I purchased the motor shield V2.3 (https://www.adafruit.com/product/1438) and am having unexpected voltage output when driving a DC motor.
I am using USB power for the Arduino and a variable voltage/amperage lab PSU to drive the motor shield. I have confirmed the input voltage is 12v, however the output voltage is only ~4.5v.
I am just running the sample code to drive one motor at 100% found here: https://learn.adafruit.com/adafruit-mot ... -dc-motors
Am I doing something wrong or is there a problem with the shield?
Motor Shield V2 Low Voltage Output
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Please be positive and constructive with your questions and comments.
- adafruit_support_bill
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Re: Motor Shield V2 Low Voltage Output
Please post some photos showing your soldering and connections to the shield.
- shadowck5000
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Re: Motor Shield V2 Low Voltage Output
Thanks for assisting.
Here are some photos: https://goo.gl/photos/1SerdwDoSi1n8bqh7
Please let me know if you want different angles or something more specific.
Here are some photos: https://goo.gl/photos/1SerdwDoSi1n8bqh7
Please let me know if you want different angles or something more specific.
- adafruit_support_bill
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Re: Motor Shield V2 Low Voltage Output
That all looks OK from what I can see. What is the motor you are trying to drive with this?
- shadowck5000
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Re: Motor Shield V2 Low Voltage Output
I have a number of motors I am trying out, however it is not specific to one. Measuring the voltage right at the M1/M3 headers I get the 4.5v instead of 12 without any motor attached.
Example motors:
https://www.amazon.com/gp/product/B01KTZXZMK
https://www.amazon.com/gp/product/B01N0UUMUW
https://www.amazon.com/gp/product/B00EDMIH7E
I had measured M1 and M3 thinking that maybe there was a problem with the M1/2 headers but both have the same issue.
Example motors:
https://www.amazon.com/gp/product/B01KTZXZMK
https://www.amazon.com/gp/product/B01N0UUMUW
https://www.amazon.com/gp/product/B00EDMIH7E
I had measured M1 and M3 thinking that maybe there was a problem with the M1/2 headers but both have the same issue.
- adafruit_support_bill
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- Joined: Sat Feb 07, 2009 10:11 am
Re: Motor Shield V2 Low Voltage Output
Unfortunately, the specifications for those motors omit the most important data point. We need to know how much current they draw at 12v.
- shadowck5000
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- Joined: Sun Aug 20, 2017 3:31 pm
Re: Motor Shield V2 Low Voltage Output
Sorry about that, for one of the 12v motors, it draws .05A no load, and .25A under load. Measured hooking directly to the PSU.
- adafruit_support_bill
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- Joined: Sat Feb 07, 2009 10:11 am
Re: Motor Shield V2 Low Voltage Output
OK. That should be no problem.
With the 12v supply connected, measure the voltage between the left side "VIN Jumper" pin and GND.
With the 12v supply connected, measure the voltage between the left side "VIN Jumper" pin and GND.
- shadowck5000
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- Joined: Sun Aug 20, 2017 3:31 pm
Re: Motor Shield V2 Low Voltage Output
I get 4.41v across VIN and GND regardless of if the PSU is on or off and the Arduino is on, and 0v when the Arduino is off.
- adafruit_support_bill
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Re: Motor Shield V2 Low Voltage Output
Hmmm. And what do you measure between the right-side VIN jumper pin and GND?
- shadowck5000
- Posts: 8
- Joined: Sun Aug 20, 2017 3:31 pm
Re: Motor Shield V2 Low Voltage Output
Was not entirely sure what VIN you were referring to, so here is a diagram of what voltages I get where, and if the Arduino is powered by USB or not.
Let me know if there is a measurement I missed.
To confirm my understanding of the VIN jumper, it should not be connected when using a different PSU for the motors correct?
Let me know if there is a measurement I missed.
To confirm my understanding of the VIN jumper, it should not be connected when using a different PSU for the motors correct?
- adafruit_support_bill
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Re: Motor Shield V2 Low Voltage Output
OK. So you are getting 12v through the reverse voltage protection MOSFET. That sounds normal.
Looking back at your earlier post...
Is not 100%.
To get 100% duty cycle, you need to do:
setSpeed(100) would give you about 39% or 4.7v.
Looking back at your earlier post...
Can you post the code you are actually using? This code:I am just running the sample code to drive one motor at 100%
Code: Select all
myMotor->setSpeed(100);
To get 100% duty cycle, you need to do:
Code: Select all
myMotor->setSpeed(255);
- shadowck5000
- Posts: 8
- Joined: Sun Aug 20, 2017 3:31 pm
Re: Motor Shield V2 Low Voltage Output
Wow I think I am about to feel silly. I was using myMotor->setSpeed(100); not 255.
Is it using PWM to reduce the average output to 4.7v? A guess my DMM is just reading that as the average.
At work right now, but will confirm this when I get home later.
Is it using PWM to reduce the average output to 4.7v? A guess my DMM is just reading that as the average.
At work right now, but will confirm this when I get home later.
- adafruit_support_bill
- Posts: 88089
- Joined: Sat Feb 07, 2009 10:11 am
Re: Motor Shield V2 Low Voltage Output
Most DMMs will integrate over a few hundred milliseconds, so a less than 100% PWM duty cycle will just appear as a lower voltage.
- shadowck5000
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- Joined: Sun Aug 20, 2017 3:31 pm
Re: Motor Shield V2 Low Voltage Output
Thank you so much for the assistance you provided. You were correct, once I changed the motor speed to 255 from 100 I was getting the full 12 reading and driving the motor at full power.
I would recommend potentially changing this value in the example docs to something besides 100 to avoid this confusion, but carefully re-reading the docs would have also solved my problem.
You have certainly earned one long time customer because of your support.
I would recommend potentially changing this value in the example docs to something besides 100 to avoid this confusion, but carefully re-reading the docs would have also solved my problem.
You have certainly earned one long time customer because of your support.
Please be positive and constructive with your questions and comments.