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All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> RE: How to convert an ATX power supply to rc use
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RE: How to convert an ATX power supply to rc use - 2/29/2008 7:35 AM   
mrasmm


 

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ORIGINAL: Tusken

Im having a problem with my power supply shutting off when i try to charge 4s packs. The psu is out of a compaq pc and is rated 8 amps at 12v. It works fine charging 3s and im getting about 12.6v under the charge load. Does it take that much more juice to charge 4s packs? or ??

Allso I had the same problem as edwal07 on page2
""and the 5v sense to the 5v. In this configuration I had voltage but no current. I removed the 5v sense and it latched on perfectly. ""

I had 12v+ but it wouldnt power anything until i disconnected the grey and red wire.

This is the charger im using if that matters. http://www.allerc.com/etecchargers.htm

Thanks
Rob


it all depends on the conversion efficiency of your charger, but yes it will take considerable more power, about 33% more assuming a 100% efficient conversion factor. If it's a compaq PSU, it's likely not very good, infact most cheap PSU's are only good for about 50% sustained draw of what they are rated for.

The simplest fix would be to just charge at a slower rate, and see how that works

basically the math of it is: max voltage of 4s lipo pack is 16.8v, at 2.5A. I assume an 80% conversion efficiency, so if you do the math you end up with 16.8v x 2.5A / .8 = 52.5w required, and if you figure your PSU, you'll need basically 4.5A sustained current @12v

In your case you run into a problem because your PSU probably just puts out 12v, and if you load it up around 4A, then the voltage drops below 12v, as soon as that happens your charger shuts off to prevent an undervolt that would fry it.

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RE: How to convert an ATX power supply to rc use - 3/1/2008 12:07 AM   
Tusken



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Status: offline 		Thank you mrasmm for the help. Does anyone have a recomendation for a good off the shelf psu i could convert to be able to charge 4s.

Thanks

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RE: How to convert an ATX power supply to rc use - 3/1/2008 5:52 AM   
mrasmm


 

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quote:

ORIGINAL: Tusken

Thank you mrasmm for the help. Does anyone have a recomendation for a good off the shelf psu i could convert to be able to charge 4s.

Thanks


sure thing. FSP group makes a good PSU for about 40 or 50 bucks that would be able to put out what the label says. If not, I'd just look for something that's more along the lines of 16 to 18A or higher on the 12v rail. if you are getting one for RC only, you may want to get a single 12v rail PSU. If I remember right the dual PSU's have a different setup process, and there would be other concerns with them as well.

Basically a simple rule is, better quality PSU's weigh more per watt they are rated for. Look for something in the 4 to 5LB range.

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RE: How to convert an ATX power supply to rc use - 3/1/2008 6:12 AM   
Andrew


 

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ORIGINAL: mrasmm
<snip>..... if you are getting one for RC only, you may want to get a single 12v rail PSU. If I remember right the dual PSU's have a different setup process, and there would be other concerns with them as well.



If you're referencing the standard dual rail ATX 12v PSU with the 4 pin motherboard connector, it will convert the same as a single rail ATX supply. Additionally, the 12V1 and 12V2 rails may be combined in parallel to increase available current. One thing to keep in mind is that you will not be able to draw full combined current for joined rails -- the specification placards on the better supplies will provide the maximum combined wattage from both rails. For example, the 12V1 rail may be rated at 130 watts and the 12V2 rail at 92, but maximum combined output may be 195 watts -- the combined output is dependent on the power distribution architecture of that particular model.

ANTEC and SPARKLE also have reputations for being good supplies. We have found Newegg to be very competitive and shipping is both quick and reasonable.

andrew


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RE: How to convert an ATX power supply to rc use - 4/26/2008 10:35 PM   
Calin666


 

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Status: offline 		HWS, I just got done doing the conversion, and it worked perfect! Excellent tutorial, and thanks for posting this!

