Original regulator with C40/1 dynamo?

[TYC601]

I have recently got my 1955 Minor engine running, but the ignition light was staying on. I tried the shorting of the two dynamo terminals and looking for volts, but having only two arms and hands struggled to get everything doing what I wanted - did manage a few sparks though

So I decided to bench test it and drive it with an electric drill: that was easier, but I still couldn't find any volts I have now stripped it down and tested the field coils, and got about 2.1A with 12V supplied, so they seem OK. The commutator brushes look good but the commutator itself has a pretty uneven wear pattern so I will skim that in the lathe at work and tidy it up.

Now to the point of these ramblings: my reference is the original factory manual and a 1967 copy of the BMC Autobook Five. The Autobook mentions that the later C40/1 dynamo (as fitted to my car) would have used an RB106/2 control box, but the original C39 should not be used with that regulator. I think my regulator is the early one (it looks like Fig.N.15 in the manual and has screw terminals) and wondered if that was still compatible with the later dynamo, if the reverse wasn't? The factory manual only has a couple of paragraphs on the 'windowless yoke dynamo' and 'modified control box' so doesn't help much?

Thanks[frame][/frame]

[chesney]

I had a 1958 948 Minor with a later C40 dynamo fitted, yet retaining the original screw terminal regulator as you have pictured.
As a daily driver car, I can confirm that it works in that fashion.

[bmcecosse]

I see no reason why that won't be suitable - assuming it's in working order. I dunno why people mess about trying to get 'volts' from the dynamo - simply join the two terminals and connect to the battery - if the dynamo runs as a motor - it will work well as a dynamo. Simples. And to check that - run the engine (having refitted the fan belt) and touch the joined wires again to the battery. The battery volts should now rise to ~ 14 volts at decent revs.... With everything reconnected to the Reg it should come up to 13.8 volts - even with the heater fan and all lights on - at decent revs of course - not when idling...

[TYC601]

Thanks guys, I don't know where or when the dynamo was changed but the last tax and MOT is from 1979, so have no idea if it was used on the road with the current combination. Had to skim about a 1/16" off the commutator diameter to get a clean, concentric surface, and it looks like it was probably already cleaned up previously - does anyone know what the original diameter is?

I'd forgotten about the 'motor' test until I came in from the garage and had a look through a few threads on here, but once I have cleaned the insulation between segments I'll stick it back together and give that a try.


UPDATE: Cleaned up, back together (after a bit of a fight with that stupid C-clip bearing retainer), and it passed the 'motor' test I'll get it back on the car at the weekend and see if I can borrow some extra arms to help with the next stage of testing.

[bmcecosse]

Well done. It will be fine as a dynamo.

[TYC601]

Well, the dynamo might be fine, but the ignition light is staying on, and it still isn't charging. Will have to check through the regulator now and see if that's at fault.

[bmcecosse]

The connections all look a bit 'grim ' - may be worth cleaning them up. And run some card through the contacts as a first step.

[TYC601]

Yes, I've taken it out and cleaned things up a bit, and re-set the gaps as instructed in the manual, re-fitted it and . . . still nothing. I tried the connecting D & F together and earthing through a DMM and got 20, 30, 40 volts and rising, so I believe that confirms the dynamo is functional?

From watching the series of Moss Motors videos on Youtube regarding the regulator, I didn't notice any buzzing or other action from it so suspect it needs more thorough attention. In one of the videos they say to test the regulator is working by touching a supply from the battery to the field terminal on the regulator, then see if it starts to charge: is this supply from the battery +ve (i.e. earth) and is it the equivalent of the D & F connected test above? They say that if the dynamo/generator starts charging, the fault is with the regulator, and if nothing happens it is probably the wire to the field tag on the dynamo. I think I'm beginning to understand how it works!

[bmcecosse]

DO NOT touch anything from 'earth'..... Yes - it is the same as you joining the terminals together, although I wouldn't let the volts rise so high - keep it sinking into the battery. It does look like another regulator is required - the dynamo is fine.

[TYC601]

Well that's that. All the smoke has escaped from the wiring.


Tried a different, NOS but untested RB106/2 regulator but with the same (lack of) results. Tried new dynamo and field leads in case the originals were causing the problem (they buzzed out OK, but would do that with a single strand left), but same thing so reconnected the original regulator. Was then measuring voltage with the engine running and found about 1.2 - 1.4V between A or A1 and ground. Then checked from one side of the regulator contacts and while doing that noticed the cutout had clicked in: measured the battery and it was charging, albeit at 15.6 - 15.8 volts. Now, I don't know what I had done to bring about this change, but decided I'd take it for its first spin round the block.

To do this I would have to move my old Toyota, but the battery was flat so had to push it around. Then I smelt burning rubber - looked to see what my neighbour was burning today and saw that the smoke was coming from my garage. S***! Ran over and saw smoke pouring from the regulator and around the dynamo, so quickly disconnected the battery. Phew! Close shave!

