Question about a converted computer power supply - RC-Monster Forums

KaztheMinotaur · **Question about a converted computer power supply -** 08.17.2009, 08:22 AM

I just bought an ATX computer power supply to convert, to power a charger, and here are the specs:

+5V at 36A
+12V1 at 34A
+3.3V at 36A
-5V at 1A
-12V at 1A
+5VSB at 2A

Question: Can I get 17 volts by combining the +12 & -5 or the +5 & -12 ? Do I just solder them together?

Wattage at 17V should be 629?

OZ-RUSTLER · 08:33 AM

You cannot combine because they have a common ground.
Have you checked out BrianG thread
http://www.rc-monster.com/forum/show...c+power+supply

BrianG · 11:01 AM

You could conceivably get 7v, 8.3v, 24v, 17v, 15.3v, and 1.7v (may have missed a couple there) from that supply. However, DO NOT simply tie the leads together. In any of those combinations, you would not use the ground lead at all. For example:

- If you want 7v: the + lead would be 12v, and the - lead would go to 5v.
- If you want 8.3v: the + lead would be 12v, and the - lead would go to 3.3v.
- If you want 24v: the + lead would be 12v, and the - lead would go to -12v.
- If you want 17v: the + lead would be 12v, and the - lead would go to -5v.
- If you want 15.3v: the + lead would be 3.3v, and the - lead would go to -12v.
- If you want 1.7v: the + lead would be 5v, and the - lead would go to 3.3v.
and so on...

Also, the output current would be limited by the current capability of the lowest rail. So, if you used the 12v (34A) rail along with the -5v (2A) rail to get 17v, your total current would be limited by the -5v line, which is 2A.

KaztheMinotaur · 08.17.2009, 12:00 PM

Bah... Well that doesn't get me anywhwere then...

17V @ 2A doesn't do much good.

zeropointbug · 08.17.2009, 12:27 PM

Why don't you just use the 12v rail, you don't need any higher voltage than that. What charger were planning on using it with?

KaztheMinotaur · 08.17.2009, 12:30 PM

I can, I was just trying to see if I can get the voltage up. I'm going to get 2chargers so I can charge 2 5S 5000 mah batteries at 5A at the same time.

whitrzac · 08.17.2009, 12:33 PM

Quote:

Originally Posted by KaztheMinotaur

I can, I was just trying to see if I can get the voltage up. I'm going to get 2chargers so I can charge 2 5S 5000 mah batteries at 5A at the same time.

put a 10ish ohm power resistor on between 5v and a ground

http://www.radioshack.com/product/in...ductId=2062288

KaztheMinotaur · 08.17.2009, 12:45 PM

Yeah, I have one. Thats on my to do list tonight. I'm going to practice on my old power supply first.

BrianG · 08.17.2009, 01:17 PM

Post a pic of the supply if you can. Particularly clear shots of the internals (looking down) and the motherboard connector. Depending on the model, there may be ways to actually boost the voltage. Adding a load to the 5v and/or 3.3v line usually just makes the voltage more stable under load at 12v, but will still dip and may fall under the 11v lower limit of some chargers. I like getting the output anywhere from 12.5v up to 14.5v.

KaztheMinotaur · 08.17.2009, 01:42 PM

I'll try to get some pics but it seems real crowded in there.

How else can I boost the voltage?

whitrzac · 08.17.2009, 03:11 PM

Quote:

Originally Posted by KaztheMinotaur

I'll try to get some pics but it seems real crowded in there.

How else can I boost the voltage?

idk how, but...

http://www.hobbycity.com/hobbycity/s...Chargers_(350W)

zeropointbug · 08.17.2009, 03:51 PM

Yes, there could be pots in there that can be adjusted to a certain degree, maybe .5 - 1.0 volts +/-.

If it's a decent power supply, they can always hold at least 11.8 volts a heavy load, some PSU's are so so stable that they don't even flinch under the most extreme loads.

Post a link to the model you purchased.

KaztheMinotaur · 08.17.2009, 04:05 PM

http://www.chiefmax.com/psu/cm650-24pin.php

zeropointbug · 08.17.2009, 07:11 PM

Well 650watts should do it, but alot (alot) of the cheapo computer PSU's have a hard time keeping up with any kind of load.

How much did you pay for it shipped?

BrianG · 08.17.2009, 08:16 PM

Quote:

Originally Posted by KaztheMinotaur

...How else can I boost the voltage?

Aside from loading the 5v/3.3v line (which simply stabilize the line if anything), the method to boost depends on the design. That's why I asked for pics. There could be a pot inside for tweaking the voltage, or the motherboard connector could have a feedback wire. From personal experience, the feedback wire makes for the best and most stable boost, but some don't have it. Like I said, it depends.

Heck, just hook her up and see what it does under load. As long as it stays at or above 11.5v at the max loaded output, then you're fine. I just personally like having a higher voltage for efficiency, and makes the charger's switching supply not work so hard.