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neweuser
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09.09.2006, 09:41 PM

Do you recommend doing both the 5v and 3.3? Or just one or the other with the options you gave ?
The other question i have, is the parallel diagram, do you put two resistors one one red(any) wire, and two on one black(any) wire? Just want to make sure. I was thinking of just removing part of the covering instead of the whole end. Also, do you just connect them to the ends and then from the resister, they go to the board? Nothing on the end but the resistor? is that right?


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squeeforever
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09.09.2006, 09:58 PM

Could somebody help me? Not sure if this thing will work, but I guess it might. Heres a picture of the PS sticker.


Last edited by squeeforever; 09.09.2006 at 10:02 PM.
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squeeforever
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09.09.2006, 10:15 PM

Quote:
Originally Posted by squeeforever
Could somebody help me? Not sure if this thing will work, but I guess it might. Heres a picture of the PS sticker.

I think I had a brain fart. Oops..I mean a brian fart :p. Anyway, I don't know what I was thinking...Theres no way in hell that thing would work...duh. Shoulda known that...Anywho, I found alot of PS's on Ebay for $30 that are rated at 24 amps at 12 volts (600 watts).
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BrianG
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09.09.2006, 10:20 PM

Quote:
Originally Posted by squeeforever
Could somebody help me? Not sure if this thing will work, but I guess it might. Heres a picture of the PS sticker.


Holy cow, that's a small PS!! Only 2A @ 12v is only ~24w. I don't think it'll work, unless you don't mind charging at 0.1A or 0.2A. :)

Neweuser: It's hard to tell which output has the regulation feedback circuit. Maybe just one, maybe all three. I think it might vary by manufacturer and model. So, I would just add the load to both the 5v and 3.3. There will be a little wasted power from those resistors, but not a whole lot.

As to your other question; I'm not sure I understand. As the diagram illustrates, the 5v or 3.3v wire hooks to the resistors in the manner shown. I tried to make the actual connections quite clear. Series hooks the resistors end to end with the wires on the very ends (kinda like a typical NiMH battery pack), while parallel hooks the ends together and then to the wires. The colors are exactly the colors as seen in the power supply.

This parallel/series connection is just a way to get the exact resistance value (and power value) needed using the resistors available. If you had an exact 2 ohm resistor, you only need to use one (as long as it is 20w instead), but the choices were limited, especially at RadioShack.

I laid out the resistors physically side-by-side just so the resulting resistor "pack" is neater, easier to wire up, and easier to insulate. You can then add heatshrink over the connections and even over the very end of the resistor(s) as long as the majority of the resistor is exposed to the air to aid in heat dissipation.

I hope I answered your question, but please forgive me if I don't understand.
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squeeforever
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09.09.2006, 10:21 PM

Brain, would the N-Powe I currently have charge 6S at 8 amps with my E-Station 701? Its 10 amps at 14 volts.

Edit: Brain, you might want to look at the post right above the one that you just posted :p.

Last edited by squeeforever; 09.09.2006 at 10:23 PM.
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BrianG
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09.09.2006, 10:22 PM

Quote:
Originally Posted by squeeforever
I think I had a brain fart. Oops..I mean a brian fart :p. Anyway, I don't know what I was thinking...Theres no way in hell that thing would work...duh. Shoulda known that...Anywho, I found alot of PS's on Ebay for $30 that are rated at 24 amps at 12 volts (600 watts).
LOL, that's OK. Just make sure those other ones are single supplies. Some listings show the total current for a dual 12v power supply. That 24A could be 12A per 12v output. That's why I use Newegg.com, the pictures help eliminate confusion.
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squeeforever
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09.09.2006, 10:26 PM

I was thinking about getting something like this.
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BrianG
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09.09.2006, 10:28 PM

Quote:
Originally Posted by squeeforever
Brain, would the N-Powe I currently have charge 6S at 8 amps with my E-Station 701? Its 10 amps at 14 volts.
10A @ 14v is 140w. As long as the charger doesn't try to draw more than that, you'll be set. To find out, just multiply the max battery voltage (4.2v per cell for Li) by the charge current. If this value exceeds 140W, then the N-Power won't be enough, unless you simply charge the pack at a lower current.

I would like to take a minute to apologize for any confusion this post might have caused. The intent was to mod a cheap computer PS for use as a generic 12v power supply. As we've seen, it might not be as easy as originally thought. Having an electronics background, I find these projects fun and easy to do, even with the little bumps along the way. However, I don't want people to spend ~$40 on a PS that might be overly difficult to get to work and then become angry if it seems complicated. I'm not trying to be condenscending, I just know how confusing things can be when just starting out.
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BrianG
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09.09.2006, 10:34 PM

Quote:
Originally Posted by squeeforever
I was thinking about getting something like this.
Yes, that looks like a single 12v output from what I can see on the label. Usually, if there are dual 12v outputs, the label will show the rating for each output seperately. And the current value looks to be adequate as well.

