan Anstead

Accuspark- C39/40 Positive Earth With Tacho Drive Dynamator - Sorry - This product is not currently available and cannot be added to the basket.

I saw this article, looks very detailed, I only quickly glanced at the photos and still got a headache. See attached PDF with thanks for the article to Dr. Hugo Holden (Jan 2011).



Nigel Atkins

Nigel,

That looks to be the same guy that did the article I posted a PDF of early regarding fitting a Bosch 30019 electronic dynamo regulator to the RB106.
David Billington

David,
I had to zoom in to find the name, I must admit I didn't look at the article as it looked far too complicated for me. After seeing the PDF you put up it reminded me I'd seen one before for repairing, not realising it was by the same person.

I see it's dated 2012 so either the Germans got at the good doctor or he's offering an update alternative to his 2011 article.
Nigel Atkins

David

That Bosch regulator looks good to me for someone who can solder a few components together. Cheapest solution if you want to keep the dynamo and far superior to the Lucas electromechanical regulator. Although, if you don't want the mechanical tach drive you might as well use an alternator which imv is superior to a dynamo.
Bill Bretherton

I think you can get an alternator conversion with the rev counter drive now
Bob Beaumont

The control box seems to be beyond redemption. After today's minor frying of wiring I am considering the alternator option. Affordable ones with tacho drive are out of stock everywhere. A classic Mini kit can be had for about £60 with bracket and belt. What to do about the tachometer? Cheap electronic tachos are widely available, but not in 100mm. This may sound mad, but what about using the guts from an 85mm 0-6000 electronic one in the original casing? I could not find anything in the archives on this.

Les
L B Rose

Les,

I've swapped the guts from an electronic Smiths tachometer into the frogeye casing and resprayed the dial and re-numbered it to cover 0 - 7000RPM to suit the engine and electronic tacho guts. Being the same make the bits swapped over easily. No idea about 85mm tachos but a quick look didn't show any apparent dial mounting unlike the Smiths which uses 2 screws.
David Billington

Blimey Dave you must be a great artist.
L B Rose

I found this video on converting the tacho:

https://www.youtube.com/watch?v=6FWwnHekeWI

The donor tacho is available, but expensive from UK sources. I can order from US at about £50 including postage. So the total cost for alternator and electronic tacho is about £110. The mechanical tacho has been a pain in the neck. I recently put a new bush in the gearbox and repaired the drive dog. I would quite like to get rid of all that.

While the dynamo is quite adequate regarding output, in the last 15 years or so I have been through 3 of them and I am getting too old to keep changing and/or rebuilding them.

Les
L B Rose

3 new dynamos in 15 years is excessive!
Maybe your regulator has been faulty all along, and getting steadily worse, -frying your dynamos. The dynamo and regulator really need to be thought of as a matched pair, regulator setting being adjusted to each specific dynamo.
GuyW

The control box was new about 10 years ago. I have never heard of resetting it to each dynamo. I suspect it also fried the electronic fuel pump recently. I've had various BMC cars since 1967 and this unreliability was unknown in the old days. I do remember getting the control box adjusted on the A35 but that was all I ever had to do.

One of the dynamos died when I hit standing water and flooded the engine bay, although I suppose it should have coped with that when dried out.

Les
L B Rose

I think Guy has hit the nail on the head there. Going b back to the comment about high currents, if there has been a consistent high load from the reg the dyno will do its best but at a cost in attrition.
Also re: getting an electronic tacho - at the risk of repeating myself why not give Andy Jennings a ring? No idea how much he sells used ones for but it might be a good starting for you. And I've always found them helpful.
Try Bad Boy Classics for an alternator. They sold me my Lucas 18ACR for less than thirty quid delivered and brackets can't be hard to get.
Sun shining here, have a good weekend everyone.
Greybeard

There aparently was/ is a quality issue with many replacement regulators. The originals used a ball bearing on the sliding tip because as it moves the contact point needs to be able to travel very smoothly over the surface of the spring blade. Replacements just use a conical point for cheapness, which is fine at first but after a while it begins to wear on the blade surface whch causes it to stick and stutter so that the contacts no longer open and close smoothly at the required voltages. The regulator still appears to work, after a fashion, but is erratic and settings randomly change with different ambient conditions of temperature and humidity, so it is no longer the precision instrument that it should be.

