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4988 Sleep Reset


#1

Has anyone experienced a stepper motor that stops rotating after 20 minutes of running? I can hear and feel the pulses being sent to the motor but no spinning. I do have the motor attached to some mechanical linkages but even if I unhook all the linkage still no luck. Nothing feels hot and the motor spins freely with no power applied. I have a 4988 driver and a NEMA 17 200 step motor. Any thoughts on this one?
Thanks in advance


#2

Hello, Eric.

Does it start rotating again for 20 minutes if you power cycle it? What are you using for your power supply? What are the electrical ratings (current, coil resistance, and voltage) of your stepper motor?

- Ryan


#3

Thank for your reply. Even if I unplug everything and plug back in still nothing. My power supply is a 12v 3a laptop power supply. The coil resistance is 1.8 ohm per coil and quite honestly I forget the voltage rating. The tag is covered by some of the linkage. One thing I need to do it measure the coil resistance after the stepper stops running. Perhaps after the coils heat up, something is shorting out. Is that that possible? I have also gone through several 4988 driver boards not thinking something could be wrong with the motor. I always though it was something that I had done mistakenly(unplug wires etc.)

Thanks Ryan


#4

I also calibrated the board as per the 4988 Getting Started Guide. The amps are set to .7 I don’t remember what the spec of the motor is but thought .7 would be a safe setting no matter what the spec was. I have discovered that the motor still doesn’t work the following day. I have hooked up my amp meter to check my cal setting. After poking around a bit, it looks like the amps swing between my setting of.7 and 0 every 5 sec or so. It holds for 5 sec on .7 amp and then goes down to 0 amps and hold about 5 sec and then back to .7 The light on the power supply goes dim while fluctuating. It acts as though something is shorting out. What am I missing?

Thanks again


#5

I suspect your power supply voltage is dropping because it cannot supply enough current. Can you measure the voltage while you are trying to drive a motor? Can you try using a power supply that can source more current and let me know if that helps?

- Ryan


#6

Ryan,

Just want to say thanks for helping me on this.

Sorry but I dont have access to another pwr supply. Here is a question. Is the Reset and Sleep supposed to be tied together and grounded or set high? Should the be separated? Right now I have them tied together and left floating. I have noticed that if i touch them to 5v my amps jump back to my preset level of .7 volts. Very interesting. As per page 7 of the 4988 data sheet, All STEP inputs are ignored until
the ¯R¯ ¯ E¯ S¯ E¯ Tinput is set to high.
Is this my issue? I was also wondering if I was getting into the Shorted-Load and Short-to-Ground Protection (page 9 data sheet) I’ll experiment and post.

Thanks.


#7

There should be a 100k pull-up resistor between SLEEP and VDD: you should not have to connect RESET or SLEEP directly to VDD if they are tied together. What you describe does not sound normal, so I suspect there is something wrong with your setup. Can you describe all of your connections and post a picture of your setup?

- Ryan


#8

After connecting Reset and Sleep to high, my project works flawlessly. As per this post from Ben, Am I missing a reset or something on a4988?
it looks as though I might be correct. The getting Started Guide doesn’t mention anything about the connection to high. Perhaps the guide needs an update since several other people have had a similar issue.

Thanks for your help and patience.


#9

I am glad you got your project working, and thanks for letting me know about it. Please note that the A4988 carrier should have a pull-up resistor between SLEEP and VDD, so your connection to high should not be necessary, unless somehow that pullup resistor got disconnected from the circuit. You should be able to test for its presence by measuring the resistance between SLEEP and VDD with everything disconnected from the driver. It should be 100k Ohms.

- Ryan


#10

OK, I’ll check for that value. Thanks again for the help.

E