Ramsey Gill
Stock configuration
- Previous bed heating was Kapton (polyamide) style.
- Heating element was bonded to borosilicate glass bed with double sided adhesive tape.
- The the bottom of the element was insulated with a sheet of cork. The cork was sagging into the Y axis belt drive mechanism.
- Heating element cabling is repurposed ribbon cable with tripled up parallel conductors on each of the power lines to handle the necessary current (increase ampacity).
- Heating element resistance is 1.2 Ohms. V/R = I (12V/1.2R = 10A) ~120Watts
- Heating element power is switched by two parallel MOSFETs on the RAMPS PCBA. (these get very hot and fail commonly, not being used IAW manufacturer documentation)
- Heated bed MOSFETs are not actively cooled or sinked into any thermal mass.
Post Modification
New bed heating element is silicone.
Signswise 200x200mm 12V 220W Silicone Rubber Heating Heater for 3D Printer Heated Beds
Signswise
Link: http://a.co/d/bCBSjx8
SPECS
- 200mm x 200mm / 8"x8"
- Thickness: about 1-1.5mm
- Rated Power: 220W
- Rated Current: 6.5A
- Thermistor: 100K "3950"
- Working temperature: -62～235℃ (suggested )
- Temperature: below 180℃
Requires PID tune and update to configuration.h
https://reprap.org/wiki/PID_Tuning
Raised bed max temp to 100C
Silicone heating element will be bonded to borosilicate glass bed with double sided thermal adhesive sheets.
Gizmo Dorks 3M 468MP Adhesive Transfer Tape Sheets 8" x 8" (5-Pack)
Gizmo Dorks
Link: http://a.co/d/hMhrvf2
The Silicone heater will not be installed with an insulator. Low risk of sagging
Heating element cabling is QTY. 2 14AWG red silicone insulated wires. (very flexible)
Heating element resistance is 0.6 Ohms V/R = I (12V/0.6R = 20A) ~240Watts
DC Solid state relay (SSR) has a switching capacity of 25A, significant passively cooled heat sink. (Fan can be added if install in a location without airflow)
Ogrmar Solid State Relay SSR-25 DD DC-DC 25A 3-32VDC/5-200V DC SSR-25DD with Heat Sink
by Ogrmar
Link: http://a.co/d/i5SM7Dq
DC solid state relay will receive its "ON" commands from the heated bed FET outputs of the RAMPs boards. (Previously attached directly to the heated bed power leads.)
WARNING: Be sure to purchase a DC rated SSR which are less common than their AC cousins. AC SSR's latch closed when used with DC power. (They tend to close and stay closed regardless of command signal) Your heated bed will turn on and dead short to the power supply. This could cause serious damage or fire if not de-energized quickly.
Other suitable high current MOSFET based switching modules.
ANYCUBIC 3D Printer Heating Controller MKS MOSFET for Heatbed Extruder MOS Module
ANYCUBIC
Link: http://a.co/d/1y3vxQn
BIQU Heat Bed Power Module Expansion Hot Bed MOS Tube for 3D Printer
BIQU
Link: http://a.co/d/gV1afo0
ReliaBot Hot Bed Power Expansion Board Heating Controller MOSFET High Current Load Module Over 30A 12V or 24V for 3D Printer
ReliaBot
Link: http://a.co/d/1SxmKC1
Post Upgrade Power Assessment
It's always a good idea to reassess the power requirements of your printer after performing a major upgrade. My primary motivation for this assessment is to understand the impact of installing the new 240W build plate heater.
The ROBO 3D R1 stock power supply is capable of delivering 12VDC 30A (360W). With that said, the power supply is of suspect quality and a as a Manufacturing Engineer, I consider it prudent to derate lightweight power supplies without a brand name on them.
For my assessment, I will consider the power supply capable of delivering 300W which could pose a problem if my build plate heater now consumes 240, leaving 60W for everything else.
Power Roll-up
- 240W - New...
Ethan Waldo
jag
lee
Orkhan AmirAslan
While there is some useful information here (thanks), there is also some misinformation. I have doubts as to whether you have actually tried this mod yourself. You link to a 220W heater but 12V at 6.5A is only 78W. You would need just over 20V to get 220W out of that heater. Thus, there is no overloading of the power supply and instead of upgrading you have downgraded. Unless you add a separate 20V power supply. Also, the heater isn't necessarily off/on. If the firmware is any good, it uses PWM on the heater (hence the PID servo parameters you mention) instead of a bang bang servo. Solid state relays are generally not designed to handle PWM; they are too slow. The EKT SSR-25DD datasheet says it takes 10ms to turn on and off. That is too slow for PWM. The OGRMAR version you link to, who knows? The anycubic driver you link to uses a 4N35 which switches in 10us but the transistor/optocoupler combination might not be that fast. It was at least made to work with ramps. But be aware that a MOSFET dissipates extra power during the PWM switching transients and weak gate drive can make that worse; on the flip side, two strong a gate drive can make lots of electrical noise. Also, watch out for dodgy counterfeit SSRs.. An inductor (with a flyback diode) would help smooth out the current draw. Another problem with the printer is the RAMPS power connector. They are already overloading the pin and I have a crispy connector to prove it. So you do need an external hot bed mosfet board if you upgrade to a higher wattage - or even if you don't. Also, when increasing the wattage of the heater, consider what happens when the thermister, heater control, or software fails and the heater goes to 100% power and stays there. The higher the wattage, the higher the risk. Also, when replacing the heater, consider the option of getting a heater with two elements that can be wired in series or parallel for different voltages and or wattages. This would give some more flexibility and might allow you to delay part of the upgrade since you could leave one winding disconnected (if they both heat the whole mat instead of one side vs the other). I didn't find one in the right size/wattage range, though. Another option is to put two heaters on top of each other (beware of bulges where wires connect or thermistors or other parts are mounted) or even overlapping (you will get different temperatures but you do already. Those could be put in series or parallel as needed or one left disconnected.