Variable speed, reversible, 90 V DC motor controller

[quarkey]

Hi everyone,
I am trying to build a pottery wheel for my mother, but I aim to incorporate several features which apparently are not offered in any ready made product, or, more precisely, the only one I have seen fitted with all these features is overwhelmingly exceeding my financial possibilities, hence my drive to make my own and the reason of this call for help.
I managed to source a 2.5 HP, 90 V DC, permanent magnets motor (off a fancy tread mill), and even if I understand that this might be a too powerful motor for my purpose, I am extremely happy with two of its characteristics: very small size (even if very heavy) and whisper quiet.
I browsed all the threads in this (and other) forums having this subject (DC variable speed, reversible controller) as an attempt to find a simple solution to power this machinery, while also implementing the reversing feature, but I have yet to find a to-the-point answer to my quest. Funny that almost all the threads dealing with this type of enquiry are dealing with a pottery wheel.
Perhaps important to also mention is that I plan on using a foot pedal to control the speed and an on board manual switch to control the direction of rotation (having to use both hands to work the clay, one can use only the foot to control the speed).
I am quite handy, posses a very well fitted workshop, electronics "division" included, and can follow schematics and make my own circuit boards and montages.
Thank you so much for any advice you can provide.
Vlad

 

[MaxHeadRoom78]

There are industrial foot pedals that have a poteniometer included, for the controller, KB motor controls have a reversing version.
Also there are the MC-60 and the PWM MC2100 TM controllers which could be used, both of these would require a relay in order to reverse.
The MC2100 requires a small add on board the supplies a PWM control signal via a pot.

 

[Diver300]

Can you use the controller from the treadmill as well?

Reversing controllers can be made for DC motors but they are more complicated, so a separate reversing relay between the controller and the controller and the motor might be easier. For that power of motor, it may not be easy to find a relay that is rated for the current and can reverse the motor.

Contactors, which are really just big relays, include a wider range that can switch motors of that power. However, contactors rarely have NC (normally closed) contacts that are rated to a high power so you may find it easier to have one contactor for forward running and one contactor for reverse running.

When doing that, it's usual to have a mechanical interlock to stop both contactors operating at the same time. Mechanical interlocks are available as accessories for many contactors.

It's also usual to have electrical interlocks as well, so that the contactors don't even try to energise at the same time.

 

[quarkey]

Hey MaxHeadRoom, thank you, I looked at KB Controls (simply blown away with their array of devices), however, I wasn't able to find anything foot operated and, honestly, I have the feeling I am opening a can of worms precisely because of that: too much to chew... To make an informed choice to navigate through their list of devices, I would probably have to first buy a manual of advanced electronics, learn everything in it and only after that I might be able to discard the items which won't help my purpose, probably to be left with at least 10 contraptions to further choose from (the fine tuning of choice so to speak). Yikes!
Also, by looking at the PWM MC2100 TM controllers, I see the need to pair it with a foot pedal, and researching for one, I now landed in the conundrum of what type of pedal to use to do just that. The way I look at it now, the simplest "pairing" would be a pedal which mechanically rotates the speed knob (probably a variable resistor), because anything electronic would add a new layer of compatibility with the input the variable resistor gives to the controller. Am I wrong?
Diver, a big thank you to you, too. Ha! I wish I'd have the treadmill controller, but the motor was already pulled when I purchased it from a garage sale. Same regret about the original 90 V power source...
After reading your suggestion, I am left with the big question - what would be the contraindication or draw back for an analog polarity switch (rated for that amperage, obviously) I am tempted to use at this stage of the planning? I mentioned that probably the manual operation to change the rotation makes the most sense (I see that most of the ready made pottery wheels have some kind of a "gear lever" which, very likely, mechanically engage a reversing pulley or something). Not the direction I want to steer towards.
Really appreciate your time (and patience...)

 

[MaxHeadRoom78]

For a foot switch there is one on Amazon that is around $10.00 but it operates an ON/OFF sw, you need a pot for variable speed, the issue is, a pot is rotary, in order to operate it, Amazon also have hobby rack and pinions where you could implement a simple linear to rotary method by modifying the FS to emulate the expensive industrial versions.
There has also been Youtube videos out there of DIY versions.
Yes, the MC2100's etc would need a reversing relay on motor output, I have used a common DPDT relay for this,
Preferably you would either need some way of preventing operating the rev SW when in either FWD or REV or ensure the motor has stopped before operating the SW..
I made up some boards for the MC2100 that simulates the PWM speed signal from the console.

 

[rjenkinsgb]

How about one of these for the pedal? It's basically a pot in a heavy duty pedal enclosure, with a three contact plug.

https://www.amazon.co.uk/Nektar-NX-P-Expression-Pedal/dp/B07CN7STLC/ref=asc_df_B07CN7STLC/

 

[quarkey]

Hi rjenkinsgb, thanks for the suggestion. Because I am not able to find out the guts or the technicality of this pedal, would you, please, be able to confirm connection compatibility with a PWM MC2100 TM controller? Essentially if it would be to connect this pedal with the controller, that should be done where in the physical board of the controller? Intuitively, I guess it should replace the variation signal of the knob, would it? Or am I wrong?

