Hi, I'm tracing a motor control circuit of a coffee grinder. Nothing is broken just doing it for educational purposes. I do not understand how the following resistors and capacitor is connected and its purpose, it doesn't look right to me as I have not seen it like this before. I am assuming its the snubber circuit.

Where is the neutral connection coming into? :S. I haven't continued tracing the rest of the circuit yet. I'm stuck at this point trying to figure out whats happening here. Maybe I'm drawing it in a way that is confusing...

The motor is an asynchronous motor.

Thanks in advance for the help

 

The N would normally go direct to the other side of the load.
Wima capacitors are used for snubbers due to their lower series resistance, and excellent dielectric qualities, when produced this way have excellent pulse and current carrying capability, as well as a very high insulation resistance.
Max.

 

I have drawn the other part of the circuit (not the gate connection though) and I'm afraid its even confusing more
View attachment 175417

 

It would need a detailed reverse-engineering of the total board, seems like there is some above normal components for a simple triac control.
Max.

 

It would need a detailed reverse-engineering of the total board, seems like there is some above normal components for a simple triac control.
Max.

Hi Max, the motor control bit is quite straight forward (even though its where I'm stuck at), there is an opto diac to trigger the gate of the triac. The other half of the board is the power supply, however there is an opto coupler which I need to find what is is used for. For sure the unit doesn't have any speed control functions.

I haven't come across many motor control circuits - so trying to figure out the snubber circuit and the triac connections.

In a simple on/off situation does it require a zero crossing detector circuit? no right?

Thanks for the response

 

It may be that the RC circuit is for a soft start function, or it may be part of an overload stall shutdown circuit. Or just a method of avoiding switching a high current. But providing a soft start makes the most sense.

 

Hi Max, the motor control bit is quite straight forward (even though its where I'm stuck at), there is an opto diac to trigger the gate of the triac. The other half of the board is the power supply, however there is an opto coupler which I need to find what is is used for. For sure the unit doesn't have any speed control functions.
I haven't come across many motor control circuits - so trying to figure out the snubber circuit and the triac connections.
In a simple on/off situation does it require a zero crossing detector circuit? no right?

Yes I noticed that there were two opto's, wondered why also?
So this is a on/off, SSR, or burst controller? Rather than phase control I assume.
If so, a zero switching opto would be used.
What is the MOC full number, couldn't quite make it out.
Take a look at the Fairchild AN-3006 and AN-3003.
Max.

 

@MaxHeadRoom - the unit doesn't have a speed control which the user could adjust. However it gives the option for how long the motor should run for a given shot. How it works is that if I want to grind lets say 100g, I could measure how many seconds it takes to grind that amount. It will show a count down timer for the set seconds every time a grinder is used for a shot.
I think the opto coupler is used to for the count down timer. (I need to confirm this though).
The opto-diac used is MOC3061.

Going back to the Triac circuit - doing some research online I came across this schematic found at https://www.nutsvolts.com/magazine/article/triac_principles_and_circuits_part_1 , it has some similarity with the circuit I have drawn. Could this be it?

 

Probably a good clue as to what else the circuit does would be provided by knowing what those other wires go to. Aside from what I am guessing is the incoming line power there are 5 more heavy wires, plus 4 more thin wires from the small connector on the other side of the board. So clearly this is a more complex grinder than mine, which only has a single on/off switch. With two of the blue/brown pairs there may be another motor being controlled. Or possibly a solenoid for some purpose. It may be that things operate in a sequence of some kind. So probably a fair portion of the system is not just starting and stopping a single motor.

Once again, without complete information a lot of what is posted is good guesses.

 

Hi @MisterBill2 - I have got the wires figured out. The Brown, Blue, Black wires are the motor connection. The two red wires are thermal cut out from the motor even though its bypassed in this grinder. The remaining two black wires are the capacitor connection for the motor. The Brown and Blue wires at the bottom just out of shot is the main Live and Neutral coming in. From the small connector red and black are the Vcc and ground for the control board. The remaining two are signal wires which I haven't figured out yet.

I am particularly interested in knowing about the 39Kohm, 180Kohm and capacitor connected to the triac. What is this configuration and what the purpose of it is. I haven't seen such a configuration before.

 

The MOC3061 is a zero crossing type, so phase angle control is not used, it would be used as a simple switch.
Max.

 

The MOC3061 is a zero crossing type, so phase angle control is not used, it would be used as a simple switch.
Max.

Back in the day when building drive circuits for lamps on a "Trolly" target system we used the Zero Cross pulsing from 0% to 100% dimmer type circuit. Didn't know you could control a motor that way. I tried fixing a light box for the church I attended once, that's when I learned about Triacs and solid state solenoids.

The MOC3061 or similar, but the one we used back then for the "Trolly" was white not black.

kv

 

Back in the day when building drive circuits for lamps on a "Trolly" target system we used the Zero Cross pulsing from 0% to 100% dimmer type circuit. Didn't know you could control a motor that way. I tried fixing a light box for the church I attended once, that's when I learned about Triacs and solid state solenoids.

The MOC3061 or similar, but the one we used back then for the "Trolly" was white not black.

kv

How did you get phase angle control from a MOC3061?
Or was it by period of burst pulsing, as is typically used in triac heating circuits.
There are two versions of the MOC3xxx .
Max.

 

How did you get phase angle control from a MOC3061?
Or was it by period of burst pulsing, as is typically used in triac heating circuits.
There are two versions of the MOC3xxx .
Max.

We had a 128 pin surface Mount, programmers made the magic happen, I just built the boards. I did some repair on them, when needed, so I learned slowly which parts were what, based on the schematic. There was a lot more happening too. Motor control, the trolly had a 12vdc motor & light for night shooting, a metal cable on each side of the trolly with cable threaded through a 700v toroid, they embedded the control in the HV, then reduced the voltage at the trolly.

They could have done either, but as I remember now, I think it was pulsing. Been to many years like 30 years ago.

kv

Edit: The MOC3041 maybe, I faintly remember.

 

The MOC3041 is zero cross also!
Max.

 

From what I have seen the two resistors and the cap have no connection.with the gate circuit and so I will not take any guesses, BUT in most triac control circuits thereis a bit of phase angle control. But with no circuit to see that is a guess as well.

 

Read Fairchild AN3006 for opto zero cross Triac drivers.
Max.