Update: The reason for the board (20A VBED fuse) heating up to extremely high temperatures has been found. It is because I wrongly assumed my heated bed to be a 180W@12V (=15A) heated bed. Instead, using a clamp meter, I measured 24A being drawn while heating. Obviously, drawing 24A through a 20A fuse is not the best idea.
Thermal testing results since I got my thermal camera. I had previously checked for temperature using a thermocouple as well as an infrared thermometer. I am posting here in case people miss the post on Github.
Running on 12V, heating up a 310mm by 310mm heated bed, the temperatures observed using a HY-18 MLX90640 thermal camera:
No active cooling: ~135degC (20A VBED fuse); ~100degC (VBED and BED connectors)
Bottom cooling: ~95degC (20A VBED fuse); ~75degC (VBED and BED connectors)
Top cooling: ~90degC (20A VBED fuse); ~75degC (VBED and BED connectors)
Top and bottom cooling: ~75degC (20A VBED fuse); ~50degC (VBED and BED connectors)
(above are temperatures during heating up phase)
Bottom cooling was a 80x25mm fan mounted 5mm below the board, directly blowing at the bottom side of the board.
Top cooling was a 80x25mm fan mounted 30mm above the board, directly blowing at the top side of the board.
Obviously, the best way to cool the board when used with 12V for the heated bed is with both top and bottom cooling. But if you cannot mount a fan to the bottom side of the board, it seems that top cooling only is a good alternative. Mounting a fan on the top side not only helps to keep the fuse (which is running current through it at close to its current limit) and the MOSFET (not really an issue) cool, it can also help to cool down the stepper motor drivers too.
Whatever the case, it is best to leave a gap of at least 5mm below the board to allow for air flow.
More thermal testing, under the following test conditions:
- Board in open air (unenclosed), mounted to top and bottom panels using spacers, and no side panels.
- 12V 40mmx40mm fan mounted 30mm above the board, blowing directly down on the top side of the board. Fan is offset by 10mm from center of board toward the edge with VBED connectors.
- Bottom clearance of 5mm below the board.
- Started heating bed from room temperature to 100degC.
- After reaching 100degC, maintained at 100degC for 10 minutes.
- Started heating hotend from room temperature to 240degC when bed reached 90degC.
- Maintained hotend at 240degC until end of test.
Observed temperatures when heating up (before bed reaches 100degC):
~130degC (20A VBED fuse); 100degC (heated bed MOSFET); 95degC (VBED and BED connectors)
Observed temperatures when maintaining 100degC:
~90degC (20A VBED fuse); 80degC (heated bed MOSFET); 70degC (VBED and BED connectors)
As expected, the fuse, MOSFET, and connectors reached high temperatures when pushing a lot of current (15A at 12V) during the heating up phase, as this is when the full current is being passed through to bring the heated bed up to the required temperature.
However, once the required temperature is reached, the current required drops, and corresponding, the temperature.
Based on this, when running on 12V:
- First and foremost, avoid having to use 12V to power the heated bed in the first place. That is why the bed control is isolated with an optocoupler. This allows a separate 24V power supply to be used to power the bed.
- If 12V must be used, it is best to avoid putting the board within an enclosure.
- If an enclosure must be used, ensure adequate air flow to remove heat from the VBED fuse, connectors, and bed MOSFET. A 80mm by 80mm fan directly blowing onto the top side of the board is recommended.
Thermal testing results since I got my thermal camera. I had previously checked for temperature using a thermocouple as well as an infrared thermometer. I am posting here in case people miss the post on Github.
Running on 12V, heating up a 310mm by 310mm heated bed, the temperatures observed using a HY-18 MLX90640 thermal camera:
No active cooling: ~135degC (20A VBED fuse); ~100degC (VBED and BED connectors)
Bottom cooling: ~95degC (20A VBED fuse); ~75degC (VBED and BED connectors)
Top cooling: ~90degC (20A VBED fuse); ~75degC (VBED and BED connectors)
Top and bottom cooling: ~75degC (20A VBED fuse); ~50degC (VBED and BED connectors)
(above are temperatures during heating up phase)
Bottom cooling was a 80x25mm fan mounted 5mm below the board, directly blowing at the bottom side of the board.
Top cooling was a 80x25mm fan mounted 30mm above the board, directly blowing at the top side of the board.
Obviously, the best way to cool the board when used with 12V for the heated bed is with both top and bottom cooling. But if you cannot mount a fan to the bottom side of the board, it seems that top cooling only is a good alternative. Mounting a fan on the top side not only helps to keep the fuse (which is running current through it at close to its current limit) and the MOSFET (not really an issue) cool, it can also help to cool down the stepper motor drivers too.
Whatever the case, it is best to leave a gap of at least 5mm below the board to allow for air flow.
More thermal testing, under the following test conditions:
- Board in open air (unenclosed), mounted to top and bottom panels using spacers, and no side panels.
- 12V 40mmx40mm fan mounted 30mm above the board, blowing directly down on the top side of the board. Fan is offset by 10mm from center of board toward the edge with VBED connectors.
- Bottom clearance of 5mm below the board.
- Started heating bed from room temperature to 100degC.
- After reaching 100degC, maintained at 100degC for 10 minutes.
- Started heating hotend from room temperature to 240degC when bed reached 90degC.
- Maintained hotend at 240degC until end of test.
Observed temperatures when heating up (before bed reaches 100degC):
~130degC (20A VBED fuse); 100degC (heated bed MOSFET); 95degC (VBED and BED connectors)
Observed temperatures when maintaining 100degC:
~90degC (20A VBED fuse); 80degC (heated bed MOSFET); 70degC (VBED and BED connectors)
As expected, the fuse, MOSFET, and connectors reached high temperatures when pushing a lot of current (15A at 12V) during the heating up phase, as this is when the full current is being passed through to bring the heated bed up to the required temperature.
However, once the required temperature is reached, the current required drops, and corresponding, the temperature.
Based on this, when running on 12V:
- First and foremost, avoid having to use 12V to power the heated bed in the first place. That is why the bed control is isolated with an optocoupler. This allows a separate 24V power supply to be used to power the bed.
- If 12V must be used, it is best to avoid putting the board within an enclosure.
- If an enclosure must be used, ensure adequate air flow to remove heat from the VBED fuse, connectors, and bed MOSFET. A 80mm by 80mm fan directly blowing onto the top side of the board is recommended.
1 comment:
I repeated the 100degC test with a 80mm by 80mm by 10mm 24V fan (my go-to setup for silent fans).
During heating up:
~110degC (20A VBED fuse); ~85degC (bed MOSFET); ~85degC (VBED and BED connectors)
Maintaining 100degC (after 10 minutes):
~75degC (20A VBED fuse); ~65degC (bed MOSFET); ~65degC (VBED and BED connectors)
Previously, I did the 80mm 12V fan testing with an 80mm by 80mm by 25mm 12V fan. Kind of noisy when I was using it.
Using a 80mm by 80mm by 10mm 24V fan running on 12V was almost silent. The only way I knew the fan was running was to feel for air flow.
Post a Comment