I have two old PSU's (a 200W AT and a 300W ATX) that I want to mod for more amperes, fun and electronics experience. I will have both the PSU's in one UV-reactive plastic casing that has enough airflow, it'll be part of the computer case I'm building. Here are the specs of the different rails in the PSU's:

Output - 300W - 200W
+12V - 15A - 8A
+5V - 30A - 20A
+3.3V - 20A - n/a
-12V - 0.5A - 0.3A
-5V - 0.5A - 0.3A

But I need some more advice on whether it is possible to 'join' the +12V of one PSU with the +12V of the other PSU, to get more amperes. I've been told that in theory it is possible to do this simply by soldering everything in parallel (giving a total of 15+8=23A on the +12V rail) but then again I think in practice the higher current of the 300W ATX PSU might try to charge the 200W AT PSU and cause a hell lotta trouble.. So I found this article on http://www.procooling.com/articles/...tween_psu_s.php, explaining how to do this using MOSFET's. These are the pro's:

"Minimal voltage drop (less than 0.2 V in most cases, mosfet resistance is 0.0078 ohms), no possibility of the supplies attempting to charge each other. It also shares the power so that both supplies share the load equally."

Does this mean that both PSU's will try to supply the same amount of amperes, either giving a lower total amperage or blowing up the weaker PSU? If this is the case, can I somehow prevent this from happening, maybe by using two different mosfets and/or fet drivers? I know I could save myself a lot of time and trouble by just buying a new (or possibly two older but equal) PSU('s), but I'm willing to learn how electronics works and I just like this project. I might post some pics here, too.

Quote: Originally Posted by xzorby I have two old PSU's (a 200W AT and a 300W ATX) that I want to mod for more amperes, fun and electronics experience. I will have both the PSU's in one UV-reactive plastic casing that has enough airflow, it'll be part of the computer case I'm building. Here are the specs of the different rails in the PSU's: Output - 300W - 200W +12V - 15A - 8A +5V - 30A - 20A +3.3V - 20A - n/a -12V - 0.5A - 0.3A -5V - 0.5A - 0.3A But I need some more advice on whether it is possible to 'join' the +12V of one PSU with the +12V of the other PSU, to get more amperes. I've been told that in theory it is possible to do this simply by soldering everything in parallel (giving a total of 15+8=23A on the +12V rail) but then again I think in practice the higher current of the 300W ATX PSU might try to charge the 200W AT PSU and cause a hell lotta trouble.. So I found this article on http://www.procooling.com/articles/...tween_psu_s.php, explaining how to do this using MOSFET's. These are the pro's: "Minimal voltage drop (less than 0.2 V in most cases, mosfet resistance is 0.0078 ohms), no possibility of the supplies attempting to charge each other. It also shares the power so that both supplies share the load equally." Does this mean that both PSU's will try to supply the same amount of amperes, either giving a lower total amperage or blowing up the weaker PSU? If this is the case, can I somehow prevent this from happening, maybe by using two different mosfets and/or fet drivers? I know I could save myself a lot of time and trouble by just buying a new (or possibly two older but equal) PSU('s), but I'm willing to learn how electronics works and I just like this project. I might post some pics here, too.

well--i dont know if they make em for that type of amps---but a zener diode would work to block the psu's from trying to :"charge" each other. im not sure if this would work tho. im a little rusty in the electronics thing right now.....

and Welcome!!!!!!!

Welcome to PimpRig xzorby.........

Quote: Originally Posted by LwrS10 well--i dont know if they make em for that type of amps---but a zener diode would work to block the psu's from trying to :"charge" each other. im not sure if this would work tho. im a little rusty in the electronics thing right now..... and Welcome!!!!!!!

you wouldnt need a zener diode for that. an normal one would be fine, but i am pretty sure you dont need anything to block them form charging each other,

but ithink a beter way of doing this would be to wire it so that when the ATX power supply is turnd on it will turn on the at.

all you have to to is take any 12v and ground line and wire it to the coil side of a relay, then insted of using the swich on the at powersupply, just disconnect the swich, and connect it to the contact side of the relay.
so that when the atx power supply turns on it eneregises the relay and automaticl starts the at power supply. with this method you dont have to worry about jouning the leads and everything. if you are interested in this method i can draw up a schematic for you. i also recomend this method because it is cheeper.

hmm Ok, (thinking) Ok got it!

