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RE: How to convert an ATX power supply to rc use - 3/7/2011 1:39 AM   
lbarnes


 

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Status: offline 		Well, go to radio shack and get a LED indicator (lot's of choices) and the dropping resistor for 12V.

Wire the dropping resistor in series with the LED and then connect the Neg side of the LED to the Neg side of your 12V output nd the positive side to the + side.

Radio Shack has a lot of options for indicator lights and you should find one fairly cheap.

Larry

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RE: How to convert an ATX power supply to rc use - 3/7/2011 1:50 AM   
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Status: offline 		Larry,

Thanks for your response, but could you explain what the 'dropping resistor' is for.

Karol

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RE: How to convert an ATX power supply to rc use - 3/7/2011 1:56 AM   
lbarnes


 

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Status: offline 		Well, LED lights just by themself operate on 2 -3VDC. This depends on the size, color and type of LED.

When you go to radio shack the package will tell you the forward working voltage of that LED. Depending on what the source voltage is (5 or 12V) you will need a dropping resistor to reduce the source voltage to the working voltage of the LED.

I have also seen some power indicators that are housed in a nice looking LED holder and then already have the resistor install in the holder so you just hook up to 12Vdc and your good to go.

Larry

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RE: How to convert an ATX power supply to rc use - 3/7/2011 2:17 AM   
karolh


 

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RE: How to convert an ATX power supply to rc use - 3/7/2011 3:03 AM   
Andrew


 

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Status: offline 		You can pick up an LED from most any electronics shop or on-line. LEDs are polarized which means that the leads must be connected to the correct positive and negative rails. If it is a new LED, the positive (or anode) connection will be longer. If used, the negative side (or cathode) will be the lead closest to the flat on the side of the base. Place a 180 ohm 1/4W dropping resistor between one of the leads and the powersupply rail - the resistor is necessary to control the amount of current passing thru the LED. Connect the positive side to the +5 rail (red) and the negative side to a ground rail.

The easiest way to mount the LED is to use a 1/8" grommet. Drill the case just large enough to snap the grommet in place and push the LED into the hole - a diffused lens LED will show up better from the side than one with a clear lens.

andrew

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RE: How to convert an ATX power supply to rc use - 3/7/2011 4:44 AM   
karolh


 

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Status: offline 		Which of the led leads is a better option to place the resistor, the negative or positive.

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RE: How to convert an ATX power supply to rc use - 3/7/2011 4:55 AM   
Andrew


 

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quote:

ORIGINAL: karolh

Which of the led leads is a better option to place the resistor, the negative or positive.



It doesn't matter.

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RE: How to convert an ATX power supply to rc use - 3/7/2011 5:10 AM   
karolh


 

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RE: How to convert an ATX power supply to rc use - 3/7/2011 2:49 PM   
lbarnes


 

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Status: offline 		Karol,

I didnt reliaze your in Jamaica.. You most likely dont have a Radio Shack down the street.

Follow Andrew's instructions and you will be ok.

Larry

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RE: How to convert an ATX power supply to rc use - 3/7/2011 11:34 PM   
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RE: How to convert an ATX power supply to rc use - 3/30/2011 2:43 PM   
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Status: offline 		Please take a quick look at this, if you get chance:-
-
http://www.rcuniverse.com/forum/m_10433998/tm.htm
-
I have now blown two ATX psus!!!
-
Many Tks, Steve

< Message edited by StevieM -- 3/31/2011 8:41 AM >

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RE: How to convert an ATX power supply to rc use - 4/1/2011 12:18 PM   
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Status: offline 		I also need some help...electrical for dummies.

I purchased a coolmax CA-400 and when I plug the PS into my old desktop, it works. Without the any connections I get no output voltage. The Users manual for the PS says the following

"A short circuit on any DC output will cause the power to latch. The power supply
will withstand a continuous short circuit to the output without damage or overseers
to the unit. The +5VSB can be shorted indefinitely and will recover automatically when
the short is removed."

I bought the 10W/10O resistor and I am pretty sure I need to solder the resistor to the +5VSB noted in the instructions above to get output voltage. Two questions:
1. Is this correct and
2. Which wires are the +5VSB? Step 5 in the original thread said to look on the big plug for a connection with 2 wires going into it...I will have to look when I get home from work, but does this sound right?

Also, the specs on the PS are:
3.3V@30A, +5V@28A, +12V1@14A, +12V2@15A, -12V@1A, +5VSB@2.5A

My thought was keep the 2 12V output separate so I could run 2 chargers from the single PS which woulud give me 168W and 180W. Any thoughts?

