thermal runaway protection

Topics around mechanical design, controller and electronics. Mods & hacks welcome.
darbyvet
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Joined: Thu Jul 13, 2017 12:22 am

thermal runaway protection

Postby darbyvet » Thu Sep 14, 2017 10:00 pm

So I have been browsing the forum and looking at the bondtech upgrade.I saw that there was an issue with the ribbon cable coming loose leading to thermal runaway. I got a bit confused reading further about a firmware update for this.So what is the current situation.Is there a firmware update or is this still an issue? I had to do some work on my extruder board and I currently dont have a zip tie around the ribbon cable.Do I need to replace the zip tie or has the firmware been updated to prevent thermal runaway?

Carl

Jetguy
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Re: thermal runaway protection

Postby Jetguy » Fri Sep 15, 2017 12:06 am

This is a hardware issue that firmware cannot fix.

You can...
#1 add the 2 each 1 meg resistors to the mainboard and solder them- thus ensuring the mainboard itself detects the error instantly regardless of firmware. This is the safest option but also requires soldering.
#2 you can make a plug in adapter to go in between the ribbon cable and mainboard- but this is not as safe because again, adding more connections and if that comes unplugged at the mainboard failure is not detected.
#3 You can wait for Raise 3D to come up with a fix.........

#4 Adding a zip tie, does not guarantee the cable cannot fail and in some cases, could accelerate a flexing failure. Not saying it's bad idea or you shouldn't do it, but understand exactly what you are doing, ensure you test and move the axis around to see any potential flexing binds or failures, and evaluate the overall condition and lifetime of your current cable. Again, while this is prevention of the failure, it does nothing to solve the actual lack of detection of a fault.

darbyvet
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Re: thermal runaway protection

Postby darbyvet » Fri Sep 15, 2017 12:20 am

Thanks jetguy for the detailed reply


Carl

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walshlg
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Re: thermal runaway protection

Postby walshlg » Sat Sep 16, 2017 7:19 pm

where do you add the 1 M resistors??
getting a new mainboard, would be a good time to add this

firesped
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Re: thermal runaway protection

Postby firesped » Sat Sep 16, 2017 9:11 pm

This is also not limited to the bondtech. it applies to all printers. I still have to see what damage it did to that hotend. I need to replace it.
RL name: Michael Nolen
printers:
raise3D N2 kickstarter Early Bird
Trinus Deluxe (running smoothieware on Azteeg X5 GT board)
Monoprice Maker Select v2

Jetguy
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Location: In a van, down by the river

Re: thermal runaway protection

Postby Jetguy » Sun Sep 17, 2017 12:06 am

viewtopic.php?f=4&t=2594&p=17406&hilit=1+meg#p17383

See this diagram from the front side of the board but remember, this is the diagram- you cannot solder on this side because the ribbon cable must plug in.
Motion board connectors safety mod schematic.jpg


So the resistors go on the backside of the board and heatshrink to prevent any possible shorts.
DSC04778.JPG


There is actually enough space if you had a surface mount version, soldering it between the 5V pin and the T0 pin for a single head extruder is simpler but for extra safety, they really both need it.

Jetguy
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Re: thermal runaway protection

Postby Jetguy » Sun Sep 17, 2017 12:20 am

Again, just understand what this mod does. The analog pins for T0 and T1 (left and right analog thermocouple pins from the output of the AD597 on the extruder breakout board) has no pull up or pull down. The pin likes to stay at whatever the last voltage read was in the event the ribbon cable comes unplugged. Also note the basic scheme of how temps are read. The AD597 outputs 10millivolts per degree C measured. So it starts at 0 representing 0C and so room temp say 23C is 230mV or 0.23V on the analog pin. 230C would be 2.3V.
The 1meg resistor is such a high value resistor, the output of the AD597 is not raised by this external input.
However, in the case of cable failure- the 1 meg from 5V to the analog pin ensures it rises to 5V. Back to the signal scheme 5V represents 500C well above any logical extruder temp and instantly invokes the safety code. Also, by raising high rather than low, again, the basic rule if safety failed is that if the reported temp is higher than the setpoint, then the heater is instantly off even beyond any safety code.

