Hot Stepper Drivers? (4899?)

I just bought a Prusa Kit, and plugged the Sanguinololu 1.3a board in to my usb port. and within a few seconds, the stepper driver chips got really super hot. I don't have anything else attached to the board.... Is this right? I've read a lot of descriptions of the 4899 chip saying it gets 'hot enough to burn' so, maybe it's ok? But, I assumed that would be 'in use'... I will be using Nema 17 steppers, do I need to worry about heat-sinking these chips?

I don't think it's a good thing to power up your drivers without motors attached.

Yeah, can't hurt slapping some heat sinks on. Pointing a fan at them isn't a bad idea either.

And yeah, don't power up the board without the steppers attached.

Edited 1 time(s). Last edit at 01/25/2013 02:17PM by akhlut.

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- akhlut

Just remember - Iterate, Iterate, Iterate!

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how can plugging the board in, without motors attached cause any problems? they motors weren't told to run, so there's no current flowing.. even with them plugged in, if not told to run, there's still no current running though them? Or do I not understand stepper motors properly?

Stepper motors recieve current when not turning to hold the motors position. They are not like DC motors.

Also, don't connect or disconnect the motor while the driver is under power. I have a couple of "souvenirs" from doing just that.

ok, so the steppers use power to hold themselves in place. But that comes from the external power supply, right? so, with no external power supply hooked up, only the usb to Sanguinololu, there should be no current there for it to be trying to pass on to the steppers, right?

My driver chips stay totally cool when in standby - they are not doing anything so should not get hot. If yours are getting "red hot" after a few seconds from power up then there's a problem somewhere.

turns out it was a bad stepper driver... so currently I only have x y and z moving, no ability to print while I wait for the replacement driver...