Rostock build Part 6: With great power comes great responsibility.

Well I switched gears.

I ordered a brand new ramps 1.4/mega/lcd as it was around 46bux shipped. The reason is simple, even though I could power the old arduino from USB and try to carry on my build, the factors to consider on this build are fairly huge and could not help but think myself into a box, and the chance of the arduino or ramps sustaining even larger damage that is unforeseen due to the short is much greater. Being that I wanted to eliminate the problem, and not go chasing redhearings I opted to spend some money.

The power equation.

I opted to use an old atx psu I had laying around, it was rated at around 22A on the 12 rail and initially it seemed like a good choice. However it seems it suffers from 12V droop. On any control mechanism it is wise to have stable and ample current. I looked at buying a dedicated 12v psu, however I don't trust most of the reasonably priced 12V power supplies out there. So within reason I remembered that most semi modern rack mount equipment uses hefty 12v power and not much else.
A quick call to my buddy Dean, and a quick rummage by him at the recycling room at his job proved to turn up two very different power supplies.
One from a Dell 2U server with a rather compact form factor and a whiny little 40mm fan, however it showed it was capable of 67.3AMPS@12V!!!! This psu will be repurposed into a capable bench PSU at a later date.
The other PSU is from a IBM 3U server. With a 80mm fan and a power rating of 53.3A@12v with input power of 100-127V, however the whole story does not finish there as it also can deliver up to 106.5A@12V with input power of 200-240V. IBM certainly over sized this psu, and its rating of 1300W is massive, in my experience having a large power domain that is unstressed makes for a stable/happy/cool running power supply and very stable voltage. Being that the 80mm fan could also be swapped with a much quieter fan that could still provide ample cooling and not make my ears bleed. I chose this psu, for nothing more than the fact that it had an 80mm fan that I could easily swap.

Here are the specs of the PSU,

However getting a server spec PSU to power on is a completely different game than the standard ATX. So I started googling around and quickly found that the mods to get this psu to work were simple. Two pins to short and we were on our way.

So I shorted the pins and the PSU started, and the delta fan spun up and sounded like a vacuum cleaner. Great!!!! Once I replaced the fan and ripped off the quick release handle it was time to solder my connectors. Pardon the 3 pin connector however it is only temporary as I will be using a proper 2 pin connector connected to a switch.

The soldering looks like hell, however it is strong enough to pick up the psu, I will be going over these in the future with my 150W soldering gun, the little 25W iron I used had some difficulty heating these large connectors. For wires I used 16 gauge wire that was left over from a speaker install. These wires supposedly can carry up to 22AMPS if its specified for 3 feet. I used about a two foot chunk and wired two sets, with space for two more sets on the PSU. I don't want to risk melting anything. Currently it has a load carrying capacity of 44amps MAX on these 4 wires. Not too shabby.

Load test.
no load = 12.5v
20W Light load = 12.45V
PCB Hot Bed load = 12.3V This also included the 20W halogen I used.

Not a bad circumstance, the ATX psu in comparison had a nearly 1v drop with the light only with no resistors on the 5V & 3.3V rail. Once I loaded it up with resistors on the 3.3V & 5V rail the drop on the 12v rail was .5V. I don’t want to consume power just to make more heat and add complexity.

Now came time to mount. This thing was designed to slide into a case and latch with the handle I ripped out. I had no intention of mounting it that way as I soldered my connections on the PSU and coming up with a latch was of no use. I thought about it, and quickly I produced an aluminum profile from my junk collection, this was once used as a blanking plate on a rack... Some bending and forming on the bench vice, and some quality time with the hammer, hack saw and grinder. The PSU was mounted with some wood screws. Not a bad solution.

For anyone considering putting together a psu for a 3D printer I think they should consider a PSU from a server.

The pros of this are.

  • Extremely stable voltage.
  • Ridiculous amounts of Amperage.
  • Very Very cheap (not uncommon to get one for 10-20bux shipped from everybody’s favorite auction house)
  • Extremely well built.
  • Clean noiseless current.

The Cons

  • You need to do some research into them on how to get them to power up.
  • They can be very loud if not modified.
WARNING:

Please be aware that these types of PSU's have some lethal voltage inside, they can and may well store this voltage for extended periods of time in their capacitors. Exercise best practices when dealing with them.

Overall I am a happy camper.

If you need to do some research on server power supplies please consult this forum where people are using these to produce some fantastic results. Some are sustaining 200+ AMPs out of these power supplies in parallel and some are modifying them to be used in a series for 24-25V@100+Amps.

http://www.rcgroups.com/batteries-and-chargers-129/

Bruno M.

Engineer, Tinkerer, Technologist, Maker.

New York

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