Post-mortem help requested

Hey,
I fried 2 stepper drivers last night. It's a Mini-Mendel as per the original concept so my electronics are between two sheets of acrylic and hard to see and get at. I will have time tomorrow night I think to carefully inspect everything, in case it was a loose wire or something simple. But I was hoping if I described the circumstances, perhaps it would ring a bell with someone who could give me some ideas where to start looking.

This machine has not yet been operational. I've had very little time lately and have just been doing a little work at a time. I've run a number of simulated prints with all 3 axes working perfectly as well as the extruder stepper control. What's been missing for me to actually start printing is the wiring for the extruder tip heater and thermistor as well as physically mounting the extruder. So I completed that last night.

The boards are all TechZone remix boards except the extruder controller board which is by Makerbot. I literally wired up the nichrome wire heater coil to some extension wire and terminated it at the B output pins on the extruder board. Then I wired up the thermistor leads to some extension wire and then terminated it at the thermistor input pins on the extruder board. Then I turned everything on to test.

Immediately, one of the stepper drivers (Z axis) smoked up. I switched everything off and tried to spot any loose wires. I couldn't see anything obvious and I thought *maybe* it was just a coincidence and I had a failed stepper driver. So I took a chance and powered it back up again. Nothing immediately bad happened and I was able to connect using ReplicatorG. I jogged the X axis to see if the other axes are still working OK and immediately the stepper driver for that axis smoked up.

Assuming for a minute that I didn't somehow accidentally pull a wire loose somewhere while connecting the 4 wires for heater and thermistor, any ideas how this could happen? It's a bummer because the machine literally has done a few hours of simulated prints without issues and I thought I was minutes away from an extruder test and then a first print test. The last thing I expected was for something to go wrong with the stuff that was already working great.

Any ideas or input would be appreciated.
Kevin

... it seems you have overpowered the drivers with to much current - best methode to avoid this is turning the potis to the left (position which defines the lowest current through the coils) and test if the motors will have enough torque and won't get hot.

Then you can increase the current as long the motors won't get hot over some minutes.

Placing coolers on top of the chips or even fix some coolers to the motors will help too ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Thanks for the reply. I don't think this problem was caused by overdriving the steppers. The system ran perfectly fine, all 3 axes and the extruder stepper working great for hours of simulated use, UNTIL I hooked up the extruder heater and the thermistor. And then instantaneously, the Z axis stepper driver burned out upon turning on power. Then the X axis stepper driver burned out immediately after sending the signal to jog a few mm.

Is there any logical reason for the heater and thermistor wiring to cause this? That's the only thing that *should* have changed. If not, then it must have been a coincidence that while attaching the wires to the terminals, I accidentally pulled something loose. I'm not seeing any obvious loose or damaged wires though.

Thanks,
Kevin

Given what you've described, I would suggest checking for a short between the thermistor and the heater element. While I can't think of a reason this should cause this issue, it would definitely explain your correlation.

Note: Make sure to check both ends of the thermistor, due to its resistance.

... what power source have you?

It could be that the heater pulls more current than the PS can deliver or your cables are very thin, so the voltage for the stepper drivers drops below safe conditions and the electronic run havoc

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

The power supply is a 25A Ham radio supply, but you guys gave me a couple of things to consider when I dig into this problem.

I appreciate the ideas. I'll update when I find the culprit.

Kevin

Is it an old power supply? If so, the added current draw (maybe even a massive current draw if you have a short somewhere) could have been effecting the output voltage fairly heavily.