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24V with Ramps 1.4 questions

Posted by AVRkire 
24V with Ramps 1.4 questions
April 01, 2013 09:03AM
Hey everyone,

I have been thinking of upgrading to a 24V, 17A 400W power supply for my mendelmax, and I was hoping some folks can help me out with some questions.

1) Has anyone who has upgraded from 12V to 24V noticed a difference? This is by far my biggest question. I can see how it would help heat the bed up faster being able to use a 24V heater in place of a 12V heater, but the steppers are only around 4V steppers, so I am not sure this would actually do anything for the steppers, but would love some opinions.

2) Is 17A enough current? My current PSU is 12V 30A so this would be a current downgrade, but a voltage upgrade.

3) I read about removing D1 on my Ramps 1.4 board, but I am wondering if there is anything else that needs to be done either to the Ramps board, or the firmware, or anything else other than just a wiring to the new PSU instead of the old one? I read that removing the D1 that you can use up to 35V
Re: 24V with Ramps 1.4 questions
April 01, 2013 11:21AM
I posted most of this elsewhere, but it applies here so I've revised it a bit to hopefully give something definitive to reference. winking smiley

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.
Re: 24V with Ramps 1.4 questions
April 01, 2013 12:47PM
Thank you very much for all of this info!

So it seems it is far more complicated than a simple swap out of 24V for 12V.

I will need to make a lot of modifications to do this the right way.

I guess I will just ask anyone who has used both 12V and 24V, if is worth it to do the upgrade.

Starting from scratch I would definitely go the 24V route.
Re: 24V with Ramps 1.4 questions
April 01, 2013 04:01PM
You could do what I have done recently which is buy a dc-dc booster rated at 600w for £16. I run an atx psu which has plenty of power but runs at about 11.5v which means my pcb bed takes a while to heat and has a max of about 90c. I have the booster set to about 14.5v which is lower than the max rating of all my ramps components.

The increase of 3v increases my beds power from 100w to 160w which heats much quicker (5 mins to 85 rather than 15).

I leave everything else running on 12v to avoid any other problems but you could run your whole rig from it and experiment with voltages.

Just an idea.

Edited 2 time(s). Last edit at 04/01/2013 04:02PM by lazzymonk.
Re: 24V with Ramps 1.4 questions
April 03, 2013 02:15PM
I conveted my mendelmax from 12-24v and my heatup times are much faster. I think it's worthwhile though I learned the hard way a few things.

I popped one of my capacitors, they were rated for 16v, so check yours as cefiar suggested.

I have a budaschnozzle and set my PID_MAX to 64 (see Configuration.h) and run it at the full 24v (I didn't disconnect the + side of the hotend and hook up to a 12v power supply). This just makes it so instead of 100% on, it is on only 25% of the time.

You will have to re-adjust your stepper drivers to give less current, otherwise they will be LOUD! Adjustment is the same, just turn all the way down and then bump up until you are happy and not skipping steps.

Fans are now all upgraded to 24v fans. I do have 12v LED strips, which I bought a cheap voltage converter off of ebay (search for LM2596 - note this will not be enough to run a hotend or heated bed, but for fans and LED strips it is enough)
Re: 24V with Ramps 1.4 questions
April 03, 2013 04:46PM
mitchese Wrote:
-------------------------------------------------------
> Fans are now all upgraded to 24v fans.

Where did you buy your fans/what model are they?

I couldn't find any 24V fans at the time. For most things, I'd prefer 24V all round, and it removes the need for the converter in my current setup.
Re: 24V with Ramps 1.4 questions
April 06, 2013 12:39AM
i wonder if there is an easy way to hack one of those 12v 30a psus to run at a variable voltage like say 24 36 or 48 volts, has anyone compared the internals of a 24v vs a 12v to see if they are even different? i know i can run mine at 15v already by just turning the voltage adjustment knob.
Re: 24V with Ramps 1.4 questions
April 06, 2013 08:15PM
A problem you will most likely find is that technically while the drive circuitry should be capable of higher voltage, the components will let you down.

eg: A max of 15V in your supply is probably due to the fact that the basic design limits the voltage to 15V, specifically because many of the components expected to be used have a max voltage of 16V (eg: capacitors).

However, because the design takes this into account, simply replacing the 16V components with say, 25+V components won't get you higher voltages. Some of the components that are the limiting factor (specifically IC's, or power modules with a number of components on them) may not be available in higher voltage versions. Even if you can change all the supporting components to higher voltage ones, you may find that the number of components you need to change is a large portion of the PSU. This all adds up in the time required to do the change, plus the cost of the components, which may then make things rather expensive, even if it's a brilliant hack.
Re: 24V with Ramps 1.4 questions
April 07, 2013 01:57AM
Cefiar: The RAMPS fan is an 80mm I rescued out of an old laser printer I took apart. 24v is a very common voltage in old (read mid-90s) laser printers which can often be had for free and have all kinds of other goodies in them.

On my carriage I have a 60mm fan I got on Ebay for a song:
[www.ebay.de]
Re: 24V with Ramps 1.4 questions
May 04, 2013 05:37AM
I had put this on hold for a while, but I really need to go to 24 v, the time it takes to Heath print bed is just killing me.

So I bought a 24v PSU, and I also bought something called Taurino from REpRapDiscount, which is basically an Aurdjni Mega beefed up to handle the higher voltages.

They told me I can use the standard Ramps shield I am using now, but my concern is the fuses.

Can anyone recommend fuses for me, and tell me how to replace them?

Thanks!
Re: 24V with Ramps 1.4 questions
May 04, 2013 08:42AM
I would replace the fuses with wire links and put in line blade fuse (car fuses) on cables between the ramps and psu
Re: 24V with Ramps 1.4 questions
May 04, 2013 01:13PM
Thanks lazzymonk.

I am not the most electronically savvy, so let me make sure I understand this.

I would basically cut the leads of each of the fuses on the Ramps shield, and just make a direct connection with a piece of wire for each fuse?

Than, where I wire from my PSU to my Ramps shield input's, put two car fuses inbetween the runs?

Assuming this is correct, what volt/amp car fuses would you recommend?

I am using a 24V, 17A PSU.

Thanks much for your help!
Re: 24V with Ramps 1.4 questions
May 04, 2013 03:15PM
Thats exactly correct.

As for the fuses. As far as I am aware ( im sure someone will correct me if im wrong) most car fuses are capable of 24v so voltage shouldnt be a problem.

Current rating is a different matter. The way I would do it is is to work out how much current each input uses. Then work the which component is rated for the lowest current (dont forget about the cables), then find a fuse that is somewhere between the 2.

Im not sure if thats the best way to do it but thats how I would do it.
Re: 24V with Ramps 1.4 questions
May 04, 2013 03:46PM
Thanks again.

I'm or exactly sure how to do this calc.

Since my PSU is rated at 17amps, is it even possible to go above that? I would think the PSU itself has some type of fuse or breaker?

Do I calc all the inputs at the same time, or do I have to figure out how much amperage can be pulled at a given time by say the heat bed, the hot end heater, the motors, fans, etc?
Re: 24V with Ramps 1.4 questions
May 07, 2013 01:40AM
Do not use a fuse >17 Amps, as otherwise you provide no protection.

I'd put either a 10 or 15A fuse on the heated bed voltage input (usually labelled 11A), and at most 5A fuse on the input that drives your hot end & motors (usually labelled 5A).

Note: Connecting up a 12V heated bed to a 24V PSU is not a good idea. You really want a 24V heated bed for a 24V PSU. To run a 12V heated bed off a 24V PSU, you need a PSU that provides somewhere around 40-45 Amps, and you can expect that the MOSFET will cook itself if you don't have a good heatsink and fan on it.

If you want your 12V heated bed to perform better, try a 13.8V or 15V PSU instead. This is enough to improve it's performance fairly dramatically, but not enough to need a horribly huge PSU or pull very high currents.
Hi all

One question: Would it be possible to simply connect 24v to the 11A input for running a 24v heatbed without changing anything on the ramps? Or would I have to swap fuses and caps and fans and all?

Florian
Re: 24V with Ramps 1.4 questions
July 02, 2013 07:37PM
You can do that, yes, but you still need to change the 11A fuse on board. That fuse is only rated to a max of 16V.

Note: When you connect the power supplies to the RAMPS board, the ground lines get shorted together. This means that your power supplies are NOT independent, so they must support this configuration.
Hi Cefiar

Thanks for clarifying. I'll check my psu's specs.
Re: 24V with Ramps 1.4 questions
July 03, 2013 01:40AM
Most should be fine, but I have seen people "think" they can get 24V out of a PC PSU using the -12V and +12V rails (as there's 24V between them). It doesn't work (not enough current for a start), and if you use try and use the same PSU to run the 12V stuff as well then you can get all sorts of issues.

If you've got dedicated 12V and 24V PSU's or a proper PSU that puts out 12V AND 24V with a common ground, you'll most likely be fine. If you're worried, first check the voltage difference between the 12V DC ground and the 24V DC ground (should not be stable value), then try and measure the current between them (should be 0 or close to it).

