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How to convert an ATX power supply to rc use

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How to convert an ATX power supply to rc use

Old 10-21-2009, 08:36 AM
  #176  
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Default RE: How to convert an ATX power supply to rc use

I've run into this problem several times with PSUs I've converted for some of my buddies. To expand a little bit on what Andrew is saying, connect the charger AND TURN IT ON before you power up the power supply. That way, the sudden increase in load caused by the charger coming on (usually the capacitors in it) won't cause the power supply to think there is something wrong and shut down. By the way, not all chargers will cause this to happen.
Old 10-21-2009, 02:35 PM
  #177  
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Default RE: How to convert an ATX power supply to rc use

Thanks for the replies...It works now..I connected the charger up first...
Old 10-23-2009, 10:32 PM
  #178  
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Default RE: How to convert an ATX power supply to rc use

Hello everyone, this is a great thread! This post is directed to Andrew (the other Andrew, that is! ), but anyone who cares to comment is more than welcome to do so.

Andrew, first thanks for all the time you've invested documenting the ATX conversion process on the Murray State site and for helping so many people here as well. After spending a few hours over the course of several days going through this thread and all the data on the Murray State site, I think I'm just about ready to tackle my first conversion. Yesterday I went out and bought a brand new Antec EA-500D because I don't have an old PSU laying around and because I want a hefty, long-lasting unit. Anyway, tonight I opened the beast, clipped the plugs off and sorted all the wires by color. After reviewing everything, I have a couple of quesitons and was hoping you might be able to offer some guidance.

First: As you probably know, this unit has two 12-volt rails. According to the specs, each one has a max output of 22 amps. I want to install two pair of binding posts so I can easily connect two chargers. Since there are two rails, it seems logical to run one rail to each of the posittive posts. Is there any problem with that or any reason why I wouldn't want to do it?

Second: Back on 9/17/08, RichT asked: "I am wondering if it will be possible / beneficial to rig up the -5v line as the negative and the +12v as the positive to get a net 17v output from the psu. Should I just stick with the healthy 17A 12v line or attempt this theoretical 17v line?" and you replied "You will get 17 volts, but if you check the current rating of the -5v rail, it will likely be around 200 to 400 ma. - however, I suspect that it will not carry much of a load since the rail will overload very quickly. Stick with your 17A 12v line." And that makes perfect sense to me. However, the specs on my PSU state that there are two 5 volt rails (5V and 5Vsb). The "5V" rail has a rated max load of 24 amps. Given that, is there a problem with using RichT's idea on my PSU? I have a charger (CellPro 10S) that would be very happy with a 17 volt input. I should note that there is no white wire present in my PSU, so this might not be possible, but I figured it couldn't hurt to ask you anyway.

EDIT: I double checked and found that the 10S has a max input voltage of 16 volts, so my second question is now moot.

Other than those two issues, I think I am ready to proceed. The PSU has it's own switch, so I'll connect the green wire to ground and use the existing switch to turn it on and off. There is a brown sense wire and an orange 3.3-volt wire terminated in postion 13 of the motherboard plug, so I will connect those two. Finally, I have four 1 ohm/10 watt wirewound resistors that I plan to wire in a 2S2P configuration across the 5 volt output. If I've done the math right, the net load will be one ohm disspating about 26.5 watts, with each resistor getting about 6.6 watts. I'll heatsink them all to the case so they should stay cool enough not to self destruct.

If you have any thoughts or suggestions, I'd love to hear them.

Thanks,

Erik
Old 10-24-2009, 10:06 AM
  #179  
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Default RE: How to convert an ATX power supply to rc use

I went to two Radio Shack stores to get the banana jacks as shown in this thread. They no longer stock them. I guess Radio Shack is abandoning its roots.
Does anyone know where I can find some of these?
Old 10-24-2009, 10:29 AM
  #180  
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Default RE: How to convert an ATX power supply to rc use

I just bought mine two days ago. The part number is 274-718 and it looks like this:



It still shows on their website. I wonder why your local store doesn't have it? You can probably find something similar at www.mouser.com . They have virtually anything electrical that you can imagine.
Old 10-24-2009, 12:03 PM
  #181  
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Default RE: How to convert an ATX power supply to rc use


ORIGINAL: JustErik

<snip>........

