RepRapPro Mono Mendel hotend problems

Hi all,
I've built a RepRapPro mono Mendel and bought the hotend form their site after an unsuccessful J's hontend mount. The hontend is a 0.5 nozzle with a big heatsing and a fan mounted over it (https://reprappro.com/wp-content/uploads/2014/07/RRP-MEN-hot-end-build-21.jpg) .This is mounted on the cartirdge and then another second fan is pointed at the extrusion point to cool the material.
The problem is that due to the intensive fan cooling of the heatsink, the temperature fluctuation is enormous. If I set it 185 for PLA, it gets between 179 and 205, which is unbearable and I think I clogged the nozzle, as it stopped extruding all the time.
I either have to slow down the fan, or somehow fix the heater of the hotend work normally for a stable temperature.

My question is what should I do? Any suggestion is welcome.

Thanks,
Boyan.

There is something wrong, Ive got a rrp mendel 3 tri colour and have two heatsinks and 4 fans, but my temperature control is perfectly stable.

Is this machine a mendel3 with the duet controller or older?

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RepRapPro Mendel 3 Tricolour
RepRapPro Fisher
-Carbon Arms
-Easy adjust Carriage+effector
-axis stiffness mods
HE3D -600 delta
-Duet 0.8.5
-PanelDue
-DC42 Height probe
-RobotDigg metal components
Simplyfy3D
RS Design Spark CAD

It's actually a prusa mendel with the reprappro mendel X cartridge and hotend/extruder and a melzi board. What do you mean the duet controller? It's a single-extruder/single board one, if this is you ask.

The duet is the new controler that replaces the melzi it may be that the duet is better at driving the hot end, you probably should ask someone who knows the difference between the melzi and duet fired machines

---

RepRapPro Mendel 3 Tricolour
RepRapPro Fisher
-Carbon Arms
-Easy adjust Carriage+effector
-axis stiffness mods
HE3D -600 delta
-Duet 0.8.5
-PanelDue
-DC42 Height probe
-RobotDigg metal components
Simplyfy3D
RS Design Spark CAD

I have the same mono mendel from RRP and I can't remember that the temp was fluctuating like that. The cooling fan on the backside shouldn't be on all the time either, check your settings in the slicer software about cooling.

I'n waiting for a new heater for my hotend so I can't check how much my temp varies right now but I'll check once I get it!

Does the Melzi have a PID controller for the hot end, could be that it just needs tuning, if you reduce the I term a little then you should see that it takes a little longer to get to temp, but should be more stable.

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RepRapPro Mendel 3 Tricolour
RepRapPro Fisher
-Carbon Arms
-Easy adjust Carriage+effector
-axis stiffness mods
HE3D -600 delta
-Duet 0.8.5
-PanelDue
-DC42 Height probe
-RobotDigg metal components
Simplyfy3D
RS Design Spark CAD

Quote
bgkdavis
Does the Melzi have a PID controller for the hot end, could be that it just needs tuning, if you reduce the I term a little then you should see that it takes a little longer to get to temp, but should be more stable.

I think it does, or atleast it's built into the firmware so running a "M303 C8 S175" will apparently tune the PID and give the correct values to enter into the firmware. (src: [forums.reprap.org])

Well, it sounds like the PID tune is seriously out of whack, the fact that the OP can get to 205 with a 185 setpoint confirms there is plenty of power in the system to handle the fans, but the lack of stability in temp would be explainable by a poorly tuned PID.

---

RepRapPro Mendel 3 Tricolour
RepRapPro Fisher
-Carbon Arms
-Easy adjust Carriage+effector
-axis stiffness mods
HE3D -600 delta
-Duet 0.8.5
-PanelDue
-DC42 Height probe
-RobotDigg metal components
Simplyfy3D
RS Design Spark CAD

What Melzi board do you have? If you have one based on the early, Melzi V1, including the 'Melzi 1.0/2.0 eBay Hybrid', these are well known for inaccurate temperature response. See: [reprap.org]

Ian
RepRapPro tech support

Assuming the board has similar issues like the Gen6 boards a closer look at C9 might help.
It is a 4.7µF electrolytic capacitor.
I would replace it with a 100nF ceramic cap and see if it helps.
Also double check all ground connections as these boards love to have troubles with it.
Might also help to check the voltages on the 5V regulator with n oscilloscope to be sure there is not already something dirty going into the supply chain.