Power Supply Confusion

[dmo]

This is my first post, it may be long but please bare with me. I really need help figuring out the right power supply. I have been digging through the threads on power supplies and haven't found one that gives a clear accurate layout on the options. There seems to be 3. I bought my Rostock in October 2015 and it shipped with the 450w ATX 22A . Like everyone I found this to be underpowered. Using a cover on the bed I could get the temp up to 100 but couldn't sustain it. There was not enough power to heat the bed and hot end at the same time. I went digging in the forums. I found a post that the ATX supplies requires a 50w lightbulb to override the power management but for a newbie I didn't quite understand this. I looked into doing the 24v supply, since I'm not an electrician I was nervous about veering that far off of the stock design. I then found a post about upgrading the 12v ATX to a better 12v ATX. People were saying they were heating their beds to 100c in 10 minutes still using 12v. That sounded like the best option so I spent $65 on a Sentey Metal Blade Power 750 Watts 80 Plus Bronze. To my dismay this made no difference. I wish I would have seen a post that SeeMeCNC had a new supply they were using. So here are my questions.

#1 Is there some kind of power management limiting what I can get out of my new Sentey 750w ATX supply. (such as hooking up a lightbulb) or using different wires coming out of it. For some reason people are saying 12v will do the job?

#2 Should I buy a supply like the new one SeeMeCNC is using? It's half the wattage but it has more amps. Are the amps what makes the difference? Amazon has them for $25.

#3 Is 24v the only way to go and down the road I'll need the power if I want to do other upgrades?

Being a newbie trial and error is a big part of learning the printing process so a bed that heats up quickly and can maintain the heat is even more important. Even though I'm not an electrician I'm very good at following instructions and enjoy learning. Thanks

[IMBoring25]

The ATX power supplies are more complex. They may provide only a certain wattage through certain wires or provide rated wattage through some wires only when there's a load on another set of wires (hence the light bulb). To give rated wattage on the monster ATX you got would probably take connecting a lot of different wires.

The LED PSUs are simpler. Subject to the voltage adjustment screw, if they're able to deliver the required amount of power/current, they will.

You can stay 12V if you want. 29-30 amps would be a good rating. That should get you attaining and holding 100 or so. If you want to do exotic filaments that will take much more than 100 on the bed I'd go to a 24V 30A supply and quality SSR, but it's not a cheap upgrade.

[Tincho85]

I agree with IMBoring25.

Before converting to 24v I too tried with a Sentey ATX PSU. But I never could stabilize the loads. The psu kept shutting down when turning the bed or the hotend on.

If you don't want to do the 24v upgrade, get a 12v 30a switching psu. With the sdjustment screw you can increase / decrease the output voltage. I've found this type of psu way more simpler and reliable than modern ATXs.

Also, while printing. Check the loads going from the rambo to the heated bed wires. If they are under 11v the psu is not up to the job.

[nitewatchman]

The overriding issue however is still the resistance of the Onyx Bed. It is about 1ohm. No matter how big the power supply is in watts or amps at 12VDC the thermal output will only be 144watts. Increasing the voltage while maintaining constant resistance will increase the thermal output of the bed by the formula W= (V*V)/R.

So the biggest bang for the buck so to speak is to raise the bed voltage and any increased amount helps by the square of the difference. A simple increase to 15VDC increases the bed thermal output to 225 Watts. For example at 20VDC that same Onyx bed delivers 400Watts or 2.8 times more heat. The same is also true in reverse, any voltage loss below 12VDC causes a very significant drop in the thermal output of the bed.

I chose to upgrade after going down the same road with a Corsair 750 p/s initially. While slightly better than the stock p/s, dish towels and heat guns got old. About a year ago I decided to convert to a 24VDC Bed and have not regretted it and nor had any problems. Depending on how well you scrounge, it should cost about $100 or less. Biggest mystery and cost for most is the SSR (Solid State Relay) and it MUST be a DC/DC type. I have used Crydoms in machines and machine tools and never had an issue or failure. I used a Crydom D1D40 in my printer. I buy these up whenever I can, average cost for the last 10 or so is about $20. I test them all and have only had on bad one out of 30 or so and it was mechanical damage. I used a Meanwell 24V-500W p/s from eBay, made an offer for $36.63 and it was accepted. Used a 24VDC to 12VDC converter from Amazon to supply 12VDC to the Rambo keeping everything other than the bed dead stock. Once in place you will not notice any difference in operation or behavior of the printer other than it get hot fast.

The only trick is to turn the voltage adjustment screw down to lower the bed load a little (remember W=(V*V)/R) not exceeding the 500W capacity of the p/s. This gives ABS bed heat times (100C) in about 5-6 minutes. PLA (70C) in half that.

Either increasing the voltage to 20VC or so or decreasing the Oynx bed resistance are the only two real solution although others and myself are looking at Silicone heater pads. The pads run on 120VAC (again and SSR is required) and have some fitment issues. http://www.amazon.com/KEENOVO-Circular- ... +pad+round

If you would like to tackle this sketches, advise, pictures and assistance is available upon request.

[dmo]

Thanks everyone. I'm starting to understand now, very good explanations. I think I'm going to go the 24v direction. I'll start tracking parts, and digging in the forum. Any other links or directions would be great.

[mattquist]

I'm having the same problem with my new machine. I can't get above 70c. Again Gary, your explanations shed light on my confusions! What I don't understand is why not just run a 24v power supply directly into the Rambo. From what I've read on the Wiki, the Rambo is capable of accepting a 24v input, and then I would assume the firmware will output the appropriate voltage to the motors, hotted, etc. Am I missing something, or will this not allow 24 volts out to the bed?

