Speed control for AC gear motor ?

[Tereci]

Hi,

I am very much a newb when it comes to electronics but I like to fix old lapidary equipment and sometimes need to learn new things
I have an AC gear motor used as a feed motor on a lapidary saw (it feeds the rock to the blade). The motor is marked Brevel products model F. Counting the rotations it seems to be 5.5RPM - which is way to fast and causes the blade to stall on hard material.
I was thinking of buying a new slower motor like 4RPM Dayton 52JE17 but it might be still too fast and I cannot find a compatible 3RPM version.

I read somewhere that it might be possible to hook up speed control to the motor - and basically have a variable speed motor that way. That would be absolutely amazing - as I could set a different speed based on the material that is being cut - but I am not sure if it's true and where to start looking.
Do you know if and what type of speed control could one use with such a motor?

Thank you,
Tereza.

 

[LarryFine]

I found it to be a 220v, 50Hz shaded-pole motor.

Since you're already looking at Dayton, check their motor speed controllers.

 

[gar]

210303-2226 EST

Tereci:

Look at Bodine. Look at DC brush type or DC brushless (really an AC synchronous) with associated motor control. You want a gear box unit selected for your maximum desired speed. Then you can expect the motor controller to provide a useful speed range of possibly 10 to 1. Get a motor controller with both speed control, and torque limit adjustable controls.

.

 

[LarryFine]

The motor I saw resembles a grill rotisserie motor, without the case.

I came across this while looking around; not claiming it's the right one:

https://www.grainger.com/product/FANTECH-Speed-Control-15W824

Thought: can the feed screw mechanism be re-fitted with a finer thread?

 

[Tereci]

Thank you both. I am afraid I don't have enough understanding to know what parameters to choose by. I was hoping for something like this:

but ideally already assembled. I also read somewhere that this might work: https://www.galco.com/buy/KB-Electronics/KBWC-13K but not sure how that would connect to the motor.

I believe the motor is 115V (it's on saw made in US and used in US) but yes, if I google it it says 250V but it's old, maybe they had multiple versions..? I know that newer types of the same saws are using the 4RPM Dayton 3M098 (predecessor of the 52JE17) so I hope that if I find something that would work with that motor it will work with mine too.

 

[drcampbell]

Photographs of your entire system, including high-resolution, in-focus photographs of any dataplates, would be quite helpful.

 

[Tereci]

@larry - yes, I already have the feed screw with finer thread but unfortunately I also need a corresponding feed nut that locks on to it and nobody manufactures those anymore. So I am looking into the motors. If I could rig up something cheap that would work to control the speed without damaging the motor it would be actually the best possible solution - you want different speeds for different hardness of stones, but most small saws (like mine) come with fixed speed feed motors.

 

[LarryFine]

If you're running it on 120v, then I would try a variable (not switched) motor controller like a ceiling-fan controller.

I will work like a rotary dimmer, but HIGH will be next to OFF instead of LOW being there, so they'll start faster.

Grainger has plenty of those, if that's where you're looking.

 

[Tereci]

@drcampbell here are the pictures. There are no data plates on the motor apart form the few marks shown in the pictures.

The whole setup - the saw is standing on it's back so you can see inside - the thing circled red is the box with the feed motor. The shaft of the motor is connected by a coupling to a threaded rod. The carriage with the stone locks onto the rod and as the motor turns is pushed forward.

The motor that is inside the box:

 

[Tereci]

@LarryFine thank you! Since I am really electrically challenged would you be able to tell me what parameters to check? Assuming the motor has parameters like these https://www.grainger.com/product/DAYTON-AC-Gearmotor-115-Nameplate-3M098 what should I look for in the fan controller? I am clear on voltage, I am not sure about amps and wattage (and if there is anything else I need to check in order to not to destroy the motor). E.g. I found this, does that look reasonable? https://www.grainger.com/product/FANTECH-Speed-Control-15W819

 

[hbiss]

Yes. A fan speed control should work with that motor. That 15W819 looks good. You can't hurt anything by trying it.

