converting threadmill motor of 100VDC to use for my project at lower rpm and high torque

Thread Starter

WolfCredence

Joined Nov 12, 2018
12
i have a project of sorting of packages on a conveyor using RFID tag. i was interested in programming only but now i have to design a conveyor as well so what i did was, i salvaged a treadmill and convert it to a working conveyor but now the problem is the motor control circuit in it is broken and now i am thinking of doing what this video below says :

my motor specs are :
permanent magnet DC motor
1.5 HP @ 100VDC
14 amps
4900 RPM

as you can see this speed is too much for my project, inside the treadmill i reduce the pulley mechanism and will remove the flywheel off the motor so it will reduce the speed (low radius pulley to larger radius pulley)(gear ratio). now if i do what this video telling me than how can i counter the fact that when load is increased speed will get much lower, i want a constant speed. i thought that i can plug current sensor and when load increases current will increase and i will control it using arduino to stabilize the current to make the speed of belt constant.

this is my final thinking
220 vac 50 hz convert from transformer to 120 vdc > scr controller > bridge rectifier > motor >sensor feedback > arduino

Please guide me.
 

Alec_t

Joined Sep 17, 2013
10,372
Welcome to AAC!
A current sensor is ok for avoiding excessive current, but what you really want is a tachometer, or shaft angle sensor, to sense and control speed.
 

Thread Starter

WolfCredence

Joined Nov 12, 2018
12
Welcome to AAC!
A current sensor is ok for avoiding excessive current, but what you really want is a tachometer, or shaft angle sensor, to sense and control speed.
Thankyou for the quick reply, aside from that is everything else applicable

and can that current sensor be used with arduino to control the speed.
Also see the transformer 120V but my dc motor is 100 V. is this okay?
 

crutschow

Joined Mar 14, 2008
23,361
can that current sensor be used with arduino to control the speed.
As Alec noted, a current sensor does not work to control speed, since that current will vary with the load at a fixed speed.
You need some method to sense the motor speed and control the motor average voltage from that using an SCR or PWM controller.
 

Thread Starter

WolfCredence

Joined Nov 12, 2018
12
As Alec noted, a current sensor does not work to control speed, since that current will vary with the load at a fixed speed.
You need some method to sense the motor speed and control the motor average voltage from that using an SCR or PWM controller.
meaning that aside that everything is fine. I will solve 1 problem at a time.
Please help me, i am in real need to finish this project.
wait thats the issue when load is increased than the current changes and the speed of conveyor will get lower. I want to make it constant. Can i apply zener here for constant voltage and omit potentiometer?
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
19,053
You could either use something like a Picmicro to provide a PWM drive, or use one of the ex T.M. MC60 SCR bridge controllers which maintain rpm by monitoring the motor current.
For your application I would not think you require precise rpm control, also using a large reduction will tend to stabilize the rpm as the load on the motor will be greatly reduced.
There is also the MC2100 PWM T.M. controller but requires a PWM input signal to control RPM, there are some 555 based circuits out there.
Max.
 

Thread Starter

WolfCredence

Joined Nov 12, 2018
12
You could either use something like a Picmicro to provide a PWM drive, or use one of the ex T.M. MC60 SCR bridge controllers which maintain rpm by monitoring the motor current.
For your application I would not think you require precise rpm control, also using a large reduction will tend to stabilize the rpm as the load on the motor will be greatly reduced.
There is also the MC2100 PWM T.M. controller but requires a PWM input signal to control RPM, there are some 555 based circuits out there.
Max.
that is true i dont need precise just enough to not indicate any large changes, so by this you mean i dont need anything else just do the above mentioned in the video.
 

MaxHeadRoom

Joined Jul 18, 2013
19,053
I would not use the simple Triac controller, there is no control at all to maintain rpm.
The better option is the ex T.M. boards or there is also controllers made by KB electronics that manuf. DC motor controllers that also come up on ebay etc, regularly.
Max.
 

