D10 Extruder led Flashing, turning on and off extruder resistor

Hello,

I have a ramp 1.4 with marlin firmware. D10 led is flashing during operation. It starts to flash near set temperature and then it keep flashing. The power to the extruder resistor is going on and off very fast. I had some issues with the heat bed, it melted the connector so, I replace the connectors and put a relay. I decided that I should avoid any more damage to the ramp, so I set up also a relay for the extruder. Now I have something like a machine gun when it is working.
I have seen some comments related to the hot bed in the clone wars section of rep rap wiki. I saw reference to hysteresis, but not sure how that works. There is no similar line for the extruder. All the search results that I have found are related to similar issues focus on the heat bed. I know the relay will eventually fail at this rate. So I am looking on how I can set slower signal for the extruder.

I have uploaded a video to youtube showing the led flashing and the noise from the relay.

Thanks in advance for any hint on this problem

Neville

Neville, firstly the wattage of the extruder is much lower than the hot bed, so that the current involved is also smaller. The diode will start to flash as the extruder nears the set temperature since the systems means of controlling the temperature is to turn off the current and then to turn it on again as the extruder cools slightly. The extruder has a much lower thermal mass than the bed so it heats and cools much faster than the latter. The rapid switching is one of the reasons that electro-mechanical relays are not recommended. Control MOSFETs are entirely solid state and for this reason make no noise. You would really do better to replace the relay with a MOSFET. Your noise problem would then go away. You shouldn't try and find a slower signal to control the relay as you are then affecting the systems ability to control the extruder temperature. Suitable control MOSFETs are pretty cheap to buy and easy to fit.

Edited 2 time(s). Last edit at 12/27/2016 02:52AM by Supermec.

Quote
Supermec
Neville, firstly the wattage of the extruder is much lower than the hot bed, so that the current involved is also smaller. The diode will start to flash as the extruder nears the set temperature since the systems means of controlling the temperature is to turn off the current and then to turn it on again as the extruder cools slightly. The extruder has a much lower thermal mass than the bed so it heats and cools much faster than the latter. The rapid switching is one of the reasons that electro-mechanical relays are not recommended. Control MOSFETs are entirely solid state and for this reason make no noise. You would really do better to replace the relay with a MOSFET. Your noise problem would then go away. You shouldn't try and find a slower signal to control the relay as you are then affecting the systems ability to control the extruder temperature. Suitable control MOSFETs are pretty cheap to buy and easy to fit.

Thanks for your quick response.
I have seen the led flashing before, but I did not worry about as it was controlled by the mosfet in the ramp. I am aware that the noise is the mechanical part of the relay going on and off.

So, should I put the extruder heater on the ramp, or should I use a solid state solution (like a mosfet) wire outside the board?

I am able to replace the screw connectors on the side of the board. But the ramp is fragile and the overheating from the heated bed and then from the iron solder is damaging the printed circuitry on the board. The copper has lift from the board in some parts. I don't think it will handle the current all the same as new. So I was trying to avoid more damage leading to replace the whole RAMP.

Thanks again for your advise. I will appreciate your input on my remaining question.

Neville

Neville,

fix the MOSFET (which is mounted on its own circuit board) anywhere on the printer that is convenient. You will need to take a seperate positive and negative supply from the PSU (12V ? depending on your bed) to the power input connections of the MOSFET (12gauge fine stranded silicon covered wire is recommended). Disconnect the existing bed heater wires from your existing relay and run them instead to the power output connections of the MOSFET (you can also replace these wires with 12gauge).

For the control wiring, take a +ve and -ve feed from the original bed heater connections on the control board (if not marked + and - on the control board then you will need to find out which is which) and run these wires to the control input on the MOSFET. This last connection does not require heavy wire since only very much lower control currents will run through it.

It is absolutely essential to connect the power input wires to the MOSFET with the correct polarity and to secure the wire ends tightly in the connectors. The control wires must also be connected with the correct polarity. Connecting either of these two cables the wrong way round will damage the device. The polarity of the wires from the MOSFET to the heat bed does not matter, as the bed heater is a resistive load, but these wires also need to be secured tightly in their connectors.

I have already place a relay outside the ramp. The wiring is done. The only thing will be exchanging the relay for the mosfet. You have cleared all my concerns in tackling this last step. Thanks for your detailed instructions.

Neville