variable motor speed with override

[DMKMM]

Hey folks, I know forum users hate it when peoples first post is to ask a question... but I’m having a serious brain f**t, and the boss keeps asking me how its going.

Disclaimer, I do not play with electronics for a living, and this is like the 3rd circuit I’ve ever tried to make. I didn’t even know what a PWM ment until this morning, but i know what it does, not how it works...

So please bare with.

Goals:
1. variable speed motor
2. be able to change motor direction
3. be able to change direction without having to adjust speed
4. have a override "fast" mode where speed adjustment can be bypassed

Questions:

1. Will this work?
2. Do I need the diode?
3. Should I implement some relays?
4. Is there a better -> cheaper way to do it?
5. Is the PWM gunna shoot 20A at the motor all the time? or will the motor just draw what it needs?
6. The motor is only rated at 16A, but this is very intermittent use...

 

[CDRIVE]

Welcome to EP. We don't dislike first posts being questions. We're not a social forum. We're here to help. We do prefer image attachments though as we don't like opening attachments. Can you do that for us?

Thanks,
Chris

 

[CDRIVE]

I converted it for you but I have a lot of questions. Burned out right now, so I'll get back to you. Answer this though.. What type of motor it this? I just bailed out of another motor control thread because information was to damn sparse. I don't want a re-run of that here. Please post the information on the data plate. Not all motors are PWM compatible.

Chris

 

[DMKMM]

Hi Chris,

Here is a link to the motor im thinking about using...

http://www.surpluscenter.com/item.asp?item=5-1754&catname=electric

the shaft though hole is a bit small so i may need to see other alternatives. What type of motor should i be looking for.

Thanks,
Dustin

 

[CDRIVE]

That's a DC motor that will lend itself well to PWM. Inexpensive PWM boards are all over Ebay.

More motors..
http://www.mpja.com/DC-Motors/products/100/

Chris

 

[DMKMM]

Well hey at least i got one thing right so far, what about the rest of the system?

Questions:

1. Will this work?
2. Do I need the diode?
3. Should I implement some relays?
4. Is there a better -> cheaper way to do it?
5. Is the PWM gunna shoot 20A at the motor all the time? or will the motor just draw what it needs?
6. The motor is only rated at 16A, but this is very intermittent use...

-Thanks

 

[CDRIVE]

Well hey at least i got one thing right so far, what about the rest of the system?

Questions:

1. Will this work?

No, we won't be using what you drew there.

2. Do I need the diode?

Refer to 1.

3. Should I implement some relays?

Probably won't need any but it's dependent on the contoller used.

4. Is there a better -> cheaper way to do it?

No but they're not expensive.

5. Is the PWM gunna shoot 20A at the motor all the time? or will the motor just draw what it needs?

The motor will draw what it needs intermittently(Pulsed).

6. The motor is only rated at 16A, but this is very intermittent use...

Yes, that means it shouldn't be run continuously. The starter motor on your car is a good example of an intermitten duty motor.

-Thanks

What will the motor be controlling? If this is some sort of CNC application then we should be looking at Servo or Stepper motors.

Also you indicate that power will be sourced from an old computer power supply . What computer do you have that's going to deliver 20A? A main-frame.?

Chris

 

[DMKMM]

What will the motor be controlling? If this is some sort of CNC application then we should be looking at Servo or Stepper motors.

Not CNC but, it is used on a Milling machine, it is just a power feed for the x axis on a small X2 mini mill, similar to the one in this link:

Also you indicate that power will be sourced from an old computer power supply . What computer do you have that's going to deliver 20A? A main-frame.?

Its just out of an old junk computer i have, its labeld as a 400w Power supply and it has a 12v rail. My understanding, from my diagram,

12v @ 20A
volts x amps = watts
12 x 20 is only 240 watts, 400w should be plenty?

Here is the PWM i was planning on using:
http://www.amazon.com/Vktech-Electr...=pwm+dc+motor+speed+controller#productDetails

 

[(*steve*)]

Check the 12V rail on that power supply. Almost all computer power supplies generate seeral rails and the power supply rating is the rating of all outputs combined.

For example, your power supply may give to 40A at 5V, 1A at -12V, and only 15A at 12V.

The details are normally printed on the power supply somewhere.

 

[CDRIVE]

What will the motor be controlling? If this is some sort of CNC application then we should be looking at Servo or Stepper motors.

Not CNC but, it is used on a Milling machine, it is just a power feed for the x axis on a small X2 mini mill, similar to the one in this link:

Here is the PWM i was planning on using:
http://www.amazon.com/Vktech-Electr...=pwm+dc+motor+speed+controller#productDetails

A Mini Mill doesn't need Mega HP to traverse the table. I have members of my SB Lathe groups that have used automobile window motors to motorize the cross feed on models that were manual. I think Tublacane made a video using one but it drove the carriage lead screw. Either way the motor in your link should be up to the job.

The controller you're looking at will probably be fine but you'd be better off with a kit. This way you'll have a complete schematic and PCB layout included. This will make any modifications much easier to do.

We just had a member post a link to a supplier that has a large selection of PWM kits and other goodies. I've spent the entire morning looking for it but nada! I think Harald or Dave replied to that topic, so hopefully one of them knows the link. I don't even remember what section of the forum it was posted in.

Chris

 

[CDRIVE]

I finally found the link. It was posted by our new member (really, really old guy) elebis, also known as Ed. This is cool stuff! You can thank him.

http://www.canakit.com/

Chris

 

[DMKMM]

Thats cool that there is kits out there... but there is a pretty good chance ill be making about a dozen or so of these. The local high shcool shop teacher knows me pretty well, and i guess this high school has a dozen Harbor freight X2 mini mills for students to learn on. The teacher asked me to make a bunch of these power feeds and sell them to the school. And for now im just kind of prototyping ideas. In the future it would be great just to sit down and put a kit together, im sure i would learn tons. But i think for now i just need something that is plug and play.

Chris,

You mentioned a different wiring diagram?

 

[CDRIVE]

Chris,

You mentioned a different wiring diagram?

Here's the problem with your schematic. We don't no if the controller you're looking at is High or Low Side switching. Perhaps other forum members will know if this issue has been standardized. I would guess that it's Low Side switching. If so your schematic would be incorrect. Another issue is your momentary pushbutton switch, presumably used for full speed override. It would be preferable to wire it into the speed pot circuit or elsewhere in the PWM control board. This way you don't need a heavy duty switch. High DC currents are brutal on switch contacts.

When you buy a product like this on Amazon it will probably not be supplied with all the tech info that will be provided with the kits I showed you. For instance check out the tech data on this model. As you can see there's a whole lot more of it than your Amazon model.

http://www.canakit.com/30a-motor-speed-controller-pwm.html

Chris

 

[CDRIVE]

After further investigation I downloaded the .pdf for this model kit.
http://www.canakit.com/30a-motor-speed-controller-pwm.html
It appears to be a kit only in the sense that it doesn't come supplied in a case. This board comes wired as shown. The pdf was specific about it being Low Side switching as I had suspected it would be. There was a place holder for the schematic but it was empty. This could be because they won't supply it without a purchase.

This model provides both frequency and PW control pots. This is important because without freq control PWM can and will generate a very annoying buzz. This enables tuning it out.

The chances are (99.99%) that the Amazon model is also Low Side switching. If you follow their links to the manufacturer you may be able to garner additional info on the product.

Chris