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RAMPS the Fire starter

Posted by hexitex 
RAMPS the Fire starter
March 28, 2011 02:53PM
Pictures speak louder than words. I have no idea why this happen whilst in mid print, it was only being driven at about 25% Nothing external was in play. Had I not been there this could have resulted in a big fire which could have resulted in death, so be warned.

Re: RAMPS the Fire starter
March 28, 2011 03:27PM
This is not a R.A.M.P.S. problem as much as it is a Pololu issue and you should contact Pololu.
Re: RAMPS the Fire starter
March 28, 2011 07:52PM
I agree, it is a driver issue, so what other drivers does R.A.M.P.S support? I already know the answer, just making a point>grinning smiley<
Bigger question is are we asking too much of those small drivers, a typical CNC machine has much larger electronic hardware. I am willing to accept that this could be a one off, maybe a bit of solder was hanging on the board and the movement of the machine released it causing a short, I haven't found any other instance of this problem on a search. Still freaked me out, and it will be a long time before i leave it running without presence. fortunately or maybe unfortunately I had 4 spare.
Re: RAMPS the Fire starter
March 28, 2011 08:36PM
Any chance you've got a loose or intermittent motor wire? The datasheet mentions disconnecting the motor during operation will likely destroy the chip.
Re: RAMPS the Fire starter
March 28, 2011 08:40PM
JohnnyR has a drop in alternative board that uses A3979 that can handle 2.5a but has only made a few.
Joe M has designed a drop in replacement that can be found here

And yes you are correct that commercial machines use a lot heavier duty drivers. But they come at a price, check here. most of which could be used as replacements with some wires and .100" headers plugged into the pololu sockets.

Edited 1 time(s). Last edit at 03/28/2011 08:41PM by Sublime.
Re: RAMPS the Fire starter
March 28, 2011 09:06PM
thanks for the links Sublime, cheap at double the price if they don't catch fire.

Wade, checked that on initial build, I did read the data sheet on purchase. I have checked again and the crimps are 100% solid with plenty of copper in contact. Anyhow, I would not have thought that a dodgy connection would be so drastic.
Re: RAMPS the Fire starter
March 28, 2011 09:49PM

i like the stats on those drivers, that would be nice to be able to get those at a good price, i wonder if any of the stores will start to carry them. i think they would run that much cooler too.

Re: RAMPS the Fire starter
March 28, 2011 10:59PM
I've done that to 4983's by removing the sense resistor. I'm sure other shorts can cause it as well.
Re: RAMPS the Fire starter
March 29, 2011 06:58AM
I have seen this before. It's a production fault on the Pololus. I've heard of it happening twice, not including your case.

Re: RAMPS the Fire starter
March 29, 2011 08:06AM
Can you see which component is at the epicentre?

Ceramic capacitors can cause fires like that. What happen is the capacitor is cracked by thermal stress during soldering. The crack lets in moisture from the air. A small current flows through the moisture and that allows metal to migrate and cause a short after maybe weeks or months. The filament of metal is so thin it has a resistance of a few ohms, so it is not a direct short. The component heats up and burns the PCB. Once the substrate of the PCB is carbonized that too conducts, gets hot and burns.

Not much you can do about electronics catching fire other that put it in a fire proof enclosure. Fuses don't help because the power required to heat up a tiny component is less that that required to run the motor.

Re: RAMPS the Fire starter
March 29, 2011 08:25AM
... here in Germany smokedetectors are obligatory from 2014 on ... but it's not a bad idea anyhow install one above the printer winking smiley

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

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