I think one way to route the wires safely to the carriage is to run the wires through a spring as was done in the Ord Bod. This would keep the wires from drooping down, and it would have avoided the problem that you encountered. I found that a plastic spiral wrap which I'm using now also works, but maybe not as good as a spring.

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Ohmarinus
I just think it's incredibly dumb to let your wires run loose like that. Lesson learned I guess? A good lesson is a lesson where nobody got REALLY in trouble.

I hope you manage to repair the machine Lucky guy!

It would be dumb to run your wires loose. That's why I am pointing this out, my wires were not loose and were tied up. I had just enough slack to reach the furthest point from the anchor point on top. This is the way it is constructed. When you get to the top of an 8" print, you are going to have roughly 12" of slack to contend with when your HE reaches the upper right corner of the build. So obviously tying up the wires is not sufficient, and some kind of chain rail is needed.

Edited 1 time(s). Last edit at 01/15/2014 07:49PM by Antslake.

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brnrd
I think one way to route the wires safely to the carriage is to run the wires through a spring as was done in the Ord Bod. This would keep the wires from drooping down, and it would have avoided the problem that you encountered. I found that a plastic spiral wrap which I'm using now also works, but maybe not as good as a spring.

I think I am going to try to incorporate something like this:
[www.thingiverse.com]

Quote
bytemedwb
Wow - I have always worried about this possibility. I have the wooden Makerfarm also. So I just went on to
amazon and bought:Flame Defender - 12 KG - 7.7' coverage
[www.amazon.com]

I don't worry as much about the type of short OP had but more the idea that the thermistor fails
and a run away hot end ignites plastic. Add to that the can of Acetone that is generally there.

I like this!

For the rest of you, If I wasn't clear, my wires were tied up. They are only untied in the photo after the fact. I wanted to see which ones got burned. I just positioned them in the spot again so you could kind of see what happened. I had wire ties, shrink wrap, and zip ties holding it all very neatly with the minimum amount require for full travel. So don't think you are safe or smarter than me because your wires are tied up!

Edited 1 time(s). Last edit at 01/15/2014 07:57PM by Antslake.

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dave3d
I also think the thermistor should have a failsafe in the firmware to guard against it being dislodged.

That's a great idea. There's no reason for the temperature to drop more than 10-20C whithin a printjob (except g code temperature changes). If this happens, the firmware could initiate an emergency shutdown after 5 seconds or so.

I would think the main point of this is make sure to be around your machine when it fails. I can not recommend it but many people sleep thru the prints and wake up when an alarm goes off.

there is a down side to using co2. it is the rapid temp drop to anything the gas touches. it will cause every part that is heated up to crack and be ruined. this includes ramps pcb, and heated bed pcb, as well as glass beds.

I had a friend that had a laser engraver laser tube that was destroyed when he used a fire extinguisher to put out a small fire caused by a part that caught fire inside of the laser engraver. when he used the co2 it put out the fire immediately, but seconds later the glass heat tempered tube exploded.

Edited 1 time(s). Last edit at 01/16/2014 03:46AM by jamesdanielv.

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Antslake

Quote
bytemedwb
Wow - I have always worried about this possibility. I have the wooden Makerfarm also. So I just went on to
amazon and bought:Flame Defender - 12 KG - 7.7' coverage
[www.amazon.com]

I don't worry as much about the type of short OP had but more the idea that the thermistor fails
and a run away hot end ignites plastic. Add to that the can of Acetone that is generally there.

I like this!

For the rest of you, If I wasn't clear, my wires were tied up. They are only untied in the photo after the fact. I wanted to see which ones got burned. I just positioned them in the spot again so you could kind of see what happened. I had wire ties, shrink wrap, and zip ties holding it all very neatly with the minimum amount require for full travel. So don't think you are safe or smarter than me because your wires are tied up!

Thats why I use a tube that guides the wire!

The insulation on wires is only to prevent leads from touching eachother, not for anything structural. The tubes I use are specifically for cable guiding, there is a special tool that you can use to insert the cable into the tube. The tube can successfully be clamped to your stepper motor with two tie-rips. I can show you a clear image if you like.

This protects the wire from wearing by movement and sliding over surfaces, and it limits motion so the wires only bend slightly when printing and it takes the weight off of the wires. It seemed like the best way of fastening and protecting a 'wireloom', and it turned out to work.

You can also print these modular cable guides which you can click into eachother.

I was using industrial heat shrink over the exposed length. I would like to see a pic.

Mmm might be time to install that smoke detector alarm I bought a while ago...

---

Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

Edited to bad information. Sorry.

