hands without shadows

After posting this a few times I figured it was time to do a proper write up with pics.

How to convert an ATX power supply to rc use

Step 1. Collect Required Materials

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Step 2. Case Design

Take the cover of your power supply, there should be 4 philips screws holding on the top. Short the two big capacitors with a screwdriver or the big resistor so you dont kill yourself. Look for a good section of room where you will be able to hide wires and have the bottom of your banana jacks not touch anything. Then mark on your case where you will mount your banana jacks. The amount of banana jacks you use is up to you, I used four commons, two +12v, a +5v, and a +3.3v. To run a charger all you need is a common and a +12v but I wanted the option to run two chargers, test radio equipment, and have a +3.3v for labs.

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Step 3. Cutting the Case

Cut out holes in the case to mount your banana jacks, switch, and led (switch and led are optional). I suggest you buy the banana plugs from radio shack and buy single ones instead of buying connected ones like I used, these ones are hard to mount, its not that I suck at metal work its just that drill bits wont drill straight when metal is this thin.

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Step 4. Completing the Case

Mount your banana plugs, switch, and led.

To make the banana jacks I used fit tightly you have to shave down the ridge on one half of the plug. I shaved down the black ones because they will be mounted inside the case.

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Step 5. The Electronics

Look at the big 20 pin plug and see if any of the pins have 2 wires going to it. One of the orange wires in the corner should have a light orange or brown wire connected to it. You may also have light red and yellow wires connected to regular red and yellow wires. These light (or brown) wires are called sense wires and must be connected to their darker coloured wires for the power supply to function. Whether you connect these separately and heatshrink them or connect them to the banana plugs is up to you, I connect them to the banana jacks. You have to connect the sense wires whether you use those voltages or not. Remember what sense wires you have and go ahead and cut of all the plugs, dont cut the wires so short that you cant connect the banana jacks but dont leave them full length either or they wont fit in the case.

Solder a red wire and a black wire to opposite ends of the big 10 watt, 10 ohm resistor. Heatshrink the ends and mount the resistor using zipties in the path of airflow. This adds a small load to the power supply which it needs to function.

Next solder 3 black wires to a banana plug, this will be common or ground, I have 4 commons. To have +12v solder 3 yellow wires and, if you have one, the +12v sense wire (light yellow) to a banana plug, I have two +12v lines. To have a +5v line solder 3 red wires and, if you have one, the +5v sense wire (light red) to a banana plug. Finally to have +3.3v solder 3 orange wires and the +3.3v sense wire (light orange or brown) to a banana plug. You dont have to use 3 wires for each plug but use at least 2.

Soldering to the plugs I used is a royal PITA so I soldered my wires to small spade terminals and bolted those on.

Optional: Solder a black wire and the green wire to the switch, if you dont want to have a switch solder the green and black wires together and cover the joint with heatshrink. The green wire must be grounded for the power supply to turn on.


Optional: Solder a 220 ohm resistor to the led cathode (-) and solder the other end of the resistor to a black wire, solder the anode (+) of the led to the gray wire. This will function as a power on light. If you don't want an led clip the gray wire short.

The colours arent as I described because I used extensions, you cant see the resistor because I covered it with heatshrink.

Check to make sure you connected everything (especially sense wires) and cut all the remaining wires short, cover the ends with heatshrink so that nothing will short inside the power supply.

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Step 6. Reassembly and Test

Carefully fit all the wire inside of the power supply and position the case on (it helps if you didn't use long lengths of wire and ziptie all the wire into a big bundle). Screw in the 4 screws that held on the case, plug it in, and turn it on. The led should light up and the fan should start running. If you didnt use a switch or led the fan should come on when you plug it in.

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Step 7. Final Check

Hook up a multimeter to all the different combinations and check voltages, your exact voltages probably wont be the same but they should be close.