Think of the PSU's at batterys (but with different amps ratings) Bat 1 has a rating of 12V @ 10A, Bat 2 Has the same rating but at 20A. Both will provide an equal amount of amps, but when Bat 1 is maxed out at 10A, Bat 2 will still provide the same Amps, and you will still have room for more current to pass. My understanding of this circuit, is once PSU 1 is maxed out, the zener prohibts anymore current from flowing (well, keeps it flowing, but blocks PSU2 from charging PSU 1) along with the mosfet. MOsfets can handle HUGE ( I mean huge..100Amps or more) Current. Mosfets are used in car audio amps btw.

Welcome to PR.

BTW, if you need anything else electronics wise, Im ya man (along with other people..I think carbon graphite is one).

Btw, I have transistors if you want some. I'll give them to you for free (I'll be posting a FS link later on. along with some other stuff .

http://forums.pcapex.com/showthread....188#post413188

@Cpl Rampage: turning on both power supplies at the same time is not much of a problem, I'll just use the AT's power on button thingy and connect it to both the supplies in parallel instead of just to the AT PSU. I can also just connect the ATX to the motherboard and the AT to all other devices, so they're seperate, but I don't want that. I want to create a higher amperage on the +12V rail.

@Nerdz: so you think it'll work with two equal mosfets?
"Both will provide an equal amount of amps, but when Bat 1 is maxed out at 10A, Bat 2 will still provide the same Amps, and you will still have room for more current to pass. My understanding of this circuit, is once PSU 1 is maxed out, the zener prohibts anymore current from flowing (well, keeps it flowing, but blocks PSU2 from charging PSU 1) along with the mosfet."
So with those batteries, would the total amount of amperes supplied be 30A? And do you think my local hardware components store will have the fet drivers, mosfets and zener diodes I need?

@ all: thanks a lot for the fast response!

Quote: Originally Posted by xzorby @Cpl Rampage: turning on both power supplies at the same time is not much of a problem, I'll just use the AT's power on button thingy and connect it to both the supplies in parallel instead of just to the AT PSU. I can also just connect the ATX to the motherboard and the AT to all other devices, so they're seperate, but I don't want that. I want to create a higher amperage on the +12V rail. @Nerdz: so you think it'll work with two equal mosfets? "Both will provide an equal amount of amps, but when Bat 1 is maxed out at 10A, Bat 2 will still provide the same Amps, and you will still have room for more current to pass. My understanding of this circuit, is once PSU 1 is maxed out, the zener prohibts anymore current from flowing (well, keeps it flowing, but blocks PSU2 from charging PSU 1) along with the mosfet." So with those batteries, would the total amount of amperes supplied be 30A? And do you think my local hardware components store will have the fet drivers, mosfets and zener diodes I need? @ all: thanks a lot for the fast response!

you cannot connect the at swich in parrell, i am talking about that pushbutton swich that is usually connected to four large guage wires and is usually mounted on the front of the case. an atx power supply does not have this swich because it is turned on by the mother board. you could not hook this up in parrell, because it is ac votage flowing thru the swich, and there is nothing like that on an atx powersupply. insted of buying these mosfets, all you need is a relay to turn on the at powersupply, when the atx is activated. then just have the atx power the mobo, and a few perfirals and have the at power the rest of the periferals. i really recoment this, because not only is it cheeper, but it is cheeper. also think if you use mosfets, they would halve to be pretty high amperage.

I did not realise that the button that turns the computer on if you have an ATX motherboard is connected to the motherboard and not the PSU. The button on the AT powersupply switches the PSU on instantly, where the ATX needs the motherboard one to be switched on, too. I guess I'll have to use a relay as well then. And the mosfets and fet drivers and such won't be that expensive.

Quote: Originally Posted by xzorby I guess I'll have to use a relay as well then. And the mosfets and fet drivers and such won't be that expensive.

yah you definatly need a relay system, but you do not need the mosfets, it would be beter if you just had the two run independantly, so that the atx will only power the Mobo and say the Vid card, and the AT will power the rest of the computer, or soemthing like that. all i can see with the mosfets is trouble, its just gonna cause problems, when you dont really need it.

