Fire Hazard

Great feedback. I have to leave this discussion behind for about two weeks as I am traveling with minimal wifi connectivity. I plan to review your suggestions (thermal fuse, redesign attachment of thermistor and heater cartridge, heater options, etc.) when I get back. I am somewhat surprised at how common this fire hazard issue has been. Running long printings is very common and just saying that one should not leave sight of the printer for any perion of time during its operation is unreasonable. These must be designed to operate with minimal potential for fire.

I mounted one of these above my printer bench. [www.amazon.com].

I find that fire detecting/extinguishing equipment can sometimes be tough to buy because as a consumer society, we like to use the products we purchase. Fire detecting/extinguishing gear are products we hope to NEVER use.

Also, as already discussed, use self amalgamating silicone tape to wrap the hotend and secure the thermistor. Lastly, PLEASE use thermal paste when you install the thermistor. The thermal past will solidify over time and act as a glue securing it in so that even if the wrap comes off the thermistor isn't coming out. I recently rebuilt a J-HEad build using htis method and I had to use a pair of pliers to pull on the thermistor wires to dislodge it from it's hole.

Install a thermal fuse NEAR the heater block. Most thermal fuses aren't rated hot enough to be mounted direclty on the heater block, however, they have a high enough rating to be mounted VERY close to the heater block. My testing showed temperatures below 220ºC at the junction between the heater block and the body of a J-Head. The thermal fuse is connected to mains via a solid state relay such that when it's tripped, it cuts off mains power before any serious heat (READ FLAMES) can develop.

I use two types of "detectors' in my workshop, too. One is an ionazation detector which is good at detecting particulates associated with smoke but detects flames poorly and the other is is a photoelectric type which detects flame but can't detect smoke well.

Your fire alarm went off after the flame erupted because it's likely the latter type rather than the former.

Safety has to be a priority with these machines!

Edited 2 time(s). Last edit at 07/02/2014 03:01PM by umdpru.

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thejollygrimreaper
i solved this problem many moons ago by using axial thermistors and insulating the leads with ptfe sleeve:

click here

using this method there is nearly no easy way to get it into a thermal runaway mode, as the thermistor cannot physically leave the heater-block,

Thermal runaway is not limited to loose thermistors. There have been failed-on MOSFETs and stuck processors.

---

"Never argue with stupid people, they will drag you down to their level and then beat you with experience."

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Hazer

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thejollygrimreaper
i solved this problem many moons ago by using axial thermistors and insulating the leads with ptfe sleeve:

click here

using this method there is nearly no easy way to get it into a thermal runaway mode, as the thermistor cannot physically leave the heater-block,

Thermal runaway is not limited to loose thermistors. There have been failed-on MOSFETs and stuck processors.

stuck processors are solvable with the usage of the watchdog timer built into the chips,

failed mosfets are a bit of a different story however they still can be protected against very easily however this comes back to the powersupply and actually having overload and short circuit protection as advertised, this is something that seems absent in most of these industrial power supplies that come in from china

what i have done to take care of this scenario in all the printers I've built is i use those 19v 180watt power bricks instead, so i have a situation where the overload protection will kick in if either mosfet fails for the bed or hotend the powersupply will shutdown until it is unplugged and plugged back in again, the downside is that these power supplies don't cope very well with the style of pwm that is used by default in marlin but it's ok thats i've solved too by switching to hardware pwm for which there is a pull-request for which gives you the choice of hardware or software pwm

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thejollygrimreaper
failed mosfets are a bit of a different story however they still can be protected against very easily however this comes back to the powersupply and actually having overload and short circuit protection as advertised, this is something that seems absent in most of these industrial power supplies that come in from china

what i have done to take care of this scenario in all the printers I've built is i use those 19v 180watt power bricks instead, so i have a situation where the overload protection will kick in if either mosfet fails for the bed or hotend the powersupply will shutdown until it is unplugged and plugged back in again, the downside is that these power supplies don't cope very well with the style of pwm that is used by default in marlin but it's ok thats i've solved too by switching to hardware pwm for which there is a pull-request for which gives you the choice of hardware or software pwm

No power supply can protect against a failed hot end MOSFET, your statement is false. Please don't spread potentially dangerous misinformation like this.

Edited 1 time(s). Last edit at 07/02/2014 09:19PM by greenman100.