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RE: How to convert an ATX power supply to rc use - 5/11/2008 1:58 AM   
hands without shadows



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RE: How to convert an ATX power supply to rc use - 6/11/2008 8:30 PM   
chadr


 

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Status: offline 		Check out this method of adjusting the voltage, no need for 4 x 1 ohm 10w resistors in series. He is using a 5k pot tied in somewhere on the control circuit of the power supply.

http://www.mp3car.com/vbulletin/power-supplies/31652-car-power-supply-battery-charger-old-pc-supply.html

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RE: How to convert an ATX power supply to rc use - 7/15/2008 10:53 PM   
dzgruntld



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Status: offline 		Greetings fellow 'PS crackers',
The trouble I am having is as follows:

I can not seem to be able to draw any current from the 12v lines.

I have red just about every forum I could find to learn how to do this PC PS conversion.

On one forum, the author even used the same PS I am using.

I have 2 sets of 10ohm 10watt resistors in parallel across some of the 5v lines.
A LED across grey and black line

The 12v line have 12.1 volts with no load
The 5v line has 5.0 volts with no load.

Connecting my AC/DC indi 16X charger to the 12v line does not turn on the chager.

I can hook up a 27 turn stock brushed motor to the 5v line and it runs with a voltage drop to 4.8 volts.
The same motor on the 12v line "kills" the PS, too much current draw??

I have tried resistors in parallel and in series but still no current from the 12v lines.
I have no other DC charger to test so i very well may have a bad chrger for all I Know.

Any ideas?

Thanks,
Dzgruntld



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RE: How to convert an ATX power supply to rc use - 7/15/2008 11:14 PM   
chadr


 

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Status: offline 		you can test the 12v output with a voltmeter. If you want something that draws a load try some 12v turn signal or similar bulbs designed for cars.

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RE: How to convert an ATX power supply to rc use - 7/16/2008 1:02 AM   
dzgruntld



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Status: offline 		Chadr,

Thanks, I hate it when I over think it.

I have my light bar for dumping my NiCds after racing. Homer moment.

A single bulb works so far, taking the light bar apart to test with more than one bulb.

Thanks again,
Dzgruntld

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RE: How to convert an ATX power supply to rc use - 7/30/2008 1:04 AM   
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Status: offline 		so simply connecting the charger (i have an apache 2500 on the way) to a 12v and ground wire from one of the dongles (molex plugs for drives) isn't possible?

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RE: How to convert an ATX power supply to rc use - 8/9/2008 1:03 AM   
zjwhitrock



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Status: offline 		well I should have read this thread first, it would have saved me about 4 zaps to the hand (still numb) if there isn't a "sensor wire" you need to hook up a resister, motor, light bulb, fan, etc between a red and black wire.

its a good thing that in one of my PC classes they taught us to use only 1 hand

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RE: How to convert an ATX power supply to rc use - 8/10/2008 10:01 AM   
mrasmm


 

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quote:

ORIGINAL: AquarianGuy78

so simply connecting the charger (i have an apache 2500 on the way) to a 12v and ground wire from one of the dongles (molex plugs for drives) isn't possible?


if you mean while your computer is running? I'm sure you could, some of the risks would include, overloading the 12v rail with instant power off (most PSU's will do this when they get an undervolt to avoid frying anything), causing a power spike on the 12v rail and possibly damaging what is connected to it, if it's a cheap PSU which most of them people have in computers they haven't custom built it could cause the PSU to fail prematurely, and sometimes when they fail they take out something like a mobo or cpu.

If you're just talking about hooking them straight up to a PSU that is not hooked to anything, nope that wont work. The PSU's have failsafe circuitry to better handle power events inside a computer and power down when they sense something like that to avoid frying something inside the computer.

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RE: How to convert an ATX power supply to rc use - 8/10/2008 10:34 PM   
Edge3644


 

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Status: offline 		Hi,
My ATX won't work when disconnected from PC. Which wires should shortened
or switch put between in order to make it run?
Thanks

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RE: How to convert an ATX power supply to rc use - 8/11/2008 7:41 PM   
zjwhitrock



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Status: offline 		read the first post please

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RE: How to convert an ATX power supply to rc use - 8/11/2008 10:09 PM   
zjwhitrock



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Status: offline 		do you think a 100ohm risistor is too big?


http://www.radioshack.com/product/index.jsp?productId=2062293&cp=


or should I get one of these

http://www.radioshack.com/product/index.jsp?productId=2062291&cp=2032058.2032230.2032267&pg=1&searchSort=TRUE&y=6&retainProdsInSession=1&x=10&s=D-StorePrice-RSK&parentPage=family
http://www.radioshack.com/product/index.jsp?productId=2062292&cp=2032058.2032230.2032267&pg=1&searchSort=TRUE&y=6&retainProdsInSession=1&x=10&s=D-StorePrice-RSK&parentPage=family

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RE: How to convert an ATX power supply to rc use - 8/11/2008 11:27 PM   
Andrew


 

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Original: zjwhitrock

do you think a 100ohm risistor is too big?



