skiddriver

Please excuse the slight thread creep, but I wanted to know if there is a commercially available product or a step-by-step DIY to make a DC-to-DC converter to change the +5VSB output to +12V. I've done an extensive Google search, and while it is evident that this is possible, all I've really been able to find are circuit diagrams that I do not have the knowledge to turn into a working device. Buy parts and solder together - yes. Decipher circuit diagram - no.

As for the "why". I want to convert an SFX PSU to use as a home power source for a car CD/receiver, and I need a constant 12V source to power the memory input. I could tap off the 110 VAC input and use a wall wart as a separate component, but as I don't have any other use for the +5VSB rail, I thought it might be a neat way to do it.

The SFX PSU +5VSB rail I'm using is rated at 2A, so the step-up output should be 500mA to 800mA which will be sufficient.

Any help would be appreciated.

Also, as for the other "why" (why try and use a car radio in the house?) I'm looking to have a receiver that has AM/FM HD radio, CD, and an IPOD input/USB input - and they just don't make those combinations for home use.

dmccormick001

Decreasing voltage is easy, you just bleed it off in some form or another, usually heat, and you're there. Increasing voltage, especially if you require higher voltage and significant current levels, is much more difficult, and requires a lot more circuitry, parts, etc. A 12 volt inverter is a good example. To increase DC voltage, you usually must first change it from DC to AC, so you can pass it through a step-up transformer, then change the higher voltage back to DC and filter and/or regulate it. It's certainly possible, but usually not efficient or cost effective. Of course, I'm just an old crumudgeon who likes to lurk around this forum, and I'm bonna-fide old school. One of these hot-shots around here may tell you there's a $.50 chip out now that will do the job, but I don't think so.

David

skiddriver

Thanks David. The circuits I found online didn't look terribly simple or cheap, though there are some encapsulated ICs in some of them that cut down on the parts count. It will be easy to use a 110V transformer and tap off the back of the PSU power cord receptacle, so I don't intend to expend much Pepsi on this issue. Still, if someone knows of an affordable and simple solution?

matthewborah

I just tried converting a 400 watt power supply but I cannot get it to work. I'm not too experienced with this stuff so I hope that someone here can help me. Here is exactly what I have done:

I went to fry's and bought a 400 watt power supply that already has an led and a switch built in.
I tested it before working on it and it worked.
I removed all of the connectors and made sure to keep the wires that were inserted into the same pin together (two gauges of orange wire and a brown and black wire).
I installed two sets of banana plugs into the case.
I soldered a red wire and black wire to a 10 watt 10 ohm resistor and installed on the case with zip ties and thermal grease.
I soldered the two sense wires to each other (light gauge orange to heavier gauge orange and brown to black) and covered with heat shrink.
I soldered 3 yellow wires to both positive banana posts and 3 black wires to both negative banana posts. I put heat shrink over all joints.
All other wires were cut off at the circuit board.

I thought everything went together really smoothly. All of my solder joints were strong and shiny. When I plugged it in and flipped the switch the led lit up. However, when I plugged in one of my chargers it did not power up and the psu fan never ran. I tried checking the voltage and it shows up as 0 volts.

I would appreciate any help.

graham p

I think you should have soldered the brown to the orange wires, and a green wire to the black wire. This is how the two I have made worked. The green/black can be connected trough a switch if you like. Good luck

dmccormick001

Could be a couple of things. The previous poster is correct, if you have a single, smallish gauge green wire, try grounding it (connect it to one of the black wires) and see if the PS latches on. You may also need to place a load on the PS to make it stay on, get a 10 ohm 10 watt sandbar-type resistor (Radio Shack) and place it across one of the red wires and a black wire. This will load the unit and make it latch on, and will also increase the output voltage slightly to be more like what you'll want for a charger.

These supplies have some circuitry in them that looks for a load from the motherboard in the PC, and if it doesn't sense everything correctly, sometimes they won't stay "on". Also, I've seen a lot of guys who didn't take care to make sure the posts of the banana jacks don't touch the case where they go through the metal housing. If they do, of course, you've shorted the whole thing out, and it will cut it's output to protect the PS.

Good luck!

David

matthewborah

I did install the 10 watt 10 ohm sandbar resistor on the 5v line.

I thought that connecting the green wire to a ground was only for power supplies that did not have a switch built in already. Since mine already had a switch I cut the wire at the circuit board. Was this a giant mistake? Is there any way to salvage the power supply by trying to "reattach" a green and black wire by soldering a wire at the circuit board level or is it hopeless?

As for installing the binding posts, the only part of the post that touches metal is the plastic housing going through the hole I drilled and the nut on the back to hold it in place. I do not see how I could avoid these parts from touching the case nor how they could cause a short since they are plastic.

dmccormick001

Yes, you probably need to short the green wire to ground even if there is a switch on the unit's case. The built in switch usually just controls the 110vAC line coming into the supply, providing a convenient way to completely shut the whole supply off, but once it's powered up, the PS still looks at the circuit the green wire is on to determine whether or not everything is OK with the motherboard before latching itself "on" and providing voltage output. You've got to fool it into thinking that the circuit it is designed to power is in place and functioning properly.

