Measuring stepper driver's voltage

Hi,

I was trying to check the voltage going through the stepper motor drivers (Pololus). The multimeter was set to read DC current , I've applied the positive probe to the trimpot and the negative probe to the second pin (one of the ground pins). I am sure that I didn't touch another pin but somehow I have seen a spark between the ground pin and the probe. I wasn't sure if that was important because the multimeter could still read the voltage. I've tried with two other drivers, which also behaved similarly. Now, I've ended up with three dead Pololus. Seems that I've fried them. Ok, I should have been more cautious after seeing the spark and stopped right there but I somehow thought that beaing still able to read a voltage meant that the driver was working. So my question is: Why did this happen? Would the results be different if I used the other ground pin (the one on the top right). I've used a cheap multimeter, can it be the reason. I am asking this question becasue I want to be able to tune the drivers as accurately as possible but I'll have to revert back to the conventional method (listening to the sound of the steppers) if there isn't a safer way.

Thanks

... connecting/disconnecting steppers from the drivers while powered, will sure blow the drivers!

For measuring the current you can measure the voltage across the shunt-resistor and use Ohms law to calculate the current values from ...

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Viktor
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Quote
drmaestro
I was trying to check the voltage going through the stepper motor drivers (Pololus). The multimeter was set to read DC current ,

I hope that you had the meter set to read DC voltage (volts) and not DC current (Amps)!!!!!

Quote
drmaestro
Hi,

I was trying to check the voltage going through the stepper motor drivers (Pololus). The multimeter was set to read DC current , I've applied the positive probe to the trimpot and the negative probe to the second pin (one of the ground pins). I am sure that I didn't touch another pin but somehow I have seen a spark between the ground pin and the probe. I wasn't sure if that was important because the multimeter could still read the voltage. I've tried with two other drivers, which also behaved similarly. Now, I've ended up with three dead Pololus. Seems that I've fried them. Ok, I should have been more cautious after seeing the spark and stopped right there but I somehow thought that beaing still able to read a voltage meant that the driver was working. So my question is: Why did this happen? Would the results be different if I used the other ground pin (the one on the top right). I've used a cheap multimeter, can it be the reason. I am asking this question becasue I want to be able to tune the drivers as accurately as possible but I'll have to revert back to the conventional method (listening to the sound of the steppers) if there isn't a safer way.

Thanks

That is the reason why I always advise people to use the power connector ground pin when checking driver voltages.

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Waitaki 3D Printer

Where is the power connector ground pin? Is it the second ground pin on the driver (the one on the right corner)?

Edited 1 time(s). Last edit at 06/17/2014 06:59AM by drmaestro.

No, not on the driver at all. The power plug from your power supply that plugs into the ramps board - the outer wire is negative on the 5A plug.

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_______________________________________
Waitaki 3D Printer