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Different input voltage on RAMPS 1.4

Posted by LHelge 
Different input voltage on RAMPS 1.4
September 13, 2012 09:23AM

My printbed is heated by 3 x 10 Ohm 100W power resistors connected in parallel for a total resistance of 3.3 Ohm. I run the hotend on 12 V, running the printbed from the same source would result in ~45 W which is a little weak, I would like to run the heatbed on 24 V instead for ~175 W of power.

I control the printer with a RAMPS 1.4 board which, looking at the schematic, should be ok with 12 V on the 5A input for powering the steppers, hotend and fans and 24V on the 11A input to power the heatbed.

Anyone tried this who can confirm that it works?

Re: Different input voltage on RAMPS 1.4
September 30, 2012 04:01PM
I can confirm this works. Make sure there's a heatsink on the MOSFET and your 24v supply can provide enough current. Like you said the input labeled 11amp is for the heat. bed. I've been running my prusa with 15v to the steppers and 24v to the heabed (my Mk2 bed won't reach 110 c otherwise) with RAMPS 1.4 for the last 6 months without any problems.
Re: Different input voltage on RAMPS 1.4
October 21, 2012 02:38AM
I would mention that the 11A polyfuse is not rated for more than about 16V, so you can expect problems there in some cases. It sort of works, but if things fail, you can expect issues.

I run 24V for my whole setup (hot end & heated bed), so I removed the diode to power the Arduino. I also replaced both of my polyfuses with wire links and use external fuses that are easily replaceable, which gets around all of the weird issues that I see with polyfuses.
Re: Different input voltage on RAMPS 1.4
October 21, 2012 05:14AM
hi cefiar,

you still use 12v on steppers? or 24v?

are your stepper drivers hot? when mine was tested they go up to 70degC no/slight load ... not sure but mine looks kinda hot to me.
Re: Different input voltage on RAMPS 1.4
October 21, 2012 06:45PM
My steppers run at 24V, yes.

They do run slightly warm, but not at 70 Dec C.

I put a fan on the extruder motor as my wades extruder (an older style too) is currently made of PLA. If the motor warms up, the PLA around the motor screws warms up enough so that the motor pushes itself away from the larger gear slowly, till it no longer meshes. The fan keeps the motor quite cool, so this doesn't happen. I run the fan at about 10 volts, so not even at full speed.

FWIW: I simply undid two of the bolts that hold the motor together (diagonally opposite), and using some M3 allthread that I had laying around, attached the fan using 2 cheap M3 metal spacers, and securing the fan with some nuts. The allthread goes all the way through the motor, replacing the function of those two bolts, and the remaining two bolts keep the motor assembly from falling apart while I did it. Didn't even need a heatsink, as the airflow over the back of the motor was more than enough.
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