I think it's important to have an actively cooled controller to cool stepper drivers and the mofsets. I tried to make a ramps enclosure that could hold a fan, but there was no way to do it economically with all wires attached to the top. I like the Melzi board with screw down terminals. It's relatively easy to blow cool air onto the electronics. The screw down terminals are really good because there's less problems with the wires coming unattached and causing shorts. The crimp on pin connectors are totally inadequate, unless you have really good wire strain relief.

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Hazer

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thejollygrimreaper
i solved this problem many moons ago by using axial thermistors and insulating the leads with ptfe sleeve:

click here

using this method there is nearly no easy way to get it into a thermal runaway mode, as the thermistor cannot physically leave the heater-block,

Thermal runaway is not limited to loose thermistors. There have been failed-on MOSFETs and stuck processors.

And bad/underspecced connectors, insufficiently sized PCB traces, etc.

3D printers should not be left unattended, no matter what. Roasting a turkey can take upwards of 6 hours, there's no way I'd leave the house with a turkey in the oven at 325F. A printer hot end runs north of 500F.

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greenman100

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thejollygrimreaper
failed mosfets are a bit of a different story however they still can be protected against very easily however this comes back to the powersupply and actually having overload and short circuit protection as advertised, this is something that seems absent in most of these industrial power supplies that come in from china

what i have done to take care of this scenario in all the printers I've built is i use those 19v 180watt power bricks instead, so i have a situation where the overload protection will kick in if either mosfet fails for the bed or hotend the powersupply will shutdown until it is unplugged and plugged back in again, the downside is that these power supplies don't cope very well with the style of pwm that is used by default in marlin but it's ok thats i've solved too by switching to hardware pwm for which there is a pull-request for which gives you the choice of hardware or software pwm

No power supply can protect against a failed hot end MOSFET, your statement is false. Please don't spread potentially dangerous misinformation like this.

it is not misinformation, it is a factual statement based on real life testing and daily use, please explain how this is potentially dangerous information.

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If the MOSFET fails on, it doesn't matter if the power supply is a $2k pro grade lab supply, the MOSFET failing on will power the heater at 100%. This will drive it to extreme overheating.

If the light switch in your house sticks on, then the light will stay on regardless of how "good" your power company is. Same story here.

I don't know how else to explain, I am 100% sure that you are wrong. Its worrisome that you don't understand this as a hardware vendor.

Edited 3 time(s). Last edit at 07/02/2014 11:39PM by greenman100.

using my setup as an example:

on my hotend i have a 40watt 12v heater cartridge and a 12v 120watt silicone bed , and i run a 19v 180watt power supply , obviously i have my max_pwm value set as to not instantly overload the powersupply but to a point where my bed and hotend can function as desired

scenario #1 : if the hotend mosfet fails, the hotend heater cartridge will want to suddenly draw around 100 watts on top on that there is the current draw from the stepper motors and the bed which still drive the powersupply into overload and shut it down.

scenario #2 : if the bed mosfet fails it will draw around 300watts well above what the powersupply can do so it'll overload and shutdown not to mention the load from the steppers and the hotend adds on top

---

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So your "safety" system is predicated on the bed heater being on, and at a temperature high enough to draw an average of 60w. Its also a recipe for disaster if you or anyone else flashes firmware with incorrect MAX_PWM values.

Hardly a good solution, and arguably less safe than using 12v power with 12v rated parts.

Edited 3 time(s). Last edit at 07/03/2014 12:12AM by greenman100.

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Gonetotx
I am somewhat surprised at how common this fire hazard issue has been.

Indeed, I've been surprised after opening discussions about your accident to hear reports about this happening before.




This includes someone mentioning a friend of him actually burning his flat down because of his prusa !


I would start delivering the kits with a smoke detector if I were a kit vendor... It's probably better not to wait for someone getting harmed !

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

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DeuxVis
I would start delivering the kits with a smoke detector if I were a kit vendor... It's probably better not to wait for someone getting harmed !

If I were a kit vendor (or electronics vendor) I would make sure I had liability insurance. You can bet that after a major fire the house insurance company would come after you if they thought you might be to blame in some way.

Andy

Yes, as soon as insurance companies are in the loop, things become very complicated...

