Dynamo, Regulator and wiggly Amps

[RobThomas]

Any experts on here? Bit of a difficult subject to pick up, this 'regulator' thing.

The car (1952 sidevalve MM) was running alright until stashed away for 12 months. Upon starting it up again I found that the ignition light bulb was blown. After changing it I could start the car but the battery had somehow discharged to 11.8-ish volts. Charged it back to 12.45-ish volts (75%) and could start the car but the battery voltage would drop slowly down but without the dash bulb illuminating. Can I assume that the bulb is merely displaying that the dynamo is functioning and not that the battery is receiving the extra volts? Changing the RB106-1 for a spare RB106-2 brings a similar discharge but the bulb glows dimly. The manual says not to run the RB106-2 on a C39 dynamo. Not sure why.
Manually closing the cut-out brings about 13.4 volts onto a totally dead (under 12v) battery. No increase seen with increased rpm.

Duff dynamo or duff regulator???

My vintage AVO has just died. Not ideal timing, eh?

[smithskids]

See if the brushes are sticking on the dynamo and if the regulator is the old type with screw connections ,check if the wires going in under the screws are tight. I have found on my MM the wire/screw connections oxidise a bit if laid up and this used to happen.

[RobThomas]

Thanks. The wire are a touch grotty due to them being 60 years old but they should be OK. I've had a peek at the dynamo and the comm looks a little bit oily so I'll whip it off and clean it out. The mica seems to be stepped down so it can't be that long ago that it was rebuilt. Still only 40K miles on the clock. Would a sticky brush drop the voltage output without cutting it off altogether? Perhaps the 13+ volts it gives out isn't enough to close the points?

[RobThomas]

Right. I've put the original reg box back on, run the engine and now the warning light no longer glows. Lucas say there are only 3 reasons for a dim lamp during driving, dirty reg points, slipping fanbelt or high resistance in the ignition switch. Cleaned the points and now that bit works. I'm still not getting good volts at the battery terminals, just the static battery reading of about 12.5, although the volts at the F terminal of the dynamo is 14.5-ish. There is arcing at the regulator points so that coil is working but the cut-out doesn't seem to connect the dynamo to the battery. I assume the cut-out should flick over at 13.5-ish volts and you'll see it move? No sign of it.

5 minutes later...

Bu66er! I think the dynamo just melted!

[Trickydicky]

Do you have a copy of the Lucas Fault Diagnosis Manual? If not pm me your email and I will send it to you.

[RobThomas]

Downloaded it today! Thanks for the offer, though.

I think I may have snagged the cut-out as I put the lid back on the regulator box, hence the hot dynamo. I hope there isn't any permanent damaged since both parts are original to the car.

[RobThomas]

Well, after reading the 50 page manual from the good Doctor Davies, I am finally in possession of a working RB106. I'm going to collect as many RB106 and RF95 (Lowlight) regulator boxes as possible now that I know how to fix them. Remarkably clever little piece of kit, once you get into them. The repro ones are sh1t3 in comparison to the originals.

If anyone has any spare contact sets for regulators then I'm on the hunt for some.

MYH247 is back on the road.