Speed Control for Single Phase AC Motor

[Rbcsci]

I’m tinkering with a 1951 Delta Rockwell bandsaw with a 1/2 HP 115VAC motor. I’d like to set this up for variable speeds. I could use a stepped pulley configuration, but I’d prefer an electronic motor control. However, I‘m not sure that such a small single phase AC motor will respond well to varying speeds without adversely affecting performance. Has anyone had any experience with a similar configuration?

 

[richard7]

I want to know too. How can you tell which ac motors you can speed control from ones you can not

 

[American Locomotive]

The vast majority of single phase ac induction motors cannot be reliably speed controlled. You need to switch to a 3 phase motor.

 

[Rbcsci]

The vast majority of single phase ac induction motors cannot be reliably speed controlled. You need to switch to a 3 phase motor.

That pretty much sums up what I’ve read. I might swap to DC before 3 phase AC though.

 

[richard7]

What is the difference between a 1 speed single phase and a 2 speed single phase motor ? Would like to hear I just need a 2 speed switch. It is an 8 amp motor belt drive exhaust fan want to slow it down sometimes. thanks

 

[nadogail]

Would pulse width modulation work for your motor?

 

[richard7]

Nice bandsaw and stand by the way.

 

[American Locomotive]

What is the difference between a 1 speed single phase and a 2 speed single phase motor ? Would like to hear I just need a 2 speed switch. It is an 8 amp motor belt drive exhaust fan want to slow it down sometimes. thanks

True two-speed single phase motors have the ability to be configured for 2 or 4 pole operation. They have a bunch of wires that get connected in different ways that physically reconfigure the electrical windings in the motor.

The 2 or 3 speed motors you see on things like portable fans are actually "multi horsepower" motors. When you select a lower speed, you're actually selecting a lower power, and the motor just "slips" a lot more because it can't keep up with the load.

 

[richard7]

Sorry for the hijack. The motor does have several extra pins that the wiring harness is not using. I wonder if moving the hot to a different pin changes the rpm.

 

[richard7]

I need to get serial # off motor and research the fan was available in 2 speed version. We have similar fans at bodyshop but they spin a good bit slower. This fan is really moving its a 36in out performing 48 in

 

[Norcal]

Delta/Rockwell made 2 different 14" saws, the wood model like the OP's, and a wood/ metal model, that has a built in gear box, step pulleys on the saw & motor is the simplest for speed control, adding a 3 phase motor & VFD, adds more range of speed.

 

[BreeStephany]

I definitely agree with @Norcal, I would replace the motor with a 3 phase motor and use a VFD for speed control. Another advantage of using a VFD is that you can run 3 phase motors on single phase circuit and you can easily add a remote start/stop switch and/or a rheostat to control speed remotely if needed.

If you wanted to build a control cabinet for your VFD, circuit protection, etc., remote controls are great.

Just my two cents.

 

[mogandave]

The vast majority of single phase ac induction motors cannot be reliably speed controlled. You need to switch to a 3 phase motor.

While the speed of the motor may not be controlled, the speed of the machine can using a variable diameter pully.

 

[Rbcsci]

The interesting thing to me is that I have this 1 HP buffer with a digital speed controller that works very well. It can be adjusted in 100 RPM increments from 900-3600 and it works flawlessly. I'd like to have this same power source for my bandsaw.

 

[mogandave]

Get variable frequency drive. A lot of motors will work fine with them, some wont. If your motor burns up, but an inverter grade motor to replace it.

 

[American Locomotive]

The interesting thing to me is that I have this 1 HP buffer with a digital speed controller that works very well. It can be adjusted in 100 RPM increments from 900-3600 and it works flawlessly. I'd like to have this same power source for my bandsaw.

The buffer either internally has a 3 phase motor and matching inverter, or uses a special single phase induction motor with a custom designed controller.

 

[PoorUB]

Just to muddy up the water, but why have multiple speeds? It is a wood cutting saw, set it up for one speed and leave it alone.

If you want to try cut steel with it I don't think you will be satisfied. Plus you will need to swap blades from wood to steel, also clean the machine well when you want to cut wood because of the steel shavings and dirty steel materiel, oil and slag.

 

[Rbcsci]

Just to muddy up the water, but why have multiple speeds? It is a wood cutting saw, set it up for one speed and leave it alone.

If you want to try cut steel with it I don't think you will be satisfied. Plus you will need to swap blades from wood to steel, also clean the machine well when you want to cut wood because of the steel shavings and dirty steel materiel, oil and slag.

I only plan to cut metal.

 

[PoorUB]

I worked at a machine shop for a few years and we had a large DoAll metall cutting bandsaw. I don't think anyone one ever adjusted the speed. It was set for a harder material, like 4140 and there it sat. It got used everyday.

 

[Rbcsci]

I worked at a machine shop for a few years and we had a large DoAll metall cutting bandsaw. I don't think anyone one ever adjusted the speed. It was set for a harder material, like 4140 and there it sat. It got used everyday.

Yeah. Ours was the same situation. I don't recall ever changing the speed. I should probably calculate my current blade speed and see if its in the range that my new blade wants to be at for cutting steel. If not, I could swap a pulley once to get where I want to be and leave it there forever. I won't be swapping between wood and steel. I just thought an adjustable motor would allow me to tune it right in for the thickness and hardness of the metal that I'm cutting at any given time.

 

[theoldwizard1]

Because you are building a custom cabinet, the simplest way to get 2 speeds is swap the driven pulley to a really big one !

 

[gorilla]

Metal cutting bandsaws use gearbox's because it's difficult to get the speed reduction needed with pulley's. You might need two jackshafts to get what you want. You are correct to think that you need to do blade speed math first.

 

[larry4406]

Put a pully on your variable speed buffer and drive your band saw.

 

[oldmachinenut]

Bandsaw from belts to chain drive

A few years ago I converted a 14" wood cutting bandsaw to metal cutting using a 3/4HP, 90V DC motor with a controller for variable speed. But I was ignorant as to how fast the blade speed actually was . I was chewing through blades at an alarming clip. I found a good website that suggested...

www.hobby-machinist.com

 

[Half-fast eddie]

I would like to slow down my grinder. Can i use this rockler controller?



.

 

[dogdog]

^^ most likely NO, that bench grinder might be a AC induction motor not a AC universial motor that have carbon brushes... if it have, then most likely Yes. Don't get me wrong, it will turn, but you will hear hums and almost have no power other than full speed and your motor will get pretty hot and might burn up... lol @$69 it's no difference than the HF one @ $20 or was $20

 

[no704]

This seems to be a perfect application for a reclaimed treadmill motor and controller.

 

[Half-fast eddie]

^^ most likely NO, that bench grinder might be a AC induction motor not a AC universial motor

it is induction … thats why i posted a picture of the grinder label.
harbor freight has a variable speed grinder for about $100 that goes from 2000 to 3000 rpm. Better than my fixed speed 3450.

 

[dogdog]

yes induction motor probably a no already. I was referring to this,... that rockler speed controller looks like that $20 one HF used to sell (function wise , not look wise) but apparently HF have discontinued it.

this looking thing.

https://www.amazon.com/dp/B095JFPYSZ/?tag=atomicindus08-20

 

[Half-fast eddie]

Fine print says “will not work with brushless”.

 

[dave*99]

I had a cheap copy of the 14" Delta saw years ago. It had a slot in the casting below the bearing for the lower wheel. I added a jackshaft using that slot as a mounting point. Put a step pulley on the jackshaft. Also put a step pulley on the motor. This gave me some variable speeds.