But it all depends what you sell: if you only sell different parts, I don't think you can be blamed. If you sell a complete kit, it can be more tricky. If it is a ready-to-use machine, no doubt that your responsability is engaged!

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Frédéric

With the arrival of kits things are getting dangerous a lot of people are buying these and assembling them and not really understanding it's an experimental machine. It's not like a toaster or microwave that is UL or CE approved they are not really ready for the average person.

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greenman100
So your "safety" system is predicated on the bed heater being on, and at a temperature high enough to draw an average of 60w. Its also a recipe for disaster if you or anyone else flashes firmware with incorrect MAX_PWM values.

Hardly a good solution, and arguably less safe than using 12v power with 12v rated parts.

He sets the MAX PWM so it does not draw more current than the brick will supply. If you set it wrong, it will trip the power supply...

Edited 1 time(s). Last edit at 07/03/2014 09:02AM by tjb1.

Again, that only works if the bed heater is active. if it isn't, you happily pump 100w through a 40w heater.

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cnc dick
With the arrival of kits things are getting dangerous a lot of people are buying these and assembling them and not really understanding it's an experimental machine. It's not like a toaster or microwave that is UL or CE approved they are not really ready for the average person.

I think that many people do understand this, but then their printer runs reliably for 100 hours and they are lulled into a false sense of security - it's human nature. How many "above average people" have had the same printer for two years and still check all the connections before every startup? Not many I bet.

I agree! That's why this thread is really a good thing. It has already been read 742 times!

---

Frédéric

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thejollygrimreaper
using my setup as an example:

on my hotend i have a 40watt 12v heater cartridge and a 12v 120watt silicone bed , and i run a 19v 180watt power supply , obviously i have my max_pwm value set as to not instantly overload the powersupply but to a point where my bed and hotend can function as desired

scenario #1 : if the hotend mosfet fails, the hotend heater cartridge will want to suddenly draw around 100 watts on top on that there is the current draw from the stepper motors and the bed which still drive the powersupply into overload and shut it down.

scenario #2 : if the bed mosfet fails it will draw around 300watts well above what the powersupply can do so it'll overload and shutdown not to mention the load from the steppers and the hotend adds on top

This is false. When a MOSFET fails, it simply becomes a short. It does not force more wattage into the loading element (the heaters in this case). So if your 40W cartridge is on all the time, it draws 40 watts (or 3.33Amps) constantly, heating your hotend up to dangerous temperatures. Same goes for your bed heater. So at full on, your PSU which is rated for 190W will easily power your 120W bed and 40W cartridge for a few hours until it burns.

To add, on the Solidoodle forums a user had most of his house burn down. For the past 4 weeks we have all been discussing fire prevention. Some of the things people should realize is that:

1.) The number of fire incidents being reported is increasing, it is not simply a matter of luck.
2.) Not a single printer being sold (exception of the big evil companies) have their machines as UL listed. They have not proven through 3rd party testing the rated failure of fire safety.
3.) Fire prevention of pretty much all of these machines is not simply a matter of a loose thermistor. The hotend can burn up due to many reasons. I have had a stuck processor with the watchdog turned on. It is community based firmware, not ironclad safety proven software. And I have personally watched a RAMPS burn up from a bad connector. On top of that, I have seen a report on a PSU catching fire.

So while some people are scampering to find solutions to each possible ignition point (while individually ignoring the rest of them) there is no mitigation through the electronics if the fire has already started. And since a thermal fuses are not rated hgih enough to watch the hotend directly, and can only detect fire AFTER ignition in other dangerous parts of the printer, you can already assume the printer is burning away.

So to be smart:

Make sure your firmware watchdog is turned on. This is just too easy not to do.

Make sure your connectors are solid, and check their temperature while printing to make sure they are not a source of ignition.

If possible, enclose your printer using polycarbonate. Not plexiglass. Plexiglass is a fuel, Polycarbonite is fire retardant.

Make sure you place your printer in a room with a smoke detector and a fire extinguisher near the door.

Do not leave prints unattended/while you sleep. If you really want unattended printing with machines the have been built at home, customized, made with any plastic components then be prepared to use all-metal table and shroud enclosure with an Automatic Fire Extinguisher.

Or be prepared for this:
beware-your-3d-printer

---

"Never argue with stupid people, they will drag you down to their level and then beat you with experience."