[Polygonhell]

I'm having the same problem with my new machine. I can't get above 70c. Again Gary, your explanations shed light on my confusions! What I don't understand is why not just run a 24v power supply directly into the Rambo. From what I've read on the Wiki, the Rambo is capable of accepting a 24v input, and then I would assume the firmware will output the appropriate voltage to the motors, hotted, etc. Am I missing something, or will this not allow 24 volts out to the bed?

The general consensus, is that many of the RAMBO parts are borderline for 24V operation, you'd also be drawing of the order of 500W (20+A) into the Onyx, I'm not sure the terminal blocks are rated for that.
As a result most people who run 24V's use it just for the bead and use an SSR.

[mhackney]

Also, you would have to make sure your fans, hot end and any other add-ons (LED lighting) are 24V or use a 24-12V convertor like the one I posted in another thread last week.

If you do go 24V for the Onyx PLEASE use an SSR and DOUBLE PLEASE make sure you get an appropriate SSR for this application. I literally had one blow up and catch fire. Unless you know exactly what you are doing, please read this post I did in December and use the recommended Auber 10A 100A #MGR-1DD80D100 SSR. You can read the thread to understand why not all SSRs are created equal and why the Auber is the one to get. At $19.95 it isn't worth risking your home and/or life to save a few bucks on an SSR that will likely fail.

[mattquist]

I'm having the same problem with my new machine. I can't get above 70c. Again Gary, your explanations shed light on my confusions! What I don't understand is why not just run a 24v power supply directly into the Rambo. From what I've read on the Wiki, the Rambo is capable of accepting a 24v input, and then I would assume the firmware will output the appropriate voltage to the motors, hotted, etc. Am I missing something, or will this not allow 24 volts out to the bed?

The general consensus, is that many of the RAMBO parts are borderline for 24V operation, you'd also be drawing of the order of 500W (20+A) into the Onyx, I'm not sure the terminal blocks are rated for that.
As a result most people who run 24V's use it just for the bead and use an SSR.

I know I'm the noob around here, so, just help me understand cause I'm a little slow.....

My Rambo 1.3 specs out at with the inputs taking up to 35volts:
Power
Three independent power rails for flexible input power configurations
Heated Bed, 15A 12-35V
Extruders + fans and logic, 5A 12-35V (fuse can be exchanged for up to 10A capacity)
Motors, 5A 12-28V (fuse can be exchanged for up to 10A capacity)
Built in SMPS for 5V generation from Extruders + fans and logic

and I was looking at this power supply (24v, 14.5 amp) for $35. http://www.amazon.com/dp/B005CLDOW8/ref ... 8CB9XRDRP0

I know I will need to run a small converter for lights and fans, but other than that, I'm just not getting it. This seems so much simpler. Is it because of a newer firmware on the Rambo that older models didn't have this flexibility, or this won't provide the optimization to hit 100-115C, or am I just an ignorant buffoon with a thick skull?

[Polygonhell]

The 35V number is based entirely on the fail voltage for the stepper drivers.
I would not run 24V through a RAMBO board, the hot end heaters and heated bed would have to be changed.
The resistance of the ONYX is a little over 1Ohm, the power draw on that for a 12V supply is 12A for a total of 144W, at 24V that's 24A for a total of 576W, thee power supply you list would power down as soon as the heated bed was turned on.
If it didn't you have the issue of the current rating on the heated bed connector, it almost certainly isn't rated for 24A and neither is the MOSFET driving the bed.
The sames true of the hotend, the base hotend is rated at about 3 ohms, so at 24V it draws Abotu 8 amps.

It's OK to say that the Rambo will take 35V input, but you have to ensure every component on the board is compatible with the things drawing power from the board.

[Eric]

Actually it says 28V for the motor input, and I'm not sure why. The drivers should be ok up to 35V, but maybe there's a capacitor on the board with a lower rating. The 35V limit on the other two rails would be either mosfet or capacitor ratings.

But the real point is not only do you have a voltage limit, you have a current limit! Raise the voltage, raise the current the bed will draw because the resistance of the bed isn't changed. 15A isn't enough anymore, and no you can't just put a larger fuse in. The SSR setup does an end run around this by moving the higher currents off the Rambo board itself.

[dmo]

After a busy winter I'm finally ready to do some major upgrades. Now I'm considering going all 24v. I'm ordering a Duet controller that can handle 24v I think. Is there an advantage in going all 24v? I'm also ordering the Cyclops hot end and I have a choice for 24v. SeeMeCnc has 24v beds, do I need that either way? I also think I would need 24v fans. Do I need to do anything with the steppers? I've been digging through the forums and can't find the info. I saw that mHackney has an all 24v system somewhere. Thanks

[Nylocke]

Motors should be fine from like 5V to 30V I think. I don't think mhackney has an all 24V system, he goes for the safety of a relay controlled bed. I do have a mostly 24V system on my X3 Pro, but the heaters/fans/LEDs rail is on a separate 5A power supply, and my bed draws less current (TAZ 5 silicone bed).

[dmo]

Safety is important. I was reading on the X3. It allows you to do 12v and 24v at the same time? What are the dangers and advantages of full 24? I keep reading conflicting things. If I go the SSR rout do I still need the 24v v3 Onix board? I primarily print large so if going all 24v helps with speed and other issues I'd like to go that rout. If not I'd rather go a simpler rout. If I order a 12v Cyclops is there a way to increase it later if I go 24v? I'm eventually going to figure this out:)

[IMBoring25]

The "24V" Onyxes are just higher-resistance boards. As long as your wiring and connections are up to the task of the current that will result when running your chosen voltage across the resistance of the bed you're using you should be fine.

Similarly, the 12V and 24V hot ends vary in the resistance of the cartridge heaters. Order the other heater and change it out, and it's basically the other hot end.