Plinth Lights Flicker When Off?!

[squiduk]

Hi guys.

Recently fitted some new plinth lights and noticed the other night that the lights would keep flashing on and off when the switch was in the off position. Today I have checked the wiring with a multimeter and when the switch is in the off position there is 44v between L-N and L-E. Any ideas why this could be happening as this is could be causing the lights to flicker.

 

[ericmark]

The answer is complex, it is a subject called transmission lines, we see it in the main with radio, talk to any CB'er and he will tell you how you need to measure the SWR. In real terms they measure the voltage standing wave ratio. So what it means is with an AC supply, any cable is a mixture or capacitance, induction and resistance. If the feed and return wires are the correct distance apart then the capacitance and induction cancel each other out, and it is called balanced.

With the system used in UK with the line only going to and from the switch the system is not balanced. The correct method would be to measure the out of balance and add a capacitance or inductance to balance the system. However in practice most lamp manufactures include a small resistance in their lamps which is normally enough to leak away the in-balance. When this fails often a capacitance and resistance unit designed to stop interference are used to remove the extra in-balance. The problem with latter is when the lamp is replaced it may not be required, and no one ever tries to remove them when replacing lamp, so it can waste power although very little.

 

[JohnW2]

The answer is complex, it is a subject called transmission lines, we see it in the main with radio ....

We do indeed see it with radio. However, as I've said to you before, unless you're talking of cables hundreds of miles long, or more, I think you can really forget about transmission line theory at 50Hz.

Kind Regards, John

 

[Taylortwocities]

Probably due to induced voltages. Try fitting one of these across one of the lights http://www.maplin.co.uk/p/rc-contact-suppressor-rg22y

 

[squiduk]

ericmark Very interesting read.

Taylortwocities I cannot fit the components suggested as the lights run off a 13amp plug (built in transformer) which in turn is switched at the light switch. I have noticed that there is also a voltage present in the pelmet circuit (when switch off) which is about 35v

 

[Taylortwocities]

You only need ONE. fit it on the output of the driver, or across any of the lights in the chain.

The 35v you are reading is the problem. It's caused by induced voltage from other circuits. You probably have your 5v LED wires running near 230v mains cables. The component will eliminate it this problem.

 

[bernardgreen]

13amp plug (built in transformer)

It is not a transformer. It is a switch mode power supply ( SMPS ). If it were a transformer then the small amount of power capacitively coupled into the switched live wire would be absorbed in the transformer and not reach the LEDs.
A switch mode power supply will accumulate that small amount of power in a capacitor and when there is enough power stored in the capacitor the SMPS will fire up and send power to the LED until the stored power has been used up.

The snubber ( http://www.maplin.co.uk/p/rc-contact-suppressor-rg22y ) absorbs the small amount of capacitively coupled power and thus prevents the capacitor in the SMPS accumulating it.

 

[Taylortwocities]

It is not a transformer. It is a switch mode power supply ( SMPS ).

Are you turning into Winston?

 

[bernardgreen]

Are you turning into Winston?

No but there are times when he has a valid point.

 

[squiduk]

Thanks again for the imput guys. I understand what you are suggesting with the driver but sadly the kit doesnt have a driver. https://www.amazon.co.uk/gp/product/B00KFEBHY4/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

Would it be as simple as to buy the supressor and just install in the back of the 13amp socket?

 

[winston1]

ericmark Very interesting read.

Taylortwocities I cannot fit the components suggested as the lights run off a 13amp plug (built in transformer) which in turn is switched at the light switch. I have noticed that there is also a voltage present in the pelmet circuit (when switch off) which is about 35v

A 13 amp socket should NOT be on the lighting circuit, especially in a kitchen waiting for someone to plug a kettle into it. So get that corrected first.

 

[bernardgreen]

Would it be as simple as to buy the supressor and just install in the back of the 13amp socket?

It might be

Where is the switch that you use to control the plinth lights and where is the socket into which their "plug " ( SMPS ) is plugged ? /

If the switch is a separate switch that switches the supply to the socket ( ie NOT the switch on the socket ) then yes putting the suppressor ( snubber ) across the Live and Neutral in the back of the socket will be OK.

 

[Taylortwocities]

Thanks again for the imput guys. I understand what you are suggesting with the driver but sadly the kit doesnt have a driver. https://www.amazon.co.uk/gp/product/B00KFEBHY4/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

Would it be as simple as to buy the supressor and just install in the back of the 13amp socket?

NO!! the supressor must be on the extra low voltage side of the black box thing that the supplier describes as a "transformer"

The description states
"Complete Kit - Includes All Bulbs / Cables / Connections. Low Voltage Outdoor Transformer (IP67 Rated). 5m Cable from Transformer to First Lamp"

So you need to connect the supressor somewhere on the output side of the black box that the supplier calls a transformer. It is the side that goes to the lamps and not the side that goes to the mains. OK?

@squiduk Beware!!!!!
In the next 260 posts there will be an arguement about that black box and if it is really a transformer, driver, SMPS, space shuttle, driverless car etc.
Ignore all of this. Go to Maplin and sort out your problem.

PS. mark that socket "lighting circuit only", just in case some idiot finds they can remove your plinth, get underneath the kitchen cupboards and plug in a MIG welder.

 

[Taylortwocities]

A 13 amp socket should NOT be on the lighting circuit, especially in a kitchen waiting for someone to plug a kettle into it. So get that corrected first.

So what? the kettle isn't going to actually do anything, is it?

Hint for the hard of thinking:
CPD on lighting circuit = 6amps. Kettle = 13 amps

 

[bernardgreen]

NO!! the supressor must be on the extra low voltage side of the black box thing that the supplier describes as a "transformer"

Sorry Taylor but in this case you are wrong. Putting the suppressor on the extra low voltage ( ELV ) output of the SMPS ( plug ) will be putting a capacitor across a ELV supply that maybe pulse width modulated or other wise rely on the load being low capacity to ensure proper and safe operation of the LED elements and could result in damage to the elements.

With out the supressor on the mains input the SMPS will still generate pulse of ELV output from the capacitively coupled power on the switched live feeding the socket.