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.

[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.

[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.

[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.

[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.

[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.

[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.

[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.

[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 !

[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.