P55NF06L is how STP55N06L is marked which is the 0.016 - 0.020 Ohm part spec'd out for use and the L at the end means you have the proper Logic Level version of the part, so you have the part that is spec'd for RAMPS 1.4Quote
ianmcmill
The three MOSFETS on my Ramps 1.4 are P55NF06L ; 7SABF ; V6 ; PHL 243. None of the ones you named there. Might this be the bottleneck ?
I insulated the alu plate with a 3mm cork sheet.
I just received my Teensylu v0.8. Gonna give this a shot as soon as I get another hotend.
ref: http://www.st.com/web/en/resource/technical/document/datasheet/CD00002690.pdf
Compared to:
http://www.irf.com/product-info/datasheets/data/irlb8743pbf.pdf
http://www.irf.com/product-info/datasheets/data/irlb3036pbf.pdf
Let me repeat myself from the first post ... the power supply and possibly wiring is most likely the factors in your problem then the MOSFETs. The MOSFETs cat improve how it works while heating up less. You could easily be loosing 0.3V or more with the current MOSFET's (depending on how much current the power supplies can actually supply). The printers I've helped build we've always used IRLB8743 combined with 30A power supplies and heavy gauge wiring and insulation below the heatbeds to maximize heating and minimize heat times. The order to check things is Power Supply, Wiring & Connections, then MOSFET's. When your on a limitted budget sometimes the power supply moves to the end unfortunately.
Full disclosure: I do sell the MOSFET's on eBay mostly to US & Canadian buyers, but I do honestly think the spec's for the RAMPS 1.4 is substandard for hotbed needs. Other boards like the Sanguish have changed to the IRLB8743 which is how I got interested in those MOSFET's to begin with. They both work better at switching high currents and heat up less (when MOSFET's get hot the let less power through)
IRLB8743PBF 30V 150A on eBay
IRLB3036PBF 60V 195A on eBay