PIR switching and use of capacitors

Alexl_82 · Nov 1, 2011

Hi guys, looking for some help and advice and wondered if any of you guys can give me some which would be much appreciated.

Im replacing switches in a stairwell in a block of flats for 2 wire PIR switches that dont need a neutral. I have replaced the switches that were simple push to make a circuit switches that controlled a timer under the stairs which in turn controlled the lights. Ive done away with the timer as the PIR switches each have their own timer built in. Now the problem is this, the lights all switch on ok but when the PIR switches have deactivated some of the lights flash. With my test lamps I can see that the voltage is fluctuating between about 40v and 150v across the switch live even though the PIR switches have not been activated. The lights are 28w2d and there are around 10 - 15. and there are about 6 of my new PIR switches all wired in parellel.

Im wondering if i Need to wire in a capacitor to fix this and if so would just 1 be ok? Also what size would i need?

Really hope someone can help with this.

Many thanks in advance,

Alex

telectrix · Nov 1, 2011

i would try a 1mfd, 400v capacitor across the switche dline and neutral for a start. then experiment if that don't work, maybe with a resistor in circuit. start around 3.3kohms.

BlueToBits · Nov 1, 2011

Have these ever worked?
The 2 wire PIR switches require a volt drop across the lamp to get a neutral. Fluorescent lights don't conduct until they have struck so they will never supply a neutral when they are off. The lights flicker when they are off because the PIR is trying to draw power through the fittings causing them to light but they aren't drawing enough to keep them lit so the go off. The voltage at the switch live will be fluctuating with the flashing. The impedance of your meter will likely be giving you false readings.

Alexl_82 · Nov 1, 2011

Hi thanks for the quick replies guys. These PIR switches have a little battery in them I think which allows them to not require the neutral. They do work as they are switching the lights on fine including the ones that flicker. I shall have a look online at those capacitors. Cheers.