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

[petergebruers 1,257]

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!

[jakub.jezek 344]

I recommend to customers or dealers contactors, if they can use it.

 

Sorry that links are in CZ:

Contactor:

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manual (should be multi lang):

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[Guest Kuuno]

i have the same thing w light tubes that are in total of ~300w

my 2 modules got stuck and never worked again

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Kuuno

[petergebruers 1,257]

i have the same thing w light tubes that are in total of ~300w

my 2 modules got stuck and never worked again

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Kuuno

Hi Kuuno, thank you for sharing. Are you talking about 1) 230V halogen lamps 2) 12V halogen lamps on classic transformer (50Hz metal core) 3) gas discharge lamps with 50Hz ballast 4) Incandescent lamps 5) Something else?

To my modest knowlege, there are 2 factors contributing to the welding of relays... A) Inrush current B) Arcing.

A 230V halogen lamp will cause inrush current because of the low cold resistance of the filament. Gas discharge lamps containing classic ballast can cause arcing because of the inductive load.

What is you solution? Keep the power < 300 Watt?

[Guest Kuuno]

i have fluorescent lamps (12 tubes total)

i tried 3kw relay instead of 2x1,5 right now but im not sure if it holds so no 100% solution yet

it seems to me that 3kw relay is actually the same as 2x1,5....!

[petergebruers 1,257]

Kuuno, I would install a very simple snubber circuit. That will reduce the sparking caused by your inductive load. I've used a resistor 1/2 Watt between 47 and 100 ohms in series with a capacitor between 100 nF and 220 nF rated 250 V AC (400 V DC). You place it in parallel with your load.

[Guest Kuuno]

ill test this!

thanks

[robmac 173]

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!

Thanks for that thought.

It is amazing these things get on the market. I always thought that items bought from a reputable dealer would be designed to damp this.

[hkmod25 0]

It was also an case for us when one customer "welded" two FGS211 switches with connected Power Supplay to Apple iMac...

[petergebruers 1,257]

It was also an case for us when one customer "welded" two FGS211 switches with connected Power Supplay to Apple iMac...

I don't have the specs of that supply... but I do have soms specs from other SMPS ranging between 35 and 300 Watt (try

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). The funny thing is, The 35 Watt has 55 A while the 150 Watt has only 40 A and a 150 W model from a different brand wants... 70 A. Difference in construction? Different types of inrush-current limiting devices?

Anyway... Rule of thumb says a relay can have 10-20 x it's specified continuous current. A little math says one Fibaro 1,5 kW relay can withstand +/- 60 - 120 A.

So one of these supplies would be on edge. If you put a few of these in parallel... you're in trouble...

Also... Most of these use a NTC resistor and this is an effective means if you cold start... But after the NTC got it's operation temperature (thing 60 - 120 degrees Celsius) it takes on average one minute to fully recover.

So when you switch on for 30 seconds, then switch off 5-10 second, switch on again and repeat that... you're going to have a higher inrush current.

What you could try is to add an additional NTC in series. Think anything from 10 tot 100 ohms and a disc between 10 an 15 mm diameter.

I don't have a MAC, but I can test it on some other equipment.

[chatting 1]

I'm stupid enough by using the Fibaro switch to turn on a relay to light up the light.

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[hkmod25 0]

I'm stupid enough by using the Fibaro switch to turn on a relay to light up the light.

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That you mean with this? As you probably have reading here the problem is poor el. design on some Power sup., lighting drivers an so on.

[petergebruers 1,257]

Thank you, chatting and hkmod25, for you joining this discussion. You are both right. First, using the Fibaro to drive a bigger, secondary relay will avoid the sticking problem, if it has higher inrush current capability. Check the specs! It was on my list of possible solutions too... Second, since you don't tackle the root of the cause, the "inrush current", you can get other problems... I remember reading on a forum that when someone switched on a certain amount of lighting equipment, sometimes the circuit breaker would trip, although the continuous current was well below the rating of the fuse!

I'll post more on this... but first I really need to read more, try more and measure more... Although I am an electronic engineer, I never had to design an "Inrush current limiter"... so I want to study a bit more... I mean... Before telling lies on the internet

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[hvb83 1]

I also had a welded relay in the past, it was connected to one of these led-controllers:

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I don't have any problems with the other relays in my house yet (pump relay, fluorescent lamp), so I also suspect that the led-controller could be a factor here.

[petergebruers 1,257]

Hoi hvb83! Your story confirms my research: inductive loads like pumps and (old style) fluorescent lamps cause less trouble than capacitive loads. But the arcing (upon opening) caused by inductive loads will degrade the contacts. Anyway... a stuck relay is definitely more of a nuisance!

I studied the pictures after your link and I don't see the power supply of the controller. It is not the controller causing the inrush current. It's the supply. Even without load. I assume the supply you used is the same style no-brand. So no way to find specifications... The only true way to measure inrush current is by using an oscilloscope...

Can you find some specifications of the supply?

[hvb83 1]

Your wish is my command, see below.

It's a no-brand psu that was ordered from the LED-strip supplier. Once you connect the power cord to it while attached to the wall outlet, it does make that distinct "arching" sound that you often hear on these kind of brick psu's.

