this is really an electronics related question...nothing to do with comps but it will go in one..

anyway.

http://www.mitedu.freeserve.co.uk/Ci...er/1230psu.htm

I built that circuit on my own PCB I drew with a program called 3001!. But I made some different changes than the circuit u see. Everything is the same, except for the transistor and transformer. I used a single BDW94C, which supplies 12 Amps. The transformer is a 18V(rms) 300mA. I figured that the transistor would create current from heating up, and would keep a constant 12 v no matter what the load. pffft boy was I wrong. 1 92 mm and 1 120mm fan, loaded it down to 12.05 from 12.45. the 120 draws about 0.6 amps and the 92 mm draws about 0.22 amps. But if I under stood right shouldnt it keep the 12 volts constant and supply current? or is there something I am missing or another design out there that could supply alot of current ?

or do I need a bigger transformer? something like 12 volts 30 amps..where I dunno where I can find <_<

and btw..this all has to fit in a cd-rom drive bay. Yes. A cd-rom drive bay. So the transformer cannot be bigger than 1.5 inchs. =/

From what I understand of electonics if something is to take a big draw on parts then you are to need a capacitor. I believe that one might help you out in this area.

I have 2 6,800 uf's wired in parallel.. which caps add (unlike resistors which u take the recprical of) which would give me 13,600 uf which should be enough.

You mean power supply not transformer, why don't you go here, and get a high current 12v powersupply, and mod it to fit into the cdrom bay? Transformers either step voltage up or down, through induction.

Hmm let me check these wiring schematics. Ahh brings back memories of my Industrial electronics class. I hated all that math, and formula's.

Ok, honestly, I would just buy a power supply from that site, and run it to the back of the case. Hell, you wouldn't even have to put the PSU inside your case, just the wires for the fans. You could get a female, and male connector (probably from that site), and make it plug into the back of the case, it would look clean.


If those fans, have 12v running to them, and you have plenty of current, it should be fine. I wouldn't reccomend using that PSU for your harddrive or anything though .

well I dont want an external transformer lol. yes the Xformer must fit.

hmm well tje purpose of this was for users, like me and u be able to create a psu from parts that are easy to get to. Its purpose was for peltier users because they need large currents I figured why not design a psu?
It also would have 2 molex connectors for ccfts.

IIve learned this stuff last year. transistors and stuff how they are used and psu regulation. This year I am learning digital electronics. we are learning binary...hex and oct..awsomeness

That site should have a higher current transformer, 300mA isn't much. I would try that.

Btw, good job on learning all that. I learned most of everything I know from a Technical school here in my town, I was in Industrial electronics class for two years, learned a lot of cool stuff, how to wire relays and timers to motors and everything.

Now I am going to that same school, except for computer electronics .

I got half of everything from mouser.com the other half from jameco.com

they had higher currents but only up to about 1 amp for like 20 bucks <_<

id say transformer too. a straight switching design would be better but that freaks some people out despite alot of things (laptop and your computer) already haveing them.
personaly lazy me would just buy an open frame supply (or take one from the junk pile)

Look here, plenty of high amp transformers. If you are making a power supply just for a 12v rail, why don't you just buy a 12v power supply for like 10bucks? Oh well, I guess doing it your way might be more fun if anything .

It is definitely the transformer. Its only capable of supplying 300mA, you need a transformer capable of 3 Amps which is 3000mA. For all the trouble you went through on this a 300mA 12v wall wart would have been much cheaper and easier.

Actually you could eliminate half of that circuit and get pretty much the same results.

All you really need is a transformer 15-36v at least a few amps, a bridge rectifier, 2 caps and a 7812 regulator with a decent heat sink. If you need more current handling capacity just wire more 7812's in paralell to the first to spread the load., which is the same concept as the transistors in the design you posted.

EDIT: I attached a schematic of an easier circuit. Just use a transformer and x 7812's to handle the current you need.

Attached Thumbnails

 

hmm then I could use the heatsink I bought for the x-sistor and use that for the Regulator...weeee...


btw the heatsink has a coeiffent of about 3.6 c/W which is good enough..

gah..

also to mention I have this u framed psu, Switching I bought from bgmicro. It provides like..8 amps or so on the 12 v, 25 amps on 5 volt and 4 amps on the 24 volt and 1.5 amps on the -12V. It nice excpet one prob..

I conencted 6 92mm fans (.22Amps each) and it loaded the whole thing down to 8 volts. >_< . It shouldnt be like that! is a 150W PSU! <_< but..in the manual it say the 5 volt line has to have a min of 2 amps draw...but there the hell am I gonna get a device that draws 2 amps at 5 volts?! O.x

Did you wire the fans in series or parallel?

Quote: Originally Posted by Nerdz gah.. also to mention I have this u framed psu, Switching I bought from bgmicro. It provides like..8 amps or so on the 12 v, 25 amps on 5 volt and 4 amps on the 24 volt and 1.5 amps on the -12V. It nice excpet one prob.. I conencted 6 92mm fans (.22Amps each) and it loaded the whole thing down to 8 volts. >_< . It shouldnt be like that! is a 150W PSU! <_< but..in the manual it say the 5 volt line has to have a min of 2 amps draw...but there the hell am I gonna get a device that draws 2 amps at 5 volts?! O.x

The problem is the +12 rail will only supply .8 amps, thats 800mA. With 6 fans at 220 mA it would need to supply at least 1.35 amps to provide stable operation.

Yes it is a 150w PSU, but thats 150w TOTAL, spread accross all the rails not just on one. The 12v rail is only capable of around 10 watts by itself.

You need a large power resistor to put a load on the 5v rail.

I didnt clearify myself..sorry lol

the 12 v rail supplies 8 Amps. Not .8 amps

and I know its 150 W Total, thats with a fan. 110 w/o a fan all outputs dereated to 75% of nominal (3/4 of 8 amps 25 amps etc...)

I wire the fans in parallel to give me 12 V [in parallel voltage is the same. The loads get a different current (I1, I2, I3...etc), but add up to total current (It)

and for the power resistors..all I got are 250 ohms but are like 25 W.... I can get some from the school I go to.
and I would wire them in parallel to give me a lower total resistance.

EDIT: http://www.xpiq.com/pdf/pu150.pdf here the link for my psu. Model number: PU150-45 ( i have the 45B version but I just use the 45)

You had two periods after that sentence before the 8 so I was assuming you meant .8 amps.

Try adding the load to the 5v rail.

XD I did add a load to the 5 volts..lol

I got it to run 1 120mm fan, and like 7 92mm and...(drumhole please) a cold cathode light..all running at 11.87 volts =D good enough for me

EXCEPT.... I need a low ohms resistor about 2.5 ohms at like 10 watts. I looked at school and found a 2.2 ohm 25 Watt resistor and some wire wound 1 ohm resistors. so I'm happy for now just have to mount the dam thing <_<