RAMPS 1.4 Umbau auf 24V Betrieb

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Cefiar
I posted most of this elsewhere, but it applies here so I've revised it a bit to hopefully give something definitive to reference.

The main things on a RAMPS that are affected by a voltage other than 12V are as follows:

1. PTC fuses (F1, F2).

The PTC fuses each have their own voltage ratings. The MF-R500 (5A) PTC fuse is rated to 30V. The MF-R1100 (11A) PTC fuse is rated only to about 16V. You may want to replace them with real fuses, or wire links and then put real fuses between your PSU(s) and the board. If you're running stuff directly instead of via the RAMPS board, you should make sure to put a fuse in between your PSU and the devices, since you're bypassing any possible fuse on the RAMPS board. (eg: Heated Bed via an Solid State Relay).

Note: I have seen PTC fuses catch fire if they pull too much current, or have too high a voltage across them. BEWARE! particularly of F2 and it's 16V rating.

2. Voltage inputs (5A and 11A) & the Arduino Mega.

The 11A input ONLY runs the heated bed (D8) output, and no other electronics. The 5A input runs the stepper drivers, the D9 (fan)/D10 (hot end) outputs and via D1 the Arduino Mega. If you remove the diode D1 you have to power your Arduino Mega separately, but you can use higher voltages on the 5A input. Some Mega clones can take 24V inputs, but most Mega's only take about 15V before they get too hot and/or fail.

You can run the 11A input on 24V and the 5A on 12V if you have either two power supplies or one that produces both voltages. If you are using two power supplies, they will be tied together via the RAMPS board on the ground pin. In 99.9% of cases this should be fine, as long as the PSU have independent grounds (some cheap knock-offs do not). You can also do the reverse if you remove the diode D1, assuming other components are rated appropriately.

Note: You don't have to use 12V or 24V specifically. I know people that use 13.8V supplies with no other changes, and a number who use 19V for fairly specific setups.

3. Capacitors.

The caps you need to check are C2, C3, C4, C6, C7, C9 and C10. The others (C1, C5 and C8) are only connected to 5V off the Arduino, so don't need high ratings. Some pre-made RAMPS boards are sold where the caps are only 16V. Caps will explode if they go over their rated voltage and the electrolyte in them is usually toxic and may be corrosive.

4. Heated Bed/Nozzle/Hot End/Fans.

Heated Beds and Nozzles/Hot Ends are simply wire heaters (using wire or a resistor to heat up the part) - even the cartridge type nozzle heaters. They have a set resistance. The more voltage you put across them, the more current they will draw, and the more power out you will get.

If you change the voltage more than 1-2 volts, you want to take this into consideration. Putting 24V across a Mark II PCB bed (which can have a resistance of as low as 0.8 ohms) draws a LOT of current: ~30 Amps, producing 720 Watts!

12V across the same bed only draws 15 Amps producing 180 Watts.

The difference for the nozzle/hot end is similar, though much lower currents are drawn all round.

For voltages such as 24V, you might want to consider:
- 24V Kapton heaters for the heated bed - These draw more power (usually 200-220W) allowing things to heat up faster, but not a huge amount more.
- Nozzle/hot ends that have a resistance of between 22 Ohms and 27 Ohms (instead of between 4.7 Ohms and 6.8 Ohms for 12V).

Fans can run at higher voltages, but it tends to wear them out (particularly DC motors. I would not recommend using more than 2-3 volts over a fan's rated voltage. They will likely be more noisy, as they will most likely spin faster, moving more air. You can either work out the current draw for the fan and then put a resistor in series, or you can find 12V somewhere to run the fan.

All the D8/9/10 outputs on RAMPS have a +V side that is always on. If you're running 24V in the appropriate input for that output (see above), it will be 24V. The FET (which acts as a switch) connects the device to ground when it gets a signal from the Arduino. This means you can disconnect the +V wire from a specific output, and run it directly to another power supply at a different voltage, so you can run the output at a different voltage (eg: 10-12V for a fan).

Some power supplies have multiple outputs, or you can buy DC-DC converters that will down-convert the voltage for you. Just make sure you get one where the ground on the input of the converter is connected to the ground of the output of the converter (common ground). Some of the 24V-12V DC-DC converters used in trucks (for connecting car stereos) are suitable for this, as long as they have a common ground.

Note: If you want to work out the calculations for other voltages (eg: things like how much a specific heated bed will draw), it's all just Ohms law. V=I*R (or I=V/R) and P=V*I. I know people who use 13.8V supplies as very simple way of overcoming issues with things like the PCB heated beds not reaching top temp easily, as the extra voltage can raise the heating power significantly (for 12V -> 13.8V, it's about 1.3 times the power output) using the same components.

5. Stepper Motors.

24V on motors should give you slightly faster axis moves, though it depends on the motors to some extent. The stepper drives only supply a fixed current. Voltage seems to make a difference if the steppers require more than about 1/4 of the supply voltage (at least in my experience with Pololu A4988 stepper drivers). Some steppers only need around 2V, so they run fine at 12V, but others that need higher voltages (3+ Volts), so increasing the voltage can make a lot of difference, particularly in the speed of each step (even with lower voltage rated steppers.

6. Wiring.

If you use 24V components (heated bed & nozzle/hot end), you don't need as high a current. This means thinner cabling is possible. For the heated bed this means you can most likely use decent 10A cable without any heating of the cable. For the nozzle/hot end, you can use slightly lighter, more flexible wiring than you might normally.

Also, as the voltage is higher, the resistance of any wiring is much less of an issue, as the wiring resistance is a much smaller component of your overall resistance. This means less cable losses, so you get more power where you need it.

If you need to keep your PSU at a distance from the machine, 24V is a much better option.

Summary

I myself use 24V for all machine functions. I find the motor speed is faster, though the motors can generate more heat. My hot ends use a 22 Ohm resistor and so heat up slightly faster than a 6.8 Ohm resistor does at 12V. I also use a 200W 24V Kapton heater (was bought from Trinity Labs) for my heatbed, which heats faster than a Mark II PCB does using 12V. I use a DC-DC converter to run all the fans off, set to 10V (slightly quieter operation, but 100% reliable).

I am using a 24V 17A PSU and it has worked flawlessly until I dropped it recently (I've put it a plastic box, so it's not dented but still, a drop is a drop). It now makes a high pitched buzzing noise sometimes when the heated bed switches on (while everything else is running), which I think means it's drawing close to it's current limit. I have found that running the PSU first for a while to heat it up stops this from happening, but I intend to replace it soon.

All in all I'm very happy with the 24V setup and I will definitely be using a 24V setup for my next printer.

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Skimmy
Wer weiß auf die Schnelle, wie hoch die Vref der Treiber bei 24V sein muss?