If you've got any stub left, just splice enough wire onto the green wire to allow you to ground it, otherwise you can remove the PC board to where you can get to it to replace it or whatever you have to do. As long as you don't do anything to release the "magic smoke", it's never hopeless.

Different posts are made in different ways, if yours has plastic nuts and mounting hardware, you should be good to go, I've just seen some guys who are really "green" at electronics who didn't realize the need to insulate the metal portion of their posts from the PS's housing, so I was trying to cover all the possibilities I could think of. Be sure to let me know if you get it working, OK?

David

Andrew

Ditto the previous post.

andrew

matthewborah

I was able to get the power supply to work. I took off the circuit board and soldered the green and black wire back in and then shorted them together. Thanks very much for your help.

Another question: when I have the power supply in the on position (with the fan running) and then try to insert the charger's power leads the charger will not turn on and the power supply's fan stops working. However, if plug in the charger's power leads first and then turn on the power supply second, it powers up fine. Is this normal? If so, when I want to have two chargers powered off the supply do I have to plug them both in before turning on the power supply?

Andrew

Matthew

I'm attaching a document that I usually send out to folks facing the same situation as you. This is explained in No. 2 of the three reasons for latch_off.

andrew

http://web2.murraystate.edu/andy.bat...OWERSUPPLY.HTM

dmccormick001

Yeah, it sounds like the PS circuitry is sensing the sudden presence of the charger as an overload condition and is shutting it down, whereas if you connect the charger before you turn the PS on, the boot process of the PS is just viewing it as a load and in effect is ignoring it. I personally haven't had that happen yet, but I think Andrew is exactly right, the filter capacitors in the charger may be placing such a large, sudden load on the PS output that, even though the drain is very brief, the PS thinks it's a problem and shuts itself down. You may find that not all of your chargers exhibit the same tendency, maybe none of the others will, but in any case I don't think it's an indication of anything wrong with your conversion. You may just have to adjust how you use it with certain chargers.

Good Job! See, I told you it wasn't "hopeless". BTW, the link Andrew posted is about the last word in information about this subject. If you can't find it on one of his pages, you don't need to know it. Great documentaion, excellent pictures, superb explanations at both the technical and non-technical levels, just a wealth of information! As far as I'm concerned, he qualifies as a "guru". [8D]

David

erocki

My Feedback: (1)

I have a interesting issue. I have converted a few of these now and all is well. The recent one I tried came up with an interesting result.

I cannot get it to move above 10 volts...if you can believe that. I have a 10/10 ohm load on the 5v line and the Grey to Black is my 'On'. It works fine but just won't give me a reading above this marker. Even the Red line is reading below 5v.

Is there a way to boost this or possibly is there something holding it back? This is an older 350W ATX model so nothing fancy here.

dmccormick001

The gray to black might be the problem. If memory serves me, the gray wire is used to supply power to LEDs that remain on while the main supply is on standby, if you have it grounded it might be dragging the supply down causing the low voltage output, although I don't understand why it wouldn't be causing the PS to shut down. Try disconnecting them and see what happens. Usually the only two wires that need to be connected together like that to latch the PS on are the green and a black wire. I usually use the gray wire as the + wire to drive an LED I add as an "on" indicator.

Red Scholefield

My Feedback: (9)

Andrew Batts has modified the PC onversion site quite a bit and added a new section on
how to draw more current from a typical PC PSU.


http://web2.murraystate.edu/andy.bat...OWERSUPPLY.HTM

sbtiger

My Feedback: (15)

I have been reading this thread for a while now and I’ve decided to take the plunge and convert a PC power supply. I paid $10 for a PC power supply from a friend who upgraded his and it’s a 580w 25amps on the +12volt side.

First I’m only going to use this for my charger and nothing else so I’m only going to put posts in for the +12v. My charger is a bantam e-station 902, and I will be charging and discharging a pair of 6v 2000Mah NiMH batteries at the same time.

Here are a few questions I have:

How many yellow +12v wires do I need to connect to my post to give me the correct amperage to the charger? I’ve read min of 2 but 3 is good, I have 7 available. My charger only tells me the required input voltage of 11-18v, but doesn’t say anything about amperage. The only thing it says is charge and discharge range of .1 to 9.9amps.

I’ve also bought a SPST switch to hook up. Do I need to do anything with the switch that’s in the power supply? Like disconnect wires, leave it in the on position, or does it get by passed once I wire in the new switch?

Note; the only sensing wire I found was a brown one connected to an orange 3.3v wire, I did not find any other sensing wires. However, I did find 2 lighter colored red wires, but they were all connected to the square area on the board. So I’m assuming these are still +5v wires, since they were not doubled up in a pin out nor did they go somewhere else on the board like the brown wire.

