Dynamator refurbishment

[David Stepney]

Dave, fortunately, my car is wired in such a way that the sidelights are on whether ,the headlamps are on or off. I think I prefer them that way for exactly the situation you had.

[Stuart Giles]

Testing at this point revealed that the rotor winding was open circuit (was this the same Dynamator that Stuart had a go at?). Oh poo.

Well done for finding and fixing the faulty rotor. Happy to confirm that all the left over Dynamator bits from the repair that I did are still lingering in my workshop somewhere  

It looks like the Dynamator I repaired using the rotor from a donated 'dead' unit has failed again, and I hope to have the unit back here in the workshop over the  next week or two. I will have a look to see if it's the rotor I replaced that has failed or whether it is some other fault this time. The other components are fairly generic so should be fixable if the regulator or such has let out the magic smoke.

Have said car and and Dynamator here now. A quick check showed  no 12v on the field/excitor connection, further poking about revealed that the ignition/charge warning lamp had blown. Simple fix, I thought; new bulb, still no charge, booger! stripping down the unit I repaired last year with a donated rotor from another dead Dynamator, revealed this bizarre fault...

Yes, that really is the stator, welded to the rotor; the whole lot has been spinning in the case, as can be seen in the rear of the photo.

Didn't need too much force in my hydraulic press to part the rotor from the stator, it appears that the epoxy which the stator has been pugged in with, has turned to crumb (it's all over the inside of the Alty) and this loose crumb has been responsible for a kind of friction welding of the whole stator to the rotor. As neither the car's owner nor myself have experienced a great deal  of reliability with the Dynamator setup , I have built up a permanent magnet alternative as described here.

The above was the wierdest Alty fault I have ever come across, not least because there is no sign of overheating on any of the alty components. However, the permanent magnet version I have built will hopefully be more reliable, and I have an improved version in development at the moment.

[Dave Mann]

Your entries on the Dynamator are very interesting Stuart. There is a considerable magnetic force between the rotor and stator which probably defeated the unsuitable glue. It is a pity because with decent quality control the Dynamator could have been a success.

[Ruairidh Dunford]

The concept is brilliant - and, when working properly, the reality is just that.

As mentioned previously, both of ours are still operating as they should (Pearl, 6v, since 2018 with a tour of France included and the Coupe, 12v, since 2021).

When they fail, I hope this thread will be of help to us.

Thanks you for sharing Stuart et al.

[Speedex750]

Bumping up and updating the progress on this thread;

My rebuilt working dynamator has expired. I’ve never tried to get it to charge a flat battery but only normal starting and running loads. Charging flickered and then stopped after a few hundred miles. Drat! Taking it apart, again, I found that one of the brushes fell out of the brush box, the braided tail having parted. Yippee thinks I - that's it! The rotor still tested out at 4 ohms with continuity through the new replacement generic brushbox and the rectifier pack tested OK with the diode facility on my multimeter. There are no obvious indications of battery drain back when turned off.

After rebuilding and getting everything back together, still no charge and the red light solidly on. It must be the (original) regulator thinks I. So I obtained the suggested generic replacement, cut out the regulator and wired that in. It was obvious which was the earth but not which way round the other two leads should be. Tried it, still no charge. All apart again and reversed the regulator connections, back in, still no charge. I may have inadvertently blown the regulator so I’ve tried a different one, wired out of the body to make wire reversals and regulator changes easier even though it looks a bit naff. Still no charge, even when the wiring was reversed.

I don't know where to go next? The rotor circuit seems OK, the diode pack tests out OK and I've tried two new regulators. Would having the regulator wired the wrong way round blow it? Is there a way of testing them?

Asking the audience for your collective experience of testing alternators in more modern machinery - is there anything else I could do or test? And as before, I’m wedded to 12 volts and have had similar difficulties with dynamos, maybe I’m the common factor in all this?

Thanks in anticipation, Dave (aka Speedex750; previously)

[andrew34ruby]

You don't need a regulator. All the regulator does is it allows different levels of feed to the Field Windings. With a couple of switches and a couple of different bulbs you can easily feed 4 levels of power to the field.

With both switches off............. no current in the field so no charging.

One switch on................small current to field, so charging maybe a couple of amps.

Other switch on (only).....bigger current to field, so charging maybe 4 to 6 amps.

Both switches on............. a bigger current to the field so more charging  maybe 8amps.

It's simple, doesn't fail, and it suits me. Instead of two bulbs I use a twin filament 12v stop/tail bulb.

I'm using the original Lucas dynamo but fitted with higher resistance field windings.

And I don't use a cut-out. Simply use a couple of diodes out of a 1980's Lucas alternator.

[Dave Mann]

Just spent a few idle minutes trawling the net and found this     
also available in 12 volt negative earth when stocks arrive.

[Speedex750]

Hi Dave,

Don't believe what is advertised, in my experience you can feel the tension if you ring up and mention A7's. They also now advertise a VW Beetle Bosch conversion. Hoping that this would be the same 3.5" body as the C35 I rang asking about spares for one, a diode pack and regulator. None available, if the there's a fault 'send it back with proof of purchase for an exchange'. I did feel rather guilty about the covert nature. One interesting thing came out of the conversation - the ignition light needs to be at least 2w, no LED's. It seems the resistance of the bulb in that circuit is crucial. A sidelight 5w bulb made no difference to mine.

I'm still trying to get to the bottom of why mine doesn't charge, any ideas from modern alternator experiences? The coils and diode pack seem to test OK and I can't find a regulator that triggers electricity, nor when I try to fool it by shorting 12v out or into the circuit.

Thank you, Dave

[worthidlj]

As a tangential thought, given that vw bosch dynamos have been used in the past; and some bosch dynamos have a Ø90 body, could the internals of one be used inside the body of a c35?

[Dave Mann]

I did wonder about how genuine the advert was, and you have provided the answer, thanks.