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Some Basic Troubleshooting

Nothing turns on
-check connections, especially sense wires, switch, and resistor connections
-check if there is a switch on the back of the power supply

No voltage on some or all lines but fan turns on
-check banana jack connections

Led doesnt light up but fan turns on
-check led polarity

Burning smell
-you messed up and let the smoke out


Please use common sense when doing this. Dont do this if you dont feel comfortable with any of the steps. Dont blame me if you screw up. If you want to post this anywhere else you can do so without contacting me but please give me credit.

If you dont feel comfortable doing any of this dont do it, r/c fan-addict's method is much easier and safer.

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R/C fan-addict

okay HWS asked me to post up my way of the same procedure. Using my method will allow you to not have to open the case. Pretty much what you do is you snip off all the connectors except for the 20/24 pin (the biggest one). Then you isolate all the yellow wires and all the black wires. Strip the ends of all the wires, twist them together, and put a dab of solder on the end. Then solder on your banana clips or if you want to go alligator clamps then just do nothing. Instead of the resistor and jumper wire you can instead use a powersupply tester. Step 1: buy a PS tester. Step 2: plug it into the 20/24 pin connector. Step 3: attach it to your PS and make sure it has good airflow since it is a resistor and it will get hot! That's it. A PS tester will run you about $5-8, if you pay more you're probably buying one with a voltage tester on it or some other completely useless crap. Just get the cheaper version, it works well. So there you go, the PS costs you $20 and another $5 for the tester and you have a fully functional R/C powersupply for $25. Sure beats paying $100 at the hobby store!

BTW: I know this is my first post in a long time, I kind of left RCU and I'm not really going to come back at least soon. I only posted this because HWS asked me to.

Andrew

[link=http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM]How to convert an ATX powersupply[/link]

hands without shadows

Thanks RC, I appreciate it. I hope you come back sometime, you were always a great help.

hands without shadows

Unless you read the design guide update carefully that method doesnt work because it doesnt refer to any sense wires besides the 3.3v sense wire (brown or light orange).

Andrew

Did you read the last paragraph in the [link=http://web2.murraystate.edu/andy.batts/ps/DESIGN_GUIDE.HTM]design guide update[/link]? I suppose the assumption was that you would read the section on remote sensing carefully -- it does reference sensing on the +5v and +12v rail. I have also seen one supply with a sense wire on ground.

I've converted around 80 or so supplies and run latch and voltage level tests on well over 200. There is a lot of variation across models - some supplies will latch and hold without a preload; some will not. A few will run without reconnecting the sense wires; the majority will not. Stability under load varies considerably -- Antec and Sparkle have performed well. To cover all the bases in the conversion process places some burden on the reader to be equally diligent.

If there is mis-information in the conversion, I would appreciate knowing.

andrew

hands without shadows

I meant that the sense wires are not mentioned in the general conversion, just in the design update.
In the few psus that I have converted I have never seen a sense wire on ground, it's interesting that it's there but I see no need for it, Ill edit my write-up (again) and add that. As far as I know all ATX power supplies require a load to function while the older AT power supplies do not, are you sure you didn't test AT ones? Please let me know so I can add that. Thanks for the info hat some psus will work without connecting the sense wires too, Ill add that in there too.

Andrew

I would not bother with adding a comment about a ground sense wire -- in probably 1500 supplies I've looked closely at, I can only recall one -- an offbrand. I don't know why it was added or what its function would be.

The majority of ATX supplies do require a load, but some will latch without a load. I got in some of the new large fan 300W Sparkles the other day that latched without a load -- measured voltage was 12.3v on the 12v rail. However, I still recommend a preload since it helps stabilize the 12v rail when under load.

I crack hundreds of boxes a year in my work -- we keep a couple of AT supplies on the shelf for Show and Tell, but we haven't had an AT box in inventory for 7 or 8 years.

andrew

GTB

Were is the battery for it?

That's not a power supply if you can't use it anywhere.

hands without shadows

It plugs into a wall......

