Pure DC computer

Discussion in 'General Hardware' started by SirLink, Feb 23, 2007.

  1. Makalu

    Makalu Ancient Guru

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    well that sucks...I assume that you have oriented the cig lighter socket so that the connectors in it line up? Maybe there's just too much resistance in the design though. Any idea what the minimum voltage the pico-psu allows?

    BTW and just in a FYI sort of way...my neighbor, being the pain in the ass that he is, just had to contact the makers and needle them about the battery cables and they said something to the effect of the large cables are needed to carry the current to the fuse in the event of a short or something that would cause the batteries to unload all of their stored power at once...so they want the fuse to do it's job and fry rather then a smaller cable.
     
  2. SirLink

    SirLink Ancient Guru

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    Well, it looks like one of those that can be spun in any orentation... :O I have tried moving it around... Thing is it looks and it's either not getting enough voltage or current... Could be you right, the resistance may be too much through the connector. My father is an electrical engineer, I am going have him help me next time he comes over... :p

    Well I can't find that right now, I know I have seen it before... :O I wanta say it was around 10.75-11.00v. Min amps is 2A and max at 10A...
    Here is the one I have...
    http://www.mini-box.com/PicoPSU-120-WI-25-12-25V-DC-DC-ATX-power-supply

    That's still seems over kill for a 2guage conductor. :p But that reasoning makes sense. You want to make sure that fuse gets the full blunt...

    I am going to work on the setup some more later, and I will get some more pics up for you guys to see... It is comming out real nice.

    Also found out my scope FINALY shipped today! :p So that's finaly on the way, I should have this wrapped up to test it off the batteries by the time it gets here... :D
     
  3. Makalu

    Makalu Ancient Guru

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    yeah they can be spun completely around but usually there's a small springy connector that needs to be lined up. Anyway, I'm sure you and your Dad will get it sorted. I certainly wouldn't think that the resistance of a plug like that would cause a voltage drop of over 1v so assuming the specs are right then it should be good. I also would think that they can handle and pass a great deal of current.

    The thing about the 2ish gauge cables is that this is a 4 battery setup...4 6 volt batteries wired together in series-parallel to produce 12v at double the amphours. Not really applicable to your setup but similar to a two 12v battery setup like was discussed. So anyway that's ALOT of energy stored that could potentially be released at once.

    Anyways, have fun :)
     
  4. Altazimuth

    Altazimuth Maha Guru

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    I think they use that gauge of wire because it's a standard size that they use for UL certification for residential areas which I believe some states require (minimum is #2 gauge); and of course the cables should always be able to carry more current than the fuse.

    As for the other thing, what with cable lengths and contact resistances etc, wouldn't it be better to use the 12v-32v range psu and two batteries in series? Or maybe even the 60 watt 6-26v PSU (Parallel). I dont like that 12v limitation it's too close.
    Also, you might be better off using a different type of connector.
     

  5. SirLink

    SirLink Ancient Guru

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    Okay. I am not seeing anything like that on this one... :O The plug has a spring loaded tip, with the fuse in it which hits the pos. pad in the bottom center of the socket. Then there are two neg "ears" on the side of the plug hit the sides of the socket...

    I wouldn't have thought so either... And looks like the voltage drop is minimal. Still above 12v easy...

    I wonder if the cord lenght could be adding to much resistance... There is about an 8ft cord from cig plug to the pc...

    It should be able to handle the current, I bought a kit at radioshack, the socket has a 10a rating, and the plug a 5a rating...

    The thing is, this acc socket connected to the batteries will also be powering a 12v telescope. That is why I am trying to keep the voltage around 12v. Just to keep the design simple...

    I am also using the cig connector cause the scope comes with one, and thought it would be good to be able to plug the pc into the car if i ever needed...
     
  6. Makalu

    Makalu Ancient Guru

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    yeah there's probably more resistance thru the 8 foot cord then there is thru the plug connection.
     
  7. SirLink

    SirLink Ancient Guru

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    I am going to make up a cable using the cig connection with just a shorter cord and see what happens... It's just very wierd. It acts like it is not getting enough power. I need to get a bigger meter to test my current draw. It may not be supplying enough current, maybe? But then I would think comming straight off the batteries would do the same... Weird... Gonna keep working on it... :p
     
  8. SirLink

    SirLink Ancient Guru

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    Ok here are some new pics...

    The lower profile heat sink allows me to keep the keyboard and trackpad in place...
    [​IMG]

    Now setup is just a matter of open case, connect power...
    [​IMG]

    The keyboard is one of those flexible ones, the trackpad is an EasyCat...
    [​IMG]

    The green button is the power, the silver jack is the power input...
    [​IMG]

    Here is the battery setup with the inline fuse...
    [​IMG]

    Here is what I get when I run through the cig adapter...
    [​IMG]
     
  9. Makalu

    Makalu Ancient Guru

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    Have you measured the voltage at the batteries or plug or pico-psu? I see you're using two batteries in parallel now rather than just one like before without the cig connector and was wondering if maybe one of the batteries has a dead cell and if that would make the output 10v.
     
