How to build a $20 47A power supply

[Metallover]

I decided I would go about building a 24v power supply. There's a guide on hooking up two power supplies in series here.

I got my power supplies from ebay yesterday and wired em up today. Now I have a 24v 1150w power supply that I paid $26 for.

The final unit is 13x7" and the output measures 25.2v. If I put the leads of my multimeter on each power supply, I get 12v between the two. I haven't touched it yet, and I don't know if it will shock me if I touch it.

I cut some pegboard to mount the power supplies on.


Testing - The power supply on the right is wrapped in clear packaging tape.


I mounted the power supplies to the pegboard with some bolts, M3 I believe. I then used some unshrunk heat shrink (1" wide) and duct tape to try to insulate the screws.


And my awesome duct tape job.


25.2v output under no load.

[snellemin]

That is some serious power supply you got there mang. I'm now thinking to do the same, but with both 12V and 24V capability. Good Job!

[Metallover]

Thanks! When hooking the power supplies up in parallel is it the same procedure as when hooking them up in series? Just change the output leads?

And I just realized you save about $200 in making one of these power supplies!

[BrianG]

Little update on boosting the output for those interested. I ended up using a couple of resistors to make the voltage divider instead of a diode; a 210 ohm and 20 ohm. This gets me ~13.2v. I was able to get to 13.6v, but the supply sometimes wouldn't turn on or stay on. 13.5v worked fine, but I brought it down to 13.2v just for a little extra wiggle room.


First, the stock power daughter board. There is a blue and purple wire which I cut. One is a 5v line, the other is a -12v line.



Then, I cut away where the 5v and -12v lines were to make room to run the wires for the voltage booster resistors. I soldered pins 6 and 10 directly to ground to turn the PS on. Even when these aren't connected, the PS is on somewhat so I figured I'd just hardwire them and use the mains plug as a power switch. I then soldered wires to a ground point, +12v point, and to pin 5 (v adjust pin).



On the other side of the daughter board, I attached those three wires to the resistors and hotglued the resistor pack to the PCB. I did have to remove the bolt lug from the case so the resistors would fit.



Here is a simple schematic to show how to arrange the resistors. The power ratings of the resistors, especially the 210 ohm one, should be 2w or more.



As you can see, I soldered the binding posts directly to the blade plugs. The soldering job is good, it just looks crappy because as I soldered one side, it would drip down. Since the pins themselves weren't being used, I ground them all down.

Here is another pic showing what I know of the pins:

[snellemin]

Wow there Brian. You like to eek out every little bit of power out of that PSU heh?!

[BrianG]

lol, why not? Gotta make the most out of $25!

[florianz]

hi there,

after I converted an other pc p/s last weekend (quite easy), I have now two p/s for my chargers, which is good.

finally I got one of those, but wonder if anyone knows about them, I got one of them for 2,5 euro...



with a maximum of 75 amps on 12v I will be safe for the next years.

thanks
florian

[Nard Cox]

Those look badass!!
930W / 75.7A ... watch out LiPo's :D

Have you searched on RC Tech? They have several of these server PSU conversion threads.

[florianz]

thanks for that hint, I'll have a look

got them on egay, used, private seller, I hope they will work...

[snellemin]

This is a good thread. I am glad to see that I'm not the only fool out there looking for some true clean dirt power source for a charger.

[BrianG]

At some point it gets a bit overkill to have such a large 12v supply unless you have multiple chargers to power at the same time. Many (if not all) chargers over 300w require a supply with higher voltage (like 24v) to be able to use it to its max output. Just a little food for thought.

[florianz]

that's the story:
I have three (2 weak, 1 strong) charger, and want to be on the safe side, even on the long run. soon I get a second strong charger with about 180watts to charge all six 5s (4000-5000mah) lipos quickly. I store my batteries low-medium charged, so when I decide on a saturday morning to go for some fun, they need to be charged in short time.

It can deliver a maximum of 75a, that doesn't mean that it has to do that all the time. with the allied p/s (500w) I have experienced that when all three chargers run on that one p/s, one charger gets problems. actually the p/s should be sufficient, but obviously it's not, even that it's a brand p/s. the other p/s (brand stuff) I have converted recently is about the same, it says 550w, but actually can handle solely the 150w charger.

overall, the p/s worked great for me. The only problem is, when it says 500w, it's all together, on all lines, but not on the 12v line (maybe 300w?).

like that, I've decided to get a big one, so I never have to worry any more.

[BrianG]

Yeah, normal PS units power ratings are all rails combined. These server supplies are just 12v, which makes it nice for us.

I know you don't "need" 75A (and it does place less stress on the supply if used under that value), I just wanted to make the point (mainly for others) that just because it is capable of near 1000w doesn't mean that some of the higher output chargers will be able to utilize it unless the voltage is higher.

[Big House]

I have a few old desk tops in storage that are not going to be used again. How can I convert one of those into a dependable PS for my charger? Thanks.

[BrianG]

http://www.rc-monster.com/forum/showthread.php?t=3962

Whether those PS units will work or not depends on how much current is available on the 12v line. The power rating is for the 12v, 3.3v, and 5v rails combined, so the 12v rail by itself will be somewhat lower. There should be a label on the case somewhere that states the current for each rail.