motorized mill

[Minbari]

So your telling me if I plug my 240v grinder into it and turn the dial back I won't slow the motor?
Wait a minute
Ok to demonstrate on the 500w jigsaw easier to handle one handed than my grinder.

Look maybe I for continuous use I'd go something exy but for 20$ plug n play I'd go this option I've actually got two of these little units that ones taken a bit of brewing abuse from me run my 3300Watt element on it let's just say 4000watt is a bit over its Safe working limit (tis what I've found).

Almost all hand tools use DC motors. The use a diode to turn the AC in to DC. That is why they can be variable speed with a knob or variable trigger and also why the power meter works.

 

[west1m]

Easy to tell, the tool motor has brushes.

 

[Limey]

AC motor speed controllers are actually fairly simple. If you are confident with a soldering iron, you can build your own, but inexpensive ones are available ready built.
https://www.electroschematics.com/motor-speed-regulator-with-triac/

 

[Minbari]

Easy to tell, the tool motor has brushes.

Not 100% true. Plenty of AC motors have slip rings with brushes to energize an eciter winding in the rotor.
But brushes that are on a commutator 180° from each other is almost always DC.

 

[GFHomebrew]

Almost all hand tools use DC motors. The use a diode to turn the AC in to DC. That is why they can be variable speed with a knob or variable trigger and also why the power meter works.

Yeah and I'd wager my money that it'd work just fine for West 1 application

+ been thinking it can vary the current in a 3300Watt AC Element how not a motor

 

[Minbari]

Yeah and I'd wager my money that it'd work just fine for West 1 application

+ been thinking it can vary the current in a 3300Watt AC Element how not a motor

No it won't. A resistive element doesn't care about AC or DC. It just gets hot.
An AC motor uses inductive flux field created by the AC voltage to rotate. It rotates at the speed of the freq it is fed. In the state that is 60hz., Same motor will turn slower at 50hz. Lowering the voltage will only lower the power the motor has up to the point it will start skipping. The speed will remain the same

 

[GFHomebrew]

No it won't. A resistive element doesn't care about AC or DC. It just gets hot.
An AC motor uses inductive flux field created by the AC voltage to rotate. It rotates at the speed of the freq it is fed. In the state that is 60hz., Same motor will turn slower at 50hz. Lowering the voltage will only lower the power the motor has up to the point it will start skipping. The speed will remain the same

Ok I've got 750w pool pump Onga it is I'm sure it's AC will plug in that PWM this evening and we will find out.

My reasoning is the power watt meter resists the current supplied to the motor therefore reducing the speed.

We will see

Hey funny thing I'm only doing this now to see if om right either way I'm glad to be proven wrong I'm just a stubborn fool sometimes when I have something stuck in my head.

In the end West 1 m is happy with his mill speed I just thought one of these PWM would be a cheep speed control.

 

[Minbari]

Ok I've got 750w pool pump Onga it is I'm sure it's AC will plug in that PWM this evening and we will find out.

My reasoning is the power watt meter resists the current supplied to the motor therefore reducing the speed.

We will see

Hey funny thing I'm only doing this now to see if om right either way I'm glad to be proven wrong I'm just a stubborn fool sometimes when I have something stuck in my head.

In the end West 1 m is happy with his mill speed I just thought one of these PWM would be a cheep speed control.

Resisting current in an AC motor only lowers power though. Not speed.

You have to know if that motor is AC though. A DC motor will work on AC with only a simple diode. If it slows down on PWM then it is DC

 

[Minbari]

Read this

https://www.explainthatstuff.com/induction-motors.html

 

[GFHomebrew]

Resisting current in an AC motor only lowers power though. Not speed.

You have to know if that motor is AC though. A DC motor will work on AC with only a simple diode. If it slows down on PWM then it is DC

Ok well I'm wrong I appreciate you taking the time to school me on the subject of AC motors.
Quote from your linky.
To control the speed of an AC motor (make it go faster or slower), you have to increase or decrease the frequency of the AC supply using what's called a variable-frequency drive.

So it's the frequency that changes the speed of the motor not the supplied current my mind is still getting around this.

As well most motors I have in use at home are AC supplied but (rectified) DC motors.
Cool

 

[Minbari]

Ok well I'm wrong I appreciate you taking the time to school me on the subject of AC motors.
Quote from your linky.
To control the speed of an AC motor (make it go faster or slower), you have to increase or decrease the frequency of the AC supply using what's called a variable-frequency drive.

So it's the frequency that changes the speed of the motor not the supplied current my mind is still getting around this.

As well most motors I have in use at home are AC supplied but (rectified) DC motors.
Cool

The reason is because of how the magnetic field lines are setup. They rotate inside the motor at the speed of the supplied freq. Increasing and decreasing voltage only changes field strength, but not freq, which is what makes the rotor go around

 

[GFHomebrew]

The reason is because of how the magnetic field lines are setup. They rotate inside the motor at the speed of the supplied freq. Increasing and decreasing voltage only changes field strength, but not freq, which is what makes the rotor go around

Yup so we have 50 Hz here in aus different to your 60hz. So the variable frequency drive lowers or increases the HZ of the power supply therefore changing the rpm if the motor ?

Oh and Hertz is the number of times the power phase of the current switches from on to off in a one second period?

So in theory let's say I did put that variable resistor before the motor and lower the current you say motor would continue at set operating speed until current to low to fire the rotor?

Does that mean also that a VFD will increase oscillations above your supplied 60 Hz too?
Very cool I see why one of these costs way more .

