Burning / Smoking Heated Bed Connector

System

This discussion was created from comments split from: Warning: Heated Bed Power Clamps.

JayJoe

Hi, today I when I was doing some printing, I started smelling some smell of plastic burning, then when I check the forum and I bump into this post and I suspect that the problem mentioned in this discussion causes some 'burning'. From the photo, you can see that there is a burning mark. When I touch it during my printing, it's hot. Is this the symptom that there's a short circuit caused by the clamp?

My bed temperature is 60 degree btw.

Samuel Pinches

@JayJoe - Hi, I've moved your post to a new thread.

It is not a short circuit, but you should be alarmed - please don't ignore this problem! What is going on here, is these connectors that are used are not rated for the high current passing through. Every electrical connection always has some kind of resistance, and wherever there is resistance, energy is converted to heat - that's how the heated bed works. In this case, the connector used has a high enough resistance that this heating is significant because of the very high current passing through it. I hope this explanation makes sense.

JGAurora has fixed this design in future A5 printers by replacing the 4-pin connecter (2 wires for thermistor, 2 wires for heater cables) with a 6 pin connector (2 wires for thermistor, 4 wires for heater cables). This reduces the current passing though each wire to be within the rated current capability of the connector.

My advice would be for you to either - ask JGAurora for a new bed heater and new bed-cable set, OR to unsolder the connector, and solder the 4 bed wires directly onto the bed heater pads. This problem will only get worse from here unfortunately.

JayJoe

Thanks Samuel.

I have just taken off the connectors. Please see the photos I attach. I have ask JGAurora for a replacement 

My printing stopped halfway, Is this means that my circuit board or heatbed is 'injured' and can no longer be used? So, is it still ok now for me to solder directly the 4 wires directly to the bed heater pads?

And how to remove the hot glue by the way? Hahah

JayJoe

Summarized:

1) Buy a new and better connector and replace them?
2) Directly solder the wires to the heatbed? 
3) Don't do anything and wait for replacement? (I don't prefer this if possible because I need to print things haha)

Here's the choices. Which one?  

Also, how to remove the hot glue? And, can I use heatshrink and wires to extend the original wires? Because I cut the wires and I think they are not long enough now

Samuel Pinches

You can buy high quality silicone insulated copper wire (AWG16 thickness) from most electronics stores, or from ebay. Joining wire should be fine, as long as the joint is not going to be inside the cable chain, or be subject to flexing forces.

Heat gun or hair dryer should help to soften the glue for easier removal.

I don't like the connector being soldered onto the board - the cable moves, and the soldering is only surface mount. I have seen several people who have ripped the connector off the board by accident, because it is only soldered to the copper plated surface of the board - it is not "through hole" soldered.

For this reason, I think the best option is to solder new cable directly to the board, and then use inline connectors with sufficient current - most RC hobby connectors are good, because they have to deal with huge currents of 80A+ at times. Most of those are gold plated, which is the ... gold standard in low-resistance high current connections. You will need a good soldering iron though, as they have a lot of thermal mass!

Have look on ebay near you for "deans" and "Xt60" connectors. You could probably even get away with PC molex or PCIe-power connectors.

The thermistor connection doesn't need to be high current or especially low-resistance, what ever you can find for those two pins should be fine.

JayJoe

I leave my solder for more than 5 minutes and the iron just won't melt. Then, I switch to removing the hot glue first. I don't have heat gun so I use hot glue gun's tip to melt the glue. Again, it wont melt. While I was removing the glue and the soldering lead, there's some twisting, and it end up the copper layer being ripped off the board... FML..

So I solder the cable directly to test whether it still work or not. unfortunately, it's no longer working. The temperature detected is -15 degree. What I should do now? Seriously why I have so many problem with this printer? 

JayJoe

Although the photo seen to be short circuit, it's not. I have checked with my multimeter. What I more concern about is the teared copper layer

Samuel Pinches

Ok, firstly don't panic too much, this looks repairable.

What kind of soldering iron are you using? Do you know what the wattage is? You will need 50W or more, I think.

If you don't have a good one, I have linked some high quality soldering irons on the wiki. If you just want something cheap, with lots of power, you can go to your hardware store and buy a gas powered soldering iron. Its more messy having to fill up gas, but that will definitely get hot enough for this purpose. Plus, they are wireless! 

With a small bit of sandpaper, or a metal object like some sharp tweezers, with some care, you can scratch off the black solder mask, to reveal more of the copper that you can solder too. I'm not 100% sure, but maybe acetone can help with this too. You may want to google for some advice on removing solder mask.

I would recommend you buy some soldering wick (braid) to remove the old solder fully. Also, you want some 60/40 or 63/37 leaded solder with flux, to help create a good mechanically solid new joint.

The reading of -15 indicates there is a break in the connection to the thermistor. Use your multimeter to check resistance across the thermistor lines. You should measure 100k at 25ºC. Scratch off more soldermask until you can find some good points for connection.

You should measure around 2ohm (corrected!) across the bed heater element.

JayJoe

Nice and clear. Thanks extremely much for your effort in helping me! And the resistance values will be very helpful. Thanks so much. I will try tomorrow and get back here soon.

JayJoe

I have just bought this 150W solder iron. Is it suitable? Just want to make sure, it won't damage my 3D printer bed circuit right while I melt the soldering lead? 

Samuel Pinches

Well, I don’t really know, 150W is massive! Is it temperature controlled in any way?  What you don’t want to do is put too much overheat for too long on the soldering joints because in the worst case, that can cause the pads themselves to lift up and tear.

