Swapping out Hall Effect Lever for Potentiometer on Sewing Machine Servo Motor?

[oceanslider]

My wire coloring for the MopHorn CS1000 as was indicated by this Amazon review is different, my wires are colored Red, Yellow, and Black.  As I have mentioned previously guys are all over the place on Potentiometer and Resistor values.  Some are also using multi rotation Potentiometers.

[oceanslider]

If any of you real electronics experts who have scopes and all the good testing equipment wanted to check this motor out for those of us who don't have the equipment or skillset, maybe do a YouTube video on what you find out  . You could buy a Harbor Freight 1x30 belt sander to install it on.  Guys are using these for sharpening with that sander from Harbor Freight.  https://www.harborfreight.com/1-in-x-30-in-belt-sander-61728.html  swapping out the motor for the Mophorn CS1000  For around $150 you'd have a better sharpener than the Work Sharp Ken Onion Edition sharpener.  I posted a picture of that setup earlier.

[mikerj]

I see no sign of an isolated DC-DC converter on the control board, so it's probably safe to assume everything is at line voltage including the hall effect wiring.  With that in mind ensure any potentiometer is rated for full mains voltage (I'd suggest a known quality item such as Bourns, sourced from a proper distributor rather than fake eBay junk), and either use a plastic knob and shield any metal parts from the user or ideally ground the body of the potentiometer.

[oceanslider]

I see no sign of an isolated DC-DC converter on the control board, so it's probably safe to assume everything is at line voltage including the hall effect wiring.  With that in mind ensure any potentiometer is rated for full mains voltage (I'd suggest a known quality item such as Bourns, sourced from a proper distributor rather than fake eBay junk), and either use a plastic knob and shield any metal parts from the user or ideally ground the body of the potentiometer.

There you go speaking that electronics mumbo jumbo LOL, thanks for educating the non-educated.  I am to assume as was previously pointed out by Ian that the "full mains" is very substantial.

[BeBuLamar]

I would measure from the 3 connections of the pedal to ground and see what kind of voltage is there. If it's high then you have to be careful. But any way connect a 5000 ohms or 10000 ohms potentiometer between 5V and 0 V. The wiper goes to the pedal. The adjustment will be below 0 speed and above max speed. You would need to measure the voltage between 0 and the wiper (pedal) to see at which voltage the motor start to run and at which it reaches max speed. The you can calculater the resistors for min and max limit. 

[Ian.M]

Odds are the control circuit is connected to the negative side of the DC bus which will effectively be half-wave rectified mains, so will peak at about -170V with respect to earth ground.   You should assume its mains live, so choose components with appropriately rated insulation, secure and insulate wiring as-if its mains and make sure the pot has either a plastic mounting bush and shaft or if metal, is mounted to a properly grounded metal panel and fitted with an insulating knob.

[oceanslider]

Odds are the control circuit is connected to the negative side of the DC bus which will effectively be half-wave rectified mains, so will peak at about -170V with respect to earth ground.   You should assume its mains live, so choose components with appropriately rated insulation, secure and insulate wiring as-if its mains and make sure the pot has either a plastic mounting bush and shaft or if metal, is mounted to a properly grounded metal panel and fitted with an insulating knob.

Thank you Ian,  glad I choose to seek out a group of guys that know this stuff.  For instance, this is one of the Potentiometers that have been recommended https://www.amazon.com/gp/product/B071X4DKV7  And just from the looks and price I would have to assume it is cheap and not of the quality you recommend.

Also as mentioned shouldn't the hall effect lever also be grounded on its own

[oceanslider]

I would measure from the 3 connections of the pedal to ground and see what kind of voltage is there. If it's high then you have to be careful. But any way connect a 5000 ohms or 10000 ohms potentiometer between 5V and 0 V. The wiper goes to the pedal. The adjustment will be below 0 speed and above max speed. You would need to measure the voltage between 0 and the wiper (pedal) to see at which voltage the motor start to run and at which it reaches max speed. The you can calculater the resistors for min and max limit.

Assuming it is high would there be any hesitation measuring this voltage with an inexpensive multimeter?  Also, I would assume this voltage to be DC.  So, the previously stated 300 and 170 volts are DC?

[Ian.M]

Actually, its *probably* good enough.  If there is 2mm creepage distance and clearance from any terminal, the track, and metal wiper contacts to the metal body and shaft, its OK for the application provided the panel is properly grounded, though I would advise adding sheet  insulation between those terminal rivets and the panel!  The problem with off-brand parts from Amazon etc. is you don't know if they are safe to use unless you buy two and tear one apart to check!