 

[west1m]

Ok here is a chart I just found on line somewhere. I tried to check the rpm on my motot today with a meter I had for model airplanes and it read about 1790. Fits this chart for no load synced. Look how much lower the rpm is for 50 hz.

 

[Minbari]

Yup so we have 50 Hz here in aus different to your 60hz. So the variable frequency drive lowers or increases the HZ of the power supply therefore changing the rpm if the motor ?

you put the VFD between the line voltage and the motor.

Oh and Hertz is the number of times the power phase of the current switches from on to off in a one second period?

kinda. the actual definition of "Hertz" is how many cycles per second. so 50 hertz is 50 cycles per sec. for AC line voltage is a sine wave that goes from off, to positive voltage, back to off, negative voltage, back to off.

So in theory let's say I did put that variable resistor before the motor and lower the current you say motor would continue at set operating speed until current to low to fire the rotor?

yes and no. as you continue to reduce the voltage it would eventually not have enough field strength to keep running at full speed, under load. the problem with it is, as you reduce voltage the current in the motor goes up to try to keep the field established. the higher current would eventually burnout the motor.

Does that mean also that a VFD will increase oscillations above your supplied 60 Hz too?
Very cool I see why one of these costs way more .

yes, different motors have different ranges of freq they will accept. but in general, the VFD has the capability to increase as well as decrease freq.

 

[GFHomebrew]

you put the VFD between the line voltage and the motor.

kinda. the actual definition of "Hertz" is how many cycles per second. so 50 hertz is 50 cycles per sec. for AC line voltage is a sine wave that goes from off, to positive voltage, back to off, negative voltage, back to off.

yes and no. as you continue to reduce the voltage it would eventually not have enough field strength to keep running at full speed, under load. the problem with it is, as you reduce voltage the current in the motor goes up to try to keep the field established. the higher current would eventually burnout the motor.

yes, different motors have different ranges of freq they will accept. but in general, the VFD has the capability to increase as well as decrease freq.

Last question so is an AC induction motor more efficientl than DC
I see electric cars mining trucks use powerful DC motors as well as our battery drills ect.

I'm guessing they both have their applications.
Sounds to me like thenac motors can operate at high torques?

 

[Minbari]

Last question so is an AC induction motor more efficientl than DC
I see electric cars mining trucks use powerful DC motors as well as our battery drills ect.

I'm guessing they both have their applications.
Sounds to me like thenac motors can operate at high torques?

DC motors are quite a bit more efficient. but they are generally noisier and because of the brushes are not as reliable.

DC motors have more torque for the same size as an AC motor. you will notice most big AC motors have a tumor off to one side of the motor, lol that is a capacitor. they need that to kick off the motor to get it started. if you look at your HVAC condenser, you will see it on the compressor motor. A DC motor has max torque at stall speed (Stopped) which is why they work great for EV cars and train locomotives, etc.

downside to a DC motor, if you stall it too long it will burn up, ussualy very dramtically. I am sure you have played with hobby motors and killed one when it wouldnt move. AC motor will stall much longer before damage is done..

 

[GFHomebrew]

DC motors are quite a bit more efficient. but they are generally noisier and because of the brushes are not as reliable.

DC motors have more torque for the same size as an AC motor. you will notice most big AC motors have a tumor off to one side of the motor, lol that is a capacitor. they need that to kick off the motor to get it started. if you look at your HVAC condenser, you will see it on the compressor motor. A DC motor has max torque at stall speed (Stopped) which is why they work great for EV cars and train locomotives, etc.

downside to a DC motor, if you stall it too long it will burn up, ussualy very dramtically. I am sure you have played with hobby motors and killed one when it wouldnt move. AC motor will stall much longer before damage is done..

And then there is these brushless motors i see in out battery tools too.
Thanks for sharing your knowledge with me Minibari!
I really appreciate it.

My kind of electronics is plug it in and let's see gets me into a lot of trouble lol.
A more measured theoretical approach is needed.
I think it's all fascinating

 

[Minbari]

And then there is these brushless motors i see in out battery tools too.
Thanks for sharing your knowledge with me Minibari!
I really appreciate it.

My kind of electronics is plug it in and let's see gets me into a lot of trouble lol.
A more measured theoretical approach is needed.
I think it's all fascinating

ya, brushless are basically the same as brushed DC motors. but instead of a commutator energizing the coils, a controller does it. they can be more reliable than the brushed ones, but ussualy the controller is the weak link.

me too man! I love messing with electronics.

 

[The Brew Mentor]

When I bought my mill I was going to use an old washing machine motor I had out in the shed. Found it was junk and didnt run ( after holding on to it for years). I couldn't seem to find one I liked on Craigs List so I bit View attachment 21748 the bullet and bought a new one .
1725 rpm, 1/2 hp definitely overkill but works great 2 inch motor pulley 5 inch on the mill.

Only problem I see is if the shaft is on bushings.
When using a direct drive setup, there isn't any side pull to wear out the bushings..
If using a side mount motor/ pulley, the mill should have bearings.
For home use, even with bushings, it should still give you a long usage time without wearing the bushings out, but finding the replacement bushings could be next to impossible.
Cheers,
Brian

 

[Minbari]

Only problem I see is if the shaft is on bushings.
When using a direct drive setup, there isn't any side pull to wear out the bushings..
If using a side mount motor/ pulley, the mill should have bearings.
For home use, even with bushings, it should still give you a long usage time without wearing the bushings out, but finding the replacement bushings could be next to impossible.
Cheers,
Brian

Good point. If it got sloppy enough to effect the performance. Prolly just machine out the bushings and install bears in it