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Switch 2x1,5kW stuck (welded) because of 20W LED driver


petergebruers

Question

Yesterday, one of my FGS221 Switch 2x1,5kW got stuck in the ON position. I immediately suspected the 20W LED floodlight connected to it. I had used this floodlight on my desk and I noticed at the time... that closing the contact to the supply of this light could give some really nice pyrotechnics. I think the driver does not have an inrush current limiter, or it uses a bad one. It is built and designed in a very big country, and I did not find specifications of this unit.

So, yesterday I had to remove my toggle switches, then gently knock five times on the Fibaro module behind it and it got unstuck... The switch seems to be OK, I left it in service.

But now... for a solution. The first thing I had in mind was a 10 - 60 ohms NTC in series of this driver. But I didn't have any at hand. So I thought... 20W is not a big deal... Why not put a 15 ohm resistor 1/2 Watt in series? Then I tried the floodlight on my desk: when closing the circuit the arcing was a lot less. I own 4 of these and I have now modified them all.

Please feel free to share you opinion on this!

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I have the same problem with my 1x3kW relay switch got stucked with a LED strip about 72W power.. After puting the switch out of the outlet and a little knocking it eventually worked again.

After 1 month of service it happened again.Got stucked in the ON position.Even when I switched it OFF from HC2, the LEDs were still powered..The ON and OFF clicks could be heard when I issued the command but the load was still powered no matter what command I did.

After a lot of rapidlly ON/OFF commands it worked and all was OK again

But maybe the LED drivers are not good/compatible with FGS ?

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Just started happening this morning on my 50W LED Floodlights in the Garden... does anybody have any idea how to resolve this by means of additional hardware components to these badly designed relays!

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Just started happening this morning on my 50W LED Floodlights in the Garden... does anybody have any idea how to resolve this by means of additional hardware components to these badly designed relays!

Don't think it is an error in design of the modules it is the nature of the load. Fibaro could not put protection in a small unit like this. It would cook.

The rating given is clearly for resistance loads. These LEDs give a bit of a kick so they are overloading the rating of the module. If you need to control them you need to look at protecting the module by making sure the led modules are suitably made or have additional components to flatten the spikes they produce by absorbing some of the energy at start.

Interesting what other impact this is all having around the circuit as we add led devices and switching power supplies.

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ok so i could just swap for 2 x fibaro dimmers in this case and disable soft start dim etc... but how do i overcome the shop scenario? well over the rated 400w dimmer capabilities... is there no solution to this? 1kw of fluorescent light tubes in total

and thanks robmac... maybe expecting to much from the relays!

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/emoticons/default_smile.png" alt=":)" srcset="https://forum.fibaro.com/uploads/emoticons/[email protected] 2x" width="20" height="20" />

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ok so i could just swap for 2 x fibaro dimmers in this case and disable soft start dim etc... but how do i overcome the shop scenario? well over the rated 400w dimmer capabilities... is there no solution to this? 1kw of fluorescent light tubes in total

and thanks robmac... maybe expecting to much from the relays!

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/emoticons/default_smile.png" alt=":)" srcset="https://forum.fibaro.com/uploads/emoticons/[email protected] 2x" width="20" height="20" />

Can't comment on the dimmers working for your LEDs but for the fluorescent you may have a faulty fluorescent unit or an incredibly bad electricity service. 1kw to overload a 3kw would not be normal.

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Dimmers will melt under led loads. What you need ia either a filtered LED (don't know if that exists) or you'd need some sort of filter to take care of the triac power supply spiking. The short of it is, that LED bulbs are good for power saving but bad for your switching components

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Would a good constant current led driver reduce the spike on the switch?

or something like this designed for the job

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That might do it. It still has a huge power spike when the LED comes on ("inrush") but it is limited somewhat.

I think that the issue might be that the relay has over current protection and this might try to cut the current when the peak occurs. This will make the relay "flutter" as it pulses on and off. This will in turn create a small ark each time the relay switches state (i assume that they are in fact relays and not triac switchers) this will create heat, and if the relay does this a few hundred times each time the lamp is switched on until the LED reaches steady state, that will not only create a risk of welding the relay but will also for certain shorten the lifetime of the relay. If this occurs, it should be audible as a humming noise from the relay as it switches on.

