Low voltage on D8 (heated bed)

Hello all,

I'll start off by saying that my bed will get up to 110 degrees C, but only after about an hour of warming up. Printer is a Makerfarm i3v 8", and it's fully enclosed.

I've been trying to speed up the heating process. I've messed with different insulations, and they've helped but it still takes way too long to get up to temp. I recently added 4R7 ohms to the 5v rail (via 4x 4R7 resistors, 2 i.n parallel + another parallel pair in series to split up the heat dissipation), that reduced the time by several minutes but I'm still looking at about an hour to get to full temp.

Using my trusty multimeter, I've found I'm getting 12v (+/- 0.1v) at both power inputs on the RAMPS board, but only 10v or so coming out on D8 to the bed. Admittedly, the power supply is pretty cheap but it's rated for 480w which should be plenty. I find it strange that I'm getting good voltage into the board but not coming out of it. Possibly a defect on the board itself?

My next step might be to put one of the legs directly onto the 12v rail of the power supply. Not the best solution but it should work better until this gets fixed.

Thanks in advance.

Sounds like you are losing 2V in the mosfet and fuse. See which one of them is getting hot, or use your multimeter to measure between the input and output to see whether the voltage drop is on the ground side (mosfet) or high side (fuse). If it's the fuse (the big square one), replace it with an auto fuse rated at 15A.

Also check the terminal block screws are tight and there is no charring anywhere on that end of the board.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks for the response. I did do some reading last night after I posted this and saw that the poly fuses could act up when they're close to their rated current. I'll try jumping them. I already have a 5A circuit breaker on the AC side of the power supply. Should I still add a fuse on the RAMPS board?

Thanks for your help!

Many 3D printer controller boards don't have fuses at all, and if you are using an ATX PSU then it's probably short-circuit proof anyway. So it's up to you whether to add a fuse or not.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

You said the power supply is rated at 480 watts, but does it say how much the 12V rail(s) are rated at? A decent amount of that may be for rails other than 12V which is what you're looking for. As a check to eliminate the electronics, hook up the heated bed directly to the power supply. See how quickly it heats. If it still is slow, it may be your power supply. Or your heated bed. What's it's resistance?