DIR line fault on High-Power Motor Driver 18v15

My Pololu High-Power Motor Driver 18v15 is drawing a lot of current on the DIR line when it is set high. The current draw is pulling down the supply power to about 4 volts. The driver still functions normally in both directions except for the high current draw. The high draw still occurs even if only DIR and GND are connected, with no motor or high power supply.

I sent a less complete email to the support address before realizing the forum was available.

Is the driver toast?

Could this damage have resulted from a +5 signal on DIR from a source that didn’t have the same ground as the motor supply? That may have happened…

The DIR pin leads to an unmarked surface mount IC. Would replacing it solve the problem? Any idea what the IC part # is?

Thanks,

Rick

Hi, Rick.

I am sorry you are having a problem with your driver. Unfortunately, we do not disclose the name of that part. The DIR pin could have been damaged when you applied that signal to it. Could you tell me some more information about your setup? How are you supplying power? What are you using to control the driver? What are the stall current and voltage rating of your motors? Could you post a picture of the top of your driver?

Also, thank you for letting us know that you emailed as well.

-Claire

Thanks Claire! The motor driven is a linear actuator, 12V 5A at full load, no stall current spec on their site.

progressiveautomations.com/linea … -p-75.html

Motor power is supplied from a 12V switching supply rated for 6A, driving only the motor power. The driver is controlled from an Arduino Uno powered by USB or a 6xAA battery pack. The DIR pin may have been connected to the Arduino 5V without the ground connection. It’s too bad about the secret logic chip because the power side of the controller seems to be working fine. Here’s a photo of the driver:

Thank you for posting the picture and answering my questions; I thought of a few more. How much current does the DIR pin draw? How are you measuring it? Also, could you post a wiring diagram of your setup or a picture with the driver connected?

-Claire

I don’t have a direct measurement and hesitate to cook my multimeter. With no other connections but the ground pin, and with the DIR pin pulled up through a 220 ohm resistor the supply stays at +5, but dir only comes up to about 1 volt. I=V/R = 4 / 220 = 18 mA at 1 volt. Dropping the resistor to 47 ohms brings the pin voltage up to about 1.5, with a current draw of 3.5 / 47 = 74 mA at 1.5 volt. A direct connector pulls the USB supply down to 4 volts, so probably 500 mA at 4 volts, or about 2 Watts, and certainly more at 5 volts.

That is the current draw with no other pins connected, besides ground.

With motor and supply connected, PWM high, DIR open, motor runs normally. Connect DIR to +5 supply and motor reverses. Connect DIR to high signal on arduino DIO pin and motor still turns normally and arduino pin is pulled low.

Hope that makes it clearer. Thanks,

Rick

Thanks for explaining how you determined the current draw. It seems like the DIR pin on your driver has been damaged. If you email us and refer to this thread, I can probably get you a discount on a new one.

-Claire

Thanks Claire! On this project I can spare the cash, but really appreciate the customer service. I already ordered a couple of Pololu Dual VNH5019 Motor Driver Shield for Arduino which are probably a better fit for where this project is going, and less likely to get misconnected along the way :wink:

As an aside, it’s usually not a good idea to provide input signals to a chip when you’re not also providing VCC (power) to that chip. Thus, when testing, you should ideally connect at least GND and VCC (+5V or whatever) before putting in signals.