However, the specs on my PSU state that there are two 5 volt rails (5V and 5Vsb). The ''5V'' rail has a rated max load of 24 amps. Given that, is there a problem with using RichT's idea on my PSU? I have a charger (CellPro 10S) that would be very happy with a 17 volt input. I should note that there is no white wire present in my PSU, so this might not be possible, but I figured it couldn't hurt to ask you anyway.

<snip> ........

Other than those two issues, I think I am ready to proceed. The PSU has it's own switch, so I'll connect the green wire to ground and use the existing switch to turn it on and off. There is a brown sense wire and an orange 3.3-volt wire terminated in postion 13 of the motherboard plug, so I will connect those two. Finally, I have four 1 ohm/10 watt wirewound resistors that I plan to wire in a 2S2P configuration across the 5 volt output. If I've done the math right, the net load will be one ohm disspating about 26.5 watts, with each resistor getting about 6.6 watts. I'll heatsink them all to the case so they should stay cool enough not to self destruct.
Erik

If you metered the voltage between the 5v rail and the 12v, it would read ~7v. The reason you can get 17v with -5v and +12 is because DC voltages are measured both by voltage differential and by which pole is considered to be "more positive". For negative voltages, DC ground could be thought of as being "more positive" and the voltage differential between -5v and ground is 5 volts. The diffenential between ground and +12v is 12 volts, consequently the diffential between -5v and +12v will be ~17. If you drew out a number line and marked places for -5, 0, +5 and +12, then counted the units between each, the units between +5 and +12 is 7. The +12 is thought of as being "more positive" than +5 since it is further from the ground plane of 0 and when metered, you would use your negative probe on +5 and the positive probe on +12. It's a bit more complicated, but voltage is only the differential between two points, taking into account polarity.

My inclination would be to initially use all 4 resistors is series for a total of 4 ohms. Adding load (reducing the resistance) when not needed only adds heat and consumes power from the PSU. Many of the newer PSUs will latch without a load, but will have a more stable output voltage on the 12v rail with a load. Your choice of resistance should be the highest ohm rating possible for good performance. If it powers your charger satisfactorily with 4 ohms, there is no gain in going any lower.

Keep us posted on how your conversion works out.

andrew
Old 10-24-2009, 04:02 PM
  #182  
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Default RE: How to convert an ATX power supply to rc use

ORIGINAL: Andrew

Erik

If you metered the voltage between the 5v rail and the 12v, it would read ~7v. The reason you can get 17v with -5v and +12 is because DC voltages are measured both by voltage differential and by which pole is considered to be ''more positive''. For negative voltages, DC ground could be thought of as being ''more positive'' and the voltage differential between -5v and ground is 5 volts. The diffenential between ground and +12v is 12 volts, consequently the diffential between -5v and +12v will be ~17. If you drew out a number line and marked places for -5, 0, +5 and +12, then counted the units between each, the units between +5 and +12 is 7. The +12 is thought of as being ''more positive'' than +5 since it is further from the ground plane of 0 and when metered, you would use your negative probe on +5 and the positive probe on +12. It's a bit more complicated, but voltage is only the differential between two points, taking into account polarity.

My inclination would be to initially use all 4 resistors is series for a total of 4 ohms. Adding load (reducing the resistance) when not needed only adds heat and consumes power from the PSU. Many of the newer PSUs will latch without a load, but will have a more stable output voltage on the 12v rail with a load. Your choice of resistance should be the highest ohm rating possible for good performance. If it powers your charger satisfactorily with 4 ohms, there is no gain in going any lower.

Keep us posted on how your conversion works out.

andrew

Andrew, thanks for the speedy reply. I follow your explanation of the differential between -5 and +12 yielding 17 volts. The isuue is there is no -5v wire (the white one) so I was just wondering if there was another way to accomplish the same thing. No matter, I'll just stick with the two 12 volt outputs, one tied to each 12 volt rail. Also, I'll follow your advice and wire the resistors in series for greater resistance.

Thanks again,

Erik
Old 10-25-2009, 05:11 PM
  #183  
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Default RE: How to convert an ATX power supply to rc use


ORIGINAL: JustErik

I just bought mine two days ago. The part number is 274-718 and it looks like this:



It still shows on their website. I wonder why your local store doesn't have it? You can probably find something similar at www.mouser.com . They have virtually anything electrical that you can imagine.
Our local stores no longer stock them. I used to get them there. They have discontinued a lot of things.
I guess I could order them. What I really want is called Pamona banana jacks. Mouser and other distributors want to sell those in lots of 10.
Old 10-25-2009, 07:49 PM
  #184  
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Default RE: How to convert an ATX power supply to rc use

Don't know nuttin' 'bout no Pamona jacks. This is all kinda new to me, so I consider myself fortunate to have you guys around.