My guess is that this could be why your dynamows have been failing.
GuyW

Thanks Guys. Grey, I've had stuff from Andy Jennings many times and he's excellent, and not far away. But the later tacho is 0-7000 while mine is 0-6000, and I want to keep the same look. Andy does them for £50 and the modern one is £55 from Amazon (post free) and 0-6000, so seems the better option.

Les
L B Rose

Guy, that makes a lot of sense, sounds like the aftermarket regs are junk. I'd convert to an alternator (well I have on the rebuild). But I didn't have a mechanical tach for the Frogeye and am happy with the later electronic tach - I've also put in a later speedo as it's matched to the 3.9 diff.

But that probably isn't what you want Les. I'm sure I read somewhere of someone who'd put the older mech. tach dial into an electronic tach I.e. like David, but retaining the older dial as is.
Bill Bretherton

Les,

What about something like this https://www.ebay.co.uk/itm/Smiths-RVI-RVC-Tachometer-conversion-board-calibration-cable-566/380578001095 and recalibrate a later tacho guts to suit your 6000RPM dial.
David Billington

C39 dynamator (alternator) on my Sebring Rep. The revcounter cable terminates out of sight as I have an electronic tachometer.

Alan Anstead

For those that fancy making there own converter http://www.dummett.net/ime/website/ime/a2z/electronic_tacho_driver_using_LM2917N.html .
David Billington

Les

Why not get a properly refurbed and set up original Lucas voltage regulator from Dr John E Davies? You may be very pleasantly surprised at the cost.

Either that or wait for for the more reasonably priced C39 Dynamo lookalike alternators with rear rev counter take off to get back in stock and do an alternator conversion.

I may be getting the wrong end of the stick, but worth noting that Mk1 Midgets had cable driven rev counters with conventional Smiths faces, rather than the Sprite Mk1 and MkII that had the Healey style dark circles pattern (but still made by Smiths; Frogeyes had ‘high beam’ warning light in rev counter and MkIIs had ‘ignition’ warning light) with MkI and MkII Sprites having the rest of the gauges (combined oil pressure/water temp and fuel gauge) with conventional Smiths faces.

Cheers
Mike

M Wood

Thanks chaps for all your interesting research. I didn't know about the recalibration boards for electronic tachos, but that route would cost about £100 - £50 for the tacho and about the same for the board. I have ordered the modern tacho for £55 (Amazon) post free, and will convert my mechanical one.

I have learned the hard way that most control boxes are rubbish these days. I don't know what damage has been done to the dynamo, although the resistance of one commutator segment is high. Investing in a good quality control box may not solve all the problems.

Meanwhile I have become tired of replacing or repairing the ruinously expensive tacho gearbox. The instrument's accuracy has always been let's say notional, and the lack of needle damping has a charm all its own. I would actually like to know that WYSIWYG.

I have ordered a 45A alternator, bracket, and adjuster. I am not bothered about an original look under the bonnet, the car is way past that. For much less than the cost of a Dynator (should it ever become available) I will have a reliable charging system. Not that the dynamo was lacking for output, it was just the unreliability that has exasperated me.

I looked up Keith Calver's article on the conversion. He says to connect the old sensor cable to the alternator, but I can't see how that's necessary as (a) the alternator has its own regulator, and (b) there is now nothing in the control box, it's just a junction box.
L B Rose

Les
Sounds a good solution to me. The alternator connects directly to the battery (via the starter switch) and you may need to upgrade your cable(s). I don't know what alternator you are getting but a Lucas has two larger spades and one smaller. The two larger are common and allow for redundancy i.e. if two cables are used (to the starter switch, as I have) then if one fails you still have a connection. The smaller 6.3 mm spade is for the ignition light and field excitation current and connects directly to it. Thinner cable is fine here - most of the time it has no current flow. Some alternators have "battery sensing" whereby a third connection is made to the battery to provide the regulator with a reference voltage. I think this is less common and most alternators e.g. Lucas ACR series use internal "machine sensing".
Bill Bretherton

