Light circuit power test

daggermark · 27 Jun 2020

I've had a series of problems with dimmer switches for lounge lighting. I've now had 3 failures where the switch runs incredibly hot and eventually gives up.

My lamps are well within the rated range of the switch and the manufacturer is scratching their head too.

Clutching at straws, but I can only think somehow too much power is being drawn to cause this to keep happening. Is there any way I can test for sure how much power this circuit is drawing? My multimeter doesn't do AC current, only DC.

I have checked the circuit and the switches and junctions are wired correctly.

bernardgreen · 27 Jun 2020

daggermark said:
My lamps are well within the rated range of the switch

The wattage of the lamps may be in the range but the way they interact may not be compatible.

What type of lamps are they ?

If they are LED then they will have an LED driver. LED lamps which connect directly to mains 230 volts have a driver inside the lamp to control the current through the LED element(s).

Not all LED drivers are dimmable, those that are dimmable fall into two main types (1) Leading Edge and (2) Trailing Edge.

Dimmers also fall into these two types,

If the driver and the dimmer are not of the same type then failures can be expected

daggermark said:
the manufacturer is scratching their head too.

Quite few companies selling lighting equipment have little if any technical knowledge about the products they sell.

daggermark · 27 Jun 2020

They're mains halogen lamps, g9.

The first 2 dimmers were leading-edge, the manufacturer then sent me a trailing-edge which also failed.

bernardgreen · 27 Jun 2020

daggermark said:
They're mains halogen lamps, g9.

Are the lamps 230 volt filaments or is there a transformer feeding lower voltage to the filaments ?.

A dimmed halogen lamp with a 230 volt filament takes less power through the dimmer but it takes it as a series of pulses, ( 100 per second ) which average out to the required current. Because the resistance of a dimmed filament is much lower than the resistance of a white hot filament the current in the pulses may be higher than the dimmer can handle.

daggermark · 27 Jun 2020

They're Osram dimmable mains-voltage bulbs, no transformers in the circuit.

My multimeter measures 247v at the switch.

flameport · 27 Jun 2020

What rating of lamps, how many of them, and the make/model/rating of the dimmer ?

daggermark · 27 Jun 2020

So its a 2-gang switch, both gangs in a 2-way config.

1 gang has 160w (4x40w) of lamps on it, the other has 240w (6x40w).

The dimmers are Varilight. I've so far had 2 master switches from the 'VPlus' range, and 1 'VPro' master switch - all 3 have failed on one gang or both. I've also gone through 2 different slave units so far.

The VPlus is rated 400w per gang.

The VPro says 150w per gang on a 2-gang switch - but the manufacturer themselves told me to try it! It's worth noting that the 1-gang version of the VPro allows 300w, and I never have both gangs switched on at the same time, so I assume this is probably actually ok.

Both 'VPlus' failed in a similar way - they'd work fine, albeit very hot, for weeks or even months at a time. Then one day, you turn them on and they give a dim light for 2 seconds before turning themselves off. This behaviour may be intermittent at first, but becomes more frequent until its permanent.

The 'VPro' has failed by refusing to turn off on one gang (the 160w gang).

The slave unit that broke just refused to control the lights, the 2nd one seems fine so far.

Both switch types are meant to have overload protection built-in, so if I had been overloading them I would be surprised.

flameport · 27 Jun 2020

Have any of the lamps failed?

daggermark · 27 Jun 2020

On the first switch, a lamp failed yes. At this time, Varilight indicated this could have damaged the dimmer. The last 2, no lamp failures.

winston1 · 27 Jun 2020

daggermark said:
The VPro says 150w per gang on a 2-gang switch - but the manufacturer themselves told me to try it! It's worth noting that the 1-gang version of the VPro allows 300w, and I never have both gangs switched on at the same time, so I assume this is probably actually ok.

You assume wrong. If it says 150W per gang that is what it means. It does not mean 300W averaged over 2 gangs.

daggermark · 27 Jun 2020

I know what you're saying winston, but the module is exactly the same as the one that is rated at 300w in a single-gang switch. So I believe the reason it is limited to 150w in a 2-gang config is because they would overheat if run side-by-side with >150w load on each one. The fact that Varilight recommended I try this switch even after I told them about the load and configuration... you'd hope they are right about their own product, but nothing would surprise me!

I'd have preferred to stick with the VPlus that is actually documented to support my config, but seeing as 2 of those have failed I was willing to give it a go!

daggermark · 2 Aug 2020

flameport said:
Have any of the lamps failed?

I've been running regular light switches for around a month now. There are 2 wall lights with 2 bulbs each. One of these 4 bulbs seems the most prone to failure. It has just gone again, making it 4 times in around 1 year, whereas some of the others have never failed! Dodgy fitting causing all my problems?

winston1 · 2 Aug 2020

daggermark said:
I know what you're saying Winston, but the module is exactly the same as the one that is rated at 300w in a single-gang switch.

Have you dissected it or are you assuming it is the same because the case looks the same?

daggermark · 29 Oct 2020

The same bulb has gone AGAIN, so 5 times in 14 months. Almost certain the fitting is killing the switches.

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Light circuit power test

Similar threads