RAMPS 1.4 Mod to get fast heat 80 C in 10-12 min


#1

I just made a mod that speeded up the heating of my bed, and greatly increased the maximum temperature. I’ve see some posts here about turning up the pot on the power supply to 13.4 volts, but mine, at least, will go to 14.85. However, there are warnings online about turning it up that high due to over-driving the Vin to the mega. New versions of the Mega 2560 are supposed to be able to handle up to 20 Volts but I don’t think ours are genuine Arduinos, so I was hesitant to do that, and I imagine that is also why folks on here only put it at 13.4 or 13.5 volts.

I read up on this and found the web page of the creator of the RAMPS board. He spoke of these issues and also recommended against turning it up over 12 volts. However he also explains that the only issue there is the Vin to the 5 Volt circuitry of the Mega 2560. There is a diode on the RAMPS board, D1, that supplies the Vin to the Mega. If that is removed, you can safely supply much higher voltages to the RAMPS. But, you’ll no longer have the 5 Volt supply, so you need to use USB power for the Mega. But there’s another way…

Now to the point! I removed the 1N4004 diode D1 and replaced it with three diodes. I used 1N4001’s because that’s what I had on hand. Any of the 1N4xxx series from 1N4001 to 1N4007 will work fine. Each Diode will theoretically drop approximately 0.6 to 1.1 volts depending on the current through the diode. In practice, the 1N4001’s each dropped 0.77 volts.

So, with the three diodes replacing the one diode, and the power supply turned up all the way, I have 14.85 volts going to the RAMPS and 12.54 volts going to the Mega’s Vin Pin. Totallly safe. The there are two 12 volt systems on the RAMPS. One supplies only the bed and hotend heaters. The other supplies the Vin to the Mega’s 5V regulator and the Steppers and the RAMPS board cooling fan and the hotend cooling fan. Both of those fans I think should be fine with a 2.85 volt overdrive. You can hear them speed up when you increase the voltage with the power supply adjustment pot. Another advantage is that the steppers will now have higher voltage available. This is fine since the drives are current-controlled. With this type of control, the higher the voltage available, the better. My cnc desktop mill has 90 volt drivers driving 3.4 volt 2 amp steppers, for instance. I won’t go into that further here unless someone wants an explanation. It’s out there, just google it.

So now for the results! My bed now heats up to 80 C in 10 to 12 minutes. 100 degrees C in 22 minutes. 105 C in 28 minutes. I used to wait 35 to 40 minutes for 80 C. Here’s the math: I know many (most) of you will know all this but for those that would like an explanation, here it is: )

The bed resistance is 1.5 ohms. At 12 volts, this gives I (current) = 12 V/1.5 ohms = 8 AMPS. The power is then V * I = 12 * 8 = 96 Watts. Coincidentally, The surface area of the board, 8 * 12 inches, is 96 square inches, giving exactly one watt per square inch. Actually I doubt that is a coincidence, but rather by design.

But, contrary to what intuition might suggest, Power is not linearly dependent on V and I. It is exponential. At 14.85 volts, the current is 14.85 / 1.5 = 9.9 AMPS. Power is now V * I = 14.85 * 9.9 = 147.015 Watts. The increase in voltage is 14.5/12 * 100 = 120.33%, but the increase in power is 147.015/96 * 100 = 153.125%. So a small increase in voltage can give a larger increase in Power. It’s because Power is also equal to I^2 R (Amps * Amps * Resistance) a non-linear relationship. You can work that out from the most basic Ohm’s law formulas. I’ll leave that to you.

Anyway, if the Arduino’s Vin max is really 20 V as the RAMPS creator states, you should be able to just max out your 12 V power supply with no changes. I decided to play it safe and make this mod. It’s not difficult, and it really sped up the heating curve.

Here’s a link to the web pages that I used, that show D1 and discuss the power issues.

http://reprap.org/wiki/RAMPS1.4#Warnings

Scroll down about half way to find the section on Power Supply, and read down from there about power supply with and without D1 installed. Then scroll down some more to find the picture of the ramps board to find D1’s placement on the board. (It’s a 1.4.2 version so it’s a little different, but it’s in about the same place as the on V1.4 boards. I don’t know if the PICA has dealty with this issue or not, that’s beyond the scope of this post. Maybe @mjrice will weigh in here on that.

