# Specific 3D Printers, Scanners, & Hardware > RepRap Format Printer Forum >  With great power comes great responsibility - A PSU Discussion.

## jaguarking11

OK since this is the reprap forum I assume most people are either buying or scavenging parts for their build.

It is fair to make some assumptions that most users here have some electrical knowledge and know how to jump an ATX psu. 

So lets discuss the different power supply types.

We have the cheapest almost free ATX.  This type of PSU has allot of rails and it is not difficult to obtain for 30-40bux shipped to your door. However there are pro's and cons associated with this type of PSU.
ATX.jpg

The mod to turn it on basically green wire into black wire (Ground)
ATX-Mod.jpg
Pros
- Readily available.
- Can be quiet
- Cheap $30-$40
- Standard form factor making them easy to replace.
Cons
- Unstable 12V due to unloaded 5v & 3.3V rail
- Expense added to add load on above rails to make it perform properly (this adds heat as well if using a resistor bank.)

XBOX 360 PSU
XBOX.jpg
The MOD
XBOX-Mod.JPG

Pros
- Quite cheap 20$ or so
- Standard form factor.
- Silent
Cons
- Quite weak, 203W is the most powerful one
- Will be running at over 70% load if you have a heated bed.

Chinese 12V PSU.
Chinese PSU.JPG

Pros
- Inexpensive
- Stable 12v rail
- Fairly compact.
- Almost if not silent
Cons
- Have to be wired for high voltage 110v US 220v rest of the world.
- May have noise in the power (High frequency whine is not unheard of) or ripple in current.
- May have false advertising (Advertises more power than it can deliver)

See on next post for server PSU.

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## jaguarking11

Server Grade PSU (DPS-1300BB)
IBM.JPG

MOD
DPS-1300-Mod.jpg

Pins123.jpg

Pros
- Very inexpensive used (Found some for $10 shipped in the US)
- Huge amperage, 50+Amps is not unheard of.
- Very robust
- Low ripple, high quality
- Built to standards that far exceed what we may subject them to. 
- No need for 5v load, as 5v is only a signal voltage generaly in the 2amp or below range.
Cons
- Generally Noisy (Unless you modify them)
- Hard to hack for 3d printing
- Power hog

I personally went with the server grade PSU. I can sacrifice some energy for the sake of a stable build with room to grow.

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## Mjolinor

PS3 PSUs are good for all sorts and cost less than £5 on ebay and elsewhere. No idea what Repraps need as I know nowt about them but it's worth checking I know that the 5 volt rail is over 30 amps so that will do most things.

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## jaguarking11

5v Rail is nearly useless on reprap based printers. Some run as high as 24v, 5v rail is unused in most DIY ramps based printers.

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## Mjolinor

> 5v Rail is nearly useless on reprap based printers. Some run as high as 24v, 5v rail is unused in most DIY ramps based printers.


Why?

I use only 5 volt on my CNC machine because PS3 supplies are so cheap and small. I don;t see why you couldn't run repraps on 5 volt, my steppers are all at least nema 24, and I thought repraps used nema 17 generally but like I say, I've never really looked at them.

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## jaguarking11

They are nema 17's. However what you don't have on your cnc is a hot end or a heated bed. Which both use normally 12v modules to keep the cables at a reasonable level. It also stands to reason the same amount of work done at 12V @ 10amps you need 24AMPS from a 5V psu while increasing the cable size dramatically. Lets say the heated bed needs 100W to operate, at 5V it needs 20AMPS, while all fine and dandy, however the cable size becomes a larger issue, now you need a 5 Gauge cable, vs at 12v you need a much thinner 12 gauge cable. Assuming 1M length. ~3feet 

Your argument may be so what? Let me tell you that most of these printers need at least one cable that is constantly flexing while being moved, and it add load to the machine if your moving battery jumper cable sized wires. That's 5mm cable vs a 16mm cable..... I am generalizing here as there are other factors in cable sizing, however higher voltage is a nice thing in these things, also most of the accessorizes are designed to run on 12v. 

I Put this together as no one in the community bothers talking about power requirements, yes I went overboard on my power domain, and yes it may cost a bit more than the ps3 power brick. The fact of the matter is that I got my server spec psu for absolutely nill, and my needs were for 12V power.

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## nka

I have a China PSU 12V 5A (No heat bed... for now). If it's not working right, I have many old server PSU I can use (from my old hardware) or even PC PSU (I use an Modded ATX for my lab).

Like on PC, people seems to cheap on the power... this is were everything start. Power blown, every electronic come with it !

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## jaguarking11

NKA;

A cheap psu can cause weird issues as well. I wish you luck. Clean reliable power is very important. For ramps they recommend minimum of 6A if I'm not mistaken though, that is with no heat bed. Be careful of the load the resistor in the hot end can draw. I would measure it first.

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## Mjolinor

Wow, I didn't realise they used 12 volt for the head heater, why does it not use mains (230 in my case) or 110. I can see no advantage for using such a  low voltage for the head heaters at all.

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## nka

I'll may move directy to my server ATX if I have the space for it.

