Stepper driver overheat causing damage?

[spaceorange12]

Hi all,
I'm back with another non-Printrbot troubleshooting question.
The DRV8825 stepper drivers on my Velleman have been acting up recently after I tried increasing the current on them. Basically, the printer was having some trouble with some high-speed travel moves, and since the drivers were stone cold, I figured I could give the pots another 20˚ or so. I tried printing the object again, and it made it through the travel move. But then it started skipping steps and the drivers were really hot.
I turned them back down to where they were, and messed around with some accel values, but now the drivers get boiling hot no matter where I have the pots at.
My question is whether it's possible for a stepper driver to incur permanent damage due to overheating. Hopefully someone with more electronics knowledge can explain what might be going on.

[RetireeJay]

Well, yes, an electronics chip of any kind can incur permanent damage due to overheating.

But on page 17 of the manual it says the chip self-protects against overheating by shutting down until the die temperature has dropped enough to operate safely again.

And almost invariably the damage from overheating (if it really happens) destroys the normal functioning of the device permanently. That is, it completely stops working. So if your motors all move back and forth and sound normal while doing so, then it's almost certain that the chips were not damaged.

Have you checked all the chips for heat? Maybe only one is overheating.

Maybe when you messed around with accel values you ended up asking the chips to perform in a way that was impossible for them. There are timing requirements on page 7 of the manual, including a maximum step frequency of 250kHz. If you're pushing the chips near the limit of the step frequency, then they'll end up burning a lot of heat internally just trying to keep up. Do you know how many microsteps you are using? What's the voltage rating of your motors? If it's too high, then the chips never get really good control of the motor current during moves; I recommend motors with a voltage rating of 2.8 volts. The chips control motor current, not voltage, and a motor with a lower voltage rating gives the chips more "headroom" to play with when changing the current (motors are inductive loads, and the nature of an inductor is to resist changes in current by exerting a counteracting "reactive" voltage).

[Mooselake]

Those drivers need heatsinks and active cooling (fancy name for a fan) to reach their maximum current limit. They often come with little aluminum heatsinks, or you can buy 20 of them for $0.94US/$1.27 Canadian. I just did, am converting my K40 to a smoothie based board and needed drivers (A4988) and heatsinks.

One caveat on lower voltage motors is that they use a higher current (power is voltage times current), which is even more likely to push you into active cooling land.

You'd be hard pressed to get even 20K steps/sec out of marlin, maybe double that with Repetier's tricky double step/interrupt tricks. If you really want to step in the 200K range look at the beagle bone black, machinekit or one of the reprap driver packages, and one of the driver capes (like CRAMPS) - but since they're a lot lower volume they'll be a lot more expensive than Arduionoish boards. The BBB uses it's internal programmable real time units (PRUs) to get a pretty amazing step rate.

Kirk

[spaceorange12]

Have you checked all the chips for heat? Maybe only one is overheating.

All of them are overheating, for sure.

Maybe when you messed around with accel values you ended up asking the chips to perform in a way that was impossible for them.

Don't think so. If anything, I made it easier for them to perform.

Those drivers need heatsinks and active cooling (fancy name for a fan) to reach their maximum current limit.

I added heatsinks and a fan immediately after I got these new drivers (over a month ago).

Essentially, none of the drivers were overheating before I increased the current.
According to what Jay said about the thermal shutdown, they don't seem to be damaged permanently either.
How would I go about fixing this?

[Mooselake]

Turn them back 10 degrees (half the initial 20) and see if that improves things. It's possible the current adjust pots aren't linear. Tweak either up or down depending on the results until you get the driver heating under control.

Kirk