-Hal

 

[LarryFine]

I am clear on voltage, I am not sure about amps and wattage (and if there is anything else I need to check in order to not to destroy the motor). E.g. I found this, does that look reasonable? https://www.grainger.com/product/FANTECH-Speed-Control-15W819

What matters:

• Voltage 115
• Max. Amps5
• Max. Wattage 575
• For Use With Fans Under 5 Amps, 50/60 Hz

 

[Tereci]

Perfect, thank you for confirming

After a bit more searching I also came across plug and play controllers like these:

https://www.amazon.com/dp/B07T9BLJ7L/ref=sspa_dk_detail_0

Suncourt 2.5-Amp Variable Speed Fan Control with Plug-in, Brown VS200 - The Home Depot

Plug-in solid state speed controller. Used with Suncourt corded in-line duct fans. Varies the speed of duct fans.

www.homedepot.com

Those would be great due to the ease of installation. That said I see confusing warnings about not using some of these with brushless motors. I assume my motor is brushless?

I am trying to understand what are the different ways in which speed can be controlled. Based on what I read so far all the at home usable methods modify voltage:

• lowering voltage using resistors - supposedly ok, but wasteful
• solid state (block part of the current during part of the cycle or cut of top of the wave) - supposedly this can cause "hum" in the motor as the wave is not a pure sine anymore.. (I won't pretend I completely understand this but it sounds like a bad thing?)
• capacitors (usually has just 3 presets) - supposedly the best way

Are there more? Are some of them better/worse for shaded pole motors or is it all roughly the same - not worth pondering over?
Additionally I understand that lowering speed in this way means lowering torque - but I am not sure by how much and if it might become a problem or not. I am looking to lower the speed at maximum by 50%. If the decrease roughly linear? As in if the motor has max torque of 18.0 in-lb and I lower the speed by 50% does the torque get to 9.0 in-lb roughly?

Thank you!

 

[Tereci]

After watching this video

I am confused. If I am not mistaken a shaded pole motor is a single phase induction motor and according to the explanation in the videos changing voltage damages them and there is no VFD for single phase ones.
I really appreciate all the input here. Thank you! And if I am making a wrong conclusion let me please know.

 

[gar]

210304-0903 EST

Tereci:

The video you posted is very good, and gets directly to the issue.

Instead of trying to use an induction motor get some shunt wound DC motor with separate field excitation, or a permanent magnet DC motor, and a variable DC voltage to the armature. This will give you a system that will work. There are a great number of surplus motors available, but I still suggest the Bodine approach.

.

 

[hbiss]

Variable voltage is a common and acceptable way to control the speed of a SHADE POLE motor. It won't work for other types of AC motors as noted in that video. If those speed controls didn't work why do you think they are made and being sold?

-Hal

 

[Tereci]

@hbiss are most of the fan motors shaded pole motors? Why do the plug and play fan speed controllers say not to use them with brushless motors? Isn't shaded pole brushless?
Additionally that guy has another video where he talks about shaded pole specifically in fans. He explains that when a very low torque is needed - like in the fan - the voltage lowering is an acceptable solution. I am not sure saw feed counts as low torque application..? I might try it, I guess if I monitor the motor temperature I should see if it starts causing issues? I am honestly trying to learn here and understand the reasons for the sometimes contradicting information I am coming across.

 

[Tereci]

@gar thank you. I'll keep that idea as a backup. I think figuring out the combination of components that would work together and could be mounted on the saw might be beyond my skill/knowledge right now but if the other way fails I'll look into it more.

 

[Tereci]

@hbiss are most of the fan motors shaded pole motors? Why do the plug and play fan speed controllers say not to use them with brushless motors? Isn't shaded pole brushless?
Additionally that guy has another video where he talks about shaded pole specifically in fans. He explains that when a very low torque is needed - like in the fan - the voltage lowering is an acceptable solution. I am not sure saw feed counts as low torque application..? I might try it, I guess if I monitor the motor temperature I should see if it starts causing issues? I am honestly trying to learn here and understand the reasons for the sometimes contradicting information I am coming across.

Ok, after yet more googling it seems that controls that have preset - high, med, low - cannot be used with brushless for whatever reason, controls that have infinite variable speed adjustment and go from off to high (solid state) can, just shouldn't set them under 50%. Which I guess is what Larry was hinting on earlier, I just didn't connect the dots, sorry.
I'll give this one a try https://www.amazon.com/KB-Electronics-8811005-Dial-Control/dp/B0087486N4 as it's the easiest one to install that I found and we'll see. I guess the only thing that could be a problem is the torque.

 

[LarryFine]

Which I guess is what Larry was hinting on earlier, I just didn't connect the dots, sorry.

Bingo, and no apologies necessary. I enjoy teaching and explaining the little bits I know and understand.

I guess the only thing that could be a problem is the torque.

I think torque is actually what you would be varying; that vs the mechanical load will determine speed and force, which sounds ideal.