I like the form of the PSU I have right now (that's why I want to use it), the model I have is 12V/5A AWSP60-12 . If 5A is not okay, I'll buy a 8A like this one : http://www.digikey.ca/product-detail...070-ND/4386541 . I did read that 5A was okay for Delta

And as Mjolinor say... I'll use a Heatbed directly to the 120V

a Recom Power would be very nice... but they are not cheap at all!  :Big Grin:

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## jaguarking11

> Wow, I didn't realise they used 12 volt for the head heater, why does it not use mains (230 in my case) or 110. I can see no advantage for using such a  low voltage for the head heaters at all.


That is a very good question. However I doubt they wanted to introduce 120V!!!! on the ramps or similar board. Once you have a heated bed on 120v it would be more complex in controling the heat. For example ABS from what im gathering needs between 50-65C to adhere well. Other plastics need less. I am aware you could put in a separate controller on the 120v heated bed to get the proper temp then its another step before printing, when its all in one, theoretically once you have your gcode generated you put it on your sd card and let her rip. Once the bed is hot enough it will start printing. 12v makes for a more user friendly environment vs the potential of killing someone who is trying to enter the world of electronics for the first time.

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## Mjolinor

Both the head and the table should be properly controlled with a PID PWM system. I assumed they were but as I say, I know nowt about Repraps. You only need one transistor to PWM the heat no matter what the voltage and the advantage of using either AC or DC 120 or 230 matters not, no need for a regulated supply, it just doesn't matter how crap the supply is if it is PID PWM controlled then it will perform correctly. Better to use a seperate board as you say but a small PCB with a PIC that is just todl what temperature you want and leave it alone is by far the best way or you could just buy a PID controller for a few quid more.

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## nka

There's a lot of relay/module to dim light using PWM and Arduino. Could still use the "all in one" solution, just running the DC to the AC relay/module.

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## printbus

Ignoring the safety concerns, you'd of course need a heat bed designed to operate off the mains voltage.  A 120V or 230V heat bed would be tougher to fabricate than one that operates on 12V. 

We can calculate the required heater resistance using R = (V * V)/P, where V is the voltage applied and P is the desired power dissipated as heat.  For a nominal 130 watt 12V heat bed, this comes up with R equal to about 1.1 ohms. Such a heat bed is readily achievable in a circuit board layout by applying the input voltage across a trace designed with a particular copper thickness, trace width, and trace length. 

For 230V mains and the same 130W heat dissipation, the same formula shows R would be around 400 ohms.  This would be extremely hard to achieve with just a circuit board trace, meaning the bed would have to be formed from a resistive material or multiple resistive components.

Those interested can play with the necessary trace characteristics using any of several online circuit trace resistance calculators.

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## nka

I might be missing a point (and I'm not an expert in electronic), but for a 130W Heatbed, you'll be running 230V@0.56A with a resistance of 400 ohms or 12V@10A with 1.1 ohms.

IMO, it's much more a problem to have 10A than 0.56A? You have much more current directly into the cicruit. Also, isnt the resistance the heatbed directly?

I will personally use this : http://www.aliexpress.com/item/Keeno...881899879.html (Custom order for my size if not available) with an SSR.

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## printbus

You are right that for the same power the current draw will be far less at 230V than it is at 12V.  I was unaware you could get heat beds that ran on 120V or 240V. The ones that run on 120V or 240V likely use resistance wire; suggested by the wirewound reference in the resistance description.  From a thermal standpoint it should work.  Most of us would just prefer to deal with low voltage at a higher current than mains voltage at a lower current.

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## jaguarking11

Again, to me I see value in having a 12v heated bed. Simply put I like being able to control the heatbed via firmware. To me having a central control point is worth wasting power. At least at this point for me. I plan on integrating a insulated and heated build chamber to my build, and that too will use a 100-200w ceramic 12 heater, and hopefully I can get the firmware to control that one too. 

I have to figure out proper fusing for my build as well.

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## nka

I think I found the perfect PSU. I may order it when I'll upgrade to a heat bed.

SilverStone ST45SF. Very small (125 mm (W) × 63.5 mm(H) × 100 mm(D)), provide 36A to the 12V and 22A to the 5V of MAX (not peak). 

It's an ATX PSU, so it will need a "load" to power it. 0.6A isnt that much, so a fan could do the job. ATX PSU are really easy to modify.

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## jaguarking11

Looks to me like a nice PSU. I have heard the latest corei7 cpu's pull more from 12v than any other rail, this is in effort to have proper power stabilization, which means that psu manufacturers have adapted to. It certainly looks like a nice piece of kit. Let us know of the outcome. My own personal update on the power matter seems to be that due to stable clean power the arduino is booting up much faster and no longer suffers from disconnecting from the serial connection as some have had issues with. It seems that the regulators on the ramps/arduino are not very capable of compensating for large power swings.

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## brainscan

A friend of mine gave me his old (basically new) gaming psu. It's way over the top for just running one printer as it has 4x12v rails capable of 18amps each plus 30 amps at 5v. 12 volt signal is clean and stable without a 5v load and it's almost silent. It will be handy for when I want to run two or three printers at once.

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