On Thu, 08 Sep 2005 23:44:06 +0100, Andy Wade
wrote:

wrote:

I'd be interested to hear the true answer. Its not wave shape, a
filament lightbulb can run off any wave shape, and with the power level
varying at 100Hz (which is what you get on a 50Hz supply) the filament
will smooth it all out no problem.

The lighting flicker you see on gennies sometimes is at much lower freq
than 50Hz, so the genny's output must be in some way modulated at a
lower frequency. I dont know what the cause is, but the only likely
candidate I can think of is the control circuitry, the regulator, where
one is fitted.

I agree. The genny will have an AVR module (automatic voltage
regulator) which senses the AC output voltage and adjusts the (DC)
current in the field windings to stabilise the output. Thus there's a
negative feedback loop involved and all the usual loop dynamics and
stability issues are present. If the loop is underdamped and there's a
varying load on the genny you get 'hunting' of the o/p voltage, which is
exactly the "modulation" you describe.

ISTR noticing as a small child the lamps on fairground rides and
sideshows being modulated the same way.

DG