Exploding A4988 Motor Drivers on Sunhokey Prusa i3

Hello all,

I posted a couple months ago about problems with exploding parts on the Sunhokey Prusa i3, here's the thread for reference: [forums.reprap.org]
So to summarize, I bought the printer and shortly after some little part labeled LG1 exploded on the board, and none of the motors or heating elements worked. I sent back for a replacement and three months later I just received the new one. Turns out both the board and all 5 motor drivers were fried. I heard many suggestions that the short was caused by a faulty power rail, and I removed the screw in the PSU housing that supposedly caused the problem. About an hour after I installed the new board, there was another explosion, except this time it was one of the A4988 motor drivers that exploded. The Y axis was homing, and when it hit the end the Y axis motor driver went up in smoke. Now none of the motors work, but unlike last time the heating elements still do. So I think the motherboard is ok, just all the motor drivers got fried. I was hoping to see if anyone else had this issue so that I don't end up frying the next batch of drivers

Ben

Did you set the motor current low enough? Rule of thumb is max.80% of either max. driver or max. stepper current. ( whichever is lower)
Did the Y-endstop cause a shortcut?
-Olaf
PS: I wouldn't wait for another 3 month and get a Ramps/Mega combo instead...

I second Olafs suggestions. My guess also is that the endstop was wired to +5V and gnd. I'd get a ramps and spend some time studying the connection diagrams:
http://reprap.org/wiki/RAMPS_1.4

Unfortunately connecting the endstop to 5v and gnd by mistake is all too easy. It would've been better if the endstops included 4.7k resistors, so that a short is prevented and 4k7 is still plenty to pull the pin to ground.

You'll need to upload marlin or repetier firmware and confgure it. See my blog for a description of the process.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

Olaf -
Where do I set the motor current? Is it in configuration.h? I assumed I wouldn't need to modify the firmware because I'm using a Marlin branch specifically for this printer: [github.com]. Or is it the potentiometers on the boards? I never turned them at all - was I supposed to?

Imqqmi-
How would I find out if the y end stop caused the short? I found it weird mostly because I had homed the y axis several times without any problems, and didn't see why a short would just randomly occur while homing. I don't see how I could have wired the end stops wrong - they are plug-terminated and go directly into the motherboard so it's pretty much impossible to connect it wrong. Do you suggest I cut the +5V (red) wire going to the end stops and solder in a resistor?

Thanks,
Ben

Search on this site for adjusting motor current, yep you're supposed to adjust it to get the motors running smoothly. Did you use triffid hunters calibration guide?

I don't know your exact wiring, there are dozens of builds out there. If it's foolproof then we'll need to look elsewhere, leave the 5v line for what it is for now.

could it be the heated bed solder pads or wiring touching the endstop pins? If 12V runs through any of the endstop wires could blow up anything that's supposed to run on 5v.
When you manually homed the heated bed was probably unpowered, during a print it is powered. Check the heated bed wiring for loose, exposed contacts and wires. Also check the continuity of the wires. If the heated bed makes entermittent contact it could send huge power spikes through the system.

Edited 2 time(s). Last edit at 11/27/2015 03:51AM by imqqmi.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

You may haven't killed the driver by an endstop shorting out, but by not providing good contact to the controller ( or not switching ? )
This could have lead to an overload situation for the driver, because it tried to move further against the endstop.
It must have been right on the edge then...I'm surprised the thermal shutdown didn't kick in before
-Olaf

Imqqmi -

Doesn't look like the heated bed wires shorted - think it would be more likely that the motor stalled and caused the motor drivers to overheat. Probably my new official A4988s will have better protection circuitry, I'll try calibrating them.

Thanks,
Ben