homemade powersupply

[demortey]

i'm thinking about making a 12V power supply with really really high amperages, but im not sure how to go about doing it, i obviously need a step down transformer and a DC rectifier circuit, but do i need capacitors anywhere to clean up the power, or anything else like that?

[demortey]

just thought i should probably say what its for too...i have an asus a7n8x-deluxe that im going to do some major voltmodding to, also im going to vmod my video card...cant decide weather to use a GeForce2 32meg, GeForce 4 MX440, or FX5200. so far the mx440 is winning, because theres more tutorials for it

[four4875]

I dont think the effort needed to make a quality high amperage 12V supply would be worth it, and it would be mroe than just buyig a quality comp psu.

To build a good psu, you'd need some way to get the voltage down from 110 to something that can be worked with. Easiest way to do so is a transformer, but then getting a high amperage one is gonna be $$$ (when i think high amperage, i think at least 50+ amps. even for like 30 amps, its still gonna be some big dollars, and weigh like 30 lbs. then you need to rectify it, not too hard, just a bridge rectifier or 2 in parallel would do it, if you had big enough of ones. then you need something to regulate it, and handle the current... thats where it gets hard. you could..... get many many 7812 regulators (12V regs, handle 1 amp each) or maybe if you can find ones thant handle more load, i dont know of any off the top of my head.

or you could design and construct a switching circuit... big pain, you're on your own on that one. around 2 years ago i had most of an expandable design for a 12V switching psu designed, my target was 40 amps, and when i compiled a price list for just the components, not adding the effort of etching the pcb and all that fun stuff, i gave up and decided for the price and effort i could buy a rackmount amp and be done with it (was aiming to power a car amp)

Why not just invest in a good PSU for the comp and be done with it? youll get cleaner power at a better cost and at much less effort.

[demortey]

deal.

[hitokiri_808]

Another alternative is car battery chargers. They put out a good about of current and arn't too expensive. Only thing is the power is dirty and I wouldn't run anything but fans, pumps, and peltiers off of it.

I wanted to make a 12v 50A 3 phase linear power supply but I gave up trying to make one cheap. Easier to buy 2 or 3 chepo psus and combine the rails.

Oh, and if you make a linear power supply you'll need a huge amount of filtering to keep the voltage stable under load. I needed more than 1 farad for mine.

[four4875]

car chargers are just scary... ever turn on a cars radio while a charger is on it? BBBVVVVMMMMMMMMMMMMMMMMM...........

id keep that FARRRR away from any data, even with an array of filtering caps big and small. and being unregulated, voltages could go crazy if the ac fluctuates.

[3DFlyer]

Nothin' like the smell of burnin' silicon in the mornins'! LOL

Word! Avoid car battery chargers. The RMI/EMI from them is tremendous. That's not even taking into account the wild current they put out.

[four4875]

well... battery chargers dont PUT OUT alot of amps, they jsut provide it. and that IS what he wants, but the power is soooo dirty, that its terrible. without tons of filtration and regulation, you dont wanan get it near the kind of didgital processing like we do. regulating the power is the hard part. the transformer will put out a rough voltage, then you rectify it, then filter, then regulating. in a non switching psu, all of the power that is taken out of the flow is dissipated as heat, so if you have somethin putting out ~15 volts, and you're taking out 3 while its pulling say 50 amps... you'll be dissipating 150 watts of heatin the regulator... and thats a fair bit of heat to tackle in just a power supply. then im sure the transformer would get itself a fair bit of heat, and those are so big and have a great mass to them... they seem to retain the heat. and im not sure how battery chargers would like a steady load over a long period of time. it seems like they're usually done with their charging after 12 hours or so, and their load tapers down as the battery is more charged. so i dunno how they would take to a steady somewhat high load over a few days.....

and ill stop rambling now haha.... basically the only way to go is a switching supply. although one way i though of to get a decent 12V supply would be mechanically convert it. get an AC motor running off of the wall, and have it turning a ar alternator, say a 140 amp, and put in a battery or a couple big caps for filtration. but this method isnt too good and im sure it would be kinda noisy. but it could be done relatively cheaply if you cant find any other alternatives for it. im not sure of the watt to horsepower conversions, but you definately wanan get a motor that could handle the laod, or it'd be burnt up after a while. but without figuring inefficiencies of the power transfer system or alternator and its regulators and rectifiers.. it would take a minimum of like 2.5 hp to provide 140 amps. just a thought.

edit: i didnt stop rambling when i said i would. sorry.

[ocZer]

I have to agree. Car battery chargers are off limits for PC's. And building a 12V powersupply with enough juice to make it worth while, you would probably either need a huuuuuge transformer and a heavyduty rectifier or make a switching PSU. To make a switching PSU, is not going to be easy. I know, because I made one once, but it could only squeeze out 4 amps running from 0,5 to 12 V.

[-maddog-]

Overclockers.com had a good artice (I think) on building a psu for a pelt. . But one for your whole pc, that's insane. The only situation I could think of is you're really good with electronics and have way too much free time on you hands.

