Classic cars forum & vehicle restoration.

euronerd · Joined: 13 Oct 2008 Posts: 16 Location: Yorkshire

Could anybody offer any advice on this please? When I start up, the ignition light stays on. When I close the cut out contacts by hand the light goes out. Charging is intermittent but the light stays off as long as the engine is running. The first symptom was that the ignition light stayed on for a few minutes after starting, then flickered and finally went out, and the charging rate increased very gradually regardless of engine speed. The electrical system is Rotax with a three-brush dynamo and no regulator. The wiring is sound.
Thanks in advance.

Geoff.

47Jag · Posted: Wed Nov 19, 2008 2:57 am Post subject:

Geoff,

The ignition light get it's return (earth) thru' the armature and by closing the cut-out points manually you are only fooling yourself. If there is insufficient votage generated it can't close the points. The regulation such as it is, is provided by the thin 3rd brush. This picks up a voltage and applies it to the field coils. The problem with this design is it will provide whatever charge it is set for regardless of demand. The problem sounds like bad brushes. If it has been working in the past then these would be the first things to check.

Art

bob2 · Joined: 06 Dec 2007 Posts: 1727 Location: Malta

Thought this had something to do with buzzy(Dave) Bee not sleeping well, hence not charging!! Very Happy

pigtin · Joined: 23 Nov 2007 Posts: 1879 Location: Herne Bay

First thing I would look for is solder thrown off the commutator segments where the windings connect. Then perhaps, if the brushes are free in their guides.
Sometimes you can solder the windings back on to the segments, I used to have to do it regularly on my first car, a 33 Standard big 9. It's as well to find what is causing the overload... perhaps the third brush is set to maximum. Surprised

Be careful operating the cutout by hand... the battery may try to drive the dynamo like a motor.
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Nic Jarman · Posted: Thu Nov 20, 2008 10:23 pm Post subject:

Hi Geoff, looking at my lucas dynamo it has brushes screwed to spring loaded arms. With a long matchstick or simillar gently push against each cable to make sure they really are connected and you can move the brushes to make sure they are not stuck. Also is your fan belt OK?

euronerd · Joined: 13 Oct 2008 Posts: 16 Location: Yorkshire

Thank you gents. Looks like the brushes are the prime suspect. The third brush is set about right - 15A max. Brushes were new about a year ago, when the dynamo was fully checked, but newly manufactured 'spec' items are not always a happy experience. Nic, the Rotax dynamo sounds similar to the Lucas and the brushes were free. Can't be the belt because there isn't one.

Geoff.

Nic Jarman · Posted: Fri Nov 21, 2008 12:24 pm Post subject:

How wonderful not to have a belt.

euronerd · Joined: 13 Oct 2008 Posts: 16 Location: Yorkshire