How to use SSR to control DC motor speed accurately?

[vntgpt]

Hi
Please guide me how I can regulate the speed of DC motor with the help of SSR? Can i control the rpm of motor also with the help of SSR.

Please reply..

 

[Skogsgurra]

Speed and RPM are the same thing. You really have to do some research on your own first. Then come here with your specific question.



Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[vntgpt]

Dear skogsgurra

I know speed and rpm are same thing in one reference, but they are actually different. There are slow speed, medium speed and high speed but there is nothing called slow rpm or medium rpm etc. The point I wanted to put was, can we control the speed i.e. slow or medium or high speed through SSR and if yes can we control the speed up to rpm level (specific revolutions per minute.

looking for your precious advise.

bye
vineet

 

[ScottyUK]

Why not just use a conventional DC motor controller? Unless you need very high accuracy a cheap back-EMF sensing design should be adequate. If you really need high accuracy or very tight speed regulation under changing load conditions there are numerous closed loop controllers using a tacho or encoder for feedback.

And 'speed' and 'RPM' are interchangeable with regard to the motor, irrespective of how you choose to interpret them in your application.

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Sometimes I only open my mouth to swap feet...

 

[itsmoked]

Hello vntgpt.

Yes you can control the speed of DC motors with an SSR.

That said, you cannot control the speed of a DC motor with only an SSR! You need lots of other bits and pieces and you need to know how those pieces will fit into the system.

You need to know the precise accuracy you require to formulate the correct system.
You need to know how much you're willing to spend.
How much time you're willing to invest.
How durable.
How much power.
What voltage.
What supply.
Which on of the dozen different types of DC motor.
On and on....

You haven't even begun to describe your need. We can't begin to imagine what they are.

Is this for a hobby?(Not allowed here!)
Is it a one piece system?
Is it going to be for production?

I believe you may be better served by going to any of a number of robotics stores or robotics forums and just reading about the subject. That is what I would do.

Look up "motor speed controllers". The first Google hit is excellent.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[OperaHouse]

I would say NO. A SSR is a black box device used by people that don't want to be involved with the electronic issues. To use a SSR, you would need to design a pulse width modulator to control it. If that is the case, you might just as well use a FET and save 90% of the cost. There are proportional SSR, but that would not compensate for supply voltage. Speed control with only voltage would be no better than 1o%

 

[vntgpt]

Dear all,
Thankx for your replies.

We have been using conventional motor drives for setting the rpm of the dc motor but now I want to remove the bulky system and replace with smaller and cheaper device. I have tried SSR with PWM but accuracy is not there. There is always a chance that ur rpms are more or less at different points, if you set it for one specific point.

Please advise wat else can be used if not SSR, which would be cheaper and more efficient.

thanks in advance for your replies.
bye bye

 

[ScottyUK]

How can we possibly help unless you tell us about the motor? Is it a tiny 1W motor or a huge multi-MW industrial machine? What voltage, current? What speed accuracy do you need? Assume we know nothing, and post some information!


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Sometimes I only open my mouth to swap feet...

 

[vntgpt]

Dear scotty

Motor 24V dc motor
1/2 horse power
Accuracy I need is +/- 2 RPM or less.

Please advise.

thanks

 

[Skogsgurra]

I still do not understand what you mean with speed and RPM being different things.

OK. At last some facts. 24 V DC and about 400 W. Accuracy needed is +/-2 RPM. I guess that this is at nominal speed, which is? Let's say 2000 RPM to have something to start with.

+/-2 RPM @ 2000 RPM translates into +/-0.1 % accuracy.

That's beyond EMF control. So you need a true speed controller and a speed measurement device (tach or encoder).

The set up would be:

A speed reference accurate to better than +/-0.1%.

A speed controller with low enough voltage and current bias and offset to maintain the accuracy.

A switching device to control the motor average EMF. This could be a single transistor, an H bridge or one or more SSR:s.

A speed measuring device that is better than your needed accuracy.

All the things above (except the power devices) can be replaced with digital signals and a micro.

All these things add up to something very similar to a standard DC mpotor speed controller.

Why not use one of them?



Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[OperaHouse]

Any reason you have to use DC?

 

[ssn596]

Kindly read the nameplate on the motor and the namaeplate on the gearbox that may be attached to it. Copy the data ALL OF IT here. They put these things on them for a reason namely so people know what the heck you are talking about.

I mention gearbox because of the + / 2 RPM criteria. If you are referring to MOTOR shaft speed which is about 2,000 RPM give or take then I cannot imagine why you need a tolerance of about two.

Dan Bentler