Quote
Hazer

Quote
thejollygrimreaper
using my setup as an example:

on my hotend i have a 40watt 12v heater cartridge and a 12v 120watt silicone bed , and i run a 19v 180watt power supply , obviously i have my max_pwm value set as to not instantly overload the powersupply but to a point where my bed and hotend can function as desired

scenario #1 : if the hotend mosfet fails, the hotend heater cartridge will want to suddenly draw around 100 watts on top on that there is the current draw from the stepper motors and the bed which still drive the powersupply into overload and shut it down.

scenario #2 : if the bed mosfet fails it will draw around 300watts well above what the powersupply can do so it'll overload and shutdown not to mention the load from the steppers and the hotend adds on top

This is false. When a MOSFET fails, it simply becomes a short. It does not force more wattage into the loading element (the heaters in this case). So if your 40W cartridge is on all the time, it draws 40 watts (or 3.33Amps) constantly, heating your hotend up to dangerous temperatures. Same goes for your bed heater. So at full on, your PSU which is rated for 190W will easily power your 120W bed and 40W cartridge for a few hours until it burns.

no, the bed is rated at 120 watts on a 12v supply ,however on my printer it is given a 19v supply so if a mosfet fails there is no pwm current control anymore and the bed will draw 300watts which will overload the powersupply and shut it down

the hotend heater cartridge under the same conditions will recieve 19v and will want to draw 100watts not 40watts, about 1/2 an hour ago i did a quick and dirty test by setting the duty cycle on my hotend to 100% without the bed turn on and it still sent my powersupply into its overload protection and shut it down so i kind of wonder what the steppers motors draw in total

most of this stuff can be verified using a ohm law calculator

Edited 1 time(s). Last edit at 07/03/2014 08:40AM by thejollygrimreaper.

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thejollygrimreaper

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Hazer

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thejollygrimreaper
using my setup as an example:

on my hotend i have a 40watt 12v heater cartridge and a 12v 120watt silicone bed , and i run a 19v 180watt power supply , obviously i have my max_pwm value set as to not instantly overload the powersupply but to a point where my bed and hotend can function as desired

scenario #1 : if the hotend mosfet fails, the hotend heater cartridge will want to suddenly draw around 100 watts on top on that there is the current draw from the stepper motors and the bed which still drive the powersupply into overload and shut it down.

scenario #2 : if the bed mosfet fails it will draw around 300watts well above what the powersupply can do so it'll overload and shutdown not to mention the load from the steppers and the hotend adds on top

This is false. When a MOSFET fails, it simply becomes a short. It does not force more wattage into the loading element (the heaters in this case). So if your 40W cartridge is on all the time, it draws 40 watts (or 3.33Amps) constantly, heating your hotend up to dangerous temperatures. Same goes for your bed heater. So at full on, your PSU which is rated for 190W will easily power your 120W bed and 40W cartridge for a few hours until it burns.

no, the bed is rated at 120 watts on a 12v supply ,however on my printer it is given a 19v supply so if a mosfet fails there is no pwm current control anymore and the bed will draw 300watts which will overload the powersupply and shut it down

the hotend heater cartridge under the same conditions will recieve 19v and will want to draw 100watts not 40watts, about 1/2 an hour ago i did a quick and dirty test by setting the duty cycle on my hotend to 100% without the bed turn on and it still sent my powersupply into its overload protection and shut it down so i kind of wonder what the steppers motors draw in total

most of this stuff can be verified using a ohm law calculator

Yup. Your right. Good point to explain that (especially since I missed the 19V myself).

So for you it is a good cover for thermal runaway of the heaters. For the rest of us, it doesnt help much. I have dual extruders, so your PSU would not help. Also I still use 12V. It also does not cover electrical based fire hazards (shorting, connectors, etc). But good for you

---

"Never argue with stupid people, they will drag you down to their level and then beat you with experience."