Also, I would like to point out that there is such a thing as a too good of a deal. Most of the units with dual fans and such maybe just a gimmick. After all, the extra "stuff" is taking space away from beefy components. For example, take a look at the difference between the guts of two power supplies here. PC Power and Cooling is the king of computer PS, and they are pricey to boot. Cheaper power supplies can certainly deliver the required current at 12v, but I tend to "derate" the specs. If the spec says 24A, I would estimate that it is really about 18A. Plus, the cheaper units will have a 12v output that will drop as more current is required. This can be overcome, but takes some work, as we've seen.
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neweuser
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09.10.2006, 11:11 AM

You got it right, wasn't sure if i was to do both or just one. Thanks brian for all your help. But i am foresurely going to need two resistors right? Not just one? Some people only use one...but I'm assuming i will need two as i probably gong to draw more juice. Thanks Again man, sorry for all the questions, just want to make i don;t fry the whole PS!!!! LOL


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BrianG
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09.17.2006, 04:40 AM

A little more in-depth information about this project for those interested. The information below DOES involve opening the case, so please heed the warning in my first post about potentially hazardous voltages!

I made another supply with an extra PS I had in my computer "junk" box (this one) just for some testing. It is an Enlight with a rating of 15A on the 12v line. This brand is generally pretty good and gets good reviews.

When I took it apart, I noticed there were a couple of small trim potentiometers near the output wires. So, with the PS on and voltmeter on the 12v line, I slowly adjusted them and one boosted the 12v from 12.1v to 12.38v. Nice. It actually boosted the 5v and 3.3v lines a little as well, but I don't care about those. The other pot didn't do anything noticable. You have to be careful here because these adjustments may be for something totally different (and potentially harming), like the PWM circuitry. So, if you decide to play with them, make sure they are put back exactly like they were if they don't affect the output. Also note that many power supplies do not have these (the first one I converted did not).

Then, I saw there were two output coils (which is usually where the circuits take a amperage sample), one on the 5v line and the other on the 3.3v line. This is a good hint that one or both are used in the load regulation circuitry. I put a 12 ohm resistor first on the 5v and then the 3.3v lines seperately. Each time, the 12v line came up a bit. However, no gains were noticed if I loaded both at the same time. I'm not saying this is true for all units, but it was for this one.

I got a couple 10 ohm 10w resistors from RadioShack and hooked them in parallel to the 5v line. This creates a 5 ohm load rated for 20W. It's a good thing too, because even though the 5v line, drawing 1A, only generates 5W, the resistors got quite warm. I mounted the resistors on a heatsink using some Arctic Silver Epoxy and that helped tremendously. I chose the 5v line because I wanted to draw at least 1A with the resistors I had. Any less and the regulation circuits may not work as well.

Now, for the test. At no load, the supply delivers 12.7v (thanks to a combination of the trim pot adjustment and the 5v load). When loaded with a 0.75 ohm load (a combo of four 3 ohm resistors in parallel), the 12v line dropped to 11.63v. This equates to 15.5A and 180 watts. Not too bad at all.

Last edited by BrianG; 09.17.2006 at 07:21 AM.
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What's_nitro?
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06.05.2007, 02:17 PM

Quote:
Originally Posted by neweuser
OK, if i mail this thing to someone!!! LOL! I'm really showing my electrical stupidity. this is way too confusing!
Ok, so the green wire, there is only one, Got that part, but which ground? My supply is much different! The volt meter, where so i hook that to test how much is going thru? And is this while you are charging? Do i cut the green wire before i plug it in then touch the grounds? It looks like you have yellow and black? Ornage and black? Red and black? what are these for?
If you ever have trouble finding a ground wire in an AC appliance with a 3-prong plug, just use the case of the appliance. They are always grounded, especially power supplies. But again only units with a 3-prong plug which I think all PSU's have anyways. Yellow, Red, and Orange represent the diffrerent voltage outputs. I believe Yellow is 12v, Red is 5v, and Orange is 3.3v, but don't quote me on that.


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BrianG
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06.05.2007, 03:25 PM

Yes;

yellow= 12v
orange= 3.3v
red= 5v

However, I would not use the chassis ground as the main output ground. Most of the time, yes, they are the same point electrically, but if the power ground is isolated from chassis ground (for regulator feedback for instance), the supply won't work right and may actually cause problems. Depends on the design of the PS...
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What's_nitro?
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06.05.2007, 08:59 PM

Oh no definitely not for the main ground! I meant for grounding the green "turn on" wire if someone had trouble finding a ground inside the chassis of the PS.


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BrianG
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06.05.2007, 09:37 PM

lol, oh ok. Just making sure... :)
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