Heatbed Mosftet to hot

hi
last night i tested my heatbed with ramps 1.4, from my powersupply i seen that heatbed was drawning 5 Amps at 12v, after afew minutes i start smelling burning and shut all up and i toutch the mosfet of ramps and was like burning

from what i see the ramps 1.4 have STB55NF06 mosfets ratings of 50 A so i would tought this would be ok to hold the 5 Amps, my guess is it shouldnt get that hot
what could be the problem?

should i replace the mosfet with the Mosfet IRF1404 that can hold up to 202 A ?
if so should i replace also the mosfet from extruder with the IRF1404?

another option could be use a relay but if the IRF404 could not get that hot then would be better option replace the Mosfet

i tought the ramps.14 design would be better prepare for 12v heatbeds system

the heatbed i have is a Reprap Standard 3D Printer 3mm MK3

Edited 1 time(s). Last edit at 09/18/2017 09:59AM by Meph.

The MOSFETs on RAMPS were poorly chosen (as on some other 8-bit 3D printer control boards) but despite the number of revisions that RAMPS has been through, the part number has never been updated.

Suitable replacements include IRLB8743 and IRLB3034.

Edited 2 time(s). Last edit at 09/18/2017 04:50PM by dc42.

---

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].

official ramps also has a heatsink around the heated bed mosfet... which no supplier provides!

but it is best to replace the mosfet with something better

i have found some IRF1404 Mosfets on my local store maybe i shuld replace all 3 mosfets with it

Edited 1 time(s). Last edit at 09/19/2017 08:50PM by Meph.

You could replace the mosfet, heatsink them, use an external mosfet for the bed, or a relay or just stick a fan over the top of them. The world's your oyster.

---

Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

IRF1404 is not a good choice because it needs a higher gate voltage than Arduino/RAMPS provides.

---

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].

IRF1404 VGS is less then 5v
i havse seen ramps 1.4 selling with IRF 1404
EX [elektronicke-stavebnice.heureka.cz]

Edited 1 time(s). Last edit at 09/20/2017 12:48PM by Meph.

Quote
Meph
IRF1404 VGS is less then 5v
i havse seen ramps 1.4 selling with IRF 1404
EX [elektronicke-stavebnice.heureka.cz]

It was designed by an amateur then.

---

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].

I have order the irlb3034 mosfets
one more question, im powering the ramps 1.4 with 12v and when i turn on bed i measure 9.5 volts on the outputs of D8 is that normal?

Quote
Meph
I have order the irlb3034 mosfets
one more question, im powering the ramps 1.4 with 12v and when i turn on bed i measure 9.5 volts on the outputs of D8 is that normal?

There will be voltage drop in the power cables between the PSU and RAMPS, in the 11A polyfuse, and in the mosfet. Replacing the mosfet by a better one will reduce its voltage drop.

---

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].