Edited 2 time(s). Last edit at 01/17/2014 09:25AM by umdpru.

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umdpru

Quote

I also think the thermistor should have a failsafe in the firmware to guard against it being dislodged.

correct me if I am wrong but Marlin uses the Min_temp setting in that exact case. You need to set it to the right temperature though. The default value is 5C. It should be much closer to your hotend working temperature, though. the thermistor will rapidly detect a decrease in heat, though, if it were dislodged. When the min_temp threshold is breached, the controller goes into failsafe and shuts down the hotend. This also protects against thermistor wiring shorts.

This kind of failsafe wouldn't have helped in this case, though, because the stepper wiring got shorted. I'd be curious to know why the Ramps fuses didn't open. There are two for the DC inputs, afterall.

Hey umdpru! Now we are talking on 2 different forums, lol.

Recently my heater cartridge started failing, and on a print the temp went below the min_temp and my printer stopped the print. Just like you can't extrude until it gets to temp.

I don't know where the fuses are in the schematic of the ramps board, but my guess is that it doesn't take much wattage to cause the stepper driver to go up in flames. The wires that shorted didn't look like they had any significant current going through them. It may have been a quick event, and the fire touched all the wires above the driver and started spreading. Remember, everything over there is rather warm, so it can catch easier.

I am definitely building a metal enclosure for the RAMPS. Think about it, any UL listed device that has that kind of power going through it is in an enclosure. I wonder if these are even UL listed.

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Antslake

I am definitely building a metal enclosure for the RAMPS. Think about it, any UL listed device that has that kind of power going through it is in an enclosure. I wonder if these are even UL listed.

This is not true. I can think of many household items that use much more power (kw or more) that are in plastic: electric drills, blow dryers for hair, iron for clothes, waffle makers. Typical 3D printers use 20 A at 12 V with 1 extruders. That's only 240 watts.

Edited 1 time(s). Last edit at 01/16/2014 10:59AM by brnrd.

As I understand it, the min temp setting in Marlin for the thermistor is for when it fails completely.
It goes open circuit and registers less than 5 deg C. The firmware then shuts down the print.

What we are talking about is a situation where the thermistor is pulled out of the hot end but carries on working. This happened with me and nearly caused a fire. The actual hotend temp races away while the indicated thermistor temp is dropping.

A couple of lines of code in Marlin could catch this. As mentioned previously, it could be if the hotend temp suddenly drops say 20 deg C in the middle of a print, it shuts down.

Instead of hanging your wires from the top, attach them to one of the carriages that the Z screws go through. That way height changes don't change the length of cable going to the extruder carriage and you just need enough for the X travel.

Quote
umdpru
This kind of failsafe wouldn't have helped in this case, though, because the stepper wiring got shorted. I'd be curious to know why the Ramps fuses didn't open. There are two for the DC inputs, afterall.

That's a good question. The "fuses" on RAMPS and some other boards are PTC's, which limit current when hot. I have come to the conclusion that they are quite bad, if not evil. They do a bad job of limiting current, and in some cases actually catch fire themselves. I think best practice is to bypass them and use external fuses inline with the supply.

I think most new controller designs now are using real fuses instead of PTCs, but there are a lot of RAMPS boards around.

I am curious as to why the stepper driver overheated. The Allegro chips have over temp protection, but I guess if it had been bumping at the 150 deg limit for a while, either the chip or something around it failed to a short.

Some of the newer driver chips have a Fault output or the temperature can be read from the chip, this might help to detect overheating earlier and enable safe shutdown.

---

What is Open Source?
What is Open Source Hardware?
Open Source in a nutshell: the Four Freedoms
CC BY-NC is not an Open Source license

The overtemp limiters on the chips are for the chips, they aren't there to prevent motor wiring shorts causing fires. I think I will be adding inline fuses to the 11A and 5A lines as a start.

Edited due to bad information, sorry.

Edited 2 time(s). Last edit at 01/17/2014 09:25AM by umdpru.

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umdpru
The overtemp limiters on the chips are for the chips, they aren't there to prevent motor wiring shorts causing fires. I think I will be adding inline fuses to the 11A and 5A lines as a start.

If there is too much current through the chip, it causes overheating of the chip, regardless of the cause.

It depends on the chip, but the A4988 has shorted load protection, short to ground protection and over temp protection. If the motors wires are shorted it should not cause a fire in the driver. Once the chip shuts down the mosfets, it doesn't matter if the motor wires are shorted.

So I am still wondering why the chip caught fire. It is not the first time we have seen that though, so either the chip protection is not really that good, or something else is going on.