For comparison, this is the pot typically fitted to mini-lathes (which also use a mains live control circuit) sold in the USA: https://littlemachineshop.com/products/product_view.php?ProductID=1282
As you can see, its very similar, except it has a closed at Zero switch on the back to inhibit starting except from zero speed.

*DON'T* attempt to measure the voltage with respect to ground with a cheap multimeter.  The multimeter needs to be high input impedance (typically 10 Meg) and both it and its test leads need to be rated for Cat II or higher use.  A low impedance meter could damage the controller and an lower category or unrated meter and /or leads (or ones with a fake rating) may fail dangerously while measuring mains, putting the user at risk of electrocution and/or severe burns.

If you are tempted to use an cheap or unrated meter, switch off the mains supply, put it on the bench with the leads away from anything else, set the range, clip or otherwise fasten its leads to the points you are testing between, and only then switch on the mains supply.  Take the measurement *WITHOUT* touching the meter or leads, and switch off the supply before disconnecting the leads.

The voltage with respect to ground is pulsing at 60Hz.  Expect to see a lot less on the meter than the -170V peak I previously mentioned - depending on the meter somewhere around -55V DC could well be 'in the ballpark'

[BeBuLamar]

I would measure from the 3 connections of the pedal to ground and see what kind of voltage is there. If it's high then you have to be careful. But any way connect a 5000 ohms or 10000 ohms potentiometer between 5V and 0 V. The wiper goes to the pedal. The adjustment will be below 0 speed and above max speed. You would need to measure the voltage between 0 and the wiper (pedal) to see at which voltage the motor start to run and at which it reaches max speed. The you can calculater the resistors for min and max limit.

Assuming it is high would there be any hesitation measuring this voltage with an inexpensive multimeter?  Also, I would assume this voltage to be DC.  So, the previously stated 300 and 170 volts are DC?

I have used the $5 Habor Freight DMM to measure 120VAC voltage but I probably shouldn't do that. All my others meters are safe to do so as I often work with 480VAC. Yes the voltage should be DC. But to be sure I would measure both DC and AC.

[oceanslider]

I would measure from the 3 connections of the pedal to ground and see what kind of voltage is there. If it's high then you have to be careful. But any way connect a 5000 ohms or 10000 ohms potentiometer between 5V and 0 V. The wiper goes to the pedal. The adjustment will be below 0 speed and above max speed. You would need to measure the voltage between 0 and the wiper (pedal) to see at which voltage the motor start to run and at which it reaches max speed. The you can calculater the resistors for min and max limit.

On the controller you can also set the max RPM limit.  That is, if you want to limit max RPM for the footpedal depressed all the way.

But assume you would want to first know the actual max of the setup.  I did find this graph for the Consew CSM1000 which is a 3/4hp motor

[BeBuLamar]

If you use the resistor values like the drawings on your second post. The one right after mine 3.3K, 10K, 6.8K then the potentiometer would vary the voltage from 1.69V to 4.17V which is close to what you have on your chart. You can just use those values and just be careful if you have high voltage. It's kind of a cheap system I think as all the drives I ever worked with the control system would have voltage of 24VDC max.

[oceanslider]

Just a follow up on these motors.  I found one of the main manufacturers on Alibaba and bought a few units from them.  So, during that transaction I asked for the 750 Watt version of their motor, what DC voltage is supplied to the motor from that little controller, and the rep said 0 to 300 volts.  Could that little controller really send 300 volts DC?

The 750-watt motor they rate as 3/4 HP, but they also make 1500-watt motors.
https://szdianji.en.alibaba.com/

They are great motors for tools because they have great torque and variable speed at a very low price compared to a traditional AC induction motor controlled by a VFD.

Grizzly Tool Company just released a belt grinder using this type of DC servo motor.  https://www.grizzly.com/products/grizzly-2-x-42-knife-making-belt-sander-grinder/t32459

And the wiring diagram for the motor and controller is found here: https://cdn0.grizzly.com/manuals/t32459_m.pdf

[Ian.M]

Just a follow up on these motors.  I found one of the main manufacturers on Alibaba and bought a few units from them.  So, during that transaction I asked for the 750 Watt version of their motor, what DC voltage is supplied to the motor from that little controller, and the rep said 0 to 300 volts.  Could that little controller really send 300 volts DC?