Thank you in advance!!

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RE: How to convert an ATX power supply to rc use - 4/1/2011 1:17 PM   
Andrew


 

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quote:

ORIGINAL: StevieM

Please take a quick look at this, if you get chance:-
-
http://www.rcuniverse.com/forum/m_10433998/tm.htm
-
I have now blown two ATX psus!!!
-
Many Tks, Steve


Will send you a PM -
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RE: How to convert an ATX power supply to rc use - 4/1/2011 1:57 PM   
Andrew


 

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quote:

ORIGINAL: bpenner697



I bought the 10W/10O resistor and I am pretty sure I need to solder the resistor to the +5VSB noted in the instructions above to get output voltage. Two questions:
1. Is this correct and
2. Which wires are the +5VSB? Step 5 in the original thread said to look on the big plug for a connection with 2 wires going into it...I will have to look when I get home from work, but does this sound right?

My thought was keep the 2 12V output separate so I could run 2 chargers from the single PS which woulud give me 168W and 180W. Any thoughts?



1. It is not correct. The +5VSB (volts standby) will meter +5 volts as long as the supply has AC power, even though the supply does not appear to be running. It's purpose is to keep the NIC (network interface card) and motherboard powered at a minimal level so that the computer may be started remotely. The is referred to as "Wake on LAN". The technique is used in corporate and educational environments where desktop computers are managed centrally. System administrators have the ability to power-up computers over the network so software and updates can be pushed from a central server even when the user may have turned the machine off. +5VSB is purple.

Your load resistor should be attached between any +5v rail (red) and DC ground (black). Even with a load resistor in place, the PS_ON rail (green) will need to be shorted to ground (black) to get the PSU to latch on.

2. The 3.3v remote sense will be either a smaller gauge brown or orange wire attached to one of the 3.3v rails (orange). These two should be tied together when you make the conversion. The remote sense wire is used by the regulation circuitry to maintain 3.3v at the point where the connector plugs into the MoBo. It was added to compensate for voltage drop on the 3.3v rail due to long cables used to fullsize towers and when the board pulls more power.

CoolMax does have a good reputation in the PSU market, but even though the specification placard states a max of 348W for 12V1 and 12V2 combined, it is likely overrated and you may not pull that level of power continuously. Some supplies have separate circuits for 12V1 and 12V2 and some simply pull both rails off the same pad. You can still run dual jacks for two chargers, but just keep in mind that full power simultaneously from both rails may not be feasible.

andrew

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RE: How to convert an ATX power supply to rc use - 4/2/2011 4:49 AM   
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Status: offline 		Andrew...thank you much for the reply. I will trying the mod hopefully this weekend.

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RE: How to convert an ATX power supply to rc use - 4/2/2011 1:40 PM   
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Status: offline 		one other question...i have a 4 pin connector that has 2 yellow and 2 black. Is it safe to assume this is the ATX12V2 line...it's not a yellow striped wire? All of the wires are yellow and none are striped.

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RE: How to convert an ATX power supply to rc use - 4/23/2011 9:41 PM   
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Status: offline 		Its been raining sideways for a week, there is no end in sight, the outlaws will be here all weekend for Easter, my wife is wired (no pun intended) so I figured; why not convert that Compaq power supply?  Shocking myself unconscious until Monday morning isn't looking like such a bad thing!

But it didn't work.  Here is what I did based on about as much reading (including this thread) that I could do:

1.  Orange and brown grouped together.
2.  Red grouped together.
3.  Black grouped together.
4.  One black to a 10-Ohm 10 watt resistor; one red to the other side
5.  One black to a LED w/built in resistor (black wire side of LED); The only grey wire present; attached to other end of LED (red wire side of LED)
6.  One black to DC switch and the only green wire present; attached to the other side of the switch
7.  The following wires are leftover (kind of like the extra bolts on that swingset from 25 years ago that is still standing in the backyard):

One yellow (minus 5 volt)
One blue (minus 12 volt)
One purple (fan off and JP16)
One white (the circuit board says 50 and JP24, can't tell which label is for the white wire)

So I plug it in and I don't get anything.  No LED, no fan, nothing.  No smoke either

I recognize that it might not be possible to get this debugged in this forum setting...that's ok.  But if someone can see a quick fix based on what I identified that would be great.  If I could just get it running I can test all the voltages with my meter and make connections to my binding posts etc.

Thanks..



