One of the first things you need to do to complete a Wanhao Duplicator I3 Plus (or Monoprice Maker Select Plus) conversion to work with RAMPS is modify RAMPS to work with a 24 volt power supply. The other option is to pull out the 24V supply and put in 12V. But that would require changing some of your other hardware and you also lose any advantage that the 24V supply gives in the first place. For me, I chose to keep the (theoretically) better 24V supply and modify RAMPS.
If you have not already bought your RAMPS board, please read through this whole post before purchasing. After reading you can make a better choice and save a little work by buying the right one.
Also, don’t power up the RAMPS board until you have completed all the steps in this post. In a later post I will show you how to wire everything up. It is probably best to wait until you get to that point before applying power.
Choosing a RAMPS Board
You should assume that your RAMPS board is designed to work with 12V. They do make boards that can accept both 12 and 24 volts, and you might want to buy one, but it is best to assume your board is 12V and confirm that it will work with 24 before plugging in the higher voltage to test.
The cost of a 12 volt board with stepper drivers and LCD screen is the same as a 12-24V RAMPS board by itself. All the 12-24V boards that I found had the Arduino Mega integrated into the same board as the Pololu shield. I personally like discrete components (as much as is practical) so that if one part dies it can be replaced without having to replace the whole system.
Therefore, my preference was to buy a $40 kit that included the Arduino, Pololu shield, stepper drivers and LCD that needed to be modified for 24V. As opposed to $40 just for the Arduino/Pololu integrated system without drivers and LCD but was already setup for 24V. You will have to decide that on your own. If you buy the 24V setup, then you can completely skip this step. But you will have to figure out the LCD and stepper drivers on your own.
For the rest of this step, I assume you have a 12V RAMPS board. You can get them at the supplier of your choice: Amazon, eBay, dx.com, AliExpress or Gearbest. There are many other places to get them, but that should get you started. I chose Amazon for this because I wanted it quickly and for RAMPS, stepper drivers and LCD in one package buying from the Chinese shippers and waiting up to 2 months was not much cheaper (if at all).
Capacitors, Fuses and Diode
Assuming you have a 12V RAMPS board, there are three types of components to check or modify to make it work with the higher voltage supply: capacitors, fuses and diode.
In the image above (you can click it to get a larger image), you will see various components highlighted with circles and arrows. Refer to this image for the parts below.
There are two different sets of large, electrolytic capacitors. They are physically different sizes which should make it easier for you to identify the different ones. In the image above the capacitors circled in yellow are the ones you need to be concerned about. The 3 circled in green should not need to be checked or modified in any way for working with 24 volts.
The 6 yellow-circled capacitors should be rated at 48V or higher. Your’s may say something like 36V, 100V or some other cryptic code for the voltage rating. A lower rating than 48V does not mean that the board is unusable. However, if they are less than 36V you really should replace those capacitors. And you can expect it to not work at all, or very unreliably until it fails, if your capacitors are 24V or less.
I am not an electrical engineer, but what I have read is that you will want to have capacitors that are rated for at least double your working voltage. In our case the working voltage is 24V, therefore these capacitors should be rated for at 48V. Currently, mine are 36V and I am going to take the risk and run with them like this. They should be fine, but we have been warned.
The reason we don’t have to worry about the green-circled capacitors and their lower rating is because they are not using the 12 or 24 volts from our power supply. That segment of the board is stepped down to 5 volts. Therefore, whatever the manufacturer originally installed for that section of the board should be sufficient.
The diode (pointed at by the pink arrow) is the path through which electricity goes into the Arduino and powers it. Since most Arduinos are rated for up to 12V of power, we don’t want to feed 24V into it. Therefore, if we get rid of this diode then we stop the 24V from going through the Pololu shield and into the Arduino. That means that after this step is complete we need to find a way to power the Arduino separately with 12V.
Removing the Diode
You can remove the pink-arrow-highlighted diode by snipping the wires on either side of it or by desoldering it. It would be very hard to get a pair of wire cutters in the space to snip the wires on the diode, but it is possible. I chose to desolder mine. You can watch a video or read an Instructable about desoldering components if you don’t know how.
My board had another diode next to the poly fuses. You should leave this one in place. Only disable the one indicated by the pink arrow.
Supplying 12V to the Arduino
Now you have to power the Arduino in some way. The way I chose to do it, and the way I recommend, is to use a step down power converter. Also called a DC-DC or buck converter. What this does is take the 24V from the main power supply and converts it (steps it down) to 12V that can be used for the Arduino (and cool looking 12V LEDs). I had already installed one of these in my printer for the purpose of powering LEDs. So this was an easy route for me.
