CF3 cut out

[bob46320]

Setup:-  C35A dynamo- third brush dynamo with brushes on hinged holders, Cut out type CF3, Switch panel type SM5 (As per fig 1 Dave Mann PW A7 Feb 2022)

First time out for a decent run this year. Initially, the dynamo output wobbled about on a 3 - 4 amp charge and after 60 miles or so settled in to a nice steady 8 amp charge at "cruising speed".  I assumed that perhaps the commutator cleaned up, brushes settle etc etc.  BUT, on occasion, when the revs drop, the ammeter shows about 2 amp discharge and the ignition light does not come on.  ALSO, on occasion, when stopping the engine and ignition OFF, the ignition light stayed on !!  Cutting the battery supply by the master cut off switch obviously put the ign light off.

Looking inside the CF3 cut out, the spring holding the contacts open looks OK as is the braided wire from the moving contact to the solenoid coil. I am reluctant to aggressively clean the contacts inside the cutout, and normally clean them by 'sanding' with a piece of clean card slid in and out a few times, then clean with alcohol.

My prognosis is that the spring inside the CF3 has become too weak to pull the contacts apart and needs to be shortened ??
What do the experts say ??
Bob

["Slack Alice" Simon]

The contacts on mine "stick" after switching off.

I assume it is a weak spring, but kicking the firewall near the box seems to do the trick without my doing anything more technical - until I really have to.

[Bob Culver]

The cutout contacts are soft silver and can be tidied with a clean fingernail file with little risk of embedding non conductive particles.

[Robert Foreman]

I certainly would not use a nail file to clean the contacts. As the other Bob wisely said a piece of card or paper with the points gently pressed against it is sufficient.

[bob46320]

Thanks for the replies - but do I update the spring which pulls the contacts apart ?

[Stuart Giles]

Could be a voltage coil issue if the cutout isn't releasing. So it could be worth checking that the cutout's earth contact is good. When the revs drop, the voltage coil to earth is held operated by virtue of the contact being closed, but the current coil which is in series with the dynamo output should be opposing; i.e current will be flowing from the battery to the dynamo via the current coil. So the magnetic flux from the two coils opposes in the core, which should pretty much release the cutout contact straight away.

[bob46320]

Thanks Stuart,  I will check the short earthing wire to the cutout, also the battery terminals as I had given the battery a long charge up just a few days beforehand.
Bob

[Bob Culver]

I dunno what the specs are but for other Lucas cutouts s mention about .010 follow through of the contact. This seems to add considerably to the final release pressure so if much reduced may encourage sticking.

[bob46320]

This makes good reading re glass paper for cleaning the contacts (Or wearing them out ??)  and adjustment of the air gap.
http://www.da7c.co.uk/History%20Section/...%20CF3.pdf

[bob46320]

Fiddling with the cutout this morning, checking voltage output at a charge rate of about +5 amps, volts +18v (for a 6 volt system) between the terminals + and E or A and E. These voltages check out with the da7c technical note BUT is this a CF3 cutout as I had always thought it was because the terminals are marked thus
+ + E A The leftmost + terminal is not used.
Its been running OK like this for 20 years with a 6 volt system - so I am confused.