 

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RE: How to convert an ATX power supply to rc use - 4/25/2011 4:24 PM   
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RE: How to convert an ATX power supply to rc use - 4/25/2011 7:32 PM   
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Status: offline 		Tom,

When I tried mine, I attached only the critical items first to ensure my PSU started. I did not and still do not have an LED or a switch. My PSU came with a switch on the back by the AC connection. I am NO expert but did get mine to work, mostly. I am still trying to figure out how to differentiate the 12V1 and 12V2 because the wires are all yellow.

The only item I notice in your write-up is the connection of the green wire to the switch. When I asked the question, I was told (ref. post dated 4/1 by Andrew) that the green needed to be shorted to ground so I connected the green and black together and mine worked.

My PSU shut off when I accidentally had it shorted out (thankfully) so I didn't smoke anything. Here's how much of an electrical idiot I am...I didn't use insulated binding posts and wondered for about a day while mine did not start. The light bulb finally went off and I figured that I had both the 12v and 5v lines shorted because of the posts I bought. I found the non-insulated posts at Radio Shack and then everything worked.

I did re-install a new resistor this weekend and got the 12v line above 12v without a load (gained about 0.10v with 10ohm/10W resistor on the 5V line). When I connected my charger this weekend I noticed the output dropped to about 11.85 to 11.9v with load.

I have 2 outstanding questions if anyone can help:
1. Is there anyway to increase my 12v voltage under load? Will a bigger resistor on the 5v line help?
2. How can I tell my 12V1 vs. 12V2 lines apart? I tied the 2 yellow wires (no stripes) off the 4pin connector and they have the same voltage with no load as the other yellow wires with load. I have 2 separate posts and 2 separate grounds with the hope of running 2 chargers from this PSU.

Thanks again...Brian.

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RE: How to convert an ATX power supply to rc use - 4/25/2011 8:16 PM   
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Status: offline 		THANK YOU FOR TAKING THE TIME TO WRITE.  PLEASE SEE CAPS BELOW:

quote:

ORIGINAL: bpenner697

Tom,

When I tried mine, I attached only the critical items first to ensure my PSU started. I did not and still do not have an LED or a switch. My PSU came with a switch on the back by the AC connection. I am NO expert but did get mine to work, mostly. I am still trying to figure out how to differentiate the 12V1 and 12V2 because the wires are all yellow. WELL, I HAVE BEEN USING A MAGNIFYING GLASS AND A FLASHLIGHT TO TRACE A WIRE BACK TO THE CIRCUIT BOARD AND USUALLY THERE IS SOME KIND OF INDICATION PRINTED AS TO WHAT IT IS FOR.  LIKE MY GREY LINE SAYS "AUX GROUND" AND I CAN FIND ALL THE -12V, +12V LINES ETC. THE SAME WAY.

The only item I notice in your write-up is the connection of the green wire to the switch. When I asked the question, I was told (ref. post dated 4/1 by Andrew) that the green needed to be shorted to ground so I connected the green and black together and mine worked.  YES, THE GREEN IS A SENSE WIRE AND BLACK (GROUND) IS THE OTHER SIDE OF THE SWITCH.  I'LL ELIMINATE THE SWITCH FOR NOW THOUGH AND SEE IF I CAN GET SOMETHING TO WORK.  I LIKE THAT IDEA.

My PSU shut off when I accidentally had it shorted out (thankfully) so I didn't smoke anything. Here's how much of an electrical idiot I am...I didn't use insulated binding posts and wondered for about a day while mine did not start. The light bulb finally went off and I figured that I had both the 12v and 5v lines shorted because of the posts I bought. I found the non-insulated posts at Radio Shack and then everything worked.  HEY...I CAN'T CALL ANYONE AN IDIOT ON ANYTHING...MY PROFESSIONAL PURSUITS ARE SO TOTALLY DIFFERENT FROM MY HOBBY THAT I CAN ONLY LEARN THIS STUFF BY READING AS MUCH AS I CAN WITH LIMITED TIME.  SOME GUYS ON RCU TALK ABOUT THIS STUFF IN THERE SLEEP!

I did re-install a new resistor this weekend and got the 12v line above 12v without a load (gained about 0.10v with 10ohm/10W resistor on the 5V line). When I connected my charger this weekend I noticed the output dropped to about 11.85 to 11.9v with load.  YOU KNOW, I JUST CONVERTED A DELL POWER SUPPLY AND THE VOLTAGE DROPPED ABOUT THAT MUCH WHEN I CHARGED ONE OF MY A123 BATTERIES.  SOMEONE SAID IT WAS MOST LIKELY BECAUSE I WAS PUSHING THE POWER SUPPLY, IT WAS PRODUCING ABOUT ALL THE AMPS THAT IT COULD AND THAT IS WHY THE VOLTAGE WAS DROPPING.  I'M HOPING THE ATX UNIT WILL DO BETTER AS I WOULD LIKE TO CHARGE MORE THAN ONE BATTERY AT A TIME.

