Trouble understanding AC motor speed regulator circuit

Hey Guys

I want to build a motor speed regulator circuit and I've came across this schematic:



Before I build it I want to understand how it works in case if I wanted to customize it. Could someone help me
understand what the following parts of the circuit exactly do:

**broken link removed**

Thanks in advance to anyone who answers :wink:

It is not a speed regulator. Instead it is a simple "light dimmer circuit" that reduces the average voltage of its output.

A speed regulator senses motor RPM then adjusts the output voltage for the speed to be regulated.

The components in the red box suppress spikes from the motor. The components in the yellow box phase advance the rectified AC from the last cycle so if we are on a positive haf cycle, C4 will have a negative voltage on it. That voltage combined with the positive from this cycle, produces a variable voltage (set by P1), when the voltage reaches a high enough value, it forces the diac to conduct and so the triac conducts.
The inductor is to keep the triac switching spikes from interfering with other equipment connected to the same mains supply.
Frank

My mistake, it is a speed controller circuit :wink:

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chuckey said:

The components in the red box suppress spikes from the motor. The components in the yellow box phase advance the rectified AC from the last cycle so if we are on a positive haf cycle, C4 will have a negative voltage on it. That voltage combined with the positive from this cycle, produces a variable voltage (set by P1), when the voltage reaches a high enough value, it forces the diac to conduct and so the triac conducts.
The inductor is to keep the triac switching spikes from interfering with other equipment connected to the same mains supply.
Frank

Click to expand...

Thank you for your input Frank however it is not as clear to me as it is to you.

1. When you say the components in the red box suppress spikes from the motor do you mean they suppress the initial surge in current like the one shown below? :


2. I don't think I understand your explanation for the yellow box, if I isolated the circuit as below would what I drawn be correct ?


I know I'm asking for much but if you could visually show me what is going on I would really appreciate that.

3. The inductor is to isolate current surges (spikes) from going into the mains supply, that's fine thank you.

Red box, not as you say, motor contains brushes, which spark as they travel over the segments on the commutator. As they are switching current in the armature coils, they generate back EMF, which are short voltage spikes that can be thousands of volts. These high voltages would break down the insulation within the triac. These components suppress these spikes.
diacs conduct when they have about 20V on them. So looking at your diagram, the green wave form gets to 20 V at T- 5 mS. This will cause the triac to switch on at T - 5 mS, which is to the left of your red wave form, the triac would then stay on until, T= 0, because that is when the volts across it fall to Zero. If its 50 HZ mains the triac would then conduct when T = + 15 mS on the positive cycle, even though the diac is now on its negative half cycle. So the triac is on for 5/20 of the time. Altering the time constant with the pot, slides the trigger point about, and hence the conduction time.
Frank