finlejb
Posts: 1
Joined: Mon Dec 31, 2018 8:26 pm

DRV 8825 Potentiometer not changing voltage

Mon Dec 31, 2018 8:29 pm

I'm trying to wire a Nema 17 stepper motor to a DRV-8825 driver by following this tutorial. I got to the part at around 7:15 where he adjusts the current with the potentiometer on the driver. This isn't working for me. No matter what I do, my meter reads ~10.8 VDC when I first measure, and over the course of around 15 seconds, it steadily drops to ~9.87 VDC.

Here is a picture what I've done.

Here is a link to the powe supply I'm using. 12V/2A.

I've confirmed that there is 12V acorss the VMot and Gnd pins, so it seems like the power supply is working right. I can't figure out why changing the potentiometer doesn't adjust the voltage.

Thanks.

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OutoftheBOTS
Posts: 711
Joined: Tue Aug 01, 2017 10:06 am

Re: DRV 8825 Potentiometer not changing voltage

Tue Jan 01, 2019 10:43 am

You won't be able to adjust the amp pot unless you have the RPi/MCU pulling the rest and sleep pins high. Make sure u have it wired up like following
0J4232.600.png
0J4232.600.png (77.16 KiB) Viewed 258 times
The voltage needs to half the desired amps

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Gavinmc42
Posts: 3158
Joined: Wed Aug 28, 2013 3:31 am

Re: DRV 8825 Potentiometer not changing voltage

Tue Jan 01, 2019 11:22 am

Think of stepper motors as current devices, the pot adjusts the maximum stall current, not voltage.
What it does is reduce the current when in stop or holding position mode.
If you don't reduce the current your motors can get quite hot when they are stopped and not doing anything.
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Brandon92
Posts: 773
Joined: Wed Jul 25, 2018 9:29 pm
Location: Netherlands

Re: DRV 8825 Potentiometer not changing voltage

Tue Jan 01, 2019 1:13 pm

Also the type of breadboard wire is not really designed to carry a large amount of current. The purpose of those wires are more for signals. And the breadboard itself can't handle a lot of current, depending on the quality.

So, you could have a significant voltage drop across the wires that deliver the large current. To the driver and the motor. And the more the current you want. The voltage drop will increase also.

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