Hi, I'm going through a broken vacuum cleaner - tracing the circuit for self improvement purpose etc.. I was hoping that you could help me out with the speed control circuit.
1. Does the load always have to be connected in series with the triac?
2. As far as I'm aware, with an inductive load there needs to be a snubber circuit, but it just looks like a normal light dimming circuit.
3. At first I drew the circuit and I assumed the live side to be neutral and the neutral to be live - the schematic looked a bit odd so I double checked and did some research online and drew it the right way round. But the problem is with the correct schematic the on/off switch is on the neutral side! wouldn't that be a problem because even with the switch off most of the parts of the circuit would still be live :S . Would that be considered as bad design? I know it doesn't effect the working of the unit and with everything screwed shut it doesn't pose a shock risk but still....(also I'm still assuming that changing the "polarities" is correct but not sure as the wire color also doesn't give it away - are the capacitors and the resistors on the right order in the voltage divider?).
4. Can I use this control circuit with another similar size motor? In other words how does the load determine the rating/type of components to be used. The time control part (RC) should work with any load right?
5. I have attached the the two drawings that I have done. I would be really grateful if you could explain the working of it (mostly about why these rated components are used and how it effects the function of the circuit).

Thanks so much

Correct version:


Wrong version:

 

Hi, I'm going through a broken vacuum cleaner - tracing the circuit for self improvement purpose etc.. I was hoping that you could help me out with the speed control circuit.
1. Does the load always have to be connected in series with the triac?
2. As far as I'm aware, with an inductive load there needs to be a snubber circuit, but it just looks like a normal light dimming circuit.
3. At first I drew the circuit and I assumed the live side to be neutral and the neutral to be live - the schematic looked a bit odd so I double checked and did some research online and drew it the right way round. But the problem is with the correct schematic the on/off switch is on the neutral side! wouldn't that be a problem because even with the switch off most of the parts of the circuit would still be live :S . Would that be considered as bad design? I know it doesn't effect the working of the unit and with everything screwed shut it doesn't pose a shock risk but still....(also I'm still assuming that changing the "polarities" is correct but not sure as the wire color also doesn't give it away - are the capacitors and the resistors on the right order in the voltage divider?).
4. Can I use this control circuit with another similar size motor? In other words how does the load determine the rating/type of components to be used. The time control part (RC) should work with any load right?
5. I have attached the the two drawings that I have done. I would be really grateful if you could explain the working of it (mostly about why these rated components are used and how it effects the function of the circuit).

Thanks so much

Correct version:
View attachment 168221

Wrong version:
View attachment 168222

One the question of snubbers - some triacs are specified as "snubberless" - find the data sheet and double check if you like, but its probably OK.

 

One the question of snubbers - some triacs are specified as "snubberless" - find the data sheet and double check if you like, but its probably OK.

Ah you're right its a "snubberless" version! I didn't know that existed before.

 

Universal Motor speed controller is the same as a light dimmer,, the load is usually in the Live wire , with the switch.

 

Just a follow up question - how does the Triac "turn off" at the point of zero crossing?

 

Because the current is at zero, and so it stops conducting.

 

Because the current is at zero, and so it stops conducting.

Probably worth fleshing that out a bit for the TS - but ICBA looking it up...…..