Of course it couldn't.  We've already found the hall sensor IC's datasheet and seen its a 3V - 6.5V part, and its abs. max supply voltage is only 8V.  300V across it would blow it to bits faster than you could blink.  Its not even correct to say its 300V with respect to ground as the control voltage is riding on top of a common that's got half wave rectified mains on it, so about 170V peak in North America and 310V - 340V peak in the rest of the world. 

However 310V is near enough 300V to a salesdroid picked for their English, not their technical knowledge!

[Nitrous]

Are the speed controllers regulating the Chinese servos all as simple as a linear Hall effect sensor and a moving magnet or are there some with more complicated circuitry?
Thanks
Doug

[perieanuo]

Are the speed controllers regulating the Chinese servos all as simple as a linear Hall effect sensor and a moving magnet or are there some with more complicated circuitry?
Thanks
Doug

i worked in the industry and repaired sewing machines, for example Brother has the same hall linear sensor approach and optical barrier for back-pedal stop and trimming.
so the speed is imposed by the hall approached by a moving magnet. they had this on regulated DC motors on older series and they switched to AC regulated motors before 2007 if i remember right, pedal control was almost the same, at least for general sewing machines.
imho, i see no reason somebody replace a hall sensor (tolerant to all kind of dirt, best approach for this job) with optical or mechanical potentiometer unless he want to have future issues with the client
for example, for speed and position detection of the sewing shaft we had thousands of sewing machines with optical sensors (brother mainly) and hall ones. which type was a pain in the ass, you guessed already.
br, ovidiu

[Ian.M]

The only reason to use a pot is to satisfy the requirement for a panel mount 1/4" shaft speed control without having to find space for the hall sensor + moving magnet assembly + design mountings for it + a mechanism to operate it with a through-panel shaft.  Everyone knows a pot is much less reliable even if you pay the premium for a wirewound or cermet element pot.  OTOH unless you specify something crazy like the Chinese mini-mills and mini-lathes with a NC inhibit switch integrated with the pot (as opposed to the usual integrated power switch NO in the fully anticlockwise position), they are cheap and reasonably easy to replace when they fail.

[Nitrous]

The other reason to switch is if you don’t have the speed regulator lever assembly.  In that case there will be a controller error and no way to control the speed of the motor.  That is the actual reason I’m inquiring.

So, simply buying a linear Hall Sensor won’t help, because I don’t have the original controller.  I’m just trying to get a functioning motor and controller.

Thanks for your comment, though.

[Bystander]

Just wondering if this issue was ever sorted by the OP as i have the same question. Operating a lever is not great where as a speed potentiometer would be great. Also the same type of controller box  is now available with a potentiometer .

[Bystander]

This was info given on a group for these mini lathes

[Ian.M]

Try a circuit like Oceanslider posted *way* back in reply#2.

As I noted back in reply#20, the AH49E Hall sensor datasheet tells us the speed control sensor output *cannot* be rail to rail, and I noted that it could typically swing from 0.8V to 4.2V assuming a 5.0V supply.  However the actual sensor + magnet assembly is likely to have a lesser range - the magnet may not be strong or close enough to reach max. output, and with no magnet present the output should actually be midrange, i.e. 2.5V so anything below this is due to the far field of the magnet curving back to its other pole.  Hence the 'endstop' resistors R2 and R3 in series with the ends of the potentiometer track in this circuit. 

A possibly easier approach to determining a good value for them would be to hook up a 10K pot without them, with a DMM on DC volts safely connected^* between Vin and 'boosted GND', and measure the min. voltage when the motor just cuts out and the voltage at which the motor reaches max. speed (past which turning the pot further does not make any difference to the speed),  then doing the math to calculate them and choosing the next lower preferred value. 

Note that there may be an internal 10K input resistor  between Vin and 'boosted GND' inside the motor controller, which affects the calculation - you can confirm if that's the case by disconnecting the mains supply, and measuring resistance between those terminals with nothing connected to them.   If there is one, a lower value pot may be desirable for better linearity, but not less than 1K, (which with endstop resistors, shouldn't pull more current than a AH49E).

If math and basic circuit analysis aren't your strong points, post your measured voltages, total potentiometer track resistance, and measured input resistance of the controller here and I'll quite happily 'crunch the numbers' and suggest resistor values.

* The whole control circuit is 'mains' LIVE  and a serious electrical shock hazard, so use clip on probes and make sure they are securely connected *before* connecting the mains supply.  If using a cheap DMM with a suspect or no CAT rating, don't touch it or its leads while mains is connected.   Also, mount the pot to something or clamp it in a rubber jawed vice so you don't have to hold it, and put a plastic knob on it, don't try to turn its shaft directly with your fingers!