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Author Topic: Concave cutting tools.  (Read 530 times)

MakkyBrown

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Re: Concave cutting tools.
« Reply #15 on: March 24, 2020, 08:28:56 AM »
Hi Guys,

Most of the off the shelf power supplues are switch mode, they convert AC to DC then switch it thousands of times per second (some 20,000 hz), feed it into a small transformer and rectify the output.  The high frequency means the transformer is much smaller and cheaper than a transformer running 50 Hz, mains supply.

In short my 25 amp 12v supply cost me about $35 from Banggood. It is ready for 254 or 110 vac to be added and wired straight to your project, lights etc.  A traditional 12v 12.5 amp supply costs about $180 for parts plus an electrician to assemble it.  The transformer is most of that cost and weight a couple of kilos. Two transhormers would be needed to rum 2 150w motors.

It is easier to buy a pulse width modulator than use an Arduino.

They are inexpensive.

I have one capable of 12 to 50 vdc input at max 10 amps.  Cost about $7.  The other is reversable, and can handle 12 to 50vdc at up to 40 amps, cost abt $20.

Roughcreations, the 775 motor is too small for driving heavy laps, i bought a 150w 12v scooter motor from Motion Dynamics (about $65 including parcel post)  as a replacement in case I could not buy replacement parts quickly but also bought a new 90vdc motor and speed controller (abt $400+) from Brett at Gem Hunters Haven.

The hum you hear is mostly full wave rectified mains hum as the speed controler full wave rectifies the mains and clips it to height.  This means your motor, being a series of inductors, acts s bit like a smoothing capacitor.  I experimented with a 350v 100 microfarad capacitor as a smoothing cap, which quietened the hum but gave a funny ringing feedback ping, so I discontinued trying in case I damaged something.  I really need a 1000 or 2000 microfarad 350v cap, but dont have one.  It may also need a series resistor to stop the cap blowing the fuse when starting up.

Next time I would replace the speed controller with a 0 to 100v 5 amp power supply.  It would remove the hum.  Or rewire with a 150w 12v scooter motor and a 15amp power supply with 40amp pwm mentioned above.

The yanks dont get the same hum from their facetrons, their supply is 110vac at 60hz, meaning full wave rectification gives 120hz, which the motor quietens easier.  It also means speed controller settings are not as critical.  With zero upper limit trimming, the supply will deliver about 90vdc to the motor, in Aust these conditions deliver about 180v to the 90v motor, which is why my motor realy spun fast before it blew.  In short Aussie Fcetron owners need to keep checking their motors don't run too fast.

 If you are in Brisbane, I'll happily check your supply voltages.  I needed to adjust the new speed controller as it was delivering 16 to 120vdc.  I trimmed it back to 13v to 86vdc.  The motor stalls below 13v.

Regards
Gordon
I agree flash, there are not many high voltage dc motor drivers available. Running a 12v 775 via with a motor driver and arduino is easy and cheap but unfortunately not the 90vdc motor.
I'll have a look and see if I can find you a 1000/2000uf capacitor, might have a 3000uf 450v will that do?
MB


MakkyBrown

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Re: Concave cutting tools.
« Reply #16 on: March 24, 2020, 08:50:34 AM »
Hi Makky,
My Facetron (a couple of years old) has a 90VDC Hill House Products motor as standard, pretty sure it's this one:
https://www.sherline.com/product/hill-house-dc-motor-2013/
An Arduino-based controller sounds very interesting, could be useful for the concave cutter projects, too. I for one would be interested in your proposal,
RC
Ardunio for the 775 motor for concave should be fine but not the 90vdc. But I have some big capacitors, as Flash say could be worth trying one to see if that quietens it might even do the same on my machine. I do have an EMI filter I pulled off a treadmill I've been meaning to fit to my machine aswell. Currently I just have a heap of ferrite magnets clipped on the power lead.
I've written code for my concave machine you are welcome to have. Display screen, speed control via key pad, PWM motor drivers. Soon I'll be back to finishing the concave machine. I am using a dc motor/wormdriver with encoder to drive the oscillation as the stepper motor was noisy and would be annoying to use.



FlashGP

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Re: Concave cutting tools.
« Reply #17 on: March 24, 2020, 08:54:59 AM »
Hi Makky,

Thanks for the offer regarding the Capacitor.  I have decided to just live with the hum now i think I have worked out the reason for the damage to my motor.

I'll be giving it an annual service by cleaning the inside of carbon buildup from the brushes and checking the speed controller adjustment. 

Roughcreations,  the gear comes off the end of the 150w motor from motion dynamics.  I chose it because it was slightly shorter than the standard Facetron motor so I didnt need to adjust the base height of my machine.

About the only thing you need to know about switch mode power supplies and pwm speed controllers is that you need to connect +12v pin on power supply to +12v pin on pwm and - to -.

Get a 250vac rated switch and switch the brown wire on the mains plug before connecting it to one of the AC inputs on the power supply, they are at one end and marked ~.  Connect the  blue wire to the other ac input, polarity does not matter as it is ac.  Green wire to the earth pin on the chassis.  That pin is marked with an earth symbol that looks like an arrow poonting down and constructed from several horizontal lines with a short vertical shaft from the longest line.

Be sure to use heavy wire for the 12v connections.  You'll be pulling up to 12 or 13 amps through the 12v lines, household power cables may not be good enough, they are rated at 10 amp.  Use 20amp wire from the auto shop, it is used for wiring  caravan batteries and the like.

Polarity on the motor side of the pwm does not matter as it is reversable.  I would put a terminal block between the motor and pwm speed controller to make it easier to remove the motor for servicing.   

The whole assembly should fit under the deck of your machine.  I would position the power supply on one of the walls away from  where you would put your hands when checking/cleaning the belt.  If possible rig up a cover for the wiring connector on your power supply to minimise the risk of accidental electrocution.  I would also use the Facetron mains wires as the insulation on the wires from China is often softer.

Regards Gordon
Yours Sincerely
Flash (Gordon)

roughcreations

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Re: Concave cutting tools.
« Reply #18 on: March 25, 2020, 11:27:58 AM »
Thank you Sir, an elegant solution for my Facetron,
RC
Rough Creations - Beauty from rough beginnings

MakkyBrown

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Re: Concave cutting tools.
« Reply #19 on: March 27, 2020, 08:54:00 AM »
Hi flash, I've got 2200uf 450v but have to de-solder, let me know if you decide you want one on day.
CheersMB

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