How to determine wiring of DC motor controller

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koyote

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I have a DC motor that came with a speed controller like in the picture. The controller is connected to the motor with a 4-pin connector. Nothing is labeled except the power source which says: 24V 4.17A 100W

I want to replace the controller with a DAC for automation and need to find out which pins of the connector do what. I could just start probing with a multimeter but I dont want to short anything. I also dont want to dissasemble the controller or the motor.

I assume:
1) two pins are power from the power source which supply the controller.
2) the other two pins are the regulated power from the controller to supply the motor and adjust its speed.

My uneducated approach would be to disconnect the controller, power up the device, and test between the pins looking for 24V. Once I find that +24 I dont know where to go from there. I'll have three pins unknown. I also suppose sparks could by flying during this process, which I dont want.

My totally ignorant next step would be to find something with resistance like maybe a 24V 100W light bulb, and test between the +24 and the other three poles. My hope would be to light up the bulb without the motor running. Then I would have found #1 above - the two pins that power the controller.

So then what? Directly wire those two pins to the other remaining pins and hope the motor turns at full speed? And if it doesnt, disconnect as quickly as humanly possible while sniffing for burning smells? Then, directly wire those two pins to the other remaining two pins and surely the motor will turn at full speed, thushly accomplishing the task.

Any ideas?
 

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Disconnected, from the open end of the plug and the motor end, test continuity of the wire and you will find out where they go and what they are for.
 
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Disconnect the motor and controller.Power on the controller alone and measure the 4-pin connector's pins to identify the power supply connections. Look for a steady 24V DC output between two pins.
 
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I took the cover off the part that connects the power supply, motor controller and motor.

Green is ground on the power supply side, chassis ground, and is routed into the controller.
Blue is +24V routed into the controller.
Red is 0 - 24V depending on speed fo motor, routed from controller to motor.
Black is ground routed from controller to motor.

I've been reading about motor controllers and it seems the only thing I'm finding for sale are PWM controllers. Is that because its trivial to wire a non-PWM motor? What is a non-PWM motor called? (my guess is "Standard DC Motor") I've been googling all week and still confused.

I did read that DC motors need a resister to stop overcurrent from damaging control circuits when the motor is turned off. I assume that's for the trivial non-PWM case. The PWM controllers would have protection circuitry included - im guessing.

I tested the output of the controller by applying power to the system, and using a multimeter to test votage between Red and Black wires. Dialing the controller from zero to maximum caused the 0-24V reading. However, I read that this could still be PWM and a multimeter will not show that because the wave form is too fast to pick up. I wonder if that also applies at very slow speeds near zero. I saw no fluctuation in signal down near 2 or 3 volts.

What would happen if I plugged a motor designed for PWM into a steady DC power?
What resister should be used in the loop to handle power surge on this 24V 4.17 Amp motor?
 
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koyote said:
What would happen if I plugged a motor designed for PWM into a steady DC power?
What resister should be used in the loop to handle power surge on this 24V 4.17 Amp motor?
Click to expand...
DC is the same as 100 % duty cycle on PWM, so a motor intended for use with PWM will just run at full speed.

If you connect the motor directly to 24 V it will take a much larger current as it starts up, but most motors can handle that. Usually they create lots of torque and start up quickly. If you limit the current to the normal running current, the motor torque will be about the normal maximum torque so start-up will be much slower.

You have said that the power supply is 24 V, 4.17 A but without knowing more details it's difficult to know what the power supply would do if connected to motor that is initially stationary.

A linear unregulated supply could well produce 20+ amps at somewhat less than 24 V and it would accelerate the motor quickly.

Switch mode supplies or linear supplies with a regulator could produce no more than 4.17 A, giving a slow increase in speed.

There are power supplies call "foldback power supplies" that only produce a fraction of the rated current if the load resistance is low, and one like that could well produce so little current for a stationary motor that the motor would not start at all if there is much friction it needs to overcome.

Some power supplies would just switch off if the current is too large.

The motor is unlikely to need a resistor in the loop for the motor, but you might well need one for the power supply.
 
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Thank you very much for this detailed answer! I'll check the current and let you know what's happening on startup and while running.

