UK Advice (please) regarding suppressor / "snubber" for LED lighting

[feisar32]

Hi all

Hoping someone might be able to advise. I've got two sets of LED lighting this is affecting. One is the plinth LEDs I originally raised a thread for some months back; one is two LED wall lights.

The problem I have is that, when the lights are off, they flash briefly every ten seconds (in the case of the plinth LEDs) and every twenty(ish) seconds in the case of the farthest LEDs wall lamp. Both sets of lights are switched; the wall lamps are switched individually, and can be switched from the three-way switch nearest the door, or from a single switch under each lamp. The plinth LEDs are switched both via a presence detector, and can be overridden by a standard grid-switch module

When I did some Googling, there was a thread I found elsewhere that suggested "[..] you can usually check for a small voltage on the switched live wire. If the circuit has two-way switching, this voltage will be more apparent on one of the "off" configurations rather than the other. Adding a suppressor (or snubber) to the circuit between the switched live and the neutral will solve the problem".

My brother-in-law is an electrician, but he says he's never heard of suppressors or snubbers. I wondered whether this issue sounds familiar to any of you and if so, whether the suppressor or snubber is the correct solution?

When I Googled snubbers, what I got back as an example was something like a "Danlers Low Load Capacitor for Low Energy Lamps" ... would that be the right sort of thing ... ?

One other query as well, if I may: anyone know of any 24v LED strip with a 50mm cut-point ... ? Or is it only 12v strip that can be put at those intervals?

Thanks in advance ...

 

[pc1966]

The "problem" with LED lights is they take so little power to operate them, and even worse they often have the ability to charge up until they conduct (and flash) then repeating this. It only takes a small current, the sort you get from capacitive couple between conductors for a 2-way switch, to make this happen.

A snubber network is a resistor and capacitor originally intended to suppress arcing at switch or relay contacts, but now they are often used to provide an alternative path for the very low capacitive current. Basically you connect one in parallel with the LED light (i.e. from L to N at one light) and it (hopefully) keeps any stray current down. Here is an example:

https://cpc.farnell.com/unbranded/xeb1201/filter-xeb1201b-fly-lead/dp/CA06044

 

[feisar32]

The "problem" with LED lights is they take so little power to operate them, and even worse they often have the ability to charge up until they conduct (and flash) then repeating this. It only takes a small current, the sort you get from capacitive couple between conductors for a 2-way switch, to make this happen.

A snubber network is a resistor and capacitor originally intended to suppress arcing at switch or relay contacts, but now they are often used to provide an alternative path for the very low capacitive current. Basically you connect one in parallel with the LED light (i.e. from L to N at one light) and it (hopefully) keeps any stray current down. Here is an example:

https://cpc.farnell.com/unbranded/xeb1201/filter-xeb1201b-fly-lead/dp/CA06044

That's really helpful, thank you ? Would I need one of those per light, or would that be one per circuit?

 

[pc1966]

That's really helpful, thank you ? Would I need one of those per light, or would that be one per circuit?

One per circuit is usually enough.

Some 'smart' controllers have DC leackage and that is not really solved by a capacitive snubber though.

 

[feisar32]

One per circuit is usually enough.

Nice, thank you very much ? I'll grab a couple then and get my brother-in-law to fit them ?

 

[Lucien Nunes]

Would I need one of those per light, or would that be one per circuit?

We should probably describe it as 'one per separately-controlled lighting group.' as that does not technically constitute a circuit, but I am sure you have the right idea.

 

[Mike Johnson]

Snubber available from Farnell, worked for me, fits neatly inside a Wago lighting box.

 

[feisar32]

Thanks @Lucien Nunes and @Mike Johnson; quick question though if I may: how would I work out which one of the Rifa PMR 209 units I need to get ... ? Looks like they're all similar prices from CPC, but I'd like to be sure I'm getting the right one ...

Is there a benefit of this one over the XEB1201B @pc1966 recommended?

 

[pc1966]

Is there a benefit of this one over the XEB1201B @pc1966 recommended?

Main advantage is it has insulated flexible wires, so is slightly easier to wire up if you are not lucky enough to have terminals neatly aligned such as the @Mike Johnson example.

 

[Taylortwocities]

The last couple I bought were from eBay.

2 x Kemet RC Capacitor 100nF 47Ω 20% 250Vac 24 x 7.6 x 14mm (Pack of 2) | eBay

Find many great new & used options and get the best deals for 2 x Kemet RC Capacitor 100nF 47Ω 20% 250Vac 24 x 7.6 x 14mm (Pack of 2) at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

They were fine. Cheap too.

 

[Lucien Nunes]

@Mike Johnson's solution is very neat as a purpose-built unit, but for installation in an existing fitting, I recommend a type with insulated wire leadouts as per the link in post#2.

Any type with 0.1 - 0.22μF plus 100-120Ω is suitable electrically. The Rifa metallised paper types with that gold-coloured element in a clear plastic moulding ought to be of good quality. However the older examples of that brand (25+ years) have gained a poor reputation in the electronics industry for going up in a cloud of smoke. I tend to avoid them, perhaps unfairly, because of that experience.

 

[LukeD]

Very interesting thread

 

[Mike Johnson]

@Lucien Nunes its not a purpose built unit, it's just the normal Wago lighting box and it all fits in neatly, just happenstance really, its what I used to update an existing set of LED GU10 downlight fittings to stop them flashing, I don't know if the number is anything to do with it, but there are twelve of them and I had to put three of these in to achieve the result.

 

[Lucien Nunes]

Sure, I meant that you had purpose-built them for the downlighters during installation, but the OP wants to add to existing fittings hence probably easier with longer insulated leads. I can't see the capacitance of yours, I wonder what length of cable is in your switch runs to create the leakage?

 

[Mike Johnson]

@Lucien Nunes total length of cable is about 15M, double switched, the snubber is this one: PRS Components - https://uk.rs-online.com/web/p/rc-network-capacitors/2067831/

 

[Papa Lazarou]

The last couple I bought were from eBay.

2 x Kemet RC Capacitor 100nF 47Ω 20% 250Vac 24 x 7.6 x 14mm (Pack of 2) | eBay

Find many great new & used options and get the best deals for 2 x Kemet RC Capacitor 100nF 47Ω 20% 250Vac 24 x 7.6 x 14mm (Pack of 2) at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

They were fine. Cheap too.

Are these exact ones definitely suitable, they are only 47Ohms which is less than others have stated is necessary. What is the implication of this? Higher current across L&N when switched on therefore more consumption and possibly heat, but also better able to discharge smaller induced currents?

Thanks, Tom

 

[Lucien Nunes]

The current when energised is determined almost entirely by the reactance of the capacitor, which is much higher than the resistor. The main purpose of the resistor is to limit the peak current on transients. If the snubber is used to suppress switch contacts or a semiconductor switch, or as a dummy load to bleed off leakage, it limits the current when the switch closes, which saves wear on the switch. It also protects the capacitor from fast-risetime spikes on the mains damaging the dielectric.

Therefore the resistor value is not very critical in this application. Too low (a few ohms) and the switch suffers wear, too high (a few kilohms) and the benefit of the wattless load of the capacitor is lost and more heat is dissipated. The worst case peak current on a switch closure is uo * sqrt(2) / R so I would tend to go for 100 ohms or so to keep it to just over 3A. I would be more interested in the quality and durability of the cap than the value of the resistor.