Hey everyone. I've had a Prusa i3 like printer for around 3 years and today I'm having some issues with the heated bed. A few seconds after it starts heating, one of the solder points of the heated bed resistance de-solders, as you can see in the video linked below:

[www.youtube.com]

It's quite scary to be honest, thinking it's getting so hot to the point of reflowing the solder. I've tried resoldering a couple of times but the problem persists. As you can see in the video, the region around the solder point is already a bit black, so there must be something wrong and I'm not sure what.

When unplugged, the heated bed resistance measures around 1.8 ohm. The voltage between the two wires, when heating, is 12.2V. From what I've read, these values seems to be ok.

Any ideas on what is causing this issue? The rest of the printer is working fine (extruder is heating normally, axis all work normally, etc).

Thank you very much!

There are many different types of solder with many temperatures ratings.


Kester Temperature Alloy Chart

Could be that the Solder you have used has too low a temperature rating. See Chart Above

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Computer Programmer / Electronics Technician

... bad connection and/or too much current ...

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There are many different types of solder with many temperatures ratings.


Kester Temperature Alloy Chart

Could be that the Solder you have used has too low a temperature rating. See Chart Above
Looked at my everyday solder melting point is 183C for my hot bed I would use A High Temp Solder See Chart Above.

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Computer Programmer / Electronics Technician

I used good old 60/40 tin-lead and it's still going strong years later. (One of these days I'll go to RoHS compliant soldering, but for hobbyist use, lead bearing solder is still far more reliable and consistent.)

Generally though I would say that if the solder is melting when you heat your bed, there's a problem. Even lower temperature solders shouldn't be letting go at any temperature that you want your heated bed at. I've never seen one that needs (or really wants) temperatures over 125 deg C, and solder shouldn't melt at that.

I'm not a fan of the wire that these things typically use. The same wire that manages the ~40W heater for the hot end is not adequate for the ~150W heated bed. I use 16AWG copper wire for mine (Or 14AWG if the wire run is going to be longer than 30cm.)

I'd want to check for a strained connection at the solder joint for any arcing or cracking. Use silicone for strain relief on the wire, to keep it from breaking where the solder flow ends. if you're repairing it after it re-flows, strip back the wire a little and make sure that isn't where it's heating inside the insulation.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Quote
SupraGuy
I'm not a fan of the wire that these things typically use. The same wire that manages the ~40W heater for the hot end is not adequate for the ~150W heated bed. I use 16AWG copper wire for mine (Or 14AWG if the wire run is going to be longer than 30cm.)

Mine is wired using the silicone-covered wire used by radio control enthusiasts to wire up their motors and batteries. Very flexible, heat-resistant, will handle high currents and not too expensive.

Re-watched the video a few times. It's a little unclear what grade wire you're using. The solder seems to have not too bad a connection tot he heated bed, and it doesn't seem to be a break inside the insulation.

Still, that behavior that soon has got to be a bad connection. If there's some sort of heat spreader, it will take a high wattage soldering iron to get that solder to re-flow well. That kind of disconnection is almost certainly a cold solder joint. It doesn't appear at all that the solder is actually melting through, since the blob on the end of the wire remains in the same shape as before, it's not softening at all.

I don't think that different solder is needed. Clean the contact patch on the heated bed with good flux, and use a high-wattage soldering iron to make a nice puddle of the solder until it flows smoothly on the heated bed contact.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Thank you for the replies. I'll try some of the suggestions and I'll let you know.

Quote
SupraGuy
It doesn't appear at all that the solder is actually melting through, since the blob on the end of the wire remains in the same shape as before, it's not softening at all.

You can't clearly notice that on the video, but when watching closely you can see the solder starting to melt right before it breaks.

Thanks again!

Edited 1 time(s). Last edit at 08/27/2018 03:34PM by Fergo.

Bad joints have resistance, and will heat up a huge amount when a lot of current is drawn - probably enough to melt solder.

As said above - buy or borrow a big, high-powered soldering iron and make a good-quality joint. I put aside my normal electronics iron and got out my old 40 watt Weller with a great big bit on the end, and made good connections in just a few seconds.

Aside from a higher powered soldering iron, preheat the pcb to about 100 degrees. Use a heat gun or an official pre heater table. This will make soldering larger areas a breeze. Also use lots of good quality soldering flux intended for pcb use. This will reduce the amount of oxygen mixed with the solder joint, it will improve conductivity and mechanically. Don't heat the pcb too quickly or create a small hot spot, make a larger heated area around the solder joint. The pcb may warp when it's not evenly heated or heated too quickly. Don't use a higher temperature on the soldering iron, it'll burn the pcb and makes it worse.

If all else fails, just replace the pcb, don't risk a fire hazard.

Edited 1 time(s). Last edit at 08/28/2018 08:16AM by imqqmi.

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Kind regards
Imqqmi

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