LED Dimmer suited for task?

[bushtech]

I bought this dimmer and the 3 led lights that it's meant to drive from an electronics place.

Worked fine for about 10 hours after which I could hear some crackling in the dimmer, upon investigation I could see some sparking in the pot.




The heatsinked transistor is a BT137. The lights are 240V AC 6W dimmable. The pot is 500K. Markings on the cap CY250 and 104J1.
Is this dimmer man enough for the job or have I been sold a lemon?

 

[kellys_eye]

I could see some sparking in the pot.

Where in the pot?

It looks like a very basic DIAC/TRIAC arrangement for dimming but doesn't seem to have any snubber components. Equally the track clearances between screw terminals is ABYSMAL !!! Dangerous etc. You may have heard arcing across them.

 

[73's de Edd]

The 0.1 ufd seems about right for being one element of a timing network + its companion resistor(s). Plus I do see at least one resistor and the BLUE diode is probably the Diac.
BT137 . . . . .
https://alltransistors.com/pdfview-s.php?doc=bt137f&dire=05

APPLICATION . . . . .
http://www.bing.com/cr?IG=31ABE68D6....gr/uploads/46/lamp-dimmer.jpg&p=DevEx,5015.1

 

[bushtech]

Thanks kellys_eye
Reinstalled the dimmer to check but couldn't reproduce the arcing, whatever is causing it has probably died.
Checking the pot: (in situ)
Note: DMM in 2M range
Left and centre pin (as per above photo): 0Ω
Left and right pin: 0.8MΩ from off click right through to max
Right and centre pin: 0.8MΩ from off click right through to max

What is the best way to sort this? Can this dimmer be made to work properly with some modifications or would it be better to build a dimmer using a 555 or some other design?

 

[73's de Edd]

Sir bushtech . . . . .

You say . . .
Left and centre pin (as per above photo): 0Ω

Right and centre pin: 0.8MΩ from off click right through to max

Whereas, you are able to get much lower ohmmage at the other Left limit . . .akin to . . . .

Making one wonder if your pot has an end of limit burnt area out at about Right extreme ?

 

[bushtech]

Thanks St Edd
Those readings persist even with the pot clicked off I think it's history.

Just need to know where to go from here as per Post #4

 

[dorke]

LED dimmer ?
Not so ,it is a continuous phase control dimmer
mainly use for A.C. halogen and incandescent bulbs light control.

While a LED dimmer should be a DC current control circuit.

 

[bushtech]

Thanks Dorke

So they sold me the wrong thing?

 

[dorke]

They did,If you are trying to control a "pure LED" lamp .
Please post the data sheet of the your lamp.
In any case it shouldn't have died,the LED would probably blow though...

 

[bushtech]

Thanks dorke. Led's still working. Wired a on/off switch in there ilo the dimmer.Data sheet is one of the PRC's usual things


This forum's resources area has an led section, thanks *steve*. It does list some dimmers and I have some 555's. But looking at the link: http://www.reuk.co.uk/wordpress/lighting/led-dimmer-circuit/ at the bottom of the page they state that it didn't work with MR16 leds and this is what I have, albeit mine are 240V and they are using 12V led's.

So a bit stuck here. Looking for the correct way to dim these critters

 

[bushtech]

Here's a design I found here: https://www.homemade-circuits.com/dimmer-circuit-for-led-bulbs/

Usable?

This will be for 18W of led's

 

[dorke]

Look at section d)
Is the one you have a dimmable bulb?

 

[bushtech]

Thanks dorke

Yes they are dimmable. Light fitting takes 3 bulbs as in first photo, each 6W

 

[dorke]

Here's a design I found here: https://www.homemade-circuits.com/dimmer-circuit-for-led-bulbs/

Usable?

This will be for 18W of led's

This isn't a very safe device,it uses no isolation to drive the 555 timer from the mains.
If you use it the least would be for the outer parts(frame/pot shaft and knob) to be well isolated (plastic).

 

[bushtech]

The switch that it will be mounted into is well insulated including the plastic knob. Can I stick an opto isolator in there? Ooops I see there is one in there. Is there a better design somewhere?

 

[kellys_eye]

Isolation isn't a specific requirement if, as mentioned, the circuit is built into an insulated enclosure and the pot shaft is likewise insulated.

The 'important' part would be the 0.33μF capacitor which should be X2 class and have a 'bleed' resistor (say 330k) across it.

 

[bushtech]

Thanks kellys_eye. Had to go and google X2 cap- had never heard of it. This is what my preferred supplier has: https://www.mantech.co.za/Stock.aspx?Query=0.33uf+x2+capsand
I see the highest they have is 275V. Will that do or do I need 400V?

Also never dealt with opto couplers and when the designer says "any optocoupler" I get miffed.

Here is a selection from my preferred supplier again: (all 327 of them): https://www.mantech.co.za/Stock.aspx?Query=opto+couplerand.
What am I looking for? Any optocoupler wtf!

If this is a good design then I am going to build this

 

[kellys_eye]

Check the data sheet - 275V AC but 560V DC - there are others in the range too.

 

[dorke]

This is the kind of stuff you better buy rather than make yourself.

 

[kellys_eye]

This is the kind of stuff you better buy rather than make yourself.

But not from the same supplier you bought the original device.........