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Dynamo failure again.

Checking on the M20 tonight.
I stripped and cleaned the dynamo a few months ago and from getting no output I had it back on the bike pushing out about 7 volts and working the lights on the revs without the battery on. Tonight its back to nothing again! Just dont know where to go with it? Get a new armature and field coil? Track down another unit?
As far as I know I have set it all up correctly..how often do I need to 'flash' it to negative earthing ?
Richard

email (option): richardpurkiss@hotmail.com

Re: Dynamo failure again.

Dear R

There are numerous websites that show how to test and repair a Lucas dyno. A Google search will turn up many.

I just went through this on my M20 E3HM dyno. The dyno would work only intermittently. So this was my procedure:

Disassemble the dyno.

Check the electrical continuity of all wires and connections with a decent volt ohm meter. all should be zero ohms. Check the condition and continuity of the brushes. brushes should be zero - 1 ohm. Disconnect the field coil and test for continuity - should be about 2-3 ohms. Finally test the armature continuity of adjacent commutator segments all around the commutator, and segments 180 degrees apart all the way around. all should all be approx. zero ohms. Test each commentator segment continuity to the steel core, each should be infinite ohms.

Inspect the armature core for signs of rubbing against the field coil. It should not touch the field coil or the steel saddle.

Inspect the armature shaft bearing and bushing. There should not be excess play or signs of excess wear.

Make sure the field coil and brushes wiring is correct. When I bought my M20, the dyno wiring was really screwed up. Best to check even the most simple things.

If all these are ok, then the issue is most probably the armature, either the armature is not true along the rotation axis, or the windings are faulty, or both.

Bench test the dyno with an electric drill and socket sized to fit the drive end fixing bolt. With the D and F terminals shorted, and a volt meter + attached to the D-F terminals, and the - to ground, the dyno should show more than 6-7+ dc volts at about 1000 1500 rpm. Don't overdo this test, prolonged power generation with this wiring can damage the dyno.

If the dyno passes the bench test, install it on the moto and test the battery voltage when the moto is running. It should be 13.5-14.5 dc volts. If not, the likely fault is the voltage regulator.

Lucas dynos are simple machines, so don't buy another one or a repair kit before diagnosing the root cause of the issue. They are relatively east to repair and are rugged and reliable once working properly.

I sent my armature to White Armature Inc., Wisconsin USA. Google them for address and phone. They rewound, lathe - trued, balanced and growler - tested it for about $100 US, not including shipping each way.

The dyno works flawlessly now.😁

Dave W.

email (option): Dwdiak4@gmail.com

Re: Dynamo failure again.

Thanks. I went through the dyno wiring again tonight. The carbon brushes in there are the original Lucas type with the strange metal coil insulating to the wire. It looked as though this wiring to the 'D' terminal in the face plate was touching the field wire terminal to 'F'. I insulated the brush wires with tape and re-assembled and now its pushing out 8-9 volts. Looks like it was a simple shorting out problem. My new charged battery is reading 6.1v and is reading 6.7v when engine running on idle so its obviously trickle charging now.!

email (option): richardpurkiss@hotmail.com

Re: Dynamo failure again.

I guess 13.5 - 14.5 volts is for a 12v battery and 12v regulator.

This voltage at the battery would fry a 6v battery and would damage a solid state 6v regulator

email (option): sacombsashtrees@hotmail.com

Re: Dynamo failure again.

Mine did something similar, it turned out the clutch mechanism on the large fiber gear was slipping as the engine warmed up. This may be something to check.

email (option): msawicki@fsu.edu

Re: Dynamo failure again.

Patrick

You are correct, I was thinking about a 12v system. An M20 E3HM dyno should be putting out 7+ volts before the regulator, depending on rotation speed.

Apologies for any confusion.

DTW927

email (option): Dwdiak4@gmail.com

Re: Dynamo failure again.

An unregulated Lucas 6 volt dynamo will produce over 12 volts....Ian

email (option): ian@wright52.plus.com

Re: Dynamo failure again.

A six volt unregulated dynamo will produce over twenty volts before it throws all the solder off the commutator.

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