Codeblack

lol, use your buttocks as a battery GTB

healthyfatboy

Will an ATX Switching Power Supply work for this mod?

Gigaah

What do you guys think of something like this? All the jumper and resistor hocus pocus wrapped into a neat package.
I made a couple for friends and myself. The unit below would be a 10amp version due to the binding posts rating, and Its only using the one yellow wire from the 20 pin connector.
This particular one is only wired for 12volts. Has an LED so you know its on. This one has no switch because we just unplugged the thing when its not in use.
I wonder if others are interested and if its worth my time to offer somethiing like this since I don't know what people would pay for it.

hands without shadows

Yes.

hands without shadows

A PSU tester is around 15 bucks and is essentially the same thing without the binding posts. I think your little box there could sell for around that mark to people that cant solder, dont want to void a warranty, or dont feel comfortable doing the mod. Personally I like the idea.

3d Marky

Amendments to the designs.

1) Why not use a 3.3 ohm ballast 10w resistor instead of a 2 ohm if you struggle to get 12v from your supply. Using 3.3 ohm means you can still use just a single 10w resistor using the case as a heatsink. Wattage will be around 8.75
I found that there is only a minimal increase of .1 - .15 of a volt between the two values.
Once you go below 3.3 ohms you must use two 10w 1ohm resistors in series (2 ohm’s) as the current will be above 13.5w and will burn out a single resistor.

2) Only bundle 2-3 wires of each colour together when soldering to the connectors. You do not need to use all the wires as stated in the tutorials as the current will never be that high. Cut off the unused wires or your end up with a mess in the case.

3) The ATX cooling fan can be very noisy so simply add a 50ohm 1/2w resistor or higher in line to the positive of the fan. This runs much quieter but still gives a reasonable air flow through the case.

hands without shadows

1) The 3 local-ish Radioshacks never seem to have anything but the 10 watt, 10 ohm resistors so thats why I went with them. The ones you listed will work if you can find them.

2) My instructions say to solder 3 wires to each plug, and later that you dont have to do 3 wires but should at least 2.

3) Good idea. Some high quality bearing oil (I use Singer bearing oil......yes the sewing machine company) or a ball bearing fan will cut down ont he noise a lot too. If you are going to oil the fan dont use wd-40.

drevil

My Feedback: (5)

Good how to. I've got a question though. On [link=http://forums.radiocontrolzone.com/showthread.php?t=238105]another forum[/link] I was told that it's better to use six 10w 10ohm resisters on the 5v side to bring up the amperage on the 12v line. Does this sound right? Every other article I've read about converting these has said to use only one 10w 10ohm resistor.

mrasmm

I would say it really dpends on your power supply. For most I think a single 10w is a bit weak, but if it works then it works =) I personally have four 1 ohm 10 watt resistors in series for a total of a 4 watt load, and a total of 6.63w power dissipation, or 1.65w per wirewound, and that brings me up to 12.2v

The main thing to remember is TPD or Thermal Power Dissipation. The resistors are designed with a 10w max load so you don't want to go over that. Above a certain point they will need to be sinked or they will get really hot. How you figure that for your 5v rail is 26.5225 divided by the # of watts you have, so if you want to have 2 watts resistance then you would have to dissapate 13.26w of power, if you only had 1 resistor it would cook, and if you had 2 of them without sinking them, they would get very hot.

hopefully that answers your q

3d Marky

Anything down to 2 ohms requires no more than two 10w resistors. If you stick to 3.3 ohns you can get away with one however always heatsink it to the power supply case with some thermal paste. The airflow from the fan/s will also keep the resistor cool. Remember wire wounds are designed to run warm but don't exceed their rating.

dondeaida

Well... Simply forget the resistor thing (just turn off or unplug the power supply when not in use) ATX Switching mode power supplies these days are designed so that it will not be damaged as long as there is a very very little load present and since all ATX power supplies have a fan in it, a small load is always present. This makes "max power save mode" possible in which all data in RAM is saved to harddisk and basically the computer shuts down (Some ATX supplies even shuts down its own fan and still no damage) A very small additional load should wake up from this max save mode to full power via implementations like mouse break or wake-on-lan. This means charging batteries alone should wake up ATX to full power (It may not in rare cases, explained later)

Bottom line: You do not need a resistor. And if you are a worrying type, do this (even though you do not need to do this) : Hook up the batteries BEFORE you plug in the ATX to the wall and when charging is done, unplug ATX from the wall first and then take those batteries out.

*
If you still cannot live without a resistor and need a heat source in cold weather, hook it up to 5v. This is because motherboard works at 5v and it is this 5v load that brings ATX supply to full power (mouse break, wake-on-lan are all 5v based) But the fan in power supply is 5v on the first place, so basically most ATX are ever-ready and you do not need a resistor in 5v line.

**
In rare cases ATX power supplies will not wake up at 12v load (A very few ATXs' can't convert 12v load into 5v load) In this case, you do need a 5v load but a small one will do (resitor is not a good idea anyways since it creates lot of heat. use a led or a fan instead. CPU fans are 5v)

motohead400

For charging batteries with this, do you need to be concerned about the amperage? Wouldn't an adjustible amperage control be needed or something?

Or is this solely for powering a DC in - DC out charger?

mrasmm

welcome to RCU =)

as far as this mod, it's basically just a power supply to power an external DC charger. I guess if you wanted to you could put control circuits in there to regulate voltage and amperage, but if you're to that point you would probably just want to custom build your own power supply that fits the purposes rather than use a pre exisiting PS that you have to mod.

motohead400

Sounds good--I figured it was probably just for use as a DC power source, but wanted to make sure.

mrasmm

hrm... I know you are trying to be helpful and conribute and help people out, and I commend that =) I'm just not sure how accurate all this info is.

when you put your computer in standby, none of the info is on the hard drive, it's all in the ram, and that is why you need to keep power to the computer and you can't unplug it. Yes it is true that some computers turn off the fans during this because it only consumes about 9 to 20w of power. With something like hibernate it writes the info the hard drive and completely shuts the machine down. You could completely disconnect and take out the power supply, put in a new one, power it on, and be right where you left off.

The 5v rail that all the stuff like WOL or WOR your mouse keyboard WOUSB and all that sort of stuff runs on a completely different rail. The 5v standby rail, which is usually rated something like 500mA to 3A or so.

Most power supplies have a fail safe ciruit in them when you don't have something hooked up to the 5v rail, it wont power on. This is to prevent shorts and frying your mobo, or causing a fire or something along those lines. Most power supplies will not run without a load on the 5v rail. I don't think a 5 to 20mA LED or a 0.20A computer fan will be enough of a load on the 5v rail to switch this protection circuitry, but I've never tried it, so I guess it could be

The main reason people are putting resistors on the 5v rail, is because this is how the PSU controls the votlage of the 12v rail. The more load that is on the 5v rail, the higher the 12v rail goes. With no load it runs right around 11v if your PSU will turn on, and if you are drawing more than a couple of amps to charge your packs you could get below 11v pretty easily. This is what's called an undervolt. If you have an expensive charger it will either pause charing, sound an alarm or turn off, or somtehing like that. If you have a less expensive charger, it could just fry it. Also running on a lower voltage basically causes more heat to build up in your charger because of conversion and inefficiency factors.

Hopefully that makes sense =)

Basically a bunch of EE's and people with electronic circuitry background would not be writing a how to guide telling you to put in this resistor if there wasn't a good reason for it =) and telling you that you have to put it in if it's not required. Some would atleast explain it is optional and what it's function is.

If you can get your PSU to run without a resistor on the load, then that's great =) and if you also have a charger that doesn't mind the lower voltage and doesn't get hot on it, then something like this would definately work for you.