Either way, adding proper fuses is a good idea.

Stupid question, but if mintemp is set to 210, how does the heater ever turn on?

---

What is Open Source?
What is Open Source Hardware?
Open Source in a nutshell: the Four Freedoms
CC BY-NC is not an Open Source license

Quote
Antslake
I was using industrial heat shrink over the exposed length. I would like to see a pic.

I am using this kind of cable guide:
[www.conrad.nl]

With this tool the wires are inserted in the cable guide:
[www.conrad.nl]

Works incredibly well!

Quote
brnrd

Quote
Antslake

I am definitely building a metal enclosure for the RAMPS. Think about it, any UL listed device that has that kind of power going through it is in an enclosure. I wonder if these are even UL listed.

This is not true. I can think of many household items that use much more power (kw or more) that are in plastic: electric drills, blow dryers for hair, iron for clothes, waffle makers. Typical 3D printers use 20 A at 12 V with 1 extruders. That's only 240 watts.

mmm, let's see. An electric drill has a motor in it that is enclosed in metal, blow dryer also has a metal shield around the heat coils, and a metal motor, and iron is metal, waffle makers are metal......yep, going with metal.

Think about our power supplies themselves, or PC power supplies with FETs, they have metal enclosures. FET's are known to burst into flames. They actually shoot flames out like a jet engine.

Edited 1 time(s). Last edit at 01/16/2014 08:03PM by Antslake.

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tjb1
Instead of hanging your wires from the top, attach them to one of the carriages that the Z screws go through. That way height changes don't change the length of cable going to the extruder carriage and you just need enough for the X travel.

This is what I am going to do, but with a wire chain. Got my parts intoday, and if everything else is ok, the first thing I am printing is the wire chain.

Quote
Antslake

Quote
brnrd

Quote
Antslake

I am definitely building a metal enclosure for the RAMPS. Think about it, any UL listed device that has that kind of power going through it is in an enclosure. I wonder if these are even UL listed.

This is not true. I can think of many household items that use much more power (kw or more) that are in plastic: electric drills, blow dryers for hair, iron for clothes, waffle makers. Typical 3D printers use 20 A at 12 V with 1 extruders. That's only 240 watts.

mmm, let's see. An electric drill has a motor in it that is enclosed in metal, blow dryer also has a metal shield around the heat coils, and a metal motor, and iron is metal, waffle makers are metal......yep, going with metal.

Think about our power supplies themselves, or PC power supplies with FETs, they have metal enclosures. FET's are known to burst into flames. They actually shoot flames out like a jet engine.

I haven't taken a hair dryer apart lately, but I have taken some apart in the past that had a plastic case and no metal shield around the heating element. Here's a youtube video or someone taking one apart:

[www.youtube.com]

I'm not saying that metal is not better. My point is that UL listed devices don't have to be in metal enclosures. We have a waffle maker that has a plastic case and my B&D electric drill has an all plastic case and thus, it has a 2-prong plug . I'm also quite sure that the Makita finishing sander that I bought a month ago has an all plastic case.

Quote
bobc
Stupid question, but if mintemp is set to 210, how does the heater ever turn on?

Not so stupid. It is the one thing that I have been wondering about. A number of people have been talking about this, but none of them seem to really know how this feature works in the firmware.

On my machine this is set to 5C and it means that in winter I can't get my printer (which lives in the garage) to even start printing unless I use a hot air gun to warm up the hot end first...

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[blogger.kritzinger.net]

Quote
CraigRK

Quote
bobc
Stupid question, but if mintemp is set to 210, how does the heater ever turn on?

Not so stupid. It is the one thing that I have been wondering about. A number of people have been talking about this, but none of them seem to really know how this feature works in the firmware.

On my machine this is set to 5C and it means that in winter I can't get my printer (which lives in the garage) to even start printing unless I use a hot air gun to warm up the hot end first...

So we need to be able to set in the firmware some kind of temperature range that is only used while the hot end is heating up or maintaining a set temp. If it drops out of that range, things need to stop...

If I understand correctly.

BTW, from what I know metal enclosures are only part of UL ratings. The contain fire to some extent, but they can pose a serious shock hazard. Hence the 2 or 3 prong thing.

Edited 1 time(s). Last edit at 01/16/2014 11:10PM by Yvan.

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Yvan

Singularity Machine

Quote
brnrd

I'm not saying that metal is not better. My point is that UL listed devices don't have to be in metal enclosures.