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Hazer

Quote
thejollygrimreaper

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Hazer

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thejollygrimreaper
using my setup as an example:

on my hotend i have a 40watt 12v heater cartridge and a 12v 120watt silicone bed , and i run a 19v 180watt power supply , obviously i have my max_pwm value set as to not instantly overload the powersupply but to a point where my bed and hotend can function as desired

scenario #1 : if the hotend mosfet fails, the hotend heater cartridge will want to suddenly draw around 100 watts on top on that there is the current draw from the stepper motors and the bed which still drive the powersupply into overload and shut it down.

scenario #2 : if the bed mosfet fails it will draw around 300watts well above what the powersupply can do so it'll overload and shutdown not to mention the load from the steppers and the hotend adds on top

This is false. When a MOSFET fails, it simply becomes a short. It does not force more wattage into the loading element (the heaters in this case). So if your 40W cartridge is on all the time, it draws 40 watts (or 3.33Amps) constantly, heating your hotend up to dangerous temperatures. Same goes for your bed heater. So at full on, your PSU which is rated for 190W will easily power your 120W bed and 40W cartridge for a few hours until it burns.

no, the bed is rated at 120 watts on a 12v supply ,however on my printer it is given a 19v supply so if a mosfet fails there is no pwm current control anymore and the bed will draw 300watts which will overload the powersupply and shut it down

the hotend heater cartridge under the same conditions will recieve 19v and will want to draw 100watts not 40watts, about 1/2 an hour ago i did a quick and dirty test by setting the duty cycle on my hotend to 100% without the bed turn on and it still sent my powersupply into its overload protection and shut it down so i kind of wonder what the steppers motors draw in total

most of this stuff can be verified using a ohm law calculator

Yup. Your right. Good point to explain that (especially since I missed the 19V myself).

So for you it is a good cover for thermal runaway of the heaters. For the rest of us, it doesnt help much. I have dual extruders, so your PSU would not help. Also I still use 12V. It also does not cover electrical based fire hazards (shorting, connectors, etc). But good for you

what i worry about is that a lot of these 12v and 24v power supplies that are comming out of china that are commonly used are advertised as having overload and short-circuit protection however when you actually test it you get a spectacular failure usually involving flames and smoke , before i started using these powerbricks i found out the hardway they the powersupplies i was using and trusting we're actually subject to the very problem, and one of them was actually bought locally at jaycar,

i have a 12v powersupply in transit and i plan to do a youtube video demonstrating this lack of short circuit protection and show exactly what happens in the process, in past had i not made sure there would be a human in the same room as my printers at all times in the past i dare say i probably could have burned down 2 houses by now.

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Hazer,

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And since a thermal fuses are not rated hgih enough to watch the hotend directly, and can only detect fire AFTER ignition in other dangerous parts of the printer, you can already assume the printer is burning away.

Your assumption here is just not grounded in engineering logic. The order of events due to a failure in which you have a runaway hotend will be:

1. Hot end begins heating up
2. Body of J-Head heats up to melting temperature.
3. Smoke
4. Fire

You can turn the machine off at #2 by making use of a thermal fuse. It DOES NOT need to mounted directly on the heater block to be effective. If you open up and look at most any heat generating appliance, you will find a thermal fuse NEAR the heating element and NEVER on it.

The temperatures at the junction between the heater block and the body can be monitored via a themral fuse. The temperatures here are much lower than the heater block temperatures and are within the operating range of a thermal fuse.

I tested my J-Head heated to ABS printing temperatures (235ºC) and probed the temperature at the juntion of the PEEK body and the heater block. See the attached pictures. As you can see, the maximum temperature at that point is only 178ish ºC. If the heater were to run away, that juntion would quickly increase in temperature to beyond the PEEK melting point (around 245ºC). I purchased these thermal fuses [www.amazon.com]. That fuse has a holding temperature of 200ºC. It will fuse and open before fire can develop at the hotend. Once it opens, the mains will be cut off and no further heating will occur and thus no fire.

YMMV if you're using a different hot end but the concept is the same. you mount the thermal fuse NEAR the heating element not on it and it will work. Major applicance manufacturers do this for the same reasons we need to - the thermal fuses can't stand the heat of the heaters.

Edited 1 time(s). Last edit at 07/03/2014 09:38AM by umdpru.

Did you try to run such overheating condition, to check how it works?

Hotend manufacturers should include a support (simple hole) for these fuses, near the top of the hotend; using a 100°C fuse should do be OK.

---

Frédéric

Quote
umdpru
Your assumption here is just not grounded in engineering logic. The order of events due to a failure in which you have a runaway hotend will be:

1. Hot end begins heating up
2. Body of J-Head heats up to melting temperature.
3. Smoke
4. Fire

You can turn the machine off at #2 by making use of a thermal fuse. It DOES NOT need to mounted directly on the heater block to be effective. If you open up and look at most any heat generating appliance, you will find a thermal fuse NEAR the heating element and NEVER on it.

