A mate brought round a dynamo and a newly-acquired CVC box yesterday.
The dynamo had been converted, very nicely, from three brush to two brush with rebuilt guts, and for 12v. It's a Marchal, a very good quality item of solid construction, typical continental design using 4 field coils and a centrally disposed armature. It had been wired to work in conjunction with a regulator of the 'Lucas' type, ie for live side regulation.
The gent who rebuilt it supplied a CVC box he'd acquired from a reputable French source as an RB108 etc replacement. He said it was new. Not one I'd seen before, being larger than the usual dodgy cheapos. He said the two together seemed to work nicely.
Well . . . maybe they did, if the only test he did was to connect the dyn to the reg and see if there was a stable output with the dyn driven by an electric drill. Which there was indeed.
However, my mate then took over, to fit the bits to whatever beast it is. But first, wisely, he tested things one more time on the bench, with a battery and ammeter in circuit and the dynamo mounted on a test rig.
And lo and behold, good output, yes sir . . . but with the battery in circuit he was disconcerted to find that the dynamo turned like a motor when the rig was stopped.
He nipped round with it for a natter, not being sure whether it was 'him' or 'it'.
A quick check of the dynamo itself showed all was well there, and a repeat test without a battery confirmed that the regulator worked after its fashion. But with a battery, same thing. Not cutting out on declining revs. So it was 'it', not 'him'.
Classic malfunction. Which, had the bits been fitted with the dynamo drive in place, could have been very expensive and smoky/smelly.
The only position of the adjuster screw in which the thing would cut-IN was the one it had been set to; so much as an 1/8th of a turn either way stopped it working at all; and there was simply NO position in which the cut-out would open as revs dropped - until the battery was disconnected.
So the tabs on the box were bent back and the guts extracted and examined. Talk about shoddy. Extensive further efforts to find any setting where the cut-out would operate properly also failed. The alignment of the various sets of points and of pretty well everything inside was terrible. Not worth bothering with for another milli-second.
This unit is a first cousin of the smaller replica Chinese boxes available everywhere, which in my experience have been equally awful. You gotta love the 'Quality Assured' stickers and the like . . .
DON'T EVEN THINK ABOUT USING ONE!
Fortunately, I had a little-used neg earth regulator lying around. Not my fave, but a V Reg I'd taken off one of my own bikes in favour of a DVR some years ago. It'll do for the time being I think, with a working cut out and a very stable regulating voltage.