120V heater pad

Intro

This page explored 120V ac heaters. Natural choices are heater pads, but these are expensive and custom items. So we made our own nichrome heaters, which have the advantage of complete flexibility for power and size. They are time-consuming to wind without a winding jig.

The nichrome DIY heater element works, but the connection from nichrome to wire is difficult as it goes from copper to steel and there is galvanic corrosion. Further, we run the heater at high temp for fast heat - so we have had the nichrome elements burn out regularly. Solutions are to run the nichrome at about 600 C max, well under its 1000C rating. Another great solution - which turns out to heat faster because it doesn't require insolation over the heater element - is a halogen light bulb.

Halogen bulbs get hot - several hundred C - and radiate about 90% of their energy as heat. Thus, they are fast, effective heaters, and becuase no insulation is used over them, they can heat the 3D printer heat bed rapidly.

Pad

• Amazon $20 - [1]
• Ebay $15 in 4 quantity - [2]
• $13 from China - [3]

Resistors

• Use resistors instead - [4]

Halogen As Heater

• Halogens are about 85% heaters.
• For 3D printers, use a 240V bulb, run it at 1/4 power with 120V (P~I^2R) so it doesn't burn out with on-off cycling - by running it only at a fraction of its rated power.
• Use a holder - 4.69 or 4-11/16" holder, for a 240V T3 bulb. [5]
• R7S is the style of holder -[6]
• 500W 240V - This bulb is T3 R7S, 118 mm long - [7]
• 1500/375W 240/120v - [8]
• Or use 2 120V 500W in series, more even bed heating, using 2 bulb holders - [9]

Data Collection

• Note that for the 6" bed D3D Universal 2, 118mm (about 4.69") is the longest that fits in the bed. Pay attention to not using longer than 118 mm for a 6" bed - but longer bulbs can be used for larger beds.
• We have had a heater element under testing 24/7 for the last 2 months - there is no indication of forthcoming failure, and we expect the lifetime of the heater to be well over the 2000 hour typical [10] lifetime of a halogen bulb if we are using 240V bulbs and running them at 1/4 power by using 120V.