Flickering lamps after dimmer fitted - possible solution

Those who have had trouble with LV lighting after fitting a dimmer switch may find this interesting.

I recently bought a couple of dimmer switches suitable for electronic transformers but when fitted, the lamps flickered at certain settings, accompanied by a buzzing from the switch. After double checking the trannies were dimmable, I rang the manufacturers who told me to try connecting a tungsten lamp across the 240 side of the tranny. She (yes, she!) told me that if it worked I'd need a load resistor connected the same way and she would send me a couple. It worked! The resistors are 4K7, 25 watt items available from RS, Maplin etc. The idea is to use one per switch to smooth out the flickering and reduce the buzzing. Not an ideal solution, but it may get you out of trouble, rather than swapping trannies and/or dimmers. I rang the tranny manufacturers who told me that the switch makers change their specs occasionally so that a dimmer that is perported to work ok with a particular tranny one week may in fact not be compatable the next.

Hope this is of some use to you.

why do i see so many people on theese forums suggest RS?

Afaict the only time RS are a good choice is if you need something not stocked anywhere else. They are one of the most expensive suppliers arround (a bit like the way i see many sparkies describe CEF).

As for maplin they are expensive too but thats offset by what you can save in delivery and time if you can get what you wan't in a local branch.

i'd try rapid farnell and CPC first (in that order) and only even consider RS if all 3 of those fail

plugwash said:

why do i see so many people on theese forums suggest RS?

Click to expand...

I totally agree

RS = Rip-off Supplier

I hear ya.

I suggested RS and Maplin as they are two names most on here would recognize. Not everyone on here is in the trade or is aware of the lesser known suppliers. Besides, how much can you save when shopping round for a £1.50 component?

Yes, RS are expensive (mostly) but they've got me out of trouble when I needed parts in a hurry and taken gear back without quibble when necessary.

BTW, it looks like CPC are part of Farnell now.

http://cpc.farnell.com/jsp/home/homepage.jsp

yes the are owned by premier farnell plc but thier stock range is quite different from farnell (inone) and thier pricing differs a bit too (generally it seems CPC have a lower first price but farnell give more bulk discount)

I fitted the resistors and all lamps are working. There's a very slight flickering at one point in the range but otherwise it's ok. I was a bit concerned about the resistor getting hot (it's a wire-wound type with it's own heatsink) so I soldered and sleeved the terminals and made a bit of a frame using a wire coat hanger formed into a coil. This is to keep the resistor in free space so as not to come into contact with cabling or the tranny. I'm going back tomorrow to do some other bits and I'll check the resistors again then. I'd much rather not have to do this. Can it be so difficult to obtain compatible kit?

I also replaced a LV ceiling fitting yesterday where the dimmer AND tranny had gone despite the dimmer being listed as suitable for LV. The fitting's instructions said nothing about dimmers although the delivery note did. 'Use halogen specific dimmers' it said. I assume that means electronic transformer specific. We did and they still went pop.

My mate tells me that MK dimmers, although expensive, give good results.

When installing the electrics in bars and pubs we use mains lamps via dimmer packs, usually mounted near the board with LV cabling to a set of sliders behind the bar. These have been 100% reliable so far and we have no reason to go back to LV.

I should correct my terminolgy here.

By LV I mean 12v, which should be referred to as ELV.

LV is the term for 240v.