Bottom line: The diodes are 11 cents or 13 cents from digikey, and they can ship USPS first class. It’s maybe a half hour job. Well worth the time spent. It will save many hours of finger tapping waiting for heat.

Oh, get some heat shrink tubing that will fit over the diodes. solder them together end-to-end with about 6 mm leads laid side-to-side, and solder a 40 - 50 mm 22 gauge wire to the far end and bring it back to the front of the assembly, after sliding the insulation over the diodes. You need the insulation to prevent any possibility of shorting against the smt resistors and the cans of the caps on the board.

I’ll probably do a video when I do the next one.
Cheers!


#2

Very clever and nice detail on the write up. Thank you.

Remo


#3

Great information thank you. Could I ask though? My Mosfet only gives me 10v max output. Is this correct? Can it be increased to Vcc ( 12v ) in the Marlin code? My heatbed won’t get up to >80degC at 10v and my PSU is not adjustable.

King regards

Antonia


#4

Marlin does not adjust the voltage to the bed. It puts out the maximum voltage and current possible from your power supply, until it reaches the set point temperature, then it outputs pulses of that same voltage and current, so the average value of power to the bed is correct to keep it at the set point. If you have an LED on your bed, when it is steady-on during the heating up phase, is when you should make your voltage measurement.

A 2 volt drop from power supply to bed is more than you should be seeing. It should be more like 1 volt or less. My PS measures 14.86 V, and the bed is at 14.01 V. Difference is 0.85 volts. I would start by checking the voltage at the PS. It might actually be more like 11 volts. Wire gauge and length matters as well. Thin, long, bad. Fat, short, good. Wish that were true for people. :slight_smile:

Regardless, you probably need a stronger PS or an adjustable one. Do you have the same power supply that Marty ships with the Wilson Kit? If so it is adjustable. There is a tiny pot with a screw slot just to the left of the screw terminal strip. Clockwise to increase. I turned mine all the way up. So far it doesn’t seem to be a problem. I do notice the PS cooling fan cycles a little more often but that’s not surprising since it’s putting out more power. I mention this because I don’t know how it may affect the PS long term. My guess is it’ll be fine, but do it at your own risk.

Make sure your thermistor is properly placed, the kapton tape has not come loose, etc. You can add insulation to the bottom of the board. I read on here someone used corrugated cardboard. That might be all you need to do to get the temp you want. Don’t use regular fiberglass like you put in walls. It has acrylic binder in it and some types have formaldehyde as well. Don’t want fumes from either one of those. Mineral wool mat used for kilns is very good insulation. You can get it in 1/2 inch thick sheets. It would need to be enclosed somehow. If you look for that, there are two types. One has silica and the fibers are toxic if inhaled. The other is a newer type that is made from calcium, and I’m told, if you should happen to inhale any particles, they will eventually just dissolve so it’s a far better product.


#5

Dear Davef

Thanks for this advice…I will have a go at mine :slight_smile:
Kind regard

Antonia


#6

@davef I presume it is the particles that will dissolve and not the lungs :slight_smile:


#7

Hi Folks

Changed my Bed to PEI and now I can print at lower bed temperatures with ABS no problem. Bed gets up to 90 deg C and sticks down very hard. Problem solved.

Regards

Antonia


#8

Wanted to add some of what I did here in the hopes that others could use this information. I had trouble getting my bed temperature up beyond 80C, which was not great. I put pipe insulation tape on the bottom of the bed in two layers so it was about 1/4-3/8" thick with the aluminum side facing down. that got me to about 90C without any assistance.

Then I would take a piece of cardboard or styrofoam and lay it on top of the bed during preheat which could get me to 100-105 but it took a while, maybe 30 minutes or so. Obviously not ideal.

I found this thread and didnt even realize that you could adjust the power supply’s voltage… big “duh” moment for me. getting out my multimeter I saw that my meter was only getting 11.3 volts to the heated bed… well that’s not ideal. and knowing that a 10% tolerance in most electronic parts is relatively safe, i decided that if I could get my supply to output more than 12 volts, I could go as high as 13.2 and be ok.

However, my power supply, as I increased the voltage would top out at 12.8. But… I can happily report that i’m able to get to 105C in just a few minutes without the need for a bed cover to help keep the heat in. Happily printing away again now. Hope it helps someone with their ABS woes.


#9

What kind of pipe insulation? Can it be bought from home depot etc?
TIA


#10

That’s good to know. I have some, just haven’t tried it yet. Thanks!