The only way however, to fully avoid this is to have a filter which can deliver the peak power output without requiring the high current input - something along what you found robmac, but with way better filtering (230 V, 48 A is way above the nominal rating of the relay).

An other possibility is that the non-resistive load of the triac dimmer might cause some funny harmonics which won't play nice with a relay designed for resistive switching, but my bet is on the high inrush current (which by the way isn't good for your electrical installations in general).

As i mentioned before, LEDs are good for power savings, but bad for the your electrical installation. Best solution if you want LEDs, is to use 12 V with a proper power supply in between... But that will ofcourse also spike a little on switch on.

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  • Would someone kindly advise me also!

    We have had 5 relays connected at our shop now with 1kw of lighting 36w each tube in the suspended ceiling!

    Every few months the relays start to stick!

    It is my personal opinion that an NTC solution for 1 KW is doable, but has one drawback: it uses big NTC's that slowly cool down. So If you rapidly switch off/on you'll still be in trouble.

    I would go for the dumb-relay option. That is, I'd buy some 230V (primary and contacts of course) relays for use in industrial automation. They would be at least as big as the Fibaro module itself... Count 15-25 EUR each...

    The suggestion from robmac,

    Please login or register to see this link.

    seems very professional to me and I do understand the working principle. It limits the inrush current to about 5x the rated current of the Fibaro relay, which is good. I didn't find price nor supplier. It does not have the "cooling problem" of the NTC solutions.

    [ Added: 2014-03-10, 14:32 ]

    I have the same problem with my 1x3kW relay switch got stucked with a LED strip about 72W power.. After putting the switch out of the outlet and a little knocking it eventually worked again.

    Assuming your power supply has a max rating of about 100 VA for 72W of useful power, you can try an NTC of 30 to 60 ohms, between 5 and 10 mm diameter (check the spec sheets when in doubt). The NTC must not touch anything. Please see the photographs higher in this topic. Let us know how it goes...

    [ Added: 2014-03-10, 15:03 ]

    Would a good constant current led driver reduce the spike on the switch?

    or something like this designed for the job

    Please login or register to see this link.

    It does not matter if the source is "constant current" or "constant voltage" for these LED things to cause trouble... Both use the same input circuit: a diode bridge plus a capacitor. In fact, I'd classify all those supplies (LED, phone charger, PC, ...) as 'dc-dc' converters. The AC source is first rectified, then applied to a capacitor. The next bit is the converter. The first step is what causes the inrush current: the charge current of the capacitor. It is high when the supply starts from "empty" and the 230V sine wave is at its highest i.e. say 330 Volt.

    In my house, all resistance from the supplier to my desk, is only 0.8 ohm. So theoretical maximum current is ... 400 Ampère! This will only be limited by the ESR of the capacitor and some resistance here and there... I'm sure it can still be about 200 A on a bad day...

    I've done some measurements and I can easily reach 70 A with one 20 W LED floodlight. Let me repeat that... 70 A with one 20 W LED floodlight. It flows for 1 millisecond, but that's the crucial moment, when the contacts close.

    If I have two of these floodlights on one 1*1.5 module, I could be out of luck. The relay was designed for incandescent, i.e. resistive loads. With halogen lamps you get a peak too... About 5-10 times the nominal current. A 240 W halogen lamp, 1 A nominal, causes 5-10 Amperè inrush current. Mind you... it takes longer to settle than the capacitor current, but that's another story.

    So to summarize: Two LED lights give 140 Amps when I switch on near a peak of the sine wave... Inrush current capability of the relay: between 5 an 10 times the nominal current +/- 10 A = 50-100 A. Double that for the 3kw relay. I'm in trouble!

    Note that the Camtec supply lists a value for the allowable capacitance: 6000 uF. To put that into perspective: I've a PC supply rated 400W using a 680 uF capacitor. You can put on ... euhm, many leds

    Please login or register to see this image.

    /emoticons/default_smile.png" alt=":)" srcset="https://forum.fibaro.com/uploads/emoticons/[email protected] 2x" width="20" height="20" />

    The Camtec stuff limits current to 48A and that's a nice value for the Fibaro relays.

    I'm not affiliated - and I doubt these things come cheap!

