CF3 cut out

[John Cornforth]

Hi bob

I attach a diagram of the CF3 internals based on the best information I have.  I suggest you check that the shunt coil is OK by using an ohmmeter with the wires to the cutout temporarily removed.  The shunt coil is usually earthed by a short link from the E terminal to a nearby earth tag on the bulkhead.

The pull-in voltage is adjusted by very slightly bending a piece of bent metal that acts as a stop for the contact assembly in its open position
  CF3 Cutout.jpg (Size: 39.13 KB / Downloads: 123)

Readings of 18 volts suggest that either the cutout isn't closing or you are using a modern electronic voltmeter which is being sent haywire by the voltage spikes present in all A7 systems. An old fashioned AVO or similar is a better bet.

[bob46320]

Thank you John, yes, the meter did read 18 volts - even 18v on a 6 volt battery !!! - but then my moving coil meter is the cheapest of the cheap range. Tried a different meter and we read 7 - 8 volts on the 50 v range - so that is the 18 volt problem kicked into touch.
Bob

[Bob Culver]

Small basic analogue meters were/are available very cheap, but, as even with the most expensive AVOs accuracy esp at small scle is not good. The digital meters genreally very accurate and can be used to calibrate the analogue, much more useful for old car work. Show fluctuations better and respnd less to the huge spark hash of all original Sevens.