Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

AC motor control with an H-bridge

Status
Not open for further replies.

ozgur84

Member
Hello Everybody,

I am new in forum and I am not an electronic engineer,I am a Physicist. That's why I need some help for a basic motor control circuit which I want to make some additions to control an AC gear motor.

I found a basic DC motor controller circuit which can drive a low voltage DC motor. **broken link removed** you can see the circuit diagram.

I also found a good electric gear motor 1r/min which can perfectly work for my application in the local store. However the motor is an 230V 50Hz 3Watts AC motor.

My plan is using the connections of two 555 IC Timer (3rd legs, at where the motor leads are connected on the circuit diagram above) with two NPN transistors (MOSFETs I think) which are capable of working at 230V. I think, I can supply the Transistor part of the circuit with 230V separated from the timer circuit and I connect the 3rd legs of 555s to the 1st connections (base) of the NPNs.

At this point, first, I want to know which transistors I can use and second, what sort of extra additions should I make

Thank you all in advance...

PS: I think I can supply the 555s with 3 to 15V. There is no limitation here.
 
This schematic is for a DC motor. It won't work for an AC induction motor.
For an AC motor you need a Triac.

If 0 to 100% speed control of an AC motor is required, then you need a variable frequency drive.

What exactly do you want to do?
 
Do you realise that the DC controller circuit in the link provides instant reversal of motor drive direction with no dead zone at which the motor is 'off' ? That is bad for the motor.
The proposed modification to the circuit makes no allowance for mains isolation and is potentially LETHAL.:eek: Also, it is unsuitable for an AC motor. If your motor has only two wires then it is not reversible.
I suggest you research 'solid state relays', which can provide both switching and mains isolation. I would also advise using a control circuit which provides for forward/off/reverse control of the motor (if indeed it is reversible).
 
Last edited:
... I also found a good electric gear motor 1r/min which can perfectly work for my application in the local store. However the motor is an 230V 50Hz 3Watts AC motor.
...

A 3W 1rev/min AC motor is a microwave turntable motor, or equivalent. You can't control the direction it will randomly start in either direction. Also it's a synchronous AC motor so you can't speed control it.

I suggest you look on ebay for "DC gearmotor" there are a ton of them sold for hobby robot use etc. These can easily be speed controlled with a PWM DC motor controller (also available cheap on ebay).

The DC motor solution will also offer more torque (and better startup performance), plus easy reverse-ability, and a good element of safety since you won't need to be messing with AC mains voltages. :)
 
This schematic is for a DC motor. It won't work for an AC induction motor.
For an AC motor you need a Triac.

If 0 to 100% speed control of an AC motor is required, then you need a variable frequency drive.

What exactly do you want to do?

Hello fernando_g, I was planing to use the outputs of the circuit for turning the motor on and changing the direction of the motor with mosfets. Because I have a 230V motor and the circuit operates with 15V maximum. Lately I discovered that I can make this happen basically by using a relay instead of a complicated mosfet array. However I also realized that the motor has 2 wires so I will not be able to change the direction anyway (I was so concentrated on another stepper motor driver, so I missed the point of I have an AC motor and I cannot change the direction). Thanks for your interest.
 
Do you realise that the DC controller circuit in the link provides instant reversal of motor drive direction with no dead zone at which the motor is 'off' ? That is bad for the motor.
The proposed modification to the circuit makes no allowance for mains isolation and is potentially LETHAL.:eek: Also, it is unsuitable for an AC motor. If your motor has only two wires then it is not reversible.
I suggest you research 'solid state relays', which can provide both switching and mains isolation. I would also advise using a control circuit which provides for forward/off/reverse control of the motor (if indeed it is reversible).

Hello alec_t, I went to the local store and I had a better look at the motor. Yes, it is unfortunately has two connections and it will not be reversible in any case(I suppose). To avoid instant reversal, I use end switches at the power input of the circuit with additional bypass switches. However, since the reversal is not possible, I decided using a DC motor instead, even though it is more expensive and hard to build with all external gear (reduction) unit...

As I explained in another answer, I could also use a relay and a switch, so, the 555 circuit would no longer necessary. Thanks for your answer.
 
A 3W 1rev/min AC motor is a microwave turntable motor, or equivalent. You can't control the direction it will randomly start in either direction. Also it's a synchronous AC motor so you can't speed control it.

I suggest you look on ebay for "DC gearmotor" there are a ton of them sold for hobby robot use etc. These can easily be speed controlled with a PWM DC motor controller (also available cheap on ebay).

The DC motor solution will also offer more torque (and better startup performance), plus easy reverse-ability, and a good element of safety since you won't need to be messing with AC mains voltages. :)

Hello Mr RB, You are absolutely right. I missed out couple of things like the motor has two wires so that it will not be reversible. And if I want to drive the motor, I can use a switch, power source (something like 12V) and a relay to control the 230V for on and off instead. I also finally switched back to the idea of using a DC motor with the circuit, although they are more expensive (not a huge price difference tough) and little bit faster like 3r/min. But I can handle that with some extra gear assembly....

The problem (idea of using the mosfets) mainly caused because that I so concentrated on another similar stepper motor driver. After I put a little bit more thinking on the circuit, I first realized the relay alternative then, the reversibility issue. Thanks for your interest and reply :)
 
Hi,


Yes controlling a DC motor will be much simpler. You might still use an H bridge, but then you dont have to worry about frequency. So you can control:
1. Speed
2. Direction
3. Braking
without too much effort ie simpler control circuit.

For the AC motor the problem is that to reduce the speed the frequency has to also be reduced. It can be done and has been done many times in the past but it requires a little bit more circuitry for the control circuit. An H bridge is still the common approach, but the control then has to be able to reduce the frequency of the drive as well as the pulse width. Basically you start with a frequency converter and then add frequency control. So you end up needing something like a VCO along with the PWM instead of just a PWM control. The nice thing is, no capacitors. The motor can usually handle the PWM without a problem even though it is an AC motor. The drawback is there is no directional control. So AC motors can be speed controlled but it requires a more complex circuit to do it right.

For exceptionally good control a tachometer is used for feedback. That means the output rotational speed will be constantly monitored and adjusted for on the fly by the control circuit usually within a millisecond or so. There are various types out there if you need this too you can take a look. It all depends how much accuracy you need in the rotation. The control circuitry is only very slightly more complicated.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top