I still have these questions though...
What is a non-PWM motor called? (is there such a thing?)
Is it trivial to wire a non-PWM motor?
Would a multimeter react fast enough to determine if the controller is using PWM?
 
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koyote said:
I still have these questions though...
What is a non-PWM motor called? (is there such a thing?)
Is it trivial to wire a non-PWM motor?
Would a multimeter react fast enough to determine if the controller is using PWM?
Click to expand...
I don't really think that there is much difference between a PWM and non-PWM motor, for permanent magnet DC motors with brushes. I would guess that there are some differences, but lots of motor are run with PWM without specifically being designed for it.

Yes, it is trivial to wire a non-PWM motor. Connect it to a power supply. For example, look at stove fans. They have a DC motor wired to a Peltier element. The Peltier element generates electricity and the motor turns. That's it. There is no control device, no switch or anything.

In the more normal case where there is supply that is switched on and off to make the motor run or stop, there will be a larger current when the motor is stationary, so some consideration of the starting current need to be made.

A multimeter on DC will never react fast enough to determine if the controller is using PWM. However, better multimeters will measure the AC component of a voltage, and ignore the DC component if the multimeter is set to AC. To test that, select AC on the multimeter and see if it reads anything when connected to a battery. If it reads zero, then you can use it to see if there is an AC component on the voltage from the controller to the motor.

It's not a perfect measure, as PWM will be in the range 1000 - 50000 Hz and multimeters are sometimes only made to read AC voltages for mains at 50 - 60 Hz.

Almost all speed controllers for DC motors are PWM.
 
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There is no such thing, PWM refers to the speed controller method in order to control the speed digitally, it is a very common method for DC brushed & PM field BLDC version of motors.
 
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Here's a pic of the power adapter. Does anything on the lable tell you if this is linear unregulated? The motor does start quickly. And the motor temporarily shuts off if it gets too hot, and then starts up again in about 15 seconds.

I read somewhere some controllers detect motor current and shut it down if the motor is too hot. I'm not sure how a hot motor draws more current. And I wonder if the controller is getting too hot and shutting down. I see some controllers have heat sinks.

Here's a pic of the controller's board. It supports wifi in addition to the potentiometer.

Maybe I'm making this more complicated than it needs to be. All I want to do is figure out what to replace this controller with so I can use something like arduino to control motor speed. This might be a good choice...

Pololu G2 High-Power Motor Driver 24v13

This discrete MOSFET H-bridge motor driver enables bidirectional control of one high-power DC brushed motor. The small 1.3″ × 0.8″ board supports a wide 6.5 V to 40 V voltage range and is efficient enough to deliver a continuous 13 A without a heat sink. Additional features of this...
www.pololu.com
 

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Yes, this will work. Use the "analog out" or analogWrite to the Arduino pin to create a PWM signal with duty cycle from 0/255 to 255/255 to create the variable power to the motor.
 
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koyote said:
Here's a pic of the power adapter. Does anything on the lable tell you if this is linear unregulated? The motor does start quickly. And the motor temporarily shuts off if it gets too hot, and then starts up again in about 15 seconds.
Click to expand...

You don't really get linear speed controllers, and certainly not small and certainly not cheap - a linear controller would be massively larger, include large heatsinks, and probably have the added 'feature' of been able to make toast.

koyote said:
I read somewhere some controllers detect motor current and shut it down if the motor is too hot. I'm not sure how a hot motor draws more current. And I wonder if the controller is getting too hot and shutting down.
Click to expand...

It monitors the current, and presumably if the motor is taking excessive current (too high a load) will shut down to protect the motor and itself.
 
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New motor control chips and modern MOSFETS have allows significantly smaller packages than in days of yore.

MOSFETS with sub-milliOhm R(on) are common. At 17A, a mosfet with 0.6mOhms on-resistance will dissipate well under a quarter watt.

Times are changing.
 
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Perhaps you should try reading the post?, what has that got to do with a linear speed controller?.
 
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A motor that draws more current will get hot. I guess some controllers model that.

Even though PWM speed controllers are quite efficient, they are not perfect so there is still some heat and heatsinks can be worthwhile. That doesn't mean that the heatsinks would be anywhere near as large as on a linear speed controller.

That speed controller would most likely be fine.
 
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