Flexydually Temperature Problems / Troubleshooting / Solution

I’m going to share one issue that I started having after upgrade my Lulzbot Taz 5 with the new Flexydually, how I troubleshoot it and how I fixed it. It might help someone.

After upgrading to the new tool head I noticed that my heat element could not maintain its temperature. I was using ABS on the extruder zero, setting it’s the temperature to 240C, but after some time the temperature would drop to around 220C.
Frist thing that you need to check is bad connection, I took my multimeter on continuity mode, and started testing the cable while moving the too head and the cable. Not an issue.

Next you need to check the heat cartridge, you can use the multimeter and measure the heat cartridge resistance and it should be around 20 ohms. You can also swap the heat cartridges from the two extruders, I did both, and it was not the root cause of my issue.

I removed my printer from the power surge protection, and tried another wall outlet, again, did not fix my problem. Also tried same test not turning on the heated bed, still no luck.
Next step I opened the control box, and with the help of the multimeter, i checked the FETs that control the heat element, no problem detected.

I then put my multmeter in series with the heat element, and started a new print, now keeping a close eye on the current and keeping note of everything that was going on, and I discovered that that was a correlation with the temperature dropping / fan speed / current for the heat element.

With the fan at 7% the heat element would draw from 0.75 to 0.8 amps and the temperature would maintain 240C.
With the fan at 15% the heat element would draw from 0.77 to 0.86 amps and the temperature would maintain 240C.
With the fan at 23% the heat element would draw from 0.83 to 0.89 amps and the temperature would maintain 240C.
With higher fan speeds (around 31% or more) the temperature would start dropping and the power consumption would increase for around 0.9 to 0.92 amps.

It is interesting that the maximum power that I got from my heat element was around 21.6 watts (0.9 amperes * 24 volts) much lower than the nominal 30 watts
On the following graph, you can see clearly that every time that I started the fan (manually from the g-code command) the temperature would start dropping, see arrows. Then when I turned off the fans Temperature would increase.
Next step I modified the fan duct file to increase its clearance from the hot end area, and added internal chamfers to force the air flow downwards. Check the pictures, old design in black new in gray.

I tested the new fan ducts, turning the fan 100% on and did not notice any temperature drop. I repeated the test going back and forth with the old design and my updated design and every time that I used the stock fan duct I would get a temperature drop.

Despite the new fan duct fix my issue, I don’t know if this issue happens across all Flexydually or the new Dual extruder or if the actual root cause is that my Rambo board / power supply is weaker than normal, and it should be able to keep up even with the stock fan duct.
I would love if anybody else could test their heat element and see if the figure of 22 watts is the maximum power that the Rambo output normally.

TLDR: Had problems with temperature, apparently related with fans blowing air on hot area of extruder, changed to new design.

Stl file of the modified fan duct attached.
Flexydually_Fan_New.stl (82.8 KB)

Just remember your 21.6 watts is a RMS reading on the meter, since it is a PWM waveform that is being read/measured.

Yeah, you are right! I’ll do the same test again with a oscilloscope…

But I guess that when the temperature was lower than the set temperature, the rambo would increase the duty cycle, and at that point the value measured by the multimeter would be closer of the value measured taking into account the PWM factor… But I’ll double check measuring the duty cycle! :slight_smile: