Need more power!

* RAMPS 1.4 from Gadgets3D
* G3D A4988 drivers or
* Pololu DRV8825 drivers
* MK2A PCB heat bed
* Marlin_V1 firmware
* Nema 23 stepper motors wired bipolar series
* 12V 500W ATX power supply or
* 24V-400W switching power supply.
* G3D Buda style hot end w/ 12 (24?) Volt cartridge heater
* Latest version of Slic3r as of March, 2013 (pre-compiled for Windows)
* Latest version of Pronterface as of March, 2013

This is a question about supplying power to the ramps board. I've built a repstrap with acme lead screws geared down 2.75:1 with belt pulleys and I've been fighting feed rates for a while now. I'm sure you understand that I've had to use an unusually high steps-per-unit setting in the firmware and this in turn has caused problems with attaining high feed rates. I've discovered that in order to use a less-than-painfully slow feed rate, to keep from missing steps, and altogether stalling the steppers, i've had to use higher voltage. I've tried 24v and my useable feed rate in Pronterface went from around 110 mm/min. at 12v to 875 mm/min. but it's also putting 24v through my hot end which I don't like. I'd like to use 12v for the hot end, fans, and heated bed (24-36v for the stepper drivers) but I don't know how to accomplish that. I haven't checked to see if my ramps board has caps that will tolerate higher than 24v but, aside from that, I have Pololu DRV8825 drivers rated for up to 45v ready to be installed. I'm confident that what I want to do here can be done. I'm also sure that there are other ways like reducing the micro stepping, different gearing, or external drivers but I'd like to know how to do what I would like to do with what I have already.
Many thanks!
joe

Note that when you go to the DRV8825's, the jumper settings for 1/16th step on a Pololu A4988 are the equivalent for 1/32nd steps on a Pololu DRV8825, so you'll definitely want to change your microstepping jumpers at that point. You could also try going to 1/8 or 1/4 feed rates stepping if you're using lead screws, as this should allow you to reduce the steps/mm in the firmware by 1/2 or 1/4 their current values accordingly.

As for using a lower voltage for the heater:

There are two pins from the RAMPS board for each FET output.

One is the FET side that switches to ground. The other is the input voltage to the board.

Simply wire one end of your hot end to the FET output, and the other end to a convenient 12V output from your PSU (instead of the 24-36V from the RAMPS board).

I use this to run my fan output at ~10V instead of the 24V I run everything else at. There is no reason you can't do this for all your switched outputs if that will do what you want. You will still need to check the voltage ratings on the caps though.

I would recommend if the board has the default STP55NF06L FET's that you replace them with better FET's like IRLB8743's. They have a much lower RDS(on), a lower gate saturation voltage, and handle higher switching speeds reasonably well. This way you'll get the most out of your 12V switching.

Notes:
Your PSU's will need to have a common ground between them.
The PTC fuses 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.
The 11A input ONLY runs the heated bed (D8) output, and no other electronics. You can feed 12V in that, while feeding 24V into the 5A input. The 5A input runs the stepper drivers, the D9 (fan)/D10 (hot end) outputs and via D1 the Arduino Mega. As long as you supply D9/D10 with their own supply directly, and remove D1, you should be fine to run 36V in, assuming the caps are rated higher than that.
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.

Edited 1 time(s). Last edit at 03/14/2013 11:34PM by Cefiar.

Thanks so much for your attention Cefair. If I may ask further…

Quote
Cefiar
also try going to 1/8 or 1/4 feed rates if you're using lead screws

Do you mean feed rates or micro stepping? I did, in fact, have to reduce the default feed rates in Slic3r from 60 mm/sec. to 14 in order to keep from missing steps and such. I'm pretty sure you mean quarter stepping or eighth stepping because that's the only way to reduce the steps-per-unit, right? But yeah. I'm not completely clear on just how 'plug and play" the Pololu's are yet either. I'll be reading the manual

I'd better go one question at a time so I don't get lost. The later it gets, the dumber I get.
Thanks!
joe

I just swapped out to DRV8825's on my X and Y axes and the difference is night and day. The little green A4988's couldn't give me enough current for my 1.7A NEMA 17's (same rating as your keling's). With the Vref properly set the 8825's have been beautiful. I'm using these from panucatt, and they're pretty damn good.

But since you're using screws why not use half-step or quarter step since they have much more resolution per turn than a belted machine? But at speed there may be other problems...whip?

For reference I'm running the steppers and hotend at 24V a well (heated bed is AC), powering the rest via USB.

---

- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

Yeah. I'm not a big fan of Panucatt. I don't have nice things to say about that company. Thanks for the input Akhlut. It's encouraging to read that someone else has been successful with what I want to do. I googled and searched many places to find info on this stuff but never quite found a match. You guys are awesome though. I was worried that I'd piss off the knowledgeable guys by asking the same darn question hundreds of other newbs have already asked. I'm going to first try less micro steps like Cefair and you have suggested and see where it goes from there. Thanks so much for your help guys. Couldn't do it without you!
joe

New video So here's my machine moving at 1200 mm/min. after changing the y driver to full step and the x to eighth step. I set up end stops for the x and y and they work for homing but as I ran a test program, the y was stalling and it eventually crunched the switch. Anybody have any idea why it would work as a homing switch but not a limit switch?
Thanks!
joe

How do you make a common ground between a 12 volt and 24 volt PSU? Is it as simple as tying the two together?