Thanks
Steve

Andrew

(1) Your supply should have 16 to 18 AWG wiring throughout, with the exception of the sense wire. A very conservative rule of thumb would be 10A per single 18 AWG 12v wire. Your runs are short and unbundled, so two wires should be more than sufficient.

(2) The switch (almost always a rocker switch) located near the AC plug on the back of the power supply is the master AC switch. When flipped off, the PSU is completely powered down. While plugged in with the master switch on, but not powered up, the PSU will still be drawing AC current and producing voltage on the +5VSB rail. Since your supply has a master switch, I would suggest that you simply solder the PS_ON (green wire) directly to any of the DC grounds (black) and use the AC master switch to power on and off your conversion - this will work just as well and save the time of installing a DC side switch. With the AC master off, your supply will be "green" and pull no current while not in use. The SPST switch is used in addition to the AC master and does not bypass it.

(3) Sense wires will be found only on the 2x10 (20 pin) or 2x12 (24 pin) motherboard connector and are identified where two wires are connected to a single pin. Normally, these are lighter gauge and will be either brown or orange for the 3.3v rail. Your MoBo connector should have 4 reds (20 pin) or 5 reds for the 24 pin connector. The key to locating sense wires is simply two connects to a single pin on the MoBo plug. Their function is to provide feedback to the PSU and allow it to adjust the voltage at the source to compensate for voltage drops over long runs (some server and full size towers have very long PSU leads) and when the PSU is under heavy load. Just reattach any sense wires that you locate at the MoBo plug.

andrew

sbtiger

My Feedback: (15)

Thanks for the tips Andrew, I will try and get some time in this weekend to start my conversion and I will post some pics of the progress.

Steve

sbtiger

My Feedback: (15)

Hey Andrew,

Did some work on the power supply conversion today. My wife's camera had a dead battery so I'm charging it now, and I will post pictures later to night.

I have most of my wiring done and here's what I have so far.

1) I connected a red and black wire to the 10ohm 10watt resister and placed some thermic grease between it and the case.
2) I connected my yellow wires to a ring spade and my black wires to a ring spade. I used 4 each.
3) I conneted one orange wire to the one brown sensing wiring.
4) I connected 1 black wire to my green "PS-ON" power supply on wire.

The only wire I have left is a gray wire that goes to the board that say's PG. Is this the power good wire? What should that be wired too? A black ground wire? Or should this go to my 220 ohm resister and then to another black wire for my LED to work?

Anything else you can think of to ask me let me know.

Steve

Andrew

Steve

It sounds good to go. Just use one of the 5v (red) wires for your LED. The Power_Good will work, but sometimes your LED will be dim when using this. Just leave the PG wire unattached.

Here is a link explaining the gray wire: http://web2.murraystate.edu/andy.batts/ps/POWER_OK.HTM

Make sure your binding posts are insulated from the case - having one of them grounded is a common cause of failure to powerup.

andrew

sbtiger

My Feedback: (15)

Well Andrew it didn't work. Can you tell from the photo if you see anything wrong or did I forget to do something. I check the fuse and seems OK, but it's solder to the board and can't remove it.

I plugged it in and turn on the master rocker switch and I get .15v on the +12v connection.

Steve

eszaqsc

need some help and advise

I'm using X-Part 350watt power supply, with +5v rated at 26A and +12v rated at 18A.

and i'm following all the instruction to convert it to DC 12v power supply

first i'm using 4x1ohm10watt in series at the red-black wire, the yellow-black wire show around 11.6x volts and it's getting warm

then i try using a generic front head car lamp rated at 12v 60/55w (is it mean 55 watt?? then whats the meaning of 60 ?), the 12v line show around 11.9x volts

is there any ways that i need to do to crank the +12v line above 12.xx volts with or without loads (i nned it to be around 12.1x - 12.3x volts)

do i need to use 2s2p 10 ohm 10 watt (2 in series and in paralel)?




btw, how is the calculation of the wattage, volts, ampere, and resistor in series and paralel ?
i know that in paralel volts will remain the same, but ampere is increase. in series volts increse and ampere remain the same.

and i did like to know is there any way to measure ampere in power supply or in battery packs using digital or analog multi meter ? if there is a way, can anyone tell me how to do it. Thanks before.



Thanks for answering.

eszaqsc

i made some modifications, i use 1 ohm 10 watt in 2 series and 2 paralel, i got 12.10volts on yellow line.

dmccormick001

So you basically have a 1 ohm 40 watt resistor on the 5 volt rail? That's what you get if you put two in series (2 ohms) and then parallel them with two more, which drops the resistance of the four back to 1 ohm. Only difference is you get the benefit of 40 watts of heat disipation. You should get the same reading with just one, but it might get a lot warmer.

eszaqsc

So I can get more at +12 volt line by making all of them paralel? (4x i ohm 10 watt in paralel)