Hi, Im trying to make my heated bed work and having trouble. The mosfet starts to become really hot (within a minute or so) when the printer is switched on. I heard the mosfets that come with the sanguino kits are the wrong type. From the wiki I found that the mosfets I have, are not the ones mentioned wiki, which leads me to think they were aware of the issue and used higher power mosfets for my kit. this is the mosfet I currently have installed: [www.fairchildsemi.com] What temperature should I expect this thing to run at? To me it seems to be running hot so I switch it off instantly due to my fear of it burning out, but maybe its normal that it feels hot to the touch? I also did the trick mentioned in the wiki about using large wires to carry the higher current on the underside of the board. Should I get a different mosfet or is there another way of making this thing run cold? https://reprap.org/forum/read.php?158,216128,216128#msg-216128 Mon, 12 Oct 2026 23:38:36 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?158,216128,217577#msg-217577 https://reprap.org/forum/read.php?158,216128,217577#msg-217577 [ultimachine.com]

Was using it in my RAMPS for a bit, then decided to try out the sanguino i had lying around. At first I didnt change the mosfet out that came soldered onto my fully assembled sanguinololu
(i bought this one: [www.ebay.com])

turned my 12v heat bed on (silicon heatbed, looks like a big orange rubber sticker that I stick under my aluminum build plate) to 60C, and before it even got there (from what I remember around 35-40ish C) it started smoking and the solder started bubbling... not a good sign.

Took the mosfets that I got from Ultimachine from my RAMPS board, put them onto my Sanguniololu, and did the heated bed trace upgrade
[create3d.com.au]

Picture and info courtesy of create3d

just to be safe I also mounted an 80mm fan blowing across my electronics (needed them for the Pololu's anyway) and added a screw on heatsink to the heated bed mosfet, everything is working great.]]> isonoob Sanguino(lolu) Wed, 12 Jun 2013 00:29:36 -0400 https://reprap.org/forum/read.php?158,216128,217543#msg-217543 https://reprap.org/forum/read.php?158,216128,217543#msg-217543 Here's one from digikey. The part number is IRLB8743PBF. Rds ON is 0.0032 ohm, which is almost a magnitude smaller than what you have now. The one I listed runs at pretty much ambient temperature with MK2 heatbed, no heat sink. But then you can find ones with even lower Rds ON.]]> lajos Sanguino(lolu) Tue, 11 Jun 2013 18:29:39 -0400 https://reprap.org/forum/read.php?158,216128,216635#msg-216635 https://reprap.org/forum/read.php?158,216128,216635#msg-216635
What mosfet do you have by the way and what temperature is it at?

From what I heard, the ideal mosfet should have a Rds of below 0.02 ohms. Mine has a resistance of 0.022 which I assume is why its so hot. Its at the limit of what is possible without a fan.

Also can anyone recommend a mosfet that runs colder than the RFP50N06 I'm using?]]> gordon13 Sanguino(lolu) Sat, 08 Jun 2013 20:46:00 -0400 https://reprap.org/forum/read.php?158,216128,216601#msg-216601 https://reprap.org/forum/read.php?158,216128,216601#msg-216601
Version 1.3b - Updated April 4, 2012
MOSFET changed to SMT versions capable of 76A drain current!]]> Mickman Sanguino(lolu) Sat, 08 Jun 2013 16:35:18 -0400 https://reprap.org/forum/read.php?158,216128,216128#msg-216128 https://reprap.org/forum/read.php?158,216128,216128#msg-216128 I heard the mosfets that come with the sanguino kits are the wrong type. From the wiki I found that the mosfets I have, are not the ones mentioned wiki, which leads me to think they were aware of the issue and used higher power mosfets for my kit.

this is the mosfet I currently have installed:
[www.fairchildsemi.com]

What temperature should I expect this thing to run at? To me it seems to be running hot so I switch it off instantly due to my fear of it burning out, but maybe its normal that it feels hot to the touch? I also did the trick mentioned in the wiki about using large wires to carry the higher current on the underside of the board.
Should I get a different mosfet or is there another way of making this thing run cold?]]> gordon13 Sanguino(lolu) Fri, 07 Jun 2013 00:27:21 -0400