    Please note that all things containing 'iron' (motors, transformers, ballasts) also exhibit inrush current but for different reasons (e.g. unloaded transformer causes core saturation)

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    Hi

    in honest power supply already NTC is installed after fuse or mains filter : results that the NTC is not a solution

    in case of inductive very high loads ( as a fluorescent lamp etc) solution is a One cheap relay and contactor a 220v coil. and needded current(KW)

    in case of small inductive and honest quality power driver for leds halogens etc is a ..VAristor275v -400v conected in paralel over output contacts

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    Would someone kindly advise me also!

    We have had 5 relays connected at our shop now with 1kw of lighting 36w each tube in the suspended ceiling!

    Every few months the relays start to stick!

    It is my personal opinion that an NTC solution for 1 KW is doable, but has one drawback: it uses big NTC's that slowly cool down. So If you rapidly switch off/on you'll still be in trouble.

    I would go for the dumb-relay option. That is, I'd buy some 230V (primary and contacts of course) relays for use in industrial automation. They would be at least as big as the Fibaro module itself... Count 15-25 EUR each...

    The suggestion from robmac,

    Please login or register to see this link.

    seems very professional to me and I do understand the working principle. It limits the inrush current to about 5x the rated current of the Fibaro relay, which is good. I didn't find price nor supplier. It does not have the "cooling problem" of the NTC solutions.

    [ Added: 2014-03-10, 14:32 ]

    I have the same problem with my 1x3kW relay switch got stucked with a LED strip about 72W power.. After putting the switch out of the outlet and a little knocking it eventually worked again.

    Assuming your power supply has a max rating of about 100 VA for 72W of useful power, you can try an NTC of 30 to 60 ohms, between 5 and 10 mm diameter (check the spec sheets when in doubt). The NTC must not touch anything. Please see the photographs higher in this topic. Let us know how it goes...

    [ Added: 2014-03-10, 15:03 ]

    Would a good constant current led driver reduce the spike on the switch?

    or something like this designed for the job

    Please login or register to see this link.

    It does not matter if the source is "constant current" or "constant voltage" for these LED things to cause trouble... Both use the same input circuit: a diode bridge plus a capacitor. In fact, I'd classify all those supplies (LED, phone charger, PC, ...) as 'dc-dc' converters. The AC source is first rectified, then applied to a capacitor. The next bit is the converter. The first step is what causes the inrush current: the charge current of the capacitor. It is high when the supply starts from "empty" and the 230V sine wave is at its highest i.e. say 330 Volt.

    In my house, all resistance from the supplier to my desk, is only 0.8 ohm. So theoretical maximum current is ... 400 Ampère! This will only be limited by the ESR of the capacitor and some resistance here and there... I'm sure it can still be about 200 A on a bad day...

    I've done some measurements and I can easily reach 70 A with one 20 W LED floodlight. Let me repeat that... 70 A with one 20 W LED floodlight. It flows for 1 millisecond, but that's the crucial moment, when the contacts close.

    If I have two of these floodlights on one 1*1.5 module, I could be out of luck. The relay was designed for incandescent, i.e. resistive loads. With halogen lamps you get a peak too... About 5-10 times the nominal current. A 240 W halogen lamp, 1 A nominal, causes 5-10 Amperè inrush current. Mind you... it takes longer to settle than the capacitor current, but that's another story.

    So to summarize: Two LED lights give 140 Amps when I switch on near a peak of the sine wave... Inrush current capability of the relay: between 5 an 10 times the nominal current +/- 10 A = 50-100 A. Double that for the 3kw relay. I'm in trouble!

    Note that the Camtec supply lists a value for the allowable capacitance: 6000 uF. To put that into perspective: I've a PC supply rated 400W using a 680 uF capacitor. You can put on ... euhm, many leds

    Please login or register to see this image.

    /emoticons/default_smile.png" alt=":)" srcset="https://forum.fibaro.com/uploads/emoticons/[email protected] 2x" width="20" height="20" />

    The Camtec stuff limits current to 48A and that's a nice value for the Fibaro relays.

    I'm not affiliated - and I doubt these things come cheap!

    Please note that all things containing 'iron' (motors, transformers, ballasts) also exhibit inrush current but for different reasons (e.g. unloaded transformer causes core saturation)

    Hi Peter,

    Thanks really useful information.

    Why does it not blow the trips? Just the tiny time it flows?