Yes, I know that. I know I could save myself a hell lotta trouble by just using them seperately, but that's no fun! And it supplies my motherboard with low amperage on the +12V and +5V rails, even if the 300W powered a motherboard and everything on it only, it wouldn't be powerfull enough for newer systems. And if I blow up both the spare PSU's, that's my own problem, but thanks for warning me.

Quote: Originally Posted by xzorby @Nerdz: so you think it'll work with two equal mosfets? "Both will provide an equal amount of amps, but when Bat 1 is maxed out at 10A, Bat 2 will still provide the same Amps, and you will still have room for more current to pass. My understanding of this circuit, is once PSU 1 is maxed out, the zener prohibts anymore current from flowing (well, keeps it flowing, but blocks PSU2 from charging PSU 1) along with the mosfet." So with those batteries, would the total amount of amperes supplied be 30A? And do you think my local hardware components store will have the fet drivers, mosfets and zener diodes I need? @ all: thanks a lot for the fast response!

If your talking about radio shack, your going to pay alot. That IC chip is a mosfet driver which they probably dont have. The driver is needed for proper biasing (or else it the mosfet will go all wack or something) If you live in the US, use either Jameco.com, Mouser.com or http://www.alliedelec.com/. They should have what you need for under 5.

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But now I still don't know if the method explained on http://www.procooling.com/articles/...tween_psu_s.php
adds up both the amperages, or multiplies the lowest amperage by two, because if it only multiplies the lowest amperage with two, I'll end up with 16A on the 12V rail, only 1A more than the 300W PSU already had. And by the way, I live in Holland. http://conrad.com/ has a Dutch section, and they have quite some mosfets and fet drivers and zener diodes too. The only problem is, which ones do I need? And I have an older AT PSU as well, I saw some mosfets on there too, maybe I can use them?

Just use the ATX supply as you normally would but limit what gets plugged into it. Modify the AT supply to use a relay as the power switch. The relay should have either a 12v or 5v coil voltage, just wire it to a molex connector in a manner appropriate for the voltage you have chosen and plug it into the power cable of the ATX PSU. I have this exact setup in my main box and it has served me well for the last 2 years. I even modified the AT PSU to fit in the casing of an old CDROM drive and stashed it in the top bay, added a couple of 40mm cooling fans. This setup(300 ATX, ~200 AT) is running a Barton 2500@3200 with 2 IDE HDD's, a CDROM drive and burner, 2 cold cathodes, several LED fans, my 4x20 lcd, miscellaneous USB stuff, and a Radeon 9200. All of this is stable enough to do some massive compiling under Linux with no errors.

If you do decide to do it the MOSFET way, avoid the super cheap ones, most of them don't switch on all the way and then when you load them up, SNAP CRACKLE POP. NTE are great, a bit pricey, but high quality. And unless you use the same thing as the diagram or cross reference you will have to spend some time on spec sheets as a number of things, including pinout, can be different. MOSFETS are bitchy at best and the only way I've been able to use them reliably long term is with a driver IC using capacitor driven charge pumps, but that was for motor controllers so your mileage with this may vary.

Check this out to see what you can get away with for load on each supply in any case.
http://www.jscustompcs.com/power_supply/

Make sure both PSU's are stable though, otherwise this whole thing will just end up creating a higher power twitchy PSU.

Quote: Originally Posted by xzorby But now I still don't know if the method explained on http://www.procooling.com/articles/...tween_psu_s.php adds up both the amperages, or multiplies the lowest amperage by two, because if it only multiplies the lowest amperage with two, I'll end up with 16A on the 12V rail, only 1A more than the 300W PSU already had. And by the way, I live in Holland. http://conrad.com/ has a Dutch section, and they have quite some mosfets and fet drivers and zener diodes too. The only problem is, which ones do I need? And I have an older AT PSU as well, I saw some mosfets on there too, maybe I can use them?

The current entering a junction must equal the current coming out of a junction, so yes the amps do add.

The mosfets you use are IRF407-ND or IRL1104 with reduced performance.

Read the article a bit (and the circuit), it will tell you what you need