I think it is worth a shot with that iron, should make things a lot easier than the old one!

JayJoe

I finally remove the soldering lead. And, I have checked the resistances. Please see the photo attached. 

JayJoe

If I am not wrong, there shouldn't be 9M ohm, should be same 100k ohm, right? I currently do not have soldering wick because I can't find any from the hardware shop I went just now. Hmm, what's my next step? 

JayJoe

Ok. This is the updated result. After some time of soldering, and I finally connect all the joints. So, here's the updated resistances.

The thermistor is ok (room temperature is around 24 degree celcius), but for the heating element, I am getting 2.3 ohm. Is this acceptable?

JayJoe

After some time, I found out that the resistance of heating element is varying and fluctuating. Now, the resistance is 100 ohm. I think the soldered layer is damaged. Sigh. 

Samuel Pinches

Less than 3 ohm is ok, more is too high. It may be 2.3 ohm at 25C but the heater element resistance will drop slightly as it heats up. 100 ohm is too high

Samuel Pinches

Bed should be ~250W

P = V * I

250 = 24 * I

hence, I = ~10

V = I * R

24 = 10 * R

R = ~2.4ohms
So anything between 2-3 ohms is expected. Sorry, my earlier bed heater element resistance was wrong...

JayJoe

ok. noted. tomorrow onward I will start removing some of the solder mask to reveal more copper, and create a better soldering joints. will take your advice and do some google-ing before the removal. feel free to let me know if you found any useful sources on how to remove the mask. thanks so mucb to you Samuel

JayJoe

I realize that the resistance between the red circles give a stable 2.3 ohm. And I solder on the places circled with red. When I look through the path circuit, I think I found the route / path of the circuit. The red arrows show the path of the circuit (I think, based on my observation)

Now,

Then I switch on the printer, and the temperature is correct. And I tried to preheat it to 30 degree C (only, because I am scared) and yea it works The solder connection is quite good, because it gives me a static 2.3 ohm. BUT and WHAT IF, the solder connection suddenly drop off after hours of printing? Worst case scenario, what if the connection short circuit? Is there any overcurrent circuit protection? I don't want to risk my circuit board and I can't afford any more problem and mistake. So, not sure whether I am good to go now

Samuel Pinches

Yay! Nice job! Well, the firmware has some safeguards built in:
- if it thinks it is putting power in, and no heating is occurring, it shuts off.
- if it is not putting power in and heating is occuring, it shuts off
- if the bed temperature reads too low (e.g. broken thermistor connection) it shuts off

So its got a few precautions already taken. You've done a good job with the cable ties, that will help remove any strain or movement from occuring at your joins. 

Few more points:
- I don't recommend tinning the ends of leads if you are putting them in screw terminals. Raw copper is better in those.
- The screw terminals you have used, I suggest checking to see that it is rated for 12-15A. Most 240V screw terminals are only rated for 10A, which is marginally sufficient for the high bed currents.

JayJoe

Yay! Thanks for the details about precautions. So it's safe and I can finally resume my printing tomorrow!! All credits to you Samuel! Thanks so much for sharing all the information and being extremely helpful. Such a wonderful person you are. JGAURORA community is so blessed to have you

Okay, I will remove some of the tin tomorrow. And for the screw terminals for heating wires, it is rated for 20A max, whereas for thermistor wires, I use 10A max since it's smallest size I have and I think only low current flowing through the sensor.

Once again, thanks so much for your kindness!

Samuel Pinches

@JayJoe  - thanks very much for the kind words. I wish you all the best making the most of your printer. As frustrating as it is to be fighting against the poor design choices of the manufacturer, I hope you feel a sense of pride and ownership having conquered these hurdles!
Kind regards, and happy printing.
Samuel

Werewolf

JayJoe,
Have you negotiate with JG support about sending a new free heating bed?

JayJoe

Werewolf, yes, they are sending me new heating bed and cable

JayJoe

Dear @Samuel Pinches ,

I have a question regarding extruder heater. Feel free to move this comment to a new thread if you find it proper to do so



May I know is it ok to leave the heating element like this? Without pushing it all the way in. The reason is because I need to heat it up first then with a large amount of force, then only the heating element manages to go in (I did unscrew the the screw before I do this). And when I need to pull out the heating element, again, heating and push/pull real hard. I am afraid that one day, I will accidentally damage it. So I just leave it there, not too tight nor too loose. Will this way spoil the heating element?

Samuel Pinches

Hmmm.. I would recommend:
- cool down the hot end

- undo the screw

- use a flat head screw driver to open the hole a little, like a lever
- press in the heater a bit more by hand

Otherwise, the exposed part of the heater will cause the heating efficiency to be reduced, which will result in slower heating, and reduced temperature stability. This may cause problems when  a powerful fan is on.

hombre666

Hey JayJoe..Im sooo glad I found this thread, couse I have the same problem...and thanks to Samuel, you guys have solved it for me )
BTW..both LED and resistor on the bed got fried...that happened to you too?

Could you just tell me what was neccessary with the JG support for bed replacement. Have you contacted them by email, or had to present pictures of the failed bed/connectors?

Thanks in advance...great support forum!

Samuel Pinches

@hombre666
You can contact JG via email or skype - details are on the wiki: jgaurorawiki.com/contact
They will ask for photos and serial number of your device.
Best of luck, and thanks