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Anet A8 allmost burned down my house

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While printing in ABS, the hotbed caught on fire, burning the printer and the entire room with it. I world seriously advise all of you to rethink owning this printer. The only thing stopping the fire from speeding was the fact that the room was closed, the lack of oxygen kept the fire from growing. Personally I have learned my lesson, 150 usd printer cost me 2000 usd worth of damage. I won't be buying any Chinese electronic such as this any time soon.

can you send more photos ? before and after if possible

Yeah,sure. Here a before and after.
By the way for All of You talking about stock firmware.. I was running merlin.

what version marlin? I tested pulling out heating element and thermistor with skynet (marlin fork) and it detected it and shut off

in that picture your thermistor and heating element are taken out of the heat block and are hanging on the side, so it is safe to assume it was a thermal runaway. also, what's that black tape looking stuff wrapped around thermistor and heating element, did you wrap the plastic coil close to hot end? it doesn't look like burnt polyimide tape but more like burnt plastic or electrical tape

I would highly recommend e3d split style heat blocks to everyone to prevent heating element coming out, skynet to prevent thermal runaway (later marlin may work but I tested skynet to work myself), and soldering heat bed wires
http://a.co/70eu85c

it goes something like this with stock firmware and a heating element and thermistor that pop out
https://www.youtube.com/watch?v=qVjWg2vuWzk

So sorry to hear what happened!
Thanks so much for the shout out, i'm gonna be keeping an eye on it whenever it's printing from now on.

That is a major bummer. I would suggest something like this: http://stovetopfirestop.com/store?gclid=CjwKCAiAx57RBRBkEiwA8yZdUB2RDNDb9NYPEeqjkpvMB_1Ikt3hrl8bWvkghieq_NJpw58YZMGLbRoCr6wQAvD_BwE#!/StoveTop-FireStop-Rangehood/p/55450142/category=14807032

For those who print unattended or with stock machines. And it is probably a good idea even for people wwith the safety mods...

So sorry that happened to you. I must have spent about $300 on this printer making it safer before I could trust it with an unattended print job. The heating element and thermistor pop out easily after a couple of long prints causing thermal runaway with stock firmware. Heat bed connectors get arcs and scorched, which is also a fire hazard. Wiring is too thin and power connector is too weak, which can cause voltage drops and high amperage, which can also cause a fire. Not to mention horrible bearings, hardware, instructions, and stripped threads on many of the pre-assembled parts. It's probably less than 30% original Anet parts now and I still have a bunch of smoke detectors in the room and don't really trust it 100%

Sorry to hear about this.
I am very glad you are ok these can be very devastating and scary. I hope we all can learn from these issues.
Could we get some details when you have time?
Did you have any modifications to the printer or was it "stock" as it comes in the box?
What were you printing material wise? Temp of bed and hot end?
How long had it been running when this was discovered?

Thank You and I hope you recover from this!

I am very sorry for your loss, both in the 3D printer and your personal belongings.
Thank you for the photos and shout-out about this important safety issue.
We suffered a complete loss of our home and belongings due to faulty electrical issues in our basement almost 3 years ago.
Everyone got out safely due to our smoke alarms.
Though it was not due to a 3D printer fire, I am fully aware of the consequences of your loss.
Good Luck with your recovery. And I hope that this does not suppress your desire to pursue 3d printing.
Sincerely,
Steve G

It looks like, that the problem was not the heated bed, but the mainboard (maybe the heated bed connector on the board). Thats why I removed the connector and soldered the heated bed cable directly to the board with a XT-60 connector in between. I also have a smoke detector above the printer + one fire-extinguisher near the printer and another one outside of the room.

In this case I think a MOSFET is a much better solution, since it also conducts the current through parts which are build for high currents. I would not trust the small MOSFETS on the board to take 10 amps, even when the connectors are sufficient.

I don't like the solution to drive a mosfet with a mosfet. If something fails, the security features of Marlin may not affect the external mosfet and the heated bed gets full current without temperature control. Instead, I changed the on board mosfet to a IRLB3034PBF mosfet, as mention in the instructable "Upgrading Your RAMPS With High Power Components". After this mod, the mosfet is now 3-5 kelvin above room temperature, instead of 60-90°C.

the security features of Marlin may not affect the external mosfet and the heated bed gets full current without temperature control

Worst case the MOSFET fries and gets stuck open and the bed constantly draws current, I don't really think Marlin can do anything about that. You would get it an error, but the bed will continue to draw current as the MOSFET wouldn't be able to switch off.

Replacing the terminals help, although I don't trust the traces either, but everyone isn't going to be comfortable making such a modification. An external MOSFET is probably the next best thing.

You can also have some form of automation with an external MOSFET. For example, in my case I have an external MOSFET and I am using relays to control 12V power to the board and the MOSFET which is controlled by Octoprint.

This way if the MOSFET dies and is stuck open things will get too hot, then Marlin will trigger an error then Octoprint will disconnect turning the power off relays.

I also changed the hotend from a 40W cartridge to a 30W cartridge. Max temp will potentially be lower, but theoretically the 40W cartridge can get hot enough to soften, or maybe even melt, the aluminum.

This sounds like a good solution too.

That's the reason why you should install the safety upgrades mentioned in several blogs and never operate a 3D printer for 150 usd in a room without a smoke detector or while noone is at home!

Also, I'd recommend never leaving a print unattended.
The heatbed connector issue is very well documented, soldering the cable directly to the heatbed is very much recommended for this exact reason. (pesky plastic connectors)
There are always risks for DIY kits, appreciate the cautionary tale for sure, but steps can be taken to avoid these risks for the most part