Molten piece

Hi,

Yesterday I felt that something was burning and also my heated bed had difficulty in maintaining its temperature at 105 degrees. Later, I've checked my printer and saw that the plastic piece joining the cable from the heated bed to the cable from the RAMPS was partially molten. What can the reason be? I don't print with ABS a lot, so I seldom needed temperatures over 60 degrees but yesterday I needed it to be at 105 degrees for 5 hours. What should I do prevent this from happening again?

Thanks
(Note: Tha attached picture demonstrates the molten piece, which I had to remove by wirecutters as I couldn't use a screwdriver due to molten plastic)

Why do you have a joiner in there in the first place? The heated bed should have one continuous cable from from the bed terminals to the Ramps connector post.

---

_______________________________________
Waitaki 3D Printer

you bed uses 11 amps. that looks like a 5amp screw terminal

either that or it wasnt screwed down very hard at it was heating up due to the bad connection.

Quote
waitaki
Why do you have a joiner in there in the first place? The heated bed should have one continuous cable from from the bed terminals to the Ramps connector post.

You are absolutely right, it is logical to have one single cable however when I've bought the bed, the cables were already soldered to it and they weren't long enough to reach the RAMPS so I had to use a joiner and more cable to make the connection. Would it be safer to cut the connections at the bed-side and use a single cable for this purpose? I am not very experienced with soldering but I assume it isn't a very complicated solder job. Could that be one of the reasons why the bed struggles to reach temperatures higher than 100 degrees (I literally need 20 minutes to reach 105 degrees)?

Quote
Dust
you bed uses 11 amps. that looks like a 5amp screw terminal

either that or it wasnt screwed down very hard at it was heating up due to the bad connection.

I didn't know there were different types of terminals (I mean I do know there are various types but didn't know they were also rated according to the amperage). What is the difference? Do they use a more heat resistant plastic type or do they have larger metallic components.? I've heard that there were ceramic components also. Should I use one instead?

It comes down to this: all conductors are also resistors, and resistors are heaters.

That terminal was higher resistance than the wire, so it got hot while conducting power. Look at your heat bed, there are no components on it (Other than the diodes and LEDs) it's just trace wires, which we'd normally consider to have no resistance, but because they're thin, and log, they do, so when we run a lot of power through them, they get hot. Quite often, the wires that come with kits (The ones in my kit certainly were) are quite thin, just barely enough to manage the power that we're running through them, so the wires will often get very warm or hot as is. Extending these to be longer isn't a really good idea, I'd recommend de-soldering the existing wires, and solder on wires of a heavier gauge and appropriate length for your application, Your heat bed will get hot faster, and you'll reduce your risk of a fire.

---

MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

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

Quote
SupraGuy
It comes down to this: all conductors are also resistors, and resistors are heaters.

That terminal was higher resistance than the wire, so it got hot while conducting power. Look at your heat bed, there are no components on it (Other than the diodes and LEDs) it's just trace wires, which we'd normally consider to have no resistance, but because they're thin, and log, they do, so when we run a lot of power through them, they get hot. Quite often, the wires that come with kits (The ones in my kit certainly were) are quite thin, just barely enough to manage the power that we're running through them, so the wires will often get very warm or hot as is. Extending these to be longer isn't a really good idea, I'd recommend de-soldering the existing wires, and solder on wires of a heavier gauge and appropriate length for your application, Your heat bed will get hot faster, and you'll reduce your risk of a fire.

Thanks for the info. What should the ideal wire gauge be? And is there an inconvenience at using a thicker wire?

I also have been told that, the hotter the wire gets, the higher the effective resistence of the wire and as the voltage is constant, the current diminishes (like form 11 Amps to 6 Amps). Is that the reason it is harder to go form 90 degrees to 100 degrees, compared to 0 to 90 degrees?

Edited 1 time(s). Last edit at 03/17/2015 02:56AM by drmaestro.

As it happens, there are several guides for what wire gauge is appropriate for what load over what distance, as this is of much interest for automotive wiring. Having too much wire in a car is a bother, but electrical fires are a bad thing.

I found a quick guide for motorcycle wiring (Which has more appropriate lengths than most of the car guides that I found) here : [www.dualsportplus.com]

I used 16AWG wire, because I have a ton of it on hand, and this is fine for lengths up to 8' to carry 11A of current. (The chart says 18AWG is good for this much, and is probably right, the chart I have for my car starts at 15')
EDIT: looking again, this chart gets a little optimistic at the higher loads, I'd never run more than 15A through 18AWG wire no matter how short the wire.

The inconvenience of thicker wire is that it`s more expensive, and may be difficult to fit into the connectors of the RAMPS board, it will also be more weight for the Y axis motor to push back and forth, etc. I'm pretty sure that I used 18AWG for my hot end, as it's less current, and the wire didn't seem to heat up at all.

Edited 1 time(s). Last edit at 03/17/2015 11:31AM by SupraGuy.

---

MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

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

If the wire is not long enough then replace the whole length, this is what I have done. I also took the opportunity to replace the cable with some silicone wire, this is the sort of cable used in radio control electrics for the high power batteries, it is super flexible, as it has thinner strands and more of them, heat resistant and designed for high current. In fact I have replaced it for the hot end as well, it's great stuff. I have also used it to replace the cable from the power unit to the printer.

Dave

I have changed the cable.

I still have a problem: If I set the hotend at 240 degrees and the heated bed at 102 degrees and I start printing, after approximately 7-8 minutes the heatedbed starts to cool down by a few degrees. The LED on the heated bed is still on, so it is trying to keep the bed at the set temperature but is unable to do so. Why do I have this problem? Is this a power supply problem or heating of the RAMPS? This is an important problem because the print fails due to warping if the heated bed temperature falls below 92 degrees.

Edited 1 time(s). Last edit at 03/21/2015 02:18PM by drmaestro.