I finished up my conversion and powered up my 10S for a test run. I hooked up a pair of 3S 3700 packs and cranked the charge rate up to 3C. The voltage on the PSU never fell below 12.2 and the peak draw was around 20 amps. The fan in the PSU was on all the time but it's one of those ultra-quiet units so the only way I could tell it was on was by looking at it or putting my hand in front of it. I'm very pleased with how well it works. Thanks again to everyone who contributed to this thread. It's a great resource.
Old 10-31-2009, 05:39 AM
  #185  
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Default RE: How to convert an ATX power supply to rc use

why do u need to add a resistor?
Old 11-01-2009, 11:20 AM
  #186  
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Default RE: How to convert an ATX power supply to rc use


ORIGINAL: wantboost

why do u need to add a resistor?
This page will answer that question. Credit to "the other Andrew."
Old 11-01-2009, 01:48 PM
  #187  
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Default RE: How to convert an ATX power supply to rc use

You don't need a resistor as long as you don't power it up without a load, i.e. only switch it on when you have the charger connected to it and ready to go.
Old 12-06-2009, 05:50 PM
  #188  
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Default RE: How to convert an ATX power supply to rc use

I need some help with my AT conversion.Powers up and works fine with no load.Voltage measures 10.8 volts.Added two 10 Ohm 10 Watt resistors in series to the 5 volt side and brought the voltage to 11.76.Do i need to change to a different Ohm resistor to get above 12 volts?
Old 12-06-2009, 06:12 PM
  #189  
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Default RE: How to convert an ATX power supply to rc use

Use a single 10 ohm 10 watt resistor. By adding two in series, your load is 20 ohms. You may see a slight increase in output voltage by dropping the resistance to 10 ohms.

andrew
Old 12-06-2009, 09:42 PM
  #190  
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Default RE: How to convert an ATX power supply to rc use

Ok,did that and the voltage came up to 11.96.Do you think that is about all i can get out of it?
Old 12-06-2009, 11:18 PM
  #191  
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Default RE: How to convert an ATX power supply to rc use

If your charger will function satisfactorily at that voltage, I wouldn't drop the resistance any further. The marginal voltage gains are usually small with an associated increase in PSU load. As a quick test, temporarily wire the second resistor in parallel to the first. This will give a 5 ohm load and you can meter to see if you get much in the way of a voltage increase.

andrew
Old 12-06-2009, 11:20 PM
  #192  
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Default RE: How to convert an ATX power supply to rc use

Will do.Thanks for your help.
Old 12-08-2009, 07:50 AM
  #193  
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Default RE: How to convert an ATX power supply to rc use

That got me up to 12.1 volts.Everything works great.Thanks for the help.
Old 12-09-2009, 11:02 AM
  #194  
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Default RE: How to convert an ATX power supply to rc use

Andrew, I need help!, Ihave two PS'S that I converted without success; #1 is a dell 1996-2000 era 12v, 200w, set up: Load=(5v)red and black to 10 ohm 10w resistor,(12v) yellow to recept., black to recpt., grey wired to black.there appears to be know "sense" wires ie; all single pin wires from the mobo connector.Battery connected to charger, charger connected to PS then PS connected to ac, result a fan bump and nothing else, no voltage. I have checked for shorts at banana plugs, foriegn matter on circuit board and no burn't odor.

# 2 PS is a compaq 250 watt.set upin 11, org and brn. wired together, pin 14 grn. to black,red and black wired to 10 ohm, 10 w resistor, ps connected to battery and charger as stated above. fan runs albeit a little slow I think but the resistor gets so hot in a matter of seconds that it cnnot be touched, then tried 4 one ohm resistors with the same results.
Thanks
Old 12-21-2009, 04:23 PM
  #195  
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Default RE: How to convert an ATX power supply to rc use

Alright I am attempting this but I have a few questions.