I have 2 outstanding questions if anyone can help:
1. Is there anyway to increase my 12v voltage under load? Will a bigger resistor on the 5v line help?
2. How can I tell my 12V1 vs. 12V2 lines apart? I tied the 2 yellow wires (no stripes) off the 4pin connector and they have the same voltage with no load as the other yellow wires with load. I have 2 separate posts and 2 separate grounds with the hope of running 2 chargers from this PSU.  TRY THE MAGNIFYING GLASS!

Thanks again...Brian.



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RE: How to convert an ATX power supply to rc use - 4/25/2011 8:38 PM  1 votes
bgosselin


 

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quote:

ORIGINAL: bpenner697
I have 2 outstanding questions if anyone can help:
1. Is there anyway to increase my 12v voltage under load? Will a bigger resistor on the 5v line help?
2. How can I tell my 12V1 vs. 12V2 lines apart? I tied the 2 yellow wires (no stripes) off the 4pin connector and they have the same voltage with no load as the other yellow wires with load. I have 2 separate posts and 2 separate grounds with the hope of running 2 chargers from this PSU.


1: Loading the 5v line usually just makes the 12v line more stable, but doesn't do a whole lot to increase the voltage. Drawing at least 1A on the 5v line helps a lot for stability. Depending on the design, there are a few ways you can actually boost the 12v line.

Sometimes (rarely), there is a small potentiometer on the board. If it's present, you can try tweaking it a little (no more than 1/8 turn at a time) and see what it does - if it does nothing, put it back where it was. Don't be surprised if you can only get around 13v or less because the overvoltage circuit may kick in.

Another way is to mess with the brown feedback wire; basically make a voltage divider that fools the PS into thinking that the 3.3v line is outputting less voltage than it really is, so it boosts the output a little more to compensate. This in turns boosts the 5v and 12v lines too. There is a limit to how much extra voltage you will get before the overvoltage circuit kicks in, but that takes trial and error. Below is a pic that gives you an idea what I mean. Note that this pic is for a different type of mod, but the principle is the same. Where is says "12 Power" use an orange 3.3v wire, where is says "12v sense", use the brown sense wire. In this pic, the use of the two diodes makes the sense wire see ~1.4v less than what there really is. This makes the regulator boost the 12v output until the sense wire is at 12v, which makes the 12v line closer to 13.4v. If you were to do this on the 3.3v line, you should only use 1 diode and even that may be too much in which case you may be forced to use resistors only to have finer control over the ratio.



A final way to boost the output would be to modify the regulator circuit itself, but that's probably beyond but a very select few to accomplish.


2: You'd have to pull the circuit board out and see where the yellow wires attach. Usually, there is a bunch of wires that go to a single solder lug, somewhat like a bullet connector, that is soldered to the PCB. So, it's usually pretty easy to see what goes where.  The grounds likely all go to one point electrically.



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RE: How to convert an ATX power supply to rc use - 4/26/2011 3:03 AM   
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Status: offline 		Eliminating the switch...for now..has helped a little bit.  I am now getting 5 volts on the single white (?), purple (fan-off), yellow (-5V) and blue (-12V) when I test voltage using grey (auxgnd) as the other lead.

No fan.  No 12 volts.

Does anyone have any additional thoughts for me?

Tom

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RE: How to convert an ATX power supply to rc use - 4/27/2011 4:39 AM   
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OK guys...not feeling too much love but that kept me working at it and I figured this out pretty good.  I went to a different power supply unit and had much more luck.  Maybe the other one was bad!

Anyway, I have a supply that is operational now.  I have a switch, LED, fan and all voltages (3, 5, 12) working properly.  I also learned that the wire labeled "SB" on the circuit board is a stand-by line...always 5 volts running through that when my unit is plugged in regardless of switch position.

Interestingly, I have a blue wire that is -12 volts when the unit is on.  When I turn it off, the voltage slowly decreases all the way to 0 volts and then increases up tp .34 volts and stays there.

Here is my question:

I would like to have four total outputs. 

1.  One 5.05 volt line (purple wire) that I can use for driving servos etc.
2.  Three 12.12 volt lines (yellow wires) that I can use for charging batteries; one yellow wire to each output.

