Computer Power Supply Converted to 13.8V for Radio

[sureshot]

When i say rails its a term for the power coming from what wires, you dont need to worry about the circuit board nothing there needs doing for this mod.

3.3 ohms is a bit to much of a load, it would be 4.7 ohms 10 watts on the +5 volt red wire and one black ground wire, or 10 ohms 20 or 25 watts on the +12 volts wire yellow and ground one of each to the leads on the resistor, a brief explanation 4.7 ohms on the 5 volt wire red and black will draw 5.3 watts your resistor is 10 watts so enough to cover the load in power terms. For the +12 volt wire yellow and black to the leads if you used a 4.7 ohm resistor it would be a load of 30.6 watts you would need a 50 watt power resistor and it would be wasting power, so on the +12 volts wires we use a 10 ohm resistor a load of 14.4 watts so a power resistor of 20 to 25 watts would be needed, your resistor must be capable of handling the power and heat generated.

You only need one load so one resistor, either on the +5 volts red wire and one black ground wire, or one load resistor on the +12 volt wire one yellow and ground one black, but as the voltage is higher on the +12 volts wires it will burn up a 4.7 ohm 10 watt resistor, as 4.7 ohms across +12 volts is 30.6 watts so a 10 watt resistor will burn out, the idea is try both but one at a time +5 volt and +12 volt separately which ever gives the higher 12 volts out put when read with a multi meter you use that resistor on those wires, as ive referred to rails this is a term for the wires out put voltage, so just one resistor either ( 20 or 25 watt 10 ohms on the +12 volt wires ) or ( 10 watts 4.7 ohms on the +5 volt wires ) but not both.

Hope that helps, the resistor once connected can be mounted inside or out side the case, if inside it must be clear of any other components normally mounted to the case.

All wires are grouped in bunches so all yellow all red all black all orange plus the brown sense wire together in there groups cover with shrink rap and terminate at 4mm sockets or binding posts, i know it looks daunting but the tutorial on jumper one is straight forward, you dont need LED's if you dont wont its up to you, but you do need a switch between the green wire and ground a black wire this is to turn the supply on.

[hdjmings1]

perfect got it , got some 4.7 ohm and 10 ohm coming from eBay as good old maplin didn't have any lol, only wanted to do the mod as would like 13.8v out of it....... but ill see what it says when i finished

[sureshot]

Maplins are typical of hardly ever having stock or components when you need them, i usually use ESR Electronics they never failed yet in over 8 years.

The out put voltage will be between 11.40 volts and 12.60 volts its normally always over 12 volts with the load resistor, if you want exactly 13.80 volts its much more complex and will involve circuit component alterations really a tall order for a beginner. Radio gear is rated for use between 11.40 volts and 14.40 volts anywhere in between is fine, they just stamp 13.80 volts as the nominal voltage to use.

Radios and amps run quit happily on just over 12 volts, i live in Ramsgate Kent and easily talk to a guy buy the name of little john in Canterbury Kent, about nearly 20 miles also another guy in Deal Kent some 15 miles ish, i could do the 13.80 volt modification but really dont see the need, if you want the full 13.80 volts your need to start back at the very beginning of this thread the original OP has done the 13.80 volt mod, but in practice it can vary from different ATX supplys as to which components are altered / added, you really need to fully understand switch mode psu theory completely, that's why a while back i said if its something you like the idea of electronics that is reading and learning the theory, but that bits up to you, you dont need super experience for this simple modification.

[hdjmings1]

o right nope that's cool, i thought that everything had to be 13.8v for radio gear and such

[sureshot]

The above voltages are fine, mines about 12.05 volts i think the one in the electric cupboard, your only drop below 12 volts with no load resistor the supply needs the load for stability, the 13.80 volt mod is also fine, but planning and precise component detail is really the only way, and can vary from one psu to another.

A reply to our friend that said good thread, its not my thread, but did not see the need to start a new thread, so both the 13.80 volt modification and the 12 volt one are covered, hope the OP did not mind as its the same subject material, will pop back from time to time good luck with the modification.

[hdjmings1]

ok just wondering, on the 12v rail it reads 17.2v with out a load resistor and on the +5v rail it reads 7.3v??? it is a brand new supply

[hdjmings1]

ok just wondering, on the 12v rail it reads 17.2v with out a load resistor and on the +5v rail it reads 7.3v??? it is a brand new supply
+5v and 5v sence are attached togeather

and 3.3v and sence are on togeather

[sureshot]

OK just wrote out a new reply stupid mistake converted a file closed Firefox ahhhhh.

Any way where missing something can you post pictures of all your wires laid out and another with multi meter connected, the meter must be on the DC range, AC will try to read RMS values.

just need to know this +5 volts sense wire color its unusual to have sense on the +5 volts rail, as its a more powerful supply that might be why, some picture would help out see whats going on, back up a bit so you get all the wires laid out in the shot if you can, below is the typical ATX industry standard pin out, if you still have the mother board connector this will show any grouped wire together on a single pin.

Both 20 pin and 24 pin shown, now days comes as 24 pin with the option to slide 4 pins off the main connector for 20 pin MB headers.

[hdjmings1]

Sorry forgot to say it's an ATX v2.3 i take it that matters lol

[hdjmings1]

right i think the psu is un-stable for some reason, the voltage keeps rising then i think it shuts the supply down as some times i just get a reading on the meter at 1.......

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[hdjmings1]

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[hdjmings1]

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the +12v reading

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the +5v reading

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[hdjmings1]

i just used the 10w 4.7ohm on the +5v line and voltage on the +12v was 12.3 when i turned on but went up to 13v after about 5/10 mins being on

found info on the supply

http://cmupload.coolermaster-usa.com/sa ... Report.pdf

[hdjmings1]

ok i got the 4.7ohm 10watt on the +5v line and when turned on the voltage slowly creeps up so far to 15v??????

just waiting for the 10ohm 20watt to come in the post hope tomorrow

[sureshot]

Sorry not got back until now, i see the thinner +5 volt sense wire so long as its connected to the other +5 volts wires, and the thin brown wire tied with the +3.3 volts line, really struggling to answer this one, try your meter on a known voltage source just to be sure the meters ok, the only other thing i can think of is the purple standby wire and grey power good might need to see the usual motherboard status, unusual but a couple of resistors and LED's would rule that out, it just seems very unstable, not sure where to go from here, ive modded half a dozen some old one new and never had this problem, do you still have the MB connector for reference to look at see if something there is tied to one of the other lines ? .