Bottom line, this is a true "fail safe".
It's on the motherboard and thus cannot come unplugged or generally flex or break. It requires no code for it to work and even would work without any safety code at all.


But just some other facts to recap in case someone asks.
No you cannot just turn on an internal pullup or pulldown in the mega 2560 because they are not the correct value and will skew readings and could maybe even damage the AD597.
This has to be a hardware fix.

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walshlg
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Re: thermal runaway protection

Postby walshlg » Mon Sep 18, 2017 12:14 pm

those 2 pictures show different wiring, is that just another source of 5V ??

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Peter
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Re: thermal runaway protection

Postby Peter » Mon Sep 18, 2017 1:40 pm

no, it's the same 5V. the two pins are conected on the PCB (printed circuit board)

Jetguy
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Re: thermal runaway protection

Postby Jetguy » Mon Sep 18, 2017 2:44 pm

Correct, I have shown a reverse engineered pinout labeling of the mainboard. These have been tested and verified several times.
As stated, both leftmost pins are 5V and you need to run individual resistors to the 2 analog thermocouple pins (TC0 and TC1) because they need to be independently pulled up equally. You can use one 5V source pin and "y" split the 2 resistors from it or just go from each 5V pin through the resistor to the individual TC pins. Electrically it works the same either way. What you don't want to do is short both TC pins together or direct short a TC pin to 5V.
mainboard ribbon cable connector detail.jpg

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walshlg
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Re: thermal runaway protection

Postby walshlg » Mon Sep 18, 2017 7:02 pm

Thanks, I get that in place when board arrives

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walshlg
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Re: thermal runaway protection

Postby walshlg » Mon Oct 02, 2017 12:29 am

Hate soldering on pc boards, seems they also use a higher melting pt solder. Spent an hour practicing and my heat shrink is terrible. Suggest- do not try this without a solder sucker. Here is my layout:

20171001_183941.jpg
Attachments
20171001_184002.jpg
20171001_184002.jpg

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walshlg
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Re: thermal runaway protection

Postby walshlg » Mon Oct 02, 2017 4:33 pm

btw going to epoxy over exposed wires, too close to pins!

Jetguy
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Joined: Tue Mar 22, 2016 1:40 am
Location: In a van, down by the river

Re: thermal runaway protection

Postby Jetguy » Mon Nov 06, 2017 9:20 pm

FWIW to the group, this mod just saved my printer. I was printing a 93 hour print and on the 3rd layer of the base while I've been sitting here answering other peoples faults, I look over to the printer and it stopped printing. Why? Because the ribbon cable came loose mid print and because I had done the mod, the board instantly went into shutdown. Now I can recover this print and continue. The extruders fans were not spinning and the first check was to look at the ribbon cable at the extruder head breakout and since I had failed to lock the connector with hot glue, the safety mod is the only thing that caught this the instant it happened.

firesped
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Location: Tucson, AZ

Re: thermal runaway protection

Postby firesped » Sat Nov 11, 2017 8:35 pm

I finally started work on getting my printer back online. the nozzles were not touched the bed after I moved the printer, as in moved via a vehicle. since I think the primary hotend is compermized, I took it all apart and I am swapping in the second hotend for the main.

the material I use for insulation was chard black on the bottom of the hotend. I have to take a pictures. This is kapton tape then ceramic fiber. I had to heat the hotend to get that part loose. as I was removing the heater rod and thermocouple anyways. I did it at the same time. There is also some kind of black material where the thermal tube connects to the heater block.

I'll have to take some pictures later.
RL name: Michael Nolen
printers:
raise3D N2 kickstarter Early Bird
Trinus Deluxe (running smoothieware on Azteeg X5 GT board)
Monoprice Maker Select v2


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