Good and bad news.
Good news: I got v1.0 of MRR ESPA (the basic 3D printer control board based on the ESP32) all soldered up. Motors with A4988 drivers working. Endstops working. Hotend was able to heat up to 240 degC and maintain it without any significant rise in the temperature of the MOSFET.
Bad news: The heat bed MOSFET smoked (almost started a fire) when I was testing it. Tried room temperature to 40 degC, and saw smoke when it started to heat up to 35 degC. Temperature on the heatsink attached to the MOSFET was reaching 120 degC. Shut off, then I tried gradual heating. Slowly went from room temperature to 35, then step up in steps of 2 to 3 degC. Eventually reached 50 degC. When going to 52 degC, there was a bit of smoke which soon stopped when temperature reached target. Then I tried 55 degC. That was when it started to smoke real bad. Like, things were melting, there was sizzling sound, and lots of smoke. Quickly shut off the mains.
This is the reverse side. The same blackish stuff was on the reverse side too, I removed it before taking the photo, though you can see some residue.
The heat bed is 180W, running on 12V, so the current draw (theoretically) is 15A. Resistance as measured from terminal + to terminal - for the heat bed was 0.9 ohms, which sounds about right. The MOSFET (IRLS3034) is driven by a voltage divider that drives the gate at 4.8V. Based on specs, the IRLS3034 should have Rds of 2.0 mOhms at 4.5V. So simple calculation says the MOSFET is dissipating 15x15x0.002 which is 0.45W. At temperature rise of 40degC/W, the MOSFET should only be rising like 18degC. I mean, even given other factors, the temperature rise should not be more than 50degC, right? But I was getting a temp rise of 100degC and more. I can't really figure out why.
If anyone has any idea, I would be open to hearing them.
Note: Issue fixed. Pre-launch version now available here. Some information on this has been updated here.
Good news: I got v1.0 of MRR ESPA (the basic 3D printer control board based on the ESP32) all soldered up. Motors with A4988 drivers working. Endstops working. Hotend was able to heat up to 240 degC and maintain it without any significant rise in the temperature of the MOSFET.
Bad news: The heat bed MOSFET smoked (almost started a fire) when I was testing it. Tried room temperature to 40 degC, and saw smoke when it started to heat up to 35 degC. Temperature on the heatsink attached to the MOSFET was reaching 120 degC. Shut off, then I tried gradual heating. Slowly went from room temperature to 35, then step up in steps of 2 to 3 degC. Eventually reached 50 degC. When going to 52 degC, there was a bit of smoke which soon stopped when temperature reached target. Then I tried 55 degC. That was when it started to smoke real bad. Like, things were melting, there was sizzling sound, and lots of smoke. Quickly shut off the mains.
You can see the black stuff that came from the MOSFET. Smoke was coming out, and when the smoke cleared, I saw that this black stuff had oozed out from the MOSFET.
This is the reverse side. The same blackish stuff was on the reverse side too, I removed it before taking the photo, though you can see some residue.
The heat bed is 180W, running on 12V, so the current draw (theoretically) is 15A. Resistance as measured from terminal + to terminal - for the heat bed was 0.9 ohms, which sounds about right. The MOSFET (IRLS3034) is driven by a voltage divider that drives the gate at 4.8V. Based on specs, the IRLS3034 should have Rds of 2.0 mOhms at 4.5V. So simple calculation says the MOSFET is dissipating 15x15x0.002 which is 0.45W. At temperature rise of 40degC/W, the MOSFET should only be rising like 18degC. I mean, even given other factors, the temperature rise should not be more than 50degC, right? But I was getting a temp rise of 100degC and more. I can't really figure out why.
If anyone has any idea, I would be open to hearing them.
Note: Issue fixed. Pre-launch version now available here. Some information on this has been updated here.
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