E3LM Field Coil replacement

[chris.shearwood]

I can't recommend the supplier as it seems his on-line presence has disappeared.

Hello Bevan,
I found the supplier from whom I received very good service: https://www.dynamosdynamos.com/

[bevanclark]

Hi folks,
A bit of background: the magdyno had been functioning perfectly for the 2000 miles I had done since getting the bike. Unfortunately, the mag and dyno were flooded with a lot of oil when the return pump failed. Both continued to work fine for around 100 mles or so after i had fixed the pump however. As an aside, I now know that I have a really good feed pump. When I came to a halt and noticed a puddle of oil underneath the bike, oil was even pissing out of the points cover at idle !

As I was concerned about the possibility of a future, inconvenient, failure I had a specialist dismantle and clean up the mag. He also cleaned the dyno, but did not disturb the field coil. He did comment that he felt the field coil covering loooked oil soaked and he had no way of thoroughly cleaning it (its resistance was around 3 Ohms which seemed ok).

On refitting, the dyno produced zero volts; even flashing it had no effect, but it did come right after I took it off and motored it.

However, a few weeks later, we were back to no charging, so I concluded that the oily field coil was probably knackered.

Well, I have today dismantled my dynamo. The old field coil certainly looks fairly dodgy. I have just replaced it with a Lucas branded "Made in England" one - it was a lot easier than I had feared, and the armature rotates without binding on the pole shoe. However, I still have problems. While I had it apart, I carefully cleaned and inspected the commutator - looks o.k. to me. I also cleaned and very lightly sanded the brushes. Resistance of the new field coil is 2.7 Ohms and from the D terminal to earth is 0.8 Ohms.

The dyno will motor fine. Once back on the bike, I flashed it briefly and then connected a 12 V bulb in the prescribed manner - it lit up brightly after a few seconds at a bit above idle - all good. But when I disconnected then reconnected it, it would not light up. Flashed it again and it would light the bulb, disconnect it, reconnect it - nothing.

I find it hard to believe that a brand new field coil has the same issue as my old one (apparently) had, so am now wondering if I am completely on the wrong track, so have some (probably dumb) questions:

- it motors in the direction of the arrow on the case. Is this correct, given that a dyno is effectively a motor running in reverse ? (I realise it is easy to reverse the direction by swapping the field coil connections).

- is it possible that the previously good brushes have become oil impregnated (and softened ?) following the pump failure and this is somehow the cause of my problems ? I did notice that there was a smear of carbon on the previously shiny clean segments after only a minute or so of running. I cleaned this off before trying again as detailed above.

- the armature looked ok and i cleaned carbon out from between the segments with a meths soaked rag and my thumb nail. They all looked pretty good under a magnifying glass, but is it possible the armature is now faulty ?

The irritating thing is that the dyno was working fine before I sent it away to have to oil cleaned out !

A next simple step I guess is to swap in the brushes from my Panther's E3LM and see if that solves the problem.

Any suggestions are most welcome !

Cheers,
Bevan

[Julian Murphy]

You might be motoring in the direction of the arrow on the casing, but is that the direction of rotation when fitted?

[bevanclark]

A good question - just went and checked; yes it does rotate on the bike in the direction shown on the case.

[Julian Murphy]

OK.

I would suggest that if the Panther dynamo is working, dont fiddle about with that by removing the brushes. You know what happens when you fiddle.

Just buy another set of brushes.

[Simon.Gardiner]

I spent months trying to sort out a dyno that motored fine but wouldn't reliably produce a charge. (I think it even passed the light bulb test.)
Eventually fixed it by replacing the armature with a new one.
Motoring a dyno isn't a foolproof test for it having good components - I suspect the commutator connections can become a bit 'dry' and intermittent (especially when they're asked to carry any load).
So as I've now got a very fine T-shirt with the slogan 'I've spent months and months playing unsuccessfully with an E3LM ' my first move now is to just replace with new rather than trying to swap in something from somewhere else.

SG

[bevanclark]

Fair comments ! The Panther dyno is working fine, so I was a bit uneasy about disturbing it.

I probably should have followed an earlier suggestion and bought the full rebuild kit from Rex's, but had trouble prizing my wallet open sufficiently.

Will get some new brushes. Guess that if its not that, then it has to be the armature.

[paul.jameson]

Try new brushes first. The ones with blue woven sleeving to the wires are a lot softer than the originals which have a yellow coiled sleeving so the new ones may be prone to giving trouble when oiled.
The dynamo on my Red Hunter has worked for many years (over 30) but never very well. A few years ago I replaced the brush end bush with a complete new end to the dynamo and it now works far better than ever it did previously. Presumably, the old bush allowed the brushes to jump up and down.

[will_curry]

Lucas E3LM dynamos rely on there being some residual magnetism in the body and pole piece to
start things off when the armature begins rotating. Once it's spinning in even a weak magnetic
field whatever current is generated goes straight back into the field coils and so strengthens
the field. In this manner the dynamo voltage rapidly rises unless some action is taken to limit
the current in the field coil.

I had understood that the reason field coils needed the tool to install them was that the fit
between the pole piece and the body had to be very snug so that the residual magnetic field was
as it should be.

Over the years I've had various armature failures, usually at the commutator but so far I haven't
had a field coil fail and some of them have been repeatedly soaked in hot, dirty oil.

As Paul says, a high resistance in the brushes and commutator can cause problems as can dirty
contacts within the Lucas control box or a high switching resistance in the electronics of various
of the electronic control box replacements.

Testing with the light bulb already connected before the dynamo is rotating might be providing
an electrical path which diverts the armature's current away from the field coil and so prevents
the magnetic field from building up.

[bevanclark]

Hi folks,
Progress at last - around 13 Volts unregulated at a bit above idle - new brushes did the trick.
Before fitting them, I compared the ease with which I could make a mark in some paper and it does appear that the old brushes are softer. And yet, the dyno functioned perfectly for the ~2000 miles I have done since acquiring it. So it may perhaps be that having been soaked in oil they softened. This is consistent with the fact that I had to re-clean black smears off the commutator after only a few revolutions following reassembly. Despite allowing the dynamo to motor, perhaps their conductivity was also reduced by the oil having penetration.
Have also taken the opportunity to clean up the pitted contacts on the old MCR2 regulator and adjust the various gaps. So hopefully I will see some charging happening tomorrow !
Thanks all for the helpful advice - all good learning for me.
Cheers,
Bevan