Solved Extruder heat loss

OK, so I tried your suggestions. Found the place to plug in the fan (thanks for the polarity tip). The polyfuses (orange plasticky components on the driver board) are not hot or cracked or visibly damaged. I checked them when the extruder temp started going down around 160-170° C

As I tinkered, I noticed that the readings started jumping all over the place during heating.
I have an older hot-end with the Kapton taped themistor. Possible that it's a bad thermistor? It's still taped snugly to the hot-end.

 

Possible but unlikely if the temp starts to drop. if you can run a continuity check across the polyfuse you'll be able to detect when it opens the circuit.

A loose thermistor may do it. Not really such a thing as a bad thermistor. It either works or it doesn't.

 

OK. I'll give that a try. I know it's not the cheapest option, but should I get a new RAMPS board? I'm not really confident in my soldering skills on small components.

 

Replacing the polyfuse is easy IMO but buying a ramps should be fine. Though it probably comes with a MFR1100 which may be a little too small to drive the bed at high temps

 

I'll look at both options. Do you have the polyfuse part number handy?
Thanks for your help today.

 

The small one is MFR500: http://www.mouser.com/ProductDetail...GAEpiMZZMsxR%2bBXi4wRUNn/Ah8aJZRgTeQ0UjkRSX4=

The larger one that you should use is a MFR1400 or MFR1500: http://www.mouser.com/Search/ProductDetail.aspx?R=RGEF1400virtualkey65000000virtualkey650-RGEF1400 Sometimes referred to as RGEF1400

 

Mark which spare would you buy???

 

I have had replace both polyfuses. My printer stop about 1h.
what happens if I don't use polyfuse?
Are there other polyfuses stronger?

 

Theses ones with 5A and 11 to 14A ?
Are they more resistives than originals with same Amper values ?
Did you have any link to find them ?

 

Hello Mike (i Come back from french forum for questions about poly fuse)
When you said MFR500 et MFR1500, Is seems to be 5A and 15A ?
I have read to another part from this forum, that certains guy use autofuse. I have found an 5A and a 15 A to replace polyfuse. Do you thing it is risk to replace theses parts with autofuse with theses intensity ?

 

OK, so I replaced the small polyfuse (MFR 500) and started up MatterControl to run a test print. Once both the bed and the hot-end heat up, the head begins to move and within a few seconds it all stops (but the software keeps going) - same problem I had before. I did notice this time that the large polyfuse is hot, and it appears to be an 1100 (11 amp). I got the 14 amp replacements, so I will replace and report back.

 

Replaced large polyfuse. Tinned and reconnected power leads. Rigged up a desk fan to blow underneath to cool the RAMPS board.
Problem persists. I did just notice a ticking / arcing sound coming from the power supply when the hot-end temp got around 190. Red light on RAMPS starts blinking at that point too.

Print starts and then stops after about 5 seconds. Here is a screenshot from Repetier Host showing the sudden drop:



I'm stuck.

What should I look at next?

 

Correct. The digits after MFR describes the amp rating as you said.

Replacing the MFR500 is largely unnecessary because that circuit doesn't pull a lot of current.

Upgrading to an automotive fuse is a common idea. Though I hear they have increased resistance across them meaning you'll have less available power for the heated bed. It should still be able to maintain 100C but it might take longer and have a harder time staying there with a breeze etc.

If you do an automotive fuse I would suggest a 20-30A fuse and not a 15. The fuse will get hot and as it gets hot the current rating drops off. The primary function of the automotive fuse is to protect the power supply, so any current rating is fine.

That drop off doesn't make sense... That seems more like a thermistor error than a fuse error. When the temp drops off is the hot end still hot enough to extrude filament?

 

Yes it is.

 

Probably thermistor then. Is it loose?