Thread Starter

WolfCredence

Joined Nov 12, 2018
12
By the way cannot be done by pwm, I mean 0-255 is the range of Arduino or resolution in which you can control motor speed 4900 rpm is too much like 1 value change is equal to above 1000 rev per second. it cant go lower than that, I think scr is the only solution.
 

shortbus

Joined Sep 30, 2009
6,985
now if i do what this video telling me than how can i counter the fact that when load is increased speed will get much lower, i want a constant speed.
Seems like everyone is approaching this strictly as an electronic problem. But when designing something mechanical you need to design from the worst case. You need to go back and figure out your heaviest ever expected load. And choose a motor that is capable of propelling your conveyor the correct speed with that load.
 

MaxHeadRoom

Joined Jul 18, 2013
19,053
A DC motor has increasing current as the load effect causes a drop in RPM, this reduction in RPM reduces the generated BEMF which therefore increases the difference between the applied and generated voltages.
Max.
 

Thread Starter

WolfCredence

Joined Nov 12, 2018
12
so respected members I have done a lot of searching and surveyed many places to figure this out, this is the knowledge I got:
1- change in ac will not create change in dc (I don't get this point and the worker did not say much maybe selling pitch as he said to make me the whole circuit board for pwm in 12000 rps or nearly 90 dollars !!!)
2- there is a transformer in the treadmill which is actually a choke and connected in series with the motor
3- by using scr if by some miracle it works scr will reduce the torque with rpm so It will become useless say I want 30 rpm from 4900 rpm of motor.

so here is the problems can someone tell me will this work or not. I know what I will do with feedback system for my Arduino, I just wanted confirmation that scr will able to run my motor. I have ordered It but they said I have to pay up front and than they will order it for me. I have read about diac and triac used in scr and know other things as well such as firing angle and zero crossing for Arduino etc. I am working hard please help me out.

*special thanks to maxheadroom I got much knowledge from you , specially about the mc series board. I have studied it more but it is still very pricey and I cant do that, I am a student and don't have that much cash.
 

Alec_t

Joined Sep 17, 2013
10,372
say I want 30 rpm from 4900 rpm of motor.
I think you will find it very difficult to get a motor rated at 4900 rpm to do only 30 rpm (1 rev every 2 seconds!) smoothly and reliably while still giving its rated torque. That is a virtually stalled condition, which could cause over-heating. A smaller motor operating through high ratio reduction gearing would seem more appropriate for the task.
 

MaxHeadRoom

Joined Jul 18, 2013
19,053
1- change in ac will not create change in dc (I don't get this point and the worker did not say much maybe selling pitch as he said to make me the whole circuit board for pwm in 12000 rps or nearly 90 dollars !!!)
If referring to a Triac operating int a DC bridge, then this is false, the DC will vary, but noisy at low RPM's.

2- there is a transformer in the treadmill which is actually a choke and connected in series with the motor
This usually applies to the SCR bridge type such as MC60, the choke is in series with the motor one purpose to smooth out the AC ripple, the MC2100 PWM's do not use one.

3- by using scr if by some miracle it works scr will reduce the torque with rpm so It will become useless say I want 30 rpm from 4900 rpm of motor.
If simple type, yes, for feedback you would need a drive with this feature such as the T.M. versions. The PWM's are best for low rpm.
Max.
 

Thread Starter

WolfCredence

Joined Nov 12, 2018
12
I think you will find it very difficult to get a motor rated at 4900 rpm to do only 30 rpm (1 rev every 2 seconds!) smoothly and reliably while still giving its rated torque. That is a virtually stalled condition, which could cause over-heating. A smaller motor operating through high ratio reduction gearing would seem more appropriate for the task.
You are right but I'm using gear reduction method aswell so it's kinda 2 gear system, drive pulley of conveyor is greater than the motor shaft so speed will reduce and torque will increase but not enough that'swhy it will be done by scr controller. You did not give the answer whether scr works or not?
Attachment as you can see of drive pulley .
 

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MaxHeadRoom

Joined Jul 18, 2013
19,053
Torque will increase at the ratio/rate of reduction.
Rather than a simple triac/bridge, the ebay PWM versions would be a step up at the same cost.
Max.
 
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