Perhaps my statement was too general, but when I wrote it I was thinking more along the lines of similar items, like power supplies, and 120v junction boxes. Obviously I am not an underwriter, but I did fire proof NYC hospitals for 11 years. We took them apart and put them back together again with the proper fire and smoke ratings. I do know a thing or two about making things safe in that department (when I apply it). All those devices you named are tested, and meet the requirements for their use, fire rating included. You obviously should not put a hair dryer under the sheets and fall asleep with it on. I also own a HVAC and plumbing business and deal with flame and fire all the time. Not just in the equipment but in the exhaust. It's just not a good idea to have a FET next to wood. I've seen to many go off like a mini rocket when they fail. Compile that with the garbage we get from China sometimes and it's a recipe for disaster. I had always had in the back of my mind worries about the wood frame. My plan was to upgrade it to metal. I am building a second i3 first, printed my own parts and looking for a metal frame, then I was going to upgrade this one.

So being that these things have gone up in flames for a few people, metal it is.

I think that the idea behind the minimum temperature parameter is to detect a thermistor failure, like when the thermistor leads break or get disconnected. In those cases, the resistance would become much higher than the resistance at 25C (usually around 100k) and the temperature would read below room temperature. It won't detect instances when the thermistor comes off the heating block. Nophead has been a proponent in the past of designing the hot end so that it can never get too hot to cause a fire if the voltage is left on continuously by choosing the correct resistance. If the hot end uses PEEK or PTFE, this means that with full power, the temperature has to stay below 300C. This is always a good idea since thermistors are mostly rated below 300C anyway.

Full power with a max temp of only 300°C would give slow heat up times no? How many watts is that?

If it does, a secondary high power heater could boost the temp up for a limited time, then shut off and never turn on again during the print.

The problem with the hot end right now is that it stays on in illogical ways, like full power for more than a specific amount of time if the thermistor is loose. Unless hot ends are sometimes on full power during a long stretch while printing? Does that happen with faster machines?

I know my slow machines never need full power while printing, so it would be nice to be able to use that in the firmware.

Still doesn't explain why the RAMPS started roasting though...

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Yvan

Singularity Machine

Quote
Yvan

Quote
CraigRK

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bobc
Stupid question, but if mintemp is set to 210, how does the heater ever turn on?

Not so stupid. It is the one thing that I have been wondering about. A number of people have been talking about this, but none of them seem to really know how this feature works in the firmware.

On my machine this is set to 5C and it means that in winter I can't get my printer (which lives in the garage) to even start printing unless I use a hot air gun to warm up the hot end first...

So we need to be able to set in the firmware some kind of temperature range that is only used while the hot end is heating up or maintaining a set temp. If it drops out of that range, things need to stop...

If I understand correctly.

.

Correct. Perhaps we should think about it like this:

• For each printer the hot end temp should increase in some ratio according to the amount of time max power is applied
• Could we track the power applied (time power was on) say over the last 5 minutes
• Track whether temp is decreasing significantly in the same time
• Correlate the 2. If we are applying power, then temp should be going up, not down

Sorry, not articulated very well. But rather than needing to set ranges or anything, the firmware should know if it is expecting the temp to rise, and if the temp actually drops, then warning bells should be ringing.

Then again, this is to cover the situation where the thermistor is pulled out of the hot end. I believe you can set Marlin to have 2 thermistors on the one hotend and stop based on a differential. This might be a quick win for people (although it presumes you have the hardware to make this a reality).

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[blogger.kritzinger.net]

Overload is very danger.

Quote
CraigRK

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bobc
Stupid question, but if mintemp is set to 210, how does the heater ever turn on?

Not so stupid. It is the one thing that I have been wondering about. A number of people have been talking about this, but none of them seem to really know how this feature works in the firmware.

On my machine this is set to 5C and it means that in winter I can't get my printer (which lives in the garage) to even start printing unless I use a hot air gun to warm up the hot end first...

Yeah, eating a bit of crow here. I neglected to say in my earlier post that it was a feature I wanted to implement but keep forgetting about. You are right, though, that it's an issue. A chicken and egg scenario. The firmware says specifically that the min temp setting is for thermistor short protection which would obviously immediately register a low temperature and it wouldn't necessarily protect against a dislodged thermistor.

Did the hot end on this machine melt the heater element feed lines and send 12v back into the chip in a way that obviously didn't make happy?

Edited 2 time(s). Last edit at 01/17/2014 06:57AM by umdpru.

I'm pretty sure MINTEMP is just a thermistor initialization check and can not be used during printing because the printer would never start if this is within 5 degrees of extrusion temp. I think the feature you are thinking of is the min extrusion temp which just prevents extrusion and would not shut the printer off.