3/4hp variable speed dc motor with control, from an untapped source

[OSidat]

This thread is quite old,

but in case someone like me is looking at it, the latest incarnation of this on eBay: "Consew-CSM3000-Sewing-Machine-Electric-Servo-Motor"

Works great for my Shop-Task 12-21!

You can actually reverse this easily without using the menu by crossing the black and red pair (2 of 3 motor coil drive wires,) then the yellow and brown pair (2 of 3 phase hall effect sensor wires) - I used a 4PDT switch to do the job. Be sure to bring the motor down to stop before reversing it, as the controller will instantly reverse the motor, but it is pretty violent.

A 1K pot works just as well as the 2.5K to replace the now magnetic speed control lever. The speed control uses a 2 to 4.6V signal, below about 1.8 to 1.9V the motor stops. From 2v to 4.1 the speed ramps linearly. The speed control lever has a +5, control and Ground wire. you can use a DMM to figure out which is which when you open it up.

Jessica, Thank you for sharing your insight into modding the consew connections.
I have another chinese model which is very similar to the consew CSM-1000/2000 series, albeit my controller has a dedicated tactical push button to change the direction of the motor, so I guess I do not need to mod the circuit for reversing the direction. However, since I had been looking up the addition of a Potentiometer as a speed control, I had been reading up various posts about it. Folks have modded this consew and similar motors and posted results on various forums since 2008 or so. One common comment on all Pot adaptations was using a 25K Pot.

Now I have tried a couple of versions and do face a common problem in all. The larger the POT resistance, the longer the controller requires to come out of its error display. Secondly, the range of turn is possibly 30 percent on all pots from motor start to maxing out in speed.

I cut out and isolated the original Hall-effect sensor circuit and measured it's resistance without it being connected to any part of the controller. I have a Red, Black and White wire on my specific model, where Red is positive, Black is ground and white is "Out". The sensor gives a idle state resistance of around 5.5K ohms. I am not an electronics person, but to me, this is indicative that when the motor/ controller set up is connected in its original form, with the foot pedal speed control assembly, the controller is getting a feedback from the foot pedal sensor of having approximately 5.5K resistance.

So, on my modification, I used a 5K Pot to have a variable speed control. When I used it as is, the controller digital display shows an error at start up. As I turn the Pot about 30 percent through its range, the error disappears and the motor starts. By the time I reach about 60 percent of turning the knob, the motor speed max out. So, taking queue from the Hall sensor resistance reading, I added a 5K fixed resistor to the black wire which in my adaptation is connected at position 1 of the POT to give me clockwise speed increment. This resulted in making the start error go away, and now the motor starts after just a fractional turn of the knob. But it is still maxing out in motor speed as I reach at around 60 percent of the turn.

I am not sure, if this partial usage of the Pots full rotation is normal or am I doing something wrong here.

I have my Red wire connected to POT 3, Black to POT 1 with a 5K added, and White is on the POT 2 Wiper connection.

Any insight would be extremely helpful.

 

[Jessica]

Hi OSidat,

The Hall sensor doesn't actually mimic a Pot, rather it is more like an OP amp. You cannot measure the output resistance with a DMM without a bit more cleverness. Its output resistance is a few to tens of ohms depending on the precise model. I don't know the precise model they are using but it is similar to an Allegro Micro systems A1308KUA-1-T. I actually worked at Allegro many years ago on Hall sensor products as my first engineering job!

Just as a basic check, When using a Pot, be sure one end of the Pot is connected to the sensor +5 and the other end is connected to sensor ground. The wiper goes to what was the hall sensor output. You must disconnect the Hall sensor output also. If it is in parallel, weird things will happen.

Really the best thing is a Pot with an op amp buffer, but a low value Pot works well on my model without errors. I also used a non-inductive Pot, but only because that is what I had in the junk box. I am not sure if a wire wound pot would be a problem, but because the original sensor is an op amp like output, I would expect some potential trouble.

The funny behavior you see is probably due to the finite input resistance of the controller circuit interacting with the way way higher resistance of the pot vs. what the hall sensor output acts like. Further if there is any sort of captive input filter in the controller, the longer delay with higher pot resistance is expected. Similarly, if too low a Pot value is used, the current draw from 5V would be much to high, and it would not work properly.

Try a 1K pot, or, lacking that, you could try lacking a 1k pot or an op amp in your hand would be to drive the speed sensor line with a variable power supply through a 100 ohm resistor. Tie the power supply negative to the negative of the sensor. Vary the voltage from 0 to 4.5V and see how the motor speed changes. It should be zero up to some threshold, then ramp fairly linearly to the max set speed if it is set up like the one I have.

 

[C-Bag]

Except for the electrical figuring this looks like a wonderful problem solver for my 9x20 and some other projects like for my sheetmetal beader. Thanks for reviving this old thread Jessica. I'd never seen it before.