pwm motor conrollers and how to build one to suit the motor available

[Eddie6775]

Hi everyone, This question was born tonight after having to cobble up a way to finish a small milling project out in the shop. I own one of those seig mini mills that you can get from Harbor Freight, and Cummings etc. and the second motor controller has burnt out. Ok....Done. I'm building my own next time! I understand how pulse width modulation works, but all of the circuits I see online are intended for a small motor. I did however find one web site that the fella built one for a motor to run a scooter or something and it looks like he simply used more that one transistor to carry the load of the motor. How does this work?

The reason I'd rather build my own is not only to learn more about pwm but also if this one conks out I'll have a better chance of fixing it instead of mail ordering ...yet another mini mill motor controller. rite now (forgive me) I'm running a household dimmer switch through a bridge rectifier. It sucks but it got the job done.

This motor is a 110 volt dc 250 watt motor. So I'm inclined to try a the 555 approach. with multiple transistors. (?)

Any suggestions, hints or smacks in the back of the head are appreciated.

 

[alec_t]

Is this DC motor a BLDC one or brushed? If BLDC how many phases/wires?

 

[Eddie6775]

Hi, It's a DC. brushed. It's got 2 wires. When I looked at it last night I had another idea I'd like to incorporate. I can probably add an H bridge on the out put and make the spindle reversible... This would save me a lot of time with tapping threads. Hmm... I'm kind of glad that controller failed now!

pwm controller DO need brushes rite?

 

[alec_t]

pwm controller DO need brushes rite?

PWM can be used with brushed or brushless DC motors.

 

[Eddie6775]

oh...ok, I didn't know that...Do you have any suggestions how to go about this? I'll admit I know just enough to dangerous. BTW, Just for giggles I looked at the web site where I bought the last controller. It's up to $197. Defiantly incentive to learn this aspect of electronics. That being said, I'm going about this very carefully.

This is what I looked at last night to get the answer to your question.

 

[alec_t]

Nice pic.
If reverse is only going to be used occasionally a manual reversing switch would be simpler than using an H-bridge.

 

[large_ghostman]

At school last year in tech, I used a mill machine with reverse, I think I was the only person to ever use the reverse! as soon as I tried it, the brushes fractured! according to my teacher the brushes wear a certain way depending on which direction you use most, and if well worn and then reversed they can fracture, no idea how applicable this is to you tho. Looks like a job for a IGBT or MOSFET

 

[Joe G]

Do you know why both controllers died? the reason I ask is because my lathe controller poped and flashed one time when I turned it on, then just stopped working. upon analyzing it, I found the remains of a pincher-bug around the blown component. and I remember that I forget to replace the dust (bug) cover on it. I replaced that said component and been fine since for what it's worth...

 

[Eddie6775]

I'm not quite sure why the first one died, the motor just gradually got more and more "choppy" until it would only ever run full speed. this one died because of an aluminum chip that found it's way in the circuitry. I plan on using a remotely mounted project box for the next one. I have an Asian mini lathe as well, but it was so problematic (motor controller) that I just found an old Atlas on Craig's list lol.
I can't stand unreliable machinery. but to find a good mill to fit in my shop for under $1500 just wont happen. And I'm better off for it, because electronics is something I'm enjoying so far.

Now....What exactly is an IGBT?

 

[large_ghostman]

Its an expensive transistor! or to be precise A Insulated Gate Bipolar Transistor

 

[Eddie6775]

Thanks, I'll do some reading about that. In the mean time, This is the link that gave me inspiration and might be helpful to others interested in this.
**broken link removed**

 

[kinarfi]

So you want forward and reverse and variable and your voltage is 120 vdc, correct, shouldn't be hard to do, what does it say on the motor, if anything. How do you want to control it, a dial, I suppose, it can be made so straight up is off, dial left for CW and dial right for CCW and fear not the H bridge, I use them a lot. the more info you supply, the easier it is to help
Kinarfi

 

[kinarfi]

Here's what I'm presently working on for controlling the motor that assists my steering wheel in on off road vehicle and with just a few modifications, it could drive a 120 volt mill motor
The FETs are remote and connected by the pins at left along with power and feed back

 

[large_ghostman]

Yeah I would go MOSFET H bridge route, IGBT's are all well and good but come at a price.

 

[Eddie6775]

kinarfi, it was mentioned earlier that reversing might not e a good idea, so I'll wait for that. as for what's on the motor? 110v dc 250 watt.

 

[large_ghostman]

I dont think there would be much of a problem, I think the main reference was to adding complexity with a H bridge, they are not that complex if you pay attention. In your case I might be tempted to use a pwm chip rather than a 555 timer, personaly I would go all the way and use a micro!
If your going to build a MUTTS NUTS controller, think about adding over current detection/protection, and maybe soft start. Or go the whole hog and add fine and coarse speed control (normal pot and ten turn pot), maybe add a RPM indicator ok I will stop before feature creep sets in !

 

[Eddie6775]

I'll bet what you just described building even with all of those features will STILL cost less than the mail order part! I have NO clue what most of those thing are!

Things are going to get interesting here lol.. I'm still doing allot of Googling for ways to do this, but there are so many different ways my head is spinning...

 

[large_ghostman]

Not sure on cost, most hobby people would have most the bits in the parts bin, rough guess I would £10 tops. Depends what you can find laying about, no idea what they want to sting you for it?? A straight forward controller with no bells and whistles should be under £5

 

[large_ghostman]

Something Like a current sensor could be as simple as a single resistor, add a comparator chip (very very cheap) and you have an adjustable current limit. So many ways to do it.
Best plan is work out exactly what you want it to do, build a simple version frst, something very basic and take it from there, two years from now you will have a home lab

 

[kinarfi]

I believe your concern about reversing the motor is unfounded, the incident mentioned earlier was probably on a motor that had very worn brushes and hadn't been looked at for ever. Looking at the brushes in you photo, I don't think you'll have a problem.
If you're interested in my design, over current could be done with a single hall effect device, take a toroid core and Dremel a slot in it and glue a $3.20 Honeywell SS490 Series Standard Miniature Ratiometric Linear Hall-Effect Sensor into the slot and run one of your feed wires through it and then compare the output to a set voltage and you have your current limit. You can have your controller for 1 quad opamp and 1 quad comparator IC, under $6.00 for 2 PFETs & 2NFETS and a handful of lesser parts.
Kinarfi