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  • Inquirer
  • Hi Peter,

    Thanks really useful information.

    Why does it not blow the trips? Just the tiny time it flows?

    Short answer: yes.

    Long answer: you first have to know the time versus current curve of your circuit breaker. I have "C curve" European Standard type, 10 or 16 A breakers. Google "EN 60898". The curve can be summarised as follows. For currents below 7 times the Ampere rating, the breaker works as a thermal system. Between 7 and 10 times the Ampere rating, the magnetic part kicks in. This is about the inrush current of a halogen lamp. So you can put 16A of halogen lamps on a 16A circuit breaker. The magnetic system is not infinitely fast, so it is specified down to 10 ms impulses. Below that, it becomes less sensitive. But you may ask... How long does it take to charge the capacitor of a 20W floodlight? Assume it contains a 33uF capacitor and that it charges with 100 A... Then the voltage will rise at 3V per usec. So the peak to charge to 300 Volts would take 0.1 ms. A good design should have an NTC or other limiter, to limit it to something like 5-10 A during 1-2 msec or better. That's my personal opinion. Then you could put several of these floodlights on one fibaro relay... Note this is all a rough estimation. If you need to know exactly... you'll have to measure it. And that's difficult. Yo need a digital scope. You need a low inductance, high inrush current capable shunt (think 10 mohm with kelvin contacts. Check, for instance,

    Please login or register to see this link.

    ). And Ideally... You need a controlled voltage source. And at 330V DC that's a very, very dangerous thing.

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    And at 330V DC that's a very, very dangerous thing.

    Yes not getting my fingers near that. The the kick from the capacitor discharge would not be nice either.

    BTW.

    Those bits of kit are relatively expensive but if you had a large room full of LED lighting they would be cheaper than welding fibaro modules. Certainly would pay for itself in a short time if you are welding modules every few months.

    I have a quote form the UK agent. If anyone is interested pm me.

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    Guest gembrain

    Possible a bit late in the day for this thread but worth it for future reference.

    To limit the inrush current you can either use a purpose designed inrush current limiter - about £60 or you can use a NTC thermistor (£10)

    Calculating what you need is the problem but the link below gives a good idea of the process:

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    If you can measure or find out the capacitance of the fitting then you can calculate what you require from:

    Please login or register to see this link.

    Makes interesting reading - and could save a few relays!

    PS - Apologies - just read the whole thread and NTC thermistors already covered.....

    The links to the reading stuff are still useful though.

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  • Inquirer
  • Some time has passed! In another topic a user told me he had read this thread, but he still didn't feel confident. So this is what I answered:

     

    I understand why you don't feel confident... It's not a standard solution. And, I never reported back because I wanted to make sure that it was a reliable solution. So I waited, and waited, and then forgot.

    Please login or register to see this image.

    /emoticons/default_icon_smile.gif" alt=":-)" /> I have 2 modules that get used at least daily and one module that I use at least once a week. They have been in use for 15 months. No stuck relay, no blown NTC, no damage to the light. I have more relays than that, but those three are connected to a load that welded my first relay within one month of regular use. I don't put an NTC in series, if I don't have too.

    If don't own the relays yet, you may want to consider the new FGD212 even for non dimmable loads. It features soft start, and can also switch non dimmable loads. It has over-current and over-voltage protection. And maybe, one day, you'd like to replace the non-dimmable bulb with a dimmable one? Please don't jump to conclusion and rush to buy one... There is also a practical limit to the amount of inrush current it can handle, but I'm 99% sure that it doesn't damage the dimmer. I recommend you to have a look at the manual, it is available under "support" on the global fibaro web site.

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    Any news abut the relays getting stuck when connected to LED lights? I suppose the situation is the same when the double or the single relay by Fibaro is connected to a led strip, right? What is the best solution? Can another cheap relay like this:

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    be intalled between the module from Fibaro and the LED light/strip?

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    I have the same probs. I ordered five of these

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    Can someone summarise when we have to use such a device in addition to the relays?

     

    When we use the relays to turn on/off LED lamps and energy saving lamps, which all have a low power consumption? So we have to connect the device after the lamp and it acts as an additional load and just ads some resistance to the circuit?

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    And on more thing, what we can use when there are "quick, periodic switching", since this device is "Not suitable for quick, periodic switching!"

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