Identify 20/24 pin connector 12V lines on PSU after they have been cut?

Discussion in 'Power Supplies and UPS's' started by Eric Oesterling, Jul 7, 2011.

  1. Eric Oesterling

    Eric Oesterling Geek Trainee

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    Alright, so I'm working on a project and seemed to have made a grievous error. I am not too well versed in electronics so I'm hoping you all can give me a little advice. I am getting rid of an old Corolla that I had put quite a nice sound system in. I wanted to take the equipment from the car and wire it up so I could use it in my new apartment. I built a box for my speakers and purchased two computer power supplies. The power supply I planned on using for my amplifier/sub woofers is a ROSEWILL| RG630-S12 630W RT. A quick search showed that the yellow wires were carrying 12V, and just as a safety check I used a multimeter to ensure that the resistance across any given yellow wire to another was ~0 Ohms. I also checked the black wires and found that any combination of black wires would still yield ~0 ohms. So, I assumed since there was no resistance they were all connected and I could take whatever yellow and corresponding black wires I so pleased. I clipped the two yellow wires on the 20/24 pin connector and the corresponding black wires as well as all of the yellow and corresponding black wires on the mole connectors and the 6 pin connectors. I put all of the yellow wires together and did the same with the black wires. I powered it up and used my trusty multimeter to make sure I was getting 12V across the two bundles of wires. I was, so I figured I was ready for a test run. I hooked it up and my head unit and... blew the fuse.

    I looked on some forums (yeah yeah I know by now most of you are shaking your heads at my utter lack of foresight), and noted that most guides said NOT to clip anything off of the 20/24 pin connector. Whoops. I also realized, quite to my dismay, that in my clipping frenzy I had clipped TWO of the ground wires from one of my mole connectors. The extra wire I clipped was the negative for a 5V wire. I have narrowed the missing 5V negative down to only a few candidates based on their position, but I don't know how to find out for sure which on them was originally paired with the 5V line. I thought that there would be some resistance between the 5V negative and any of the 12V negatives if they were on a different board, or rail, or whatever the correct term is, but any given combination of clipped black wires still yields close to 0 Ohms. I also have no idea how to determine which two yellow and black wires were originally on the 20/24 pin connector. I have successfully powered my head unit with the other power supply by clipping only the yellow wire and corresponding black wire from the mole connectors. So, what I need, is for one of you awesome circuitry masters to give me a nifty trick I can use to determine which wires I need to reconnect.
     
  2. violetblueskies

    violetblueskies Big Geek

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    just a few ideas that came to mind.
    you could take apart the other identical power supply and trace the wires.
    also i'm not sure if this is correct but are the ground for 5v and 12v on a separate line?
    perhaps continuity can tell you which is which?
    let us know how it goes...

    edit:
    what your setup consist of?
    what amp/subs?
    just thinking would 50a be enough to power any amp these days with all the bass enthusiasts?
    from what i know, lots of amps tend to use what they are fused and will not operate unless they have the power available.
     
  3. Eric Oesterling

    Eric Oesterling Geek Trainee

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    Well, the other power supply isn't identical. The head unit and speakers don't demand nearly as much power as the amp/subs so I purchased different PSUs.
    I checked the resistance across two ground wires and found the resistance to be 0 ohms. I then took one of those ground wires and checked it against every other ground wire I had clipped, and the resistance was also 0 ohms, so it appears that I should be able to put any given ground wire back into the 5v circuit, but that did not seem to work.

    I have a Kicker ZX750.1 Amp (750 Watt RMS) and two Kicker CVRs wired in parallel which gives it a 2 ohm impedance and 800 Watts RMS.
    I know 50a is not enough to fully power it but I have the amplifier turned down as low as possible as well as the bass control on the head unit. Either way, I tested the PSU in question on the head unit and blew the fuse on the head unit. It wasn't an issue of drawing too much power from the PSU.
     
  4. violetblueskies

    violetblueskies Big Geek

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    okay i see what your saying.
    besides resistance, are all the ground wires interconnected?
    i was saying you could use continuity check to differentiate between the ground wires if they are on separate line.
    for example all the 5v ground wires if all interconnected will sound off any way they are tapped.
    whereas 12v might not be connected with the 5v wires.
    also couldn't you just measure the voltage of the clipped wires and find where they go from there?
    i know they have a schematic for the 24pin end and all the molex wiring is standard too.
    there is also something called testing voltage drop on ground but i don't know too much about this.

    interesting setup i have to say.
    i've had one of those amps before and remembered them to be something like 2x 40a fuses?
    well i also remembered how the amp wouldn't turn on properly when having inline fuse less than 70a.
    it would basically go into protect with the red light that is until i put in 80a fuse.
    so i'm curious how the power supply that has [email protected] will even turn on the amp or am i missing something here?
    i know this is unrelated to your issue i was curious really.
     
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  5. Eric Oesterling

    Eric Oesterling Geek Trainee

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    OK I wasn't sure what you meant by continuity but I get it now. Every single ground wire is on the same line and all of the 12v wires are on the same line. My mistake was taking wires off of the non-molex connectors. I don't know why this was causing the problem, but I reconnected all the clipped wires on the non-molex connectors to the corresponding color (not the same wires, but since they are on the same line I figured it shouldn't matter) and it worked!

    Unfortunately, you are correct in assuming that 50a is not enough to properly power the amplifier. There are indeed two 40a fuses. I figured that I could start with the volume as low as possible and work up until it drew more power than the PSU could handle and just never turn it up higher than that. Wrong. Whats curious is that it does turn on and the led goes green, but only for a few seconds before it demands more current than my PSU can supply. I know very little about the inner workings of amps but I suppose there is a capacitor (or series of capacitors) in there that is demanding more than 50a while it charges. I know people have done this with only one PSU for their amplifier (and with a weaker PSU), but they must be using a much weaker amp. I suppose it wouldn't be too difficult to find someone willing to trade for a weaker amp, or just buy another PSU. Thanks for the input.
     
  6. violetblueskies

    violetblueskies Big Geek

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    well i think the amp just requires this power to even begin to work.
    you could have the gains all the way down and not even have the wires from the sub connected and it will still trip into protect without the right power amount. (at least in my experience)
    do you live in a place where bumping bass isn't an issue? really 2 cvr's is a lot of bass. hell even 1 is a lot. i know they aren't cvx's but still... they will hit pretty hard when powered adequately.
    from what i know most subs you buy with a home stereo system tend to use paper woofers which requires less power to push. what you got requires more power to push.
    you can go several ways about it. ideally that amp you have was designed to bass and was specifically designed for the cvx 12.
    more power doesn't necessarily mean better quality sound. it just takes more power to push those subs as oppose to paper subs in standard applications.
    if i was you, i would leave those items for the car and just get you a good 5 piece system with subs from best buy or something.
    if you really wanting to makes this work anyway, then you need to get a stronger power supply.
    i recommend going a little higher than the requirement from you amp say 100a. pushing max amps on your power supply will cause it to overheat.
    something like this:

    http://www.newegg.com/Product/Product.aspx?Item=N82E16817256069
    http://www.newegg.com/Product/Product.aspx?Item=N82E16817159123
     
  7. violetblueskies

    violetblueskies Big Geek

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    you could also get a lower power amp used off craigslist cheap and just power one sub.
    i think each of your subs require 400w rms for optimal sound quality.
    so even if you got an amp that put out 200-300w rms it would still push it.
    a little underpowered but wont be so bad if you set the gains just right.
    however, its not really good for subs to be underpowered in the long run.
    imo 300w rms should be okay though.
     

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