Just because something is easy, doesn’t mean it is best. However, in this case, I think this is the best way to go about powering your Arduino. The other option is to have an external 12V source for the Arduino. It can be a battery (which could leave you with a dead Arduino in the middle of a print) or it could be a second supply plugged into the wall (which is an extra external component). In either case, you need to tie the ground of the battery or secondary supply to the ground of the 24V supply. Too much work.
Use a Step-Down / DC-DC / Buck Converter
A small buck converter will take the 24 volts from our current supply and easily convert it to usable 12 volts. That is what it is designed to do.
My converter (shown above) can take up to 32 volts as input. Then there is a screw adjustment to dial in the output voltage.
Tie Into the Power Supply
I soldered wires from the IN+ and IN- side of the buck converter and ran those to the extra screw terminals on the power supply. Wasn’t it nice of them to leave an open spot for us to use? Make sure the IN+ goes to the 24V+ terminal and the IN- goes to the 24V- of the power supply. The following picture shows where I tied in my buck converter. The first and fourth screw terminals (from the left) on my power supply were empty. These were the ones I used.
Turn the adjustment screw (actually a multi-turn potentiometer) on the buck converter until your volt meter reads 12V as output voltage on the other side of the DC-DC converter. That is where you will get the 12V that will be fed into your Arduino’s barrel jack.
Protect From Shorts
I printed a small sled for the converter to sit on and then hot glued the converter to the sled and sled to the frame of the printer. (This was when my printer still worked.) For the time being, you can just put tape on the bottom of the buck converter to keep any solder joints from shorting out until you can print an insulating sled.
With the diode removed no voltage will pass from the Pololu shield to the Arduino. Therefore the Arduino will get all it’s power from the 12 volts of the buck converter. Since it is all tied into the same power supply, when you turn on the printer it will turn on all the different components like it did originally. The only difference is that part of the system is getting 24 volts and part is only getting 12 volts.
You need to check that the fuses on your RAMPS board are capable of handling the higher voltage. The fuses are indicated with the red arrow in the picture above. One of these fuses on my board (the one closest to the power plug) needed to be replaced. It can be replaced with another resettable fuse of an appropriate capacity, or a different fuse type altogether. In my case I chose to use a fuse made for car applications.
The original fuse on my board was an MF-R1100 poly fuse. It is rated at 16V and 11 amps. Because the voltage is lower than what we need, then this one must be replaced. The other poly fuse on my board is rated up to 30V; therefore, it does not need to be replaced.
I replaced mine by desoldering the current fuse and making a holder for an automotive fuse. I did this by soldering 2 wires of about 1-1/2 inches (length is not critical) to the board. Then I soldered the other end of the wires to female spade connectors appropriately sized for my fuse. You will see in the picture above that I am using a 5A fuse. I don’t know that this is the right amperage. But I chose a low number to start with so that I can ensure it will burn out before I burn down my house (at least from that component). I will update this when I figure out the right amperage if it needs to be greater than 5A. But at this time I have not seen a definitive answer as to what the new fuse rating should be for 24V.
I said at the beginning of this post that after reading through this you will have a better idea of how to make a better RAMPS choice.
As mentioned previously, you can buy a RAMPS setup that is already made for a 24 volt supply. That is probably the simplest thing that you can do. However, I prefer to have as many discrete components as is practical.
If you are going with one of the cheap RAMPS setups (there are many for $40 or less on Amazon), then here are some of the things to look for.
- Has 36V or higher capacitors (preferably 48V or greater).
- Includes LCD (unless you really don’t want one).
- Includes the stepper driver modules.
- Includes the Pololu Shield and the Arduino Mega.
The cheap ones will have to be modified. But if you aren’t wanting to do that, then you are missing out on the fun.
I was helped through this step by reading other forum questions and watching videos. This video is one that made sense to me after I had done a lot of other reading. It doesn’t tell you everything you need to know, but it is a great start with this step.
Maybe some of these questions that others have asked will have an answer that makes this step clearer. Here is a Reddit question about the conversion. This forum thread gets a little deep in the weeds, but reading the first response to the question may help clear up what I have posted above.
You can also read this very detailed explanation. It gets into much of the theory as to why you would want to do the conversion. We already know we need to because our printer is already a 24V printer and we have a 24V power supply.