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12v 5a PWM, how to test

pevweb

Nov 6, 2020
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As the controller linked in post #18 is specifically designed to drive motors, a flyback diode is probably already on board.
In any case, as Bluejets stated, you can mount the flyback diode also in parallel to the motor connections. No need to solder it to the controller pcb.
This is all new territory for me so pardon the newbie questions :)
how would you go about choosing such a thing and would that be wired to the motor leads? simply connect a diode to one of the leads and hook wide to other end and of you go or is more complex than that?

thanks
 

Harald Kapp

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I'd use a leaded diode and solder it to the connectors of the motor. If the leads aren't long enough, add a length of wire to one lead.
 

pevweb

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well, now I'm confused again
I wanted to see if my PWM was damaged or not so I took a 12v fan from an old computer and hooked it up to the PWM. it worked perfectly. going from zero speed to full speed when I turned the knob, as expected. then I figured I would check voltage just for fun. when knob was set on high I would get 21v but if I turned the knob down it would lower the voltage towards zero. I was under the impression that the PWM did not affect voltage but only the amount of amps. In the description of most PWMs I saw they talk about going from Xamps to 0 amps. not voltage. does it make sense that the I got those readings?
 

Harald Kapp

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I was under the impression that the PWM did not affect voltage but only the amount of amps.
Your impression was wrong. While pwm switches between "on" (full voltage, 12 V) and "off" (no voltage, 0 V) the effective voltage is proportional to the duty cycle. Your voltmeter is not able to measure the instantaneous voltage levels (0 V, 12 V) of the two states of the pwm signal. Instead the meter averages the measured voltages to somewhere in between these two levels, depending on duty cycle.
This is the same effect that happens when this pwm signal is applied to e.g.:
  • A motor. The motor will draw an average current depending on the duty cycle of the voltage and thus the motor's speed can be controlled.
  • A lamp. The lamp will draw an average current depending on the duty cycle of the voltage and thus the brightness of the lamp can be controlled.
  • An oven. The oven will draw an average current depending on the duty cycle of the voltage and thus the temperature of the lamp can be controlled.
  • etc. etc.
 

pevweb

Nov 6, 2020
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Your impression was wrong. While pwm switches between "on" (full voltage, 12 V) and "off" (no voltage, 0 V) the effective voltage is proportional to the duty cycle. Your voltmeter is not able to measure the instantaneous voltage levels (0 V, 12 V) of the two states of the pwm signal. Instead the meter averages the measured voltages to somewhere in between these two levels, depending on duty cycle.
This is the same effect that happens when this pwm signal is applied to e.g.:
  • A motor. The motor will draw an average current depending on the duty cycle of the voltage and thus the motor's speed can be controlled.
  • A lamp. The lamp will draw an average current depending on the duty cycle of the voltage and thus the brightness of the lamp can be controlled.
  • An oven. The oven will draw an average current depending on the duty cycle of the voltage and thus the temperature of the lamp can be controlled.
  • etc. etc.
ah, well at least it's working as it should. I'll be reading the info in that l ink you sent to better understand how this works.
thanks
 

pevweb

Nov 6, 2020
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so I ordered another PWM (rated at 40A) and it works like a charm! thanks all for the tips, truly appreciated. little vid of the motor and PWM in action :)
 

ratstar

Aug 20, 2018
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Your voltmeter is not able to measure the instantaneous voltage levels (0 V, 12 V) of the two states of the pwm signal. Instead the meter averages the measured voltages to somewhere in between these two levels, depending on duty cycle.

I didnt know that, thats terrible! talk about how confusing that is, u cant trust your readings on your measuring equipment...

[addendum] can u get a reliable reading on the output of a step up transformer with a voltmeter?
 
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Harald Kapp

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u cant trust your readings on your measuring equipment...
Yes you can - if you know how to use the equipment correctly. Or which equipment to use for which measurement.

In the same way you can for example use a scale (measuring grams) to determine a volume (measured in milliliters) if you know the specific weight (in grams/milliliter). All that is required is some math.
 

pevweb

Nov 6, 2020
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Question....is it normal for the motor to get hot after a few minutes of operation? how hot is normal i guess it the question
 

pevweb

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also, I've noticed that motor will change speed on its own...sometimes I turn it on and it goes quite fast then others when I turn it on it goes almost half the speed. Would this be a sign of a failing motor? what could I check to see if something is up?
 
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