The temperatures at the junction between the heater block and the body can be monitored via a themral fuse. The temperatures here are much lower than the heater block temperatures and are within the operating range of a thermal fuse.

I tested my J-Head heated to ABS printing temperatures (235ºC) and probed the temperature at the juntion of the PEEK body and the heater block. See the attached pictures. As you can see, the maximum temperature at that point is only 178ish ºC. If the heater were to run away, that juntion would quickly increase in temperature to beyond the PEEK melting point (around 245ºC). I purchased these thermal fuses [www.amazon.com]. That fuse has a holding temperature of 200ºC. It will fuse and open before fire can develop at the hotend. Once it opens, the mains will be cut off and no further heating will occur and thus no fire.

YMMV if you're using a different hot end but the concept is the same. you mount the thermal fuse NEAR the heating element not on it and it will work. Major applicance manufacturers do this for the same reasons we need to - the thermal fuses can't stand the heat of the heaters.

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fma
Did you try to run such overheating condition, to check how it works?

Hotend manufacturers should include a support (simple hole) for these fuses, near the top of the hotend; using a 100°C fuse should do be OK.

Tripping that fuse would likely kill the hotend since the hotend is already sitting at 235c with 22c left before you hit the HOLDING temp of the fuse. I don't think it will work, by the time that fuse would hit 240c I would guess the heater block would have already fallen out of the PEEK especially if the extruder is still driving.

I would rather use something a little closer like this - [www.digikey.com]

Yes, it's above the holding temperature but until someone tests what happens when it is run above the thermal hold I guess we won't know what will happen.

Edited 2 time(s). Last edit at 07/03/2014 11:14AM by tjb1.

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thejollygrimreaper
i have a 12v powersupply in transit and i plan to do a youtube video demonstrating this lack of short circuit protection and show exactly what happens in the process,

I'm presently self studying the type of power supply requirements of a hybrid stepper motor, and I don't know what type of power supply is more safe than another.

It appears that a switching power supply is not recommended, because it doesn't satisfy the power requirements of the stepper motor, (I don't know if there is a safety issue with these types of PS when used with a hybrid stepper motor).

There are two types of recommended power supplies for hybrid stepper motor:
constant current.
constant voltage.

Is this what we should be looking for in a safe/appropriate power supply for a hybrid stepper motor?
Unregulated linear, constant current, toroidal, un-switched power supply, with a chopper control driver.


Some of my notes:
Unregulated power supplies are best suited for step motor applications. Their behavior is superior to other power supplies such as switching power supplies especially in situations where there is a sudden increase in current demand. [web.archive.org]

Chopper control is a way to limit the current in the winding of a stepping motor when using a high voltage supply (a voltage higher than a motors rated voltage). [web.archive.org]

Chopper control: A pulse-width modulated waveform is used to create an average voltage and an average current equal to the nominal voltage and current for the winding. [web.archive.org]

High performance stepping motors are intended to be driven at higher voltages with current limiting considerations. [web.archive.org]

The drive circuitry should never permit currents exceeding IMAX. [web.archive.org]

Typically a power supply capable of delivering ½ or more of the peak phase current should be sufficient. For example, if you are using a motor with a maximum phase current of 4A per phase and assuming the drive is set to this maximum value, a power supply capable of delivering 2A or more will be adequate in most applications. [web.archive.org]

When connecting several drives / motors to one power supply, the current draw for all drives need to be added together to yield the requirement for the power supply. [web.archive.org]

As a rule, constant current drivers have the most problems with resonances in the low frequency region. [web.archive.org]

For a constant current driver, it is normally possible to use an unregulated supply voltage. The motor current, and thereby also holding torque and power dissipation, is controlled by the driver itself. [web.archive.org]

Constant voltage drivers normally have problems with resonances at medium and/or high frequencies. At these frequencies, neither half - nor microstepping can reduce the resonances. This limits the usage of this type of drivers at medium and high frequencies to driving high-damping loads. [web.archive.org]

For all drivers of constant-voltage type, regulated power supplies are normally required. [web.archive.org]