I have a quick question on the yellow wires. They are 18 guage and I have three of them; each rated for 90 degrees C and 300 volts.  I was reading a wire guage amperage table which indicated 18 guage wire can handle 16 amps (I believe I am interpreting that correctly).  The biggest batteries I have are 11.1 volt bind and fly stuff and usually I am just charging some 6 volt A123's and some 4.8 packs for my son's trainer.  I'm sure the power supply can handle any of those items individually.

I know its been talked about here before, but I am still unclear on how I can anticipate using these outputs at the same time.  For example:

Output 1:  Quick field charger for the 4.8 volt NiCad
Output 2: Multi 4 charger for the 6.0 volt A123
Output 3: The cigarette lighter type charger that comes with the bind and fly stuff to charge the 11.1 volt Lipo

How do I calculate the total demand and I guess I would compare that to the 8A that the power supply is rated for on the 12 volt line (250W total for the supply)?  Sorry guys.  I know this stuff has been kicked around before but I am just not smart with this.

What can you tell me please about calculating the total demand?

Thanks very much!

Tom



 



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RE: How to convert an ATX power supply to rc use - 4/29/2011 3:54 PM   
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Status: offline 		Tom, it's good to hear that you are having more success...I unfortunately can't answer your question. The only thing I would know to do is compare the consumption in terms of watts of the chargers (should vary with the batteries being connected I would think) to the output of the power supply. I understand that most PSUs are overrated for marketing purposes so a 250w PSU may only actually output 200w. A question on your setup: Did you combine your 3 12v outputs into a singe terminal or do you have them as separate terminals? I would be interested to see what kind of performance you are seeing...12v voltage with load vs voltage without load.

On my PSU there are 2 separate 12v lines so I made 2 separate 12v terminals (3 yellow wires combined to 1 post, 1 yellow wire to the other post). I was using 1 output for one of my chargers and then connected a second charger to the second output. The result was my PSU shutting off immediately because I think I created a short. What I believe is going on is that the two 12v outputs are not the separate lines they are on the same line so I need to figure out the 12V1 and 12V2, which I just haven't had a chance to do yet.

BGOSSELIN - thanks for the info...I am going to try the diodes this weekend. I notice there are several kinds of diodes (zener, barrel, rectifer, etc). I found a rectifer diode...will this work?

link: http://www.radioshack.com/product/index.jsp?productId=2036270

the product information

Your project may not be simple, but finding the right parts for it is. 30 amp surge. Type: 1N4004. Peak Inverse Voltage (PV): 400.

Peak Reverse Voltage: 400V (Max)
DC Blocking Voltage: 400VDC (Max)
Forward Rectified Current: 1A
Silicon Rectifier
Diffused junction
Maximum Average Forward Voltage Drop: VF= 0.8 Volts
Non-repetitive Peak Surge Current: IFSM= 30 amps for 1 cycle
Maximum Reverse Current @ 25 degrees C: IR= 10uA
If I read the tech information, I should bump up 0.8 x 2 = 1.6v + 12v = 13.6v projected output...does this seem right?

One last question, you show a squiggly (resistor I think) on the diagram after the diode to 12v sense connection before the connection to ground. What's the purpose and do I need one? If so, what size?

Thank you in advance!!

< Message edited by bpenner697 -- 4/29/2011 4:22 PM >

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RE: How to convert an ATX power supply to rc use - 4/29/2011 4:11 PM   
bpenner697


 

Posts: 12
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From: Houston, TX, USA
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How do I calculate the total demand and I guess I would compare that to the 8A that the power supply is rated for on the 12 volt line (250W total for the supply)? Sorry guys. I know this stuff has been kicked around before but I am just not smart with this.

TOM - It's a bit of a slow day at work so I am going to make a run at your calculation for my own edification:

DEMAND:
quick charger = 4.8v x 1500ma battery = 4.8 x 1.5A = 7.2W
multicharger = 6v x 2000ma battery = 6.0v x 2.0A = 12W
lipo = 11.1v x 2200ma battery = 22.2W
consumption to operate chargers = no clue but they use some amount of power...assume 12v x 1A each = 12W x 3 chargers = 36W

So adding up the total DEMAND = 7.2 + 12 + 22.2 + 36 = 77.2W

SUPPLY:
8A max on your 12v line x 12v = 96W
20% overstated capacity = 96W x .8 = 76.8W

I would say the chances of operating all 3 chargers at the same time is very questionable...but that's my math. I'd like a guy who knows this stuff better to chime in...

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