So, the loom is now compromised and as the dynamo was very hot I suspect that may have also suffered. I don't think I would waste my time replacing all that with the same so I may just stick an alternator on it and be done with it. I have never been particularly sure if I would be keeping the Minor once it was done, and although the original plan was to keep it as original as possible, I would probably be doing me and/or a new owner a favour by converting it to -ve earth and an alternator. If I do that, what years' loom should I be looking for? Would an alternator on a Minor have been a one-wire one, or would it have had a separate controller?

All suggestions welcome.

[bmcecosse]

Your 15.6 volts was FAR too high. The dynamo has been running flat out. That shouldn't really have been a problem but I suppose with no load, the volts would rise higher and higher - the field current higher and higher and basically it becomes a 'run away train'....
Alternators just need a power wire to the main battery terminal (usually on the solenoid/pull start) and a sensing wire from the Ign warning light.

[TYC601]

Tried the dynamo motor test and it ran, so wired in the new RB106/2 regulator, replacing the damaged earth wire and the melted dynamo wire - and got same results as originally, i.e. ignition light staying on and no charging, and nothing occuring inside the regulator. Also tried the test in the Autobook, joining D and F at the dynamo and measuring volts to ground on the casing at tick-over and low revs. Now, the book is old and says use a 20V moving coil gauge, and all I have is a modern DMM, but all that measured was less than 1V, which implies knackered windings.

Removed the dynamo ready to launch it towards the scrap pile and thought I'd give it the 'motor test' again. With it laying on the floor it was rocking back and forth as it ran, even if I held it. Had a look in the end at the commutator and I could see two bright segments 180 degrees apart, and lots of dark segments elsewhere, so I guess when whatever shorted did so, the bright segments were the ones contacting the brushes. The rocking is presumably caused by the intertia of the 'motor' coasting over parts of the windings that were damage/shorted, and this didn't show up when solidly mounted to the engine.

I am sorting out an alternator for the car, so will be converting to negative earth, and maybe replacing the fuse box while I'm at it. Elsewhere on the forum it has been said that all I need to do is swap battery terminals, swap coil wires, and the job's done? I'm assuming the starter still runs in the right direction, but there are other things that some people have suggested might be problematic:
Fuel gauge: mine (1955) has the central speedo with gauge at the bottom, and it appears to work at the moment - will it be the same with opposite polarity or do I have to change the wiring to/from it?
Fuel pump: some have suggested that the points will need to be dressed perfectly flat so they can start to pit in the opposite direction? Same for the ignition points?
Indicators: my trafficators have been 'de-commissioned' and replaced with indicators: do I need to change the supply or anything for these?

Anything else I should be aware of?

Thanks in advance. Again.

[bmcecosse]

If a silver fuel gauge you need to swap the wires. And yes - clean the dizzy and fuel pump points .

[TYC601]

It's getting silly now. Switched to negative earth, installed the alternator and started the car up. It ran fine for less than half a minute before petering out - long enough to see the ignition light go out when it started, so that was promising.

So now what? One thing I noticed with the ignition on was that the fuel pump was rattling away much faster than before. Ah! must have run out of fuel. Stuck a gallon in but still no start. Disconnected fuel lines and blew back through in case sediment had blocked the line, but following that, still no start. Dismantled the fuel pump to see if I had upset something when cleaning the points (as instructed for change of polarity) and found a pin hole in the diaphragm. Oh well, after a week of faffing around a friend found me a good used one - he asked questions about if it was a high or low pressure pump, which I couldn't answer, but I stuck the diaphragm in the pump and put it back together. Put it on the car, started up and all ran fine - great, I'll take it for a spin, as it's taxed and insured now.

But no. Now there are no brake lights! After finding the switch, which was a pleasant surprise after expecting it to be wedged down in the chassis behind the master cylinder or somewhere equally inconvenient, I checked it. There is 12V to one side, and the other is earthed. With the ignition off, if I check the terminals with a DMM on 'continuity' it buzzes as connected. If I remove one of the wires then it doesn't buzz, so presumably there is a back feed through the bulbs or something? If I operate the brakes the switch then buzzes as 'closed', so it is operating. So, wires back on, ignition on, but still no lights, however if I simply short the terminals on the switch I get brake lights!?! What's up?

[bmcecosse]

The switch must be faulty.. good enough to operate the meter - but not the lights.......

[TYC601]

Update: fixed the brake lights (at least in the short term) by installing a standard 30A relay, on the assumption that if the switch buzzed out then maybe enough current would flow to operate it. And it worked, somewhat surprisingly

Went for a short drive (its first time on the road for possibly 35 years) and once I'd cleared the kangaroo from the tank it drove OK, if a little flatly.

So I thought I'd see why the heater fan wasn't working: this seemed to be an assembly issue as I eventually got it back together with the fan spinning and blowing air out! Of course in doing this I upset one of the hoses and ended up with a puddle on the floor, but managed to fix that . . .