Les,
I don't know but wonder if these crap modern control boxes are even good enough to be used as a gutted connection box. It'd be a shame to go to all the trouble of conversion to be let down but this aspect. Perhaps the modern box connections are good or can be made good by being reinforced. Or perhaps if there's an old faulty control box but hasn't been damaged you could gut and recycle that instead.
Nigel Atkins

If you swap from dynamo to alternator, do you also have to swap from +ve to -ve earth? Or am I talking b*llocks? (Sorry, I'm not an electrical person, but thought I should ask the question, just in case.)
Jon
Jonathan Severn

The point about crap connections in the box is a fair one. I already had to repair one of them. The rivets under the terminals corrode. If it fails again I can always ditch in in favour of an ordinary terminal block. At least I will be fairly sure of what has failed as everything else will have been replaced.

The car has been negative earth for nearly 40 years!

Les
L B Rose

Jonathan
Correct, an alternator is -ve earth, I assumed Les had considered that. The only standard component affected is the tachometer which must be -ve earth. I converted a Smiths RVI tach. A radio, if fitted, needs to be -ve earth too. The starter, heater and wiper motors will be quite happy.
Bill Bretherton

Personally I'm not a fan of the Lucas alternator connections as I found they needed cleaning every few years to maintain a decent connection and the common between the 2 large spades can't always be relied on as I found out on a mates Caterham where the wiring loom assumed a good connection between the 2 and it didn't run well when it failed. The Caterham was wired battery to one large spade and everything else off the other large spade so failure of the common was an issue, I've always bridged the 2 spades in the loom connector. I much prefer a stud connector as on the dynamo IIRC and many other makes of alternator such as Bosch, Magneti Marelli etc.
David Billington

Unlike David I've never had a problem with the Lucas connections or needed to clean them but the modern made wiring plug kit (GEU250) I got the plastic plug and metal connections felt a little flimsy but have done the job without problem for many years now.
Nigel Atkins

I find that most spade connectors corrode, sometimes so badly that it's hard to get them off.

Having re-read the Keith Calver article I realise that the sensor wire is needed, as it's no longer used for the sensor but for the ignition light. Hence I have just put it back in the loom!

Well all this gives me the opportunity to refurbish the paintwork in the electrics area. I have inserted rivnuts where all the self-tappers were causing rust.

Les
L B Rose

I normally coat the internal spade connections (if I remember). Perhaps the plug set on the alternator gives more protection too.

I did expected to have to change the plug to individual spades after a time but have never needed to.

I've had so, soooo, many problems with various of these overpriced old cars we call 'classics' but never the connections to the alternators - no doubt I will now.
Nigel Atkins

Alternator installed. Surprisingly the existing belt still fits. Works perfectly of course. Really weird to see the battery charging at a rock steady 6A whatever the engine speed. Battery is a bit low at present, I expect the rate to settle further with a longer run. I should have done this years ago. Too much money wasted on dodgy regulators and dynamos.

Now I await the electronic tachometer that's coming from the USA.

Les

L B Rose

The new tacho arrived from the US a week early! I spent an interesting Sunday butchering its plastic case to get at the bits I needed, and then working out how to graft it all into the Smiths case. I went one better than the originator of the idea, in that I managed to use the Smiths needle. I explain how in the comments to the video:

https://www.youtube.com/watch?v=6FWwnHekeWI&t=6s

Just been for a run. What a joy, steady battery charging and tacho reading that doesn't flap about. All for less cost than a new dynamo - and I would still be stuck with the unreliable control box and tacho gearbox.

Now I just have to get a stable idle, which seems all but impossible with a 276 cam in a 998....

Les
L B Rose

Great news Les, well done.

It also means you can get rid of that ammeter now as you don't need and it'd be a constant reminder that you should have installed the alternator years back. Plus with one less gauge you can concentrate on your new tacho needle at idle - or turn your tickover up so it's more stable and sit at idle a lot less and for shorter periods, see what you think of the idle as you motor along. 😊
Nigel Atkins

Well done Les - great job!
Bill Bretherton

This thread was discussed between 07/03/2021 and 22/03/2021

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