Hello, thank you and Help...

[Chris Vine]

Hi All,

Thank you for the mine of information which resides in this forum!

I have just acquire a Lister generator, ST3 coupled to Brush SCTF 320.
There has been an incident in the past which resulted in a burnt cable (neutral/earth) to the control box on top, However the machine doesn't seem to have done a lot of work.
Cable replaced.

Thanks to the amazing information on this site, I have now nearly worked out all its problems.
I have a replacement silicon bridge rectifier arriving in a couple of days, and can make a heat sink in a few minutes.
Also, have managed to work out which cables are which at the selenium rectifier so that I can connect up the auxiliary field coils the correct way round!

While motoring over on the starter windings, it generates some 80 volts and is sufficient to lock up the decompressor solenoid, so all is looking good so far.
However, I have a question on the auxiliary field winding:  What should its resistance be - even approximately - please?
Measuring, it seems to be very low, almost zero.  Maybe this is correct, maybe it is a problem?

If anyone has a scan of the manual for the SCTF style Brush generator, I would love a copy.  There is one vital page on this forum which has helped a lot, but the rest would be magic.

Thank you in advance!
All best wishes
Chris Vine.

[Chris Vine]

PS,

After taking the dog for a walk, I think I may have answered my question? maybe?...

I now realise that some/all the output current from the slip rings (rotating winding) goes through the auxiliary field winding and then re-joins the output through the bridge rectifier.
So, the auxiliary field winding is effectively in series with the output and needs to have a very low resistance.

If I have understood this correctly, then the aux field winding is a few turns of thick copper, carrying a high current.
Luckily the silicon rectifier I have ordered, to replace the selenium one, is rated at 100 amps (1600 volts), so should be ok.

Have I got this right, or have I got the wrong end of the stick please?

Pretty certain I will bump into some other problems very soon...
Thanks
Chris.

[ajaffa1]

Hi Chris, glad to see you have resolved most of the Brush alternator issues. Sadly I now have to work from memory as all my technical data and service manuals where destroyed in a bush fire. I hope that some of my earlier posts were informative.

Bob

[Chris Vine]

Hi Bob,

It is largely thanks to your previous posts that I have got to where I am.

Looking at other sources about compound wound alternators, with the auxiliary field coil in series, it looks as though its resistance is in the order of 0.1 ohm to 0.01 ohm.  No wonder it looked as though it was shorted!!

Will let you know progress...

Thanks again,
Chris.