It's a 450w ATX switching power supply.
The wiring is wierd, at the P1 connector (20 pin) There are 2 sets of combined wires.
Orange and Orange
Black and Black
They are not darker nor lighter from the rest of them but I am assuming they are the sensing wires, I soldered orange to orange and black to black.

I put the only green wire on a switch with ground
Gray is not connected to anything as of right now cause I'm going to be using it as a LED.

Now, since I am snowed in I couldn't go to radio shack but I found a car bulb to use to test.
First I tried the yellow and a ground with OUT a load on the 5v rail. I got nothing.
Then I tried to use the bulb as a load on the 5v rail and when I flipped the switch, the fan did not turn on. Now I know you say don't assume the fan works. Just assume that the fan works.

What am I doing wrong? Any ideas?
Old 12-21-2009, 04:33 PM
  #196  
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Default RE: How to convert an ATX power supply to rc use

Alright, I figured out what was wrong. It MIGHT help to actually plug the thing in. It worked and yes the fan turned on.

Now instead of buying a 10w 10hm resistor, can I use that bulb as a load? I don't have a volt meter to use right now but just wondering if it will work?
Old 12-21-2009, 05:01 PM
  #197  
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Default RE: How to convert an ATX power supply to rc use

ORIGINAL: jtnktz

Alright, I figured out what was wrong. It MIGHT help to actually plug the thing in. It worked and yes the fan turned on.

Now instead of buying a 10w 10hm resistor, can I use that bulb as a load? I don't have a volt meter to use right now but just wondering if it will work?

Found my volt meter. No load I am getting about 12.14v with the bulb as a load I'm getting 12.20.

Do I need a load for 12.14v or can I charge 11.1v Lipos with the Apache 2500 Smart Charger efficiently?
Old 12-28-2009, 01:01 PM
  #198  
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Default RE: How to convert an ATX power supply to rc use

Hi All i'm new on here, i don't use RC any more but did at one time. Due to recomendations of a member here i bought the Accucell-6 for maintaining my nicd and nimh batteries that i use in my metal detectors, while waiting for it to arrive from hong kong i modified a 420w big fan ATX power supply using this thread as a guide and its working fine. I only had a 30w 22ohm aliminium shod resistor handy so i used that on the 5v rail inside and it gives me 12.06v with no load and it drops to 11.96vwith the Accucell-6 on a 2amp charge(i don't usually charge this high). I also put a 5v as well as the 12v power takeoff on the outside using banana jacks.  If i put a car bulb on the 5v rail(in the bananas) the output goes up to 12.48v on the same 2amp charge, this will do for me and i would like to thank all that have posted in this thread(and others) as it has been a great help to getting this up and running. At a future date i will change the 22ohm resistor for something bigger, i think i have a 50w 2.2ohm with aluminium heat sink  lying around somewhere so i might give it a try if i can find it. Do you think it might be too much? the +5v is rated at 20amps and the 12v 16amps

jtnktz
if the 12v output rail is only giving 12.14 when not under load it will probably drop when charging to just under the 12v like mine did, this should still charge as long as the charger will accept the lower input

Merry christmas and happy new year to all and thanks for he great info on the site
Old 02-05-2010, 11:23 AM
  #199  
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Default RE: How to convert an ATX power supply to rc use

I had to do this with my Hyperion EOS 1210i chargers, works fine now, it would shut down when I plugged it into the charger.

Unexpected Shutdown I've made the recommended changes, but when I connect my charger, the PS still shuts down. Now what?? The usage of a PC powersupply as a substitute for a field charger power source falls far outside the intent of the original design specifications. Once the PS is running and stable, the overload circuitry is tuned to detect high current sinks and shut the PS down under normal usage, these sinks would be indicative of an internal short in the PC. When a microcomputer is running, powersupply demands change, but these are minimal and are usually associated with optical, hard or floppy drive usage or USB devices being attached. Some field chargers produce a high current sink when first attached and generate a latch into the overload state as designed. The specifications state that the PS will remain latched until the load is removed from the rail the PS will either automatically reset or may require at least one PS_ON cycle. Even though your PS may have sufficient wattage to effectively drive the charger, the load change is the problem. One method that has been effective is to attach the charger before powering up to the PS, the charger now appears as a high draw motherboard and not as a potential short occurring after the PS is stable

Thanks for the links to trouble shoot it.

Just using 1 10 ohm, 10watt R.
Old 03-04-2010, 10:45 AM
  #200  
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