Hi,

I am pretty new to designing circuits, but have been playing about with the Ltspice software with some opto triacs and traic to design a 3 phase motor controller from a STM32 blue pill.

I have the blue pill programmed and that is all working well to switch on LED's one for forward and one for reverse.

What I would like is for someone to have a look at my circuit to see if I've made any glaring mistakes before I make the PCB on KiCAD and send away for the BOM.

Thanks Dave

 

hi dave,
Welcome to AAC.
It runs OK for me.
Be aware that your LTS Vac's are RMS not peak.
If you are on 230Vac RMS mains, use V=325Vac.

Some of the MOC resistor are different values and in different locations,.
Eric
BTW: I had to use my Triac.lib path
Don't leave the Triac trigger open circuit, add resistive path

 

L can see all seems fine as you are using V1 as a pulse control for th NPN to turn on the three optocouplers and then trurning on the TRIAC which then conduct into the motor as three phase.All seems ok,maybe l am an amateur but as l see it all is well.

 

Don't leave the Triac trigger open circuit, add resistive path

Can i ask why this is good practice? I would have assumed the load of the motor would be sufficient?

Just to confirm it is the 1k resistor on the ESP1 image you sent?

Also why is it you get such a large voltage drop from 325Vac input to 255Vac output on all three phases?

 

hi,
Look at this edited asc, Mains supply Vpk =325Vac
E

 

Yeah I've done just that. What do these resistors achieve?

Is the voltage drop due to the triacs?

What software is that you're using? I like the way you can view 3 plots at the same time.

 

Download the MOC3023 d/s, it indicates that the 'usual' 1k resistor are not required.
I guess you know that the MOC3023 is a random phase device, ie: no zero cross detection.?
I am using the same LTS as you, I think.

Look at this image for getting more plot panes.

Right click on the plot window for that pop up menu

EDIT:
To move a trace to a different plot window, left click on the plot label and drag the label to the new window,

 

After running a sim with one phase with a 1k resitor and on without i get this current from the gates if the BTB08's and the output waveform?

Any ideas why?

 

I cannot duplicate what you are getting, it looks OK here.
Post your modified asc file and I will try it out.

BTW:
If you go to Tools/Color Preferences/Waveform and set the background as per the image.
This makes the uploaded images easier to read.

 

Compare the current at U6 gate and U5 gate

 

Perfect! Thanks!

Much more clear!

 

With the 1K resistor i'm getting around 70mA waveform flow of current through the gate of the triac U5

Without the resistor i'm getting triggers of around 50mA at U6 gate.

What would be the pros and cons of each? I'm assuming without would be better but that is a big assumption on my behalf with the little experience I have.

 

I have run that, used u4, u5 and u6 assuming that u4 is the mains reference phase.
The difference you see in the voltage level is due to the phase LTS reference node, IMO it is not a problem

BTW:
In your initial image you have the 560R in the wrong place for u4.

 

hi,
To rotate the TEXT on a component, F7 then left click the TEXT and the Ctrl key down and press the R key

 

Ah yeah thanks for that. I was playing about and forgot to change it back before sending the image.

You can see the current on gate U5 is a waveform and on the trigger for U1 it just small peaks.

When comparing this to U6 without the bypass resistor its just small peaks.

What is the better way of doing things?
Dave

 

I have rechecked the MOC d/s and is does not indicate the resistor is required, so I would follow the d/s circuit.

When you run a sim it is a good idea to add a ID label at the test point , use F4

 

Ok thank you for your help Eric.

Also for the tips on LTS. You have been very helpful.

This will be my first every PCB so I'm wanting to take the time to get it right with it being such HV. LTS is very good at giving confidence in a circuit before committing to purchasing components. Its my new found love! Haha!!!

 

hi dave,
I would recommend that you check the power dissipation in the Triacs, before you start the project build, you can do this in LTS.
Ref this image.
E

 

Hi Eric,

I've just seen this message. Sorry for the late reply. I only just came back on here to ask the very same problem.

With having limited experience with AC circuits of 325v I am struggling to figure out what current limiting resistors R1-R6 should be selected.

By my calculations at 325v and 0.05amps for the gates of U4-U6 the resistors would need to be 16.25watts which isn't really feasible on a pcb in my mind. Am I missing something?

Dave

 

The actual power through the triac itself should be fine by the rating I'm guessing as the motor should only draw no more than 1.5amps and the in rush around 10 amps on start up.

I'm just baffled by the gate side?!