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DC Motor spinning with battery, but not after DAC

Harald Kapp

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Looks like the module is made for 100 mA load current (the specs are not very precise there). Your motor may draw a higher current and thus drive the modul into overload. Measure the output voltage and current with the motor attached. Give us more details on the motor.
 

wilkinsaf

Dec 24, 2022
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Thank you for the quick response @Harald Kapp .

I have a lion battery that I attach directly to the motor that spins it. It outputs 7.9 volts and 3 amps.

I have adjusted my DAC to output 7.9 volts and 3 amps (using multi-meter), but whenever I attach the motor the volts drop to 0 and the motor does not spin.

I know this sounds crazy, but these have been the readings I've seen
 

Harald Kapp

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I have adjusted my DAC to output 7.9 volts and 3 amps
How do you adjust the current? The potentiometer is there to adjust voltage only.
The "data" (not that it deserved the name) on the A... website states nothing about th emax. output current of the module. The only statement is "operating voltage 12 V - 30 V > 100 mA. There is no obvious power transistor on the module, nor a heatsink. I very much doubt that the module is capable of driving more than a fe mA, let alone 3 A. This is a converter, not a power stage. You'll have to connect the analog output of the module to a driver circuit (amplifier) to get 3 A.

Question: Why do you use this module at all? Driving a motor with pwm directly is much more efficient than driving it from an analog voltage.
Of course, you will need a driver board, too, to supply the high current to the motor. The pwm output from your controller will not supply that much current.
 

wilkinsaf

Dec 24, 2022
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How do you adjust the current? The potentiometer is there to adjust voltage only.
The "data" (not that it deserved the name) on the A... website states nothing about th emax. output current of the module. The only statement is "operating voltage 12 V - 30 V > 100 mA. There is no obvious power transistor on the module, nor a heatsink. I very much doubt that the module is capable of driving more than a fe mA, let alone 3 A. This is a converter, not a power stage. You'll have to connect the analog output of the module to a driver circuit (amplifier) to get 3 A.

Question: Why do you use this module at all? Driving a motor with pwm directly is much more efficient than driving it from an analog voltage.
Of course, you will need a driver board, too, to supply the high current to the motor. The pwm output from your controller will not supply that much current.

How do you adjust the current? -> I did not, it just happened to be at the same current of the battery that worked with the motor

I very much doubt that the module is capable of driving more than a fe mA, let alone 3 A -> Apologies, I am not sure what "fe mA" means but I believe I get the sentiment of what you are saying which is "this board needs to feed into a larger power source to drive a motor"

Of course, you will need a driver board, too, to supply the high current to the motor -> That would be great! Do you have any recommendations? I am a software engineer and trying to get my hands more involved in the hardware. Thank you for your wisdom
 

wilkinsaf

Dec 24, 2022
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Is that the normal running current of the motor? If so, the start-up current would normally be several times greater.

Ah, so what you are saying is that to initially start motor spin the current would need to be much larger than that. Makes sense. I have tried to manually spin the motor to see if that might help us.
 

kellys_eye

Jun 25, 2010
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The key issue is WHY you're trying to control motor speed this way. It's almost 'impossible' without some form of feedback and the motor will not maintain a steady speed using this method. Getting it going from standstill will be a 'hit and miss' affair.

As mentioned above, you really should use a PWM controller.
 

wilkinsaf

Dec 24, 2022
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The key issue is WHY you're trying to control motor speed this way. It's almost 'impossible' without some form of feedback and the motor will not maintain a steady speed using this method. Getting it going from standstill will be a 'hit and miss' affair.

As mentioned above, you really should use a PWM controller.
To be honest, I thought the controller I got was a PWM controller. I am giving it a PWM signal and a voltage as input, and i can modulate the voltage output using the PWM signal.
However, I did find this: PWM Controller which might be perfect for what I need
 

davenn

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Apologies, I am not sure what "fe mA" means

a typo fe = few mA ( mA = milliAmp)

To be honest, I thought the controller I got was a PWM controller. I am giving it a PWM signal and a voltage as input, and i can modulate the voltage output using the PWM signal.

No as per the title on the part page you linked to .....

PWM to Voltage Module 0%-100% PWM to 0-10V Voltage​

that is, it converts a PWM signal to a voltage

so where is your PWM signal coming from that you are supplying to this converter board ?

The next thing, in the title, you needed to note was .......

Suitable for Signal Interface Switching for PLC or Other Industrial Control Boards​


this tells you that is is to be used to supply low current loads = other control boards that will drive motors etc

However, I did find this: PWM Controller which might be perfect for what I need

no, that isnt a PWM controller, that's a motor driver board that can be controlled from the output of a PWM board

cheers
Dave
 

wilkinsaf

Dec 24, 2022
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a typo fe = few mA ( mA = milliAmp)



No as per the title on the part page you linked to .....

PWM to Voltage Module 0%-100% PWM to 0-10V Voltage​

that is, it converts a PWM signal to a voltage

so where is your PWM signal coming from that you are supplying to this converter board ?

The next thing, in the title, you needed to note was .......

Suitable for Signal Interface Switching for PLC or Other Industrial Control Boards​


this tells you that is is to be used to supply low current loads = other control boards that will drive motors etc



no, that isnt a PWM controller, that's a motor driver board that can be controlled from the output of a PWM board

cheers
Dave

Thanks for the knowledge Dave!

"so where is your PWM signal coming from that you are supplying to this converter board ?"

I have a pixhawk autopilot board that outputs a pwm signal and was going to plug it in to a board that can modulate voltage to drive a DC motor
 

wilkinsaf

Dec 24, 2022
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Thanks for the knowledge Dave!

"so where is your PWM signal coming from that you are supplying to this converter board ?"

I have a pixhawk autopilot board that outputs a pwm signal and was going to plug it in to a board that can modulate voltage to drive a DC motor
So I think, in summary, I need to get a better motor driver board as the one I linked is setup to convert PWM to voltage, but not supply enough current to actually drive motors off of.
 

wilkinsaf

Dec 24, 2022
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Searching for "Motor driver boards" is returning more products than the keywords I was using before "PWM to voltage boards".

This one looks promising as it can drive 2 motors, and do reverse as well: Motor Driver Board #1
This one looks rather straight forward as well: Motor Driver #2

Still not sure why the board mentioned above does not work as it LOOKED like it was supplying the right voltage and current. But, these boards look more promising.

Thanks for taking the time to check out my post and give a newbie some advice.
 
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