SCR speed brushed DC 180v motor control does not work

why my schematic not working.. speed control brushed 180v Dc motor.
I used BT 150 and used PWM to trigered gate of SCR.

thank you.

Hi,

"not working" is no error description.

Tell us your
* test setup
* your expectation
* what's not like expected
* your debugging results

Klaus

- - - Updated - - -

Hi,

It seems there is a big misunderstanding how an SCR works.
Please read "how to control SCRs".
Especially what gate voltage referenced to what SCR pin you need to trigger the SCR.

Note:
Once an SCR is triggered it will be ON until the current becomes zero. Thus a usual "PWM" is not suitable to control an SCR.
You need a zero cross circuit and variable delay.
(There are many threads in this forum explaining this. Read through the theads)

If you are not experienced with SCR circuits ...
...I recommend to use freely available application notes, design notes or other proven circuits.

Klaus

i will made that schematic for speed 180vdc brushed motor. but the output voltage very low just have 3 VDC , I have check on gate of both SCR have PWM signal by code AnalogWrite (pin9, 100) on arduino;( just with voltmeter, because I not have oscilloscope to know the peak ).

so whether my schematic are right or not?

Thank you for your answer.

Hi,

I have check on gate of both SCR have PWM signal by code AnalogWrite (pin9, 100) on arduino;( just with voltmeter, because I not have oscilloscope to know the peak ).

Click to expand...

Let me guess: you measured gate voltage w.r.t GND. This is wrong. You need to connect both voltmeter wires directly at the SCR.

And: lend a scope.

Still unclear: your test setup. You need to connect a valid load for tests, otherwise the SCRs can't trigger correctly, because they need load current.

Urgent for yourself:
Draw the signals in scope style: (paper and pencil is OK)
* input waveform
* waveform at the SCRs
* trigger signal input
* trigger signal at the SCR

Klaus

Missing connection between "GND" and SCR cathodes. Please notice that the control circuit GND, Arduino etc. carries mains voltage, with or without this ground connection. You need an isolator, e.g. trigger transformer to avoid dangerous voltage at the control circuit.

Looks like a recipe for disaster to me. Being part isolated and part live, including live external connections is extremely dangerous unless care is taken. I'm not sure why two DC rails are needed and the value of the reservoir capacitor looks suspicious. Regardless, the SCRs will not trigger and if they did, unless single cycle PWM is being used (at < line frequency) they will not be controlled in any case.

BRain.

so maybe can I use Ac zero crossing detector for input to arduino then can set the PWM to triac to control voltage AC ouput.. until now I confuse how to made cheap speed control brushed 180vdc motor 0.3A.

thank you.

fvm said:

missing connection between "gnd" and scr cathodes. Please notice that the control circuit gnd, arduino etc. Carries mains voltage, with or without this ground connection. You need an isolator, e.g. Trigger transformer to avoid dangerous voltage at the control circuit.

Click to expand...

i updated my schematic below. This is okay or still not??

Hi,

Brian is correct. It is very dangerous.
And the OP seems not to be experienced enough to know and keep on safety regulations.
I don´t want to be responsible if anybody gets hurt or killed.

Thus I´m off.
(Until the OP reliably shows that he is able to care about safety)

Klaus

yophi said:

why my schematic not working.. speed control brushed 180v Dc motor.
I used BT 150 and used PWM to trigered gate of SCR.

thank you.

Click to expand...

Here is a very similar schematic that shows ...
a) Opto-Isolators as the SCR Gate drivers
b) A Zero-Cross Detection circuit

Typically, an adjustable Phase Angle from the Zero Crossing is used to trigger the SCR's , not PWM.

Yophi;

You have to use a power topology as shown in the attached image. The SCR gates are driven from a gate driver transformer which provides isolation.


completely scrap your circuit. It is fundamentally wrong.

summitville said:

Here is a very similar schematic that shows ...
a) Opto-Isolators as the SCR Gate drivers
b) A Zero-Cross Detection circuit

Typically, an adjustable Phase Angle from the Zero Crossing is used to trigger the SCR's , not PWM.

Click to expand...

I forgot to add the URL ...

Arduino Controlled Full Bridge SCR with Opto-Isolators
https://simple-circuit.com/arduino-controlled-bridge-rectifier/

summitville said:

I forgot to add the URL ...

Arduino Controlled Full Bridge SCR with Opto-Isolators
https://simple-circuit.com/arduino-controlled-bridge-rectifier/

Click to expand...

Thank you for your link.very helpful.
But how if my motor voltage use 180VDc?

But how if my motor voltage use 180VDc?

Click to expand...

Good question. A possible solution is to use MOC3021 opto triacs instead of the low voltage opto couplers.

Opto triacs would be my choice. The gates still won't trigger in the new schematic in any case.
Yophi, why are you suggesting PWM? The only way you will get PWM to control speed in a triac circuit is if you use it at very slow speed so it allows varying width bursts of whole cycles to pass. That may be OK at full motor speed but consider at low speed that you might be trying to achieve it by turning the power on and off with several seconds gap between switching periods. The motor speed would be constantly accelerating and decelerating to try to find the average you want.

Phase control with zero crossing would be far more effective and precise. You still need some line isolation and a zero crossing detector though.

Brian.

Sorry Brian..i dont know PWM is Can not use for SCR. I think it will same like I used Mosfet. I have try made H bridge mosfet with IR2110 for drive all mosfet.but I still cant handle the spike after the motor turn off and delay 5 sec for reverse rotating. So i think SCR can more simple to made speed motor control,

I dont have osilloscope to know the peak. Thats the my problem too.

You can use SCRs but not using PWM, I'll try to explain:

PWM = Pulse Width Modulation, in other words the amount of power you want is represented by the width of the pulses. With bipolar or MOSFET devices it will work because those devices can be turned on and off according to how long they are turned on by the pulse.

SCRs will not work though, because they have no mechanism to turn them off, once they are triggered, they stay fully conducting until the voltage across anode and cathode drops to zero. So if you use PWM, the moment the first edge of the first pulse reaches the gate, it turns on and stays on until the end of the AC half cycle. As PWM outputs from microcontrollers is generally at high frequency, the SCR will fire almost immediately and from then on not be controllable.

What you probably want is phase control. It is not PWM but a way of controlling when the SCR fires relative to the start of the AC cycle. Remember that the SCR turns off when the voltage across it is close to zero, if you trigger it near the end of the AC cycle, only the power in the remaining time between triggering and zero voltage is available to power the motor so it is low. If you fire it earlier in the AC cycle more of the power is available before the next zero so the motor turns faster. You can control the motor power by moving the trigger time earlier (fast) or later (slow) from the beginning of the AC cycle. It is the time you change and nothing else. The problem is that time is measured from the beginning of the AC cycle so you need to know where it is, that is why a zero crossing detector (ZCD) is used.

The principle is:
1. wait for zero crossing,
2. wait a time determined by how much power (= motor speed) you need.
3. trigger the SCR.
4. go back to step 1.

The difference between minimum power and maximum power is the time taken by one AC cycle so it will typically be 20mS for 50Hz mains and 16.6mS for 60Hz mains. This is the maximum delay you need in step 2 above.

Brian.