 

[rjenkinsgb]

I've never used one, but the general data on such pedals implies they are just a pot in a pedal housing, so the three connections from the plug substitute for the three connections to a pot in the PWM circuit.

I've found a diagram of the MC2100 board and the terminals the PWM add-on connect to are isolated from power, so only low voltage is present on the pedal unit connections.

https://www.wolfteck.com/assets/mc2100-schematic.pdf

 

[quarkey]

Brilliant, JRW. It now sounds like a plan. Thank you for the diagram - it is now clear where to hook the pedal on the board.
I will definitely come back with the results of this setup, for the future posters to know if it works (or, if not, how to deal with the issue).
Genuinely appreciated to all three of you, guys !

 

[MaxHeadRoom78]

For the MC2100 versions you need a PWM commnd board that plugs into HD2 socket.
I made some from a 8 pin micro, using a stop/start and pot control, there are others out there using a 555 etc.
When I have time, I mean to include a reversing circuit.

 

[rjenkinsgb]

it is now clear where to hook the pedal on the board.

As Max has said you must use a PWM adapter between the pot and the MC2100, if it is like the one in that diagram.

 

[MaxHeadRoom78]

If you hook up a PWM board to the MC2100, you must suitably size the series resistor into the HD2 socket Opto isolator as the one in circuit is very low.

 

[quarkey]

When I have time, I mean to include a reversing circuit.

So, Max, is there any schematic for the reverse feature you could provide? I am asking in the hope that you'd accept to take me - let's call it "under supervision", while I build/test this adaptation (this way you won't waste your time with the build itself and your knowledge can be put at work). Don't worry if it wouldn't work out of the bat, I like tinkering and going back and forth for a purpose and learning.
Secondly, that would be unbearably neat... to have a pedal with a "horizontal" neutral position, and with two directions of movement, to trigger direction. Wow !
Lastly, the dimensioning of the resistors - I might need some help with this one since I'm under the (wrong?) impression that the pedal itself runs into the low current side of the circuit (as per JRW), even if it triggers on/off values for the high current (pretty much like an automotive relay, right?). So why would I need to use resistors for the pot interface? I need to understand the principle behind this functioning. Thanks

 

[MaxHeadRoom78]

If you trace HD2 pin 4 it end up at an opto but only has a 22ohm series resistor for the diode you need to add one depending on the level of the signal you are inputing.
HD2 pin 4 is the PWM command signal.
The relay I used was a K10P-11DT5-12 this has a 12v coil

 

[rjenkinsgb]

There is a design for a PWM adapter in this article, using a couple of 555 timer ICs.
The pedal pot would replace the 10K trimmer, directly if the pot is also 10K or with a capacitor change if its a different value.

https://el34world.com/Misc/Cnc/Files/Terrys_Dual_555_MC_2100_Driver_Circuit.pdf

 

[MaxHeadRoom78]

I can post the relay connection tomorrow.

 

[quarkey]

So, I've had a little time to read about this controller https://www.kb-controls.com/product.sc?productId=75&categoryId=21, and beside the fact that it controls motors of maximum 2 HP (mine is 2.5 HP), I believe this would serve my purpose. It looks like they don't make controllers for motors over 2 HP ??. By the way, what practical limitation derives from it being limited to 2 HP ? If I run it with my motor, I will burn the controller or the motor won't reach its full potential?
Also, with the above controller, the NEKTAR pedal JRW suggested, would still work, right? I'm ready to pull the trigger

 

[MaxHeadRoom78]

As long as you do not exceed the set current, the 2.5hp should work OK, also you need the suitable current set resistor, usually purchased separately,
Get the lowest resistance version.
The current limit can also be set with a pot, as long as your loading does not exceed the 2hp limit, the drive should work fine.

 

[quarkey]

Can you suggest a practical method of determining the upper threshold for the load? What I am thinking essentially is that if I turn on the pottery wheel, throw a piece of clay and start working it, the "graph" of resistance from working the clay will probably have a lot of variances (not linear at all), and the way I see it, I should be able to determine the "peak" of these values and translate that value in dimensioning the resistance accordingly. How am I doing this?
And what would you do to implement these limitations in the entire set up? I am certain that I won't ever need the entire 2.5 HP, so I could limit the output to a certain value, but what is the practical way of applying this limitation to the motor itself? Or perhaps the controller?

 

[MaxHeadRoom78]

It also depends on how the motor is connected to the wheel, gearing? belt/pulley reduction etc.
Here is the rev relay, if needed, as already mentioned, do not throw it in reverse or fwd when running.