Phase angle control blinking

[Farmer]

Hello guys!
I would really appreciate your help here, I'm trying to fit my drilling machine (for the table, whats the english word?) with an universal motor, and first of I'm trying with a very simple circuit. Phase angle control with a triac and diac, and in the testing im just using a normal bulb so i dont get hurt! Its working, and I have very neat dimming of the bulb, though it seems like it dims in "steps" and not linear, and worst of all its blinks annoyingly at some points - like 5 times/second. My guess is that there must be some kind of interference or noise, but I havent been able to find an answer anywhere, because it should be "just that easy". Why could it be?

I have my first home-etched board ready, so I'm pretty woohoo! about the project, and looking forward to seeing the motor spin

Ive attached the inspiration circuit and the modified one for my project.
220V by the way

Thanks in advance guys!

UPDATE: The z-diodes are BZX79, eagle just didnt have any 79's in stock.

 

[ccurtis]

Which circuit did you build? The one of the left, or the right? The zeners in the circuit on the left are only 3.3V and I would be surprised if the diac turned on at all.

 

[Farmer]

I've build the circuit on the left, but I've spotted 2 errors in the schematic already, the zeners are BZX79 as on the original(wrong number), and the var. resistor is 20k(no value). I'll update the schematic, so you dont have to waste your time.

 

[Boncuk]

Driving inductive loads it is always good to add an RC-snubber circuit in parallel with the varistor.

 

[Farmer]

Boncuk: Ok, I'll have to look into that, could the missing circuit cause the blinking?

Updated the circuit with the correct diodes, and gave the var. resistor a value.

 

[Gayan Soyza]

BT series triacs requires more gate currents.I use sensitive gate triacs so they work charm in all four quadrants..

 

[ccurtis]

I can only theorize that the triac gate current is great enough to steal enough current from the zeners so that the zeners don't avalanche, possibly causing erratic triac trigger point.

Maybe try (1) a larger capacitor, say .022uF, and 100K pot to reduce the load on the zener combination (2) a triac with a smaller gate trigger current (3) increasing the 20 ohm resistor.

 

[Farmer]

Thanks for the postings! I've been browsing a little, and found a tip somewhere that I should try and hook up the motor. Its exactly the same story as the lamp, there is some hysteria at certain points in the "dimming".

Gayan: You think theres a problem with not enough gate current? what triac do you recommend?

ccurtis: I havent been able to try your tips yet, but im going to. You mean a 100k resistor in series with the zeners?