Read the theory section in this page. It will explain why resistance levels are chosen and why a 100 ohm resistor imposes a lighter load than a 10 ohm resistor. There is a BACK link at the bottom of the page that will take you to the home page for the PSU Conversion site.

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RE: How to convert an ATX power supply to rc use - 8/12/2008 12:09 AM   
zjwhitrock



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quote:

Original: zjwhitrock

do you think a 100ohm risistor is too big?



Read the theory section in this page. It will explain why resistance levels are chosen and why a 100 ohm resistor imposes a lighter load than a 10 ohm resistor. There is a BACK link at the bottom of the page that will take you to the home page for the PSU Conversion site.



Ok, it makes some since

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RE: How to convert an ATX power supply to rc use - 9/11/2008 3:06 AM   
DeadSticker



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Status: offline 		So is there a way to get 13 volts outta these PS's? Mine (antec 550 with an 18a 12+}with 2 ice's charging 2 2s lipos at 4.5a puts out 12.08 volts. The reason i am asking is because my backlights are really dim on my chargers now lol... it works great but kinda annoying that if there is a light on in the room or after it gets dark with my pit light on its really hard to see. The guy up a few posts hooked the 5v and 3v sense wires together and got 13 v...what colors are the 3v and 5v sense wires?

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RE: How to convert an ATX power supply to rc use - 9/11/2008 3:21 AM   
Savage03


 

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Status: offline 		Little off topic but anyone tell me how to test a PS thats in the PC? Thinks its bad and fried my motherboard wanna make sure what I need to buy first.
THanks

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RE: How to convert an ATX power supply to rc use - 9/11/2008 5:50 AM   
kinzuagolfer


 

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Status: offline 		I happened to have an old PSU left over from upgrading my computer some time ago. Not sure if it has been mentioned, but if you have a square four pin (for the cpu) connector you might not need to mess with the sense wires. I didn't.
I only had to cut off the connector and used the two yellow and black for my positive and negative, and make a jumper from the green wire in the big (20 pin?) plug to a negative lead in the same plug.

I wired the positive and negative to terminals for my chargers clamps. I used a part that had four female plugs for audio cables on a TV (those red and white/black ones). Very simple.

Thank you for the guide. I would of never figured out that green wire without it.

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RE: How to convert an ATX power supply to rc use - 9/15/2008 7:08 PM   
chadr


 

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Status: offline 		any idea what needs to be done for this kind of power supply to work? I've already done an atx supply using these instructions but I can't figure out how to turn this one on...



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RE: How to convert an ATX power supply to rc use - 9/15/2008 11:03 PM   
Andrew


 

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Status: offline 		Your power supply is one of the older AT designs and is hard switched, i.e., it will not have a PS_ON line and cannot be powered off and on by the motherboard. Most of the AT PSU's will run without a pre-load resistor, but you may improve voltage stability and voltage levels by adding one.

You will need a double pole single throw switch - wire the switch so that white connects to white and black connects to black on the pigtail when the switch is on. Your particular supply does not follow the industry standards for AT's. Normally, wire colors are black, white, blue and brown. When your power supply is plugged into the wall AC outlet, the pigtail will be HOT, so don't get it crossed up or handle it.

I've attached a pic of a typical AT switch.

andrew

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RE: How to convert an ATX power supply to rc use - 9/15/2008 11:46 PM   
chadr


 

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Status: offline 		thanks, so i can't connect the white to white wire and the black to black without this special switch so its on whenever the power supply is plugged in?

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RE: How to convert an ATX power supply to rc use - 9/16/2008 2:28 AM   
Andrew


 

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Status: offline 		You can, but the power supply will power up when plugged in and continue running until it's unplugged from the wall. The switch simply adds some convenience.

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