The maximum torque,efficiency, and output power from a given motor is achieved with the bipolar chopper driver. [web.archive.org]

For the same power dissipation in the motor, the current may now be increased by 40%. Therefore, the 5A motor will accept 7A with the windings in parallel, giving a significant increase in available torque. Conversely, connecting the windings in series will double the total resistance and the current rating is reduced by a factor of 1.4, giving a safe current of 3.5A for our 5A-motor in series. [web.archive.org]

As a general rule, parallel is the preferred connection method as it produces a flatter torque curve and greater shaft power. Series is useful when high torque is required at low speeds, and it allows the motor to produce full torque from a lower-current drive. [web.archive.org]

Care should be taken to avoid overheating the motor in series since its current rating is lower in this mode. Series configurations also carry a greater likelihood of resonance due to the high torque produced in the low-speed region. [web.archive.org]

Edited 1 time(s). Last edit at 07/03/2014 01:01PM by A2.

I'm currently building my first printer, and this (as well as other, similar threads) has scared the C**P out of me!

I am a fire alarm technician, and in the excitement of building my printer, I forgot that these are experimental devices, not ULC (Canada) or CSA listed.

My plans for fire safety are as follows:

1) Thermal cutouts near the hot end, near the heat bed heater, and above the power supply will hold a continuous-duty relay on. When any of the thermal cutouts 'activate', the relay de-energizes, cutting the power. I suppose the relay is not really necessary, since these things are usually designed for 10-15A.

*EDIT*
I thought about this a bit more, and I will ABSOLUTELY have a relay involved in #1. That way, I am routing 12VDC around the moving/hot things and not 120VAC!

2) On the ceiling above the printer, a CF-135C heat detector connected to a SECOND continuous-duty relay that will cut power immediatly after the wall plug. Envision a metal enclosure with a cord and a standard receptacle on it. The cord plugs into the wall outlet and the printer is plugged into the receptacle on the box. The CF-135C is the opposite of heat detectors used in fire alarms in that it has normally closed contacts that open when the detector trips - this holds the relay on until the ceiling temperature hits 135F - at that point, the relay will deenergize, cutting power to the machine.

3) Speaking to my boss, we have a surplus 5lb halon extinguisher that has a 155 degree sprinkler head on it (similar to Fire Defender - just using Halon). He said I can have it for nothing. It will be hung above the printer as the 'final solution'.

4) A smoke detector in the workshop, tied into the existing smoke detector network of the house.

I can't believe I didn't think of this stuff already - considering the business I'm in!

Edited 2 time(s). Last edit at 07/03/2014 05:59PM by andy.wpg.

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"I have noticed that even those who assert that everything is predestined and that
we can change nothing about it still look both ways before they cross the street"

-Stephen Hawking

The point I have been trying to make is that you need more than just temperature-cutoff devices in order to eliminate the potential for fire. As mentioned, if you do not have the thermal cut-off directly on your heat block, then you run the risk of your hotend dropping out of its plastic fixture before the thermal cut-off does its job. And even then, there is no guarantee that the thermal cutoff will trip BEFORE the ignition occurs (and if your already on fire, who cares about disbaling the power to yuor hotend). You can only solve thermal runaway if your trip device is designed for the media you are heating in the first place.

In the case of thermal cut-offs in appliances, you forget that the high voltage heater element is attached through metal fixtures that wick away the heat by design and that is what the thermal cut-off is attached to. It is directly coupled to the secondary heated material. Now you could say by attaching a thermal cutoff to the top of your all-metal hotend would work, except 99% of those designs have a fan blowing on that portion of the hotend, and thermal runaway would still occur.

And all of this does not cover the electrical fire potential. I have seen some people place extra thermal cutoffs around the electronics, but they would not trip out until the fire has already ignited. So what does cutting power do when the flames are already there?

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"Never argue with stupid people, they will drag you down to their level and then beat you with experience."

"To get
the maximum performance from this
type of system, the gear rate should
normally be designed so that the load
inertia seen by the motor is close to
the motor internal inertia"
Sort of an eye opener for me. Something I could have come to if I thought about it, but no one can think of everything on their own. So many things I lack in knowing motors and drivers, the beef of movement, right behind it is the linear system. Guess I really need to reconsider buying another set of motors and looking for better steppers.

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus