Safety Improvement for MakerBot Safety Cutoff Switch, Rev C
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Published on October 12, 2011
Derived from
MakerBot Safety Cutoff Switch Kit, Rev B
by MakerBot
Description
The Rev C MakerBot Safety Cutoff Switch operation depends on the E-stop cable to function. If the cable is unplugged or fails then the safety cutoff is unable to interrupt the power to the heater element. This modification allows the Safety Cutoff Switch to operate without the E-stop cable, ensuring that the heater will be shut off if required.
This mod also adds a snubber diode to the relay coil to reduce power surges when the relay shuts off.
NOTE: These instructions are ONLY applicable to the Rev C Safety Cutoff Switch.
This mod also adds a snubber diode to the relay coil to reduce power surges when the relay shuts off.
NOTE: These instructions are ONLY applicable to the Rev C Safety Cutoff Switch.
Instructions
Making the modification:
1. Remove the Safety Cutoff Switch from the Thing-O-Matic.
2. Put the board in the vise with the solder side facing you and the Alert and Temp Cutoff connectors at the top. It should look like the first photo.
3. Install D1 between the Alert connector and the FET pin as shown in the second photo. Make sure that the banded end (cathode) is towards the bottom of the board.
4. Install D2 across the Relay coil as shown in the second photo. Make sure that the banded end (cathode) is towards the bottom of the board.
5. Install the modified Safety Cutoff Switch in the Thing-O-Matic and perform the following tests.
Testing the modification:
1. Turn on the TOM and bring up the ReplicatorG control panel. The NORMAL light should be on.
2. Disconnect one of the Temp Cutoff leads. The FAULT light should be on.
3. Reconnect the Temp Cutoff lead. The FAULT light should still be on (the Safety Cutoff is designed to latch in the fault mode until the power is shut off).
4. Shut off the TOM power and wait for the relay to release and the FAULT light to go out. Turn the TOM power back on, The NORMAL light should be on.
5. Unplug the Alert cable from the Safety Cutoff Switch. The NORMAL light should be off. (Without the Alert cable to provide a ground path the modified Safety Cutoff Switch will only operate if the Extruder Controller is sending power the heater. Of course if the Extruder Controller isn't sending power to the heater then there isn't a problem.)
6. Use the ReplicatorG control panel to set the extruder temperature to 50C. The NORMAL light should be on.
7. While the extruder is still heating up, disconnect one of the Temp Cutoff leads. The FAULT light should be on.
8. Set the extruder temperature to 0C in the control panel. The FAULT light should be off.
9. Congratulations! Your modified Safety Cutoff Switch is working correctly. Reconnect the Temp Cutoff lead and plug in the Alert cable.
1. Remove the Safety Cutoff Switch from the Thing-O-Matic.
2. Put the board in the vise with the solder side facing you and the Alert and Temp Cutoff connectors at the top. It should look like the first photo.
3. Install D1 between the Alert connector and the FET pin as shown in the second photo. Make sure that the banded end (cathode) is towards the bottom of the board.
4. Install D2 across the Relay coil as shown in the second photo. Make sure that the banded end (cathode) is towards the bottom of the board.
5. Install the modified Safety Cutoff Switch in the Thing-O-Matic and perform the following tests.
Testing the modification:
1. Turn on the TOM and bring up the ReplicatorG control panel. The NORMAL light should be on.
2. Disconnect one of the Temp Cutoff leads. The FAULT light should be on.
3. Reconnect the Temp Cutoff lead. The FAULT light should still be on (the Safety Cutoff is designed to latch in the fault mode until the power is shut off).
4. Shut off the TOM power and wait for the relay to release and the FAULT light to go out. Turn the TOM power back on, The NORMAL light should be on.
5. Unplug the Alert cable from the Safety Cutoff Switch. The NORMAL light should be off. (Without the Alert cable to provide a ground path the modified Safety Cutoff Switch will only operate if the Extruder Controller is sending power the heater. Of course if the Extruder Controller isn't sending power to the heater then there isn't a problem.)
6. Use the ReplicatorG control panel to set the extruder temperature to 50C. The NORMAL light should be on.
7. While the extruder is still heating up, disconnect one of the Temp Cutoff leads. The FAULT light should be on.
8. Set the extruder temperature to 0C in the control panel. The FAULT light should be off.
9. Congratulations! Your modified Safety Cutoff Switch is working correctly. Reconnect the Temp Cutoff lead and plug in the Alert cable.
License
Safety Improvement for MakerBot Safety Cutoff Switch, Rev C by RonG is licensed under the Creative Commons - GNU GPL license.
More from RonG
Hi! the resistor below my relay is always very hot (I measured more than 60
ºC), this mod will help with this?
Thanks! The REV. D also has the same issue
Short answer: No, but there is nothing to worry about. Power resistors are designed to operate at high temperatures. Resistors like this one are designed to operate safely at over 150C, so 60C is not all that warm.However, that is why the instructions note that it should be up and away from the board. If it were close to the board the board itself could be damaged by the heat. I assume that you put the board on the side of the Z-axis as recommended, where it can get at least some cooling air. The earlier extruders used simple power resistors as the heating element for the hot end, and they run at over 225C.
I used to work on medical electronics equipment that had no external ventilation holes so that it was easier to keep clean. No ventilation meant that it got quite warm inside, and most of the boards were badly discolored around the power resistors but still operated reliably.