Power factor laws and phase cut dimmers

[cupoftea]

Hi,
Obviously the easiest and cheapest way to dim a room-full
of lights (or even an office block full of lights) is to have a phase cut dimmer. you simply phase
cut the mains to the lights. This method needs no extra signal
wires to go to the lights.
Also, purists would criticise the poor power factor of this method.
However, since the phase-cut lamps draw less energy than non-phase-cut
lamps, this is actually a moot point.
If you are drawing less current by way of phase cutting, then the overall current draw
is likely to be less, and thats what power factor laws are mainly about.

So as we know, multi kilowatt mains phase cutting lamp drivers are
allowed by all regulations the world over. The mains harmonics regulations
state that their requirements are not needed for phase cut dimming systems.
So forget EN61000 for your 120A mains phase cut dimmers...its juts not required.

But why do we not see "symmetrical" phase cut dimmers"? (SPCD)
SPPCD's cut the mains half cycle on both trailing and leading edges so that
the power factor is improved.
I realise that the standards don't look at power factor (or mains harmonics) for phase cut dimming systems,
but wouldn't it be a good thing? (SPCD)

 

[betwixt]

Whether cutting leading or trailing edges, dimming like that will not work with most modern light fittings so I guess there isn't much appetite for developing it. The vast majority of 'office block' lights are fluorescent and will flicker if the cycles are shortened and decent LED fittings will convert to DC and not dim anyway.

Brian.

 

[cupoftea]

Thanks, I take your valid point. ..but there is still very much an appetite of office block owners to install cheap lighting/dimming systems....and so they buy lamps which are phase cut compatible.
The lack of signal wires means its much cheaper. Multi kilowatt Phase cutting systems for lighting are in high demand.
Plenty of even LED lamps can sense the phase cut and dim accordingly.
The customers simply buy lamps which are phase cut compatible.

The suppliers of hundred Amp plus phase cut dimmers often make their own range of compatible lamps, for the customers.

The other added benefit of hundred plus Amp phase mains cut dimmers is that they are allowed by all the EN regulations.
Mains harmonic laws do not apply to them. This is one of the reasons they are so popular still.

I mean, you want to light up 1000's of luminaires in an office block...and you want them dimmable?.....easy....just forget about mains harmonics and PFC and choose a several 100 Amp phase cut dimming system and you're quids in......no need to bother about Active PFC....in some locations the electricity company may charge you a bit extra for the poor power factor, but its still cheaper to go Phase cut.

 

[Easy peasy]

Hmm - there was a product developed some years ago - called the Light Manager

It had an auto transformer - 230Vac and 200Vac tapping

it had a clever system of smoothly going from the 230V tapping ( no losses in the auto Tx ) to the 200V tapping over 10 sec - to reduce lighting draw ( fluoro systems ) - such that the staff would not notice the reduced light output ( very much ) - it would work for any lighting load.

Up to 10 A per phase as I recall.