Edited 1 time(s). Last edit at 03/16/2013 02:00PM by cncjoe.

cncjoe Wrote:
-------------------------------------------------------
> I set up end stops for
> the x and y and they work for homing but as I ran
> a test program, the y was stalling and it
> eventually crunched the switch. Anybody have any
> idea why it would work as a homing switch but not
> a limit switch?

Marlin is configured to ignore the endstops unless it's homing.

Missing steps usually means insufficient stepper current or a mechanical problem.

Do you have this section correctly filled out for your machine in configuration.h?

#define min_software_endstops true //If true, axis won't move to coordinates less than HOME_POS.
#define max_software_endstops true //If true, axis won't move to coordinates greater than the defined lengths below.
// Travel limits after homing
#define X_MAX_POS 205
#define X_MIN_POS 0
#define Y_MAX_POS 205
#define Y_MIN_POS 0
#define Z_MAX_POS 200
#define Z_MIN_POS 0

#define X_MAX_LENGTH (X_MAX_POS - X_MIN_POS)
#define Y_MAX_LENGTH (Y_MAX_POS - Y_MIN_POS)
#define Z_MAX_LENGTH (Z_MAX_POS - Z_MIN_POS)

As far as a common ground a single jumper between the 12V supply ground and the 24V supply ground should suffice.

---

- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

Thanks AK. I'll check that out. I like your blog, by the way.

Thanks Stephen. So, ideally 'just don't miss steps' but can't that be reconfigured just in case? Actually, feedback would be ideal; like linear scales but that's down the line.

I need to do that Cefiar Mosfet hack. Can I just tie the 12V and 36V ground of the power supplies together? The caps on my ramps shield are 35V. I know what I know but I don't know what I don't know and logic escapes me sometimes! And if I paid more attention to what people write, life would be easier! Sorry AK!
Thanks so much guys!
joe

Edited 1 time(s). Last edit at 03/16/2013 10:11PM by cncjoe.

This is what I have the end stop stuff set to. I assumed that since I'm sending the axis to the furthest negative travel limit for their home positions, that would be zero or MIN_POS(ITION) because I don't want to extrude or machine using negative coordinates. My experience with the Cartesian plane is y+ is away from me looking at the front of the machine. X+ is to my right, and z+ is like a tree grows (up). If I position my part further away from me on my table I like to think that I've placed it further y+ although my TABLE moves towards me for y+ moves. All that said, my table moves away from me towards the home/limit switch when I home the y to it's furthest negative travel limit, my x axis moves to my left towards the limit switch when I home it to it's furthest negative travel limit, and I haven't set up home/limit switches for my z yet.

// ENDSTOP SETTINGS:
// Sets direction of endstops when homing; 1=MAX, -1=MIN
#define X_HOME_DIR -1
#define Y_HOME_DIR -1
#define Z_HOME_DIR -1

#define min_software_endstops true //If true, axis won't move to coordinates less than HOME_POS.
#define max_software_endstops true  //If true, axis won't move to coordinates greater than the defined lengths below.
// Travel limits after homing
#define X_MAX_POS 381
#define X_MIN_POS 0
#define Y_MAX_POS 584
#define Y_MIN_POS 0
#define Z_MAX_POS 150
#define Z_MIN_POS 0

#define X_MAX_LENGTH (X_MAX_POS - X_MIN_POS)
#define Y_MAX_LENGTH (Y_MAX_POS - Y_MIN_POS)
#define Z_MAX_LENGTH (Z_MAX_POS - Z_MIN_POS)

// The position of the homing switches
//#define MANUAL_HOME_POSITIONS  // If defined, MANUAL_*_HOME_POS below will be used
//#define BED_CENTER_AT_0_0  // If defined, the center of the bed is at (X=0, Y=0)

//Manual homing switch locations:
#define MANUAL_X_HOME_POS 0
#define MANUAL_Y_HOME_POS 0
#define MANUAL_Z_HOME_POS 0

As Akhlut said, you should just be able to tie the grounds together.

I would however do this directly between the PSU's, and then try them out WITHOUT them connected to your electronics.

The wire you use to tie them together should NEVER get hot. If it gets hot, you've got a lot of current flowing between the two supplies, which indicates that the Ground on the DC side isn't independent.

The best way to test this is to use a multimeter in place of the ground wire initially. First, set it on "DC voltage". If you see any large voltages, and they "stay" at that voltage (don't fluctuate) then you may have a problem. If it's negligible (eg: <0.2V), change the multimeter to "DC current" (10A scale - may require you to move the probes on the meter about). As long as there is almost no current flowing, you're good to go. Note that most multimeters have a 10A fuse on the 10A scale, so if you draw too much current the fuse in the meter may blow (protecting your meter).

Note: 99% of the time it's not really necessary to test this, but I put it here because it's better to know how to test it. The issue is that some really cheap supplies tie some internal DC voltage line to the AC ground line. If they do this, usually it's DC ground, but in some rare cases it's some other voltage which causes the current to flow from the DC ground of one PSU to the other.

I hooked up the 12v to the 11A connection and the 24v to the 5A connection then tested the heated bed. The led on the ramps and the led on the bed blink and when they blink the lcd pulses and pronterface stops communicating with the ramps. Any ideas?
Thanks !
joe

Have you removed Diode D1?

If you're using >12V on the 5A connection, you MUST remove D1, else you may fry your Arduino Mega (depends on the mega/mega clone in question). This also means you cannot run the board without a USB power source (eg: a PC) unless you somehow connect up power to the Arduino Mega (eg: via the DC socket on the side of the Mega).

I just cut one leg of the diode and bent it away a little. I didn't desolder it...