[sunrunner20]

Building a power supply for a computer would be more costly than to simply buy one that has sufficient power. A high quality high wattage power supply from somewhere like PCP&C will run in the 2-3 hundred range. It will provide more than enough power. As for trying to build a comparable power supply it would cost a person at LEAST the equivalent of $200 in design time and ordering the PCB. You can't use linear regulators for the amperages that computers draw without a cooling solution that would make HSF's like the xp-120 soil itself. Instead, they use switching. Switching power supplies are sensitive and require rather advanced knowledge to get one working accurately. Then there is the fact that you will want to include over voltage and over current protection. Not to mention, most new power supplies have a microcontroller inside to monitor and do other things like actively monitoring voltages to adjust them.

Jjust a little background. As for just 12v, you can still run into similar problems. You will indeed need a step down circuit and a full wave bridge. You will likely then pass the power through a cap. and a large linear regulator. Large enough that it will likely need a active heatsink. Give www.digikey.com a look at for regulators.

[bri1]

Building a power supply for a computer would be more costly than to simply buy one that has sufficient power. A high quality high wattage power supply from somewhere like PCP&C will run in the 2-3 hundred range. It will provide more than enough power. As for trying to build a comparable power supply it would cost a person at LEAST the equivalent of $200 in design time and ordering the PCB. You can't use linear regulators for the amperages that computers draw without a cooling solution that would make HSF's like the xp-120 soil itself. Instead, they use switching. Switching power supplies are sensitive and require rather advanced knowledge to get one working accurately. Then there is the fact that you will want to include over voltage and over current protection. Not to mention, most new power supplies have a microcontroller inside to monitor and do other things like actively monitoring voltages to adjust them.

Jjust a little background. As for just 12v, you can still run into similar problems. You will indeed need a step down circuit and a full wave bridge. You will likely then pass the power through a cap. and a large linear regulator. Large enough that it will likely need a active heatsink. Give www.digikey.com a look at for regulators.

ya sounds like in the time it would take you to make a psu you could ezily just work and buy a psu lol

[-maddog-]

ya sounds like in the time it would take you to make a psu you could ezily just work and buy a psu lol



I think anyone who does this is doing it for the heck of it or has specail needs for it.

[apu318]

Yeah he does got too much time on his hands. But gee, he sure does take his goddamn sweet time getting over to my house so we can go for coffee.

[K15]

i'm thinking about making a 12V power supply with really really high amperages, but im not sure how to go about doing it, i obviously need a step down transformer and a DC rectifier circuit, but do i need capacitors anywhere to clean up the power, or anything else like that?



To get 120 volts @60hz down to 12 volts in itself would need a GIGANTIC transformer. I think the only way to get from 120 to 12 easily (aka, without a coffee pot sized transformer) would be to make it a switching PSU (aka, taking the hz WAY higher before stepping down), but good luck there :eh?:

[L337 M33P]

Building a power supply for a computer would be more costly than to simply buy one that has sufficient power.

And comes with a warranty. And less risk of electrocuting yourself. And involves less maths.

[zebkoolindc]

Big ol' transformer (http://mpja.com/productview.asp?product=7846+TR)

12V @ 20 amps for $16 Two in parralle will get you 40 Amps. A bridge that big is about $8 .
If you can find some used Caps from old tv's psu's. A quick simulation tells me if you put a 4 4700uF caps after that you still have a 8V ripple. 9 leaves a 6V ripple.
Some how you can use chokes to filter AC but I don't know how.

If you step up the frequency to 120hz the ripple is about 3V. I don't know how high of freqency this transfomer will take. But 240 has 2V ripple, and 5KHz ripple is .1V.

You just have to chop your AC really fast and find a transformer that will take it ;)

[ocZer]

Thats what a switching PSU does

[zebkoolindc]

Its kind of like a switching PSU in a pc. But the PSU in you pc has a PWM circuit that lowers the voltage coming out of the transformer when load is low and raises it under heavy load.

That is complicated to do.

[RoadWarrior]

Just put a bigass rectifier straight on the 120V line and run 10 mobos wired to it in series... :beer:

what? not everyone runs 10 mobos at once? :D

[zebkoolindc]

Just put a bigass rectifier straight on the 120V line and run 10 mobos wired to it in series... :beer:D

Do I even want to start on why that won't work? Athough you would save money on PSU's ;)

[Super Nade]

Car battery chargers are noisy, but the batteries themselves are not. Plus, there are elegant ways of filtering noise, so that should not be a problem. A simple configuration would be to add bypass capaitors. Make sure you use large value electrolytic and tantalum capacitors as a bank. (see attached picture of a + - filter example...sorry about the poor quality!)

The good thing about SMPS is that your transformer NEED NOT be bulky. In fact that is the whole point of chopping the signal. :)

E=Electrolytic Cap
T=Tantalum Cap

[four4875]

http://www.mpja.com/productview.asp?product=14635+PS

12V / 50A. if i had the change id grab one.

[theELVISCERATOR]

i'm thinking about making a 12V power supply with really really high amperages, but im not sure how to go about doing it, i obviously need a step down transformer and a DC rectifier circuit, but do i need capacitors anywhere to clean up the power, or anything else like that?


I think the first part answered your own question.

Electricity is not very forgiving of mistakes made by novices or experts for that matter!

Buy a power supply. Try some Salvage places or ebay.

You can find some awesome 12v supplies out there surplus.

[four4875]

i linked to a surplussite ;-)

but really, $120 is the cheapest ive seen for anything near 12V / 50A, if you know of anything better please share, im sure anyone looking for high amperage supplies would love to see it.