There are other ways to check to see if your PSU's have independent DC grounds, so do a few google searches and you should find them.
Re: 24V with Ramps 1.4 questions
July 13, 2013 05:57PM
The info in this thread is fantastic. thumbs up
Re: 24V with Ramps 1.4 questions
November 01, 2013 08:48AM
Cefiar:

I'm having a heatbed issue, probably due to the heatbed resistence which is 1.7-1.8Ohm approx.
My kit comes from [www.reprap-france.com]. I have a power switching PSU (12V - 33A - 400W)
The power loss due to the resistence not being 1.2-1.6 is approximatively 15-30%.

Do you think that increasing the PSU voltage to 13-13.5V would be a solution, without comprise?

Thanks.
Re: 24V with Ramps 1.4 questions
November 01, 2013 08:50AM
compromise*
Re: 24V with Ramps 1.4 questions
November 01, 2013 11:26PM
You can usually run more than 12V into the RAMPS board, BUT you need to beware of the voltage from RAMPS that gets fed into the Arduino Mega.

If you've got a Mega Clone that can handle higher voltages (eg: Taurino Power, etc), then you can just do that without a problem.

If it's a standard Mega then you should be able to get to about 14V (input to RAMPS) without problems, but it all depends on the Mega, so it can be a really fine line. If in doubt, check the specs of the regulator on your Mega/Mega Clone.

Basically for the Mega, the voltage on the 5A input (as this input powers the Mega, via D1) is the one that matters. D1 drops the voltage by ~0.6V, which gives you a bit of leeway. If you've got a spare diode around, you could power the 5A side through a second diode to cut another 0.6V off the voltage going into the 5A input (make sure you put the Diode in the + wire, and the bar - aka the Cathode - goes toward the RAMPS board). This should give you a bit more leeway in voltage.

I would also check for any voltage loss in your wiring (use a voltmeter and measure it). If this is the case, you can probably replace some of your cabling with lower resistance thicker cabling (eg: RC cable such as from Hobbyking, etc).

Also check for a voltage drop across F2, as the closer they get to their current limit, the more likely they'll drop a voltage due to the nature of how they work.

Lastly, remember that the default FETs for RAMPS can get warm, and as they get warm, they will drop a higher voltage. If the FET for the heated bed is hot, put a heatsink on it (be careful it doesn't short to any other components) and make sure it's cooled by a fan. This will help with any voltage drop.
Re: 24V with Ramps 1.4 questions
November 22, 2013 04:11AM
Hi,

does anyone know if the Reprapdiscount Fan Extender is capable of 24V If the Ramps is on 24V, there will be 24V at the output that is labeled 12V, where the Fan extender is connecting to the power via a cable.


Gruß, Ralf

Mendel 90 breit, hoch, 24V

Meine Erfahrungen im EngineeringSpot-Blog: EngineeringSpot
Re: 24V with Ramps 1.4 questions
November 22, 2013 04:54AM
@ralfsteck: I built my extender based on THIS PART and according to the Mosfet specs found here it can handle up to 100V. I run my machine on 24V and it works fine. The Mosfet doesn't even get warm. The bed heats super fast compared to my old 12V.
Re: 24V with Ramps 1.4 questions
November 22, 2013 05:07AM
Argh,

then I fear I already killed the Mosfet on the Fan extender because if I read the spec sheet right, it only can take 20Volts :-(((

Am I right?


Gruß, Ralf

Mendel 90 breit, hoch, 24V

Meine Erfahrungen im EngineeringSpot-Blog: EngineeringSpot
Re: 24V with Ramps 1.4 questions
November 22, 2013 04:33PM
You are reading the spec sheet correctly, that's a 20V part.
Re: 24V with Ramps 1.4 questions
January 25, 2014 04:18PM
amazing post, I just fried my F2 fuse today and I run a 24V power supply. I am going to switch to a different fuse system as Cefiar suggested. Once again, you guys are awesome

V/R

ND
Re: 24V with Ramps 1.4 questions
January 29, 2014 09:30AM
Here was my solution for the F2 replacement.

Followed lazzymonk's idea and this is what it looks like:

Fried F2


Jumpers on where fuses used to be:


Put an inline metal blade fuse directly inbetween the PSU and Ramps (+) input:

Inline fuse holder


fuses


put in place


I am running a 10A fuse on the 11A side, and a 5A fuse on the 5A size. I decided to replace both because I didn't like the idea of any fuse having the ability to light on fire instead of just popping the fuse and shutting off. There was nothing wrong with the 5A fuse. I have been able to print with no power issues so it seems to be holding up. Can't say thanks enough to everybody here. Hope this helps out others.

V/R

ND
Re: 24V with Ramps 1.4 questions
February 10, 2014 06:56AM
If you need more power on the heat bed only why not run it on AC off of a suitable stepdown transformer and use the 12v output
of the RAMPS to power a SS Relay to switch the primary of the transformer?
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