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[Guest mixzlan]

What you could try is to add an additional NTC in series. Think anything from 10 tot 100 ohms and a disc between 10 an 15 mm diameter.

you think this NTC will be hot or can i put it behind the switch/reley?

something like this (swedish)

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or this is better : I've used a resistor 1/2 Watt between 47 and 100 ohms in series with a capacitor between 100 nF and 220 nF rated 250 V AC (400 V DC). You place it in parallel with your load.

[petergebruers 1,257]

@hvb83 - a no brand no spec supply... It is suspect. Since all readers of this forum are clever, responsible electricians, I can say this: yes, you can use your eyes and ears to estimate inrush current, if you don't have an oscilloscope. Like you did.

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/emoticons/default_icon_smile.gif" alt=":-)" /> I did that too and was rather amazed by the intensity of the contact arc. I thought I accidentally short-circuited the thing... Please, allow at least 30 seconds between each try. If the supply does have a NTC based limiter, it takes some time to reset. And to discharge the primary capacitors.

@mixzlan - temperature is an issue I would like to answer in detail. It is difficult to answer in general. In short... the most correct answer is, you choose the resistance depending on the inrush current. That depends on the primary capacitance of the supply and is equivalent power rating. If the design is correct, you should be able to dissipate less than 1% in the NTC (even less than 0,1%). So, if you have a LED strip of 20 Watt, it's less than 0,2. That won't make a difference next to the Fibaro module that is specified at <0.8 Watt. Even when put in a pattress. But I wouldn't do that.

But if you are talking about a 300 Watt supply... Count on 3 Watt. I wouldn't put that near a module and I would avoid proximity to cabling. I definitely do need to do more tests...

So you see... The NTC depends on the load. And that's the reason why I'd put on the load, not on the module.

It's interesting you mention a second circuit, known as a snubber. They are not equivalent. In fact, they are sort of opposites. Snubbers are for inductive loads like motors and devices with ballasts. They won't help with power supplies, like for LED. There is no harm in putting a snubber in parallel with your load... It will cause < 0.1 W power loss and is very reliable if used with a high voltage capacitor, like you said. But it won't help with inrush current and welding.

I'm glad you found an NTC with full spec sheet! Nice! The NTC that you have found may work for < 10-20 Watt devices. But... To be tested. It's not designed for that. It is a temperature sensing NTC. It is not designed for handling inrush current. How can you tell? I've read many data sheets and I think it is not obvious at all. But I'll give away the clues... It's not disk shaped and "big". They are 2-5% tolerance, whereas limiters are 15-25%. The specs contain several pages documenting temperature characteristics, but there is no table listing their current handling capability or rated primary capacitance... I have a few of these and I'll put one of them on an appliance, just to see how it behaves.

[ Added: 2014-01-12, 12:03 ]

@mixzlan - I checked your supplier site and it -does- list NTC for input current limiting.

I even understand the Swedish name!

"transientströmsskydd"

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Do you see wat I mean? See the 33 ohm listed: it has 2.5 A current capability instead of 0,5 for the temp. meas. NTC you mentioned. And 20% tolerance.

[Guest mixzlan]

Thanks for the reply. I'll watch this.

So for each load to use so you need to figure out what is needed.

I have both 30 w LED and 30w compact fluorescent lamps on the same relay.

So if i take the 33ohm 2,5 A, then i can use around 500 w , right?

[petergebruers 1,257]

Thanks for the reply. I'll watch this.

So for each load to use so you need to figure out what is needed.

I have both 30 w LED and 30w compact fluorescent lamps on the same relay.

So if i take the 33ohm 2,5 A, then i can use around 500 w , right?

Right. You can mix LED an CFL. And the 2,5 A deduction is correct, but... at 2 or 2,5 A the temperature would be very high... according to the specs 175 degrees C. It would produce about 3 Watt (for a 500W load, so < 1% like I said). I've tested a different brand NTC but similar to the EPCOS device and I measured 136 degrees open air when on a 2A load. If you look at the T versus I curves, you'll see that you have to stay below 0,5 A for 75 degrees. I measured a temperature of 55 degrees with my no-brand NTC on a load of 0,35 A. So 75 degrees at 0,5 A seems possible.

[ Added: 2014-01-17, 10:15 ]

I'm still working on this... I don't yet fully understand the selection criteria. But I already want to share this with you: it is very important that the NTC does not touch anything. So I went out to buy some small enclosures. I mounted the NTC on an epoxy board in series with a replaceable fuse. I know myself: I'll forget the rating of the NTC. Here are some photo's. The NTC is a 15 mm disk, 60 ohm. Fuse is 1,6 AT. When running for 15 minutes on a 500 W load, the top of the enclosure measures 45 degrees C. I'm not saying that this particular value/type is the ideal solution for all problems... still working on that!

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[deanrparry 19]

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!

Could someone advise on this snubber circuit and what i would need and how to connect it to the module 1 x 3kw fibaro module!

It is REALLY annoying as a member of staff has to climb ladders and tap the relay to get it working each time!

Many thanks!