  10. SirLink

    SirLink Ancient Guru

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    yeah i have... I have 12.86v at the battery terminals (for both, slightly discharged, they float around 13.5v), and at the socket I have the same 12.86v. At the connector that connects to the pc, and at the pico imput I also have 12.86.

    Now when running the voltage at the pico drops to 11v when routed through the cig connection. So there is the problem. :(

    Now with it wire straight to the batteries, while running, there is 12.5v at the pico... :)

    So the question now is why is there a voltage drop under demand?

    [​IMG]
     

  11. Makalu

    Makalu Ancient Guru

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    well increasing the current (load) increases the resistance and that lowers the voltage...so you either need a larger gauge wire or a shorter wire or a tighter connector or some combination of the above
     
  12. SirLink

    SirLink Ancient Guru

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    That's true... Didn't think of that. :O

    Okay. I will try a higher gauge wire first. I don't need such a long cable. I am going to put the pc case on a stand, and the batteries on the floor, so 4 feet would suffice... :) Thanks for the info! :p
     
  13. Altazimuth

    Altazimuth Maha Guru

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    To make the load equal on the batteries, you should take the Positive connection from the Positive Terminal of one battery and the Negative connection from the Negative Terminal of the other battery.

    There must be quite a big resistance there; fuses and all those connections will also increase resistance - you only need one fuse. I'm not quite sure how you plan on connecting it all, how are you going to get power to the computer and the scope?
     
  14. SirLink

    SirLink Ancient Guru

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    Good point... That's a good idea!

    Yeah, I think the fuse in the connector is not helping in addition to the length of cord. I was going to get one of those cig addapter spitters, but I might just put another socket in parallel with the other.
     
  15. SirLink

    SirLink Ancient Guru

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    Ok here is another update...

    I went to a barrel connector for the pc connection... There is 12guage from the batteries to the jacks.
    [​IMG]

    The cable between the battery box and the pc case is 14guage...

    [​IMG]

    The voltage coming into the psu under load is still a little lower that I would like... It's definatly the LCD thats causeing the extra draw... :( I am beginng to understand why they had 2 12v lines going from the origninal LCD power supply to the LCD controller...

    I have increased the gauge where I can, and shortened what I can. I am thinking my only other option to reducing the load off the psu is to give the LCD it's own 12v line off the batteries... :(
     

  16. Roger_D25

    Roger_D25 Ancient Guru

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    Have you tested after making those modifications Link and if so did it make any difference? I would image going to larger guage wire and shortening cables as much as possible will help but the power draw will probably still be about as high as it was. I think trying to supply both the PSU and LCD separetly is a good idea.

    With that said though, the PSU most likely puts out a much cleaner and more stable voltage than coming direclty off the battery so you might want to at least keep that in mind when coming directly from battery to LCD controller. I'm no expert with this stuff but the controller is probably sensitive to voltage/current changes so it is at least worth thinking about before trying it so that your LCD doesn't get messed up. Good luck Link!
     
  17. SirLink

    SirLink Ancient Guru

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    Yeah... I did... It's like .3v too low... Now some of that can be due to the battery being low, but at the same time... I need to maximize it so I can keep the running time long enough...

    The larger guage helped... But it is just barely not enough... :( I got a 5a fast blow fuse between the batteries and the jacks... Hopefully that will suffice... LCD should be fine, if it undervolts, it just goes off... I have seen that enough already...lol :p

    So here is my quick fix for now...
    [​IMG]

    [​IMG]
     
  18. SirLink

    SirLink Ancient Guru

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    After going back and re-reading what you said, it reminded me of something else I tried... :D

    If I power the LCD of the output side of the psu, it does the same thing. The voltage drop it too great when it's on the 12v rail...

    This thing was connected with two 12v lines... I couldn't figure out why when I was disasembling it... So in my harness I just spliced the two into one. Tied the two 12v's together and the two grounds together... Since I don't have two seperate 12v rails they would just get combined at some point anyway...

    Just thinking out loud... :p
     
  19. Altazimuth

    Altazimuth Maha Guru

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    I don't know how you are going to overcome the voltage drop problem, what you really need is a higher voltage and lower current (for the computer).
     
  20. SirLink

    SirLink Ancient Guru

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    Well I thought about just running the pc off 24v and the telescope of just 12v. But them I am still left with the LCD. And if I still need to run a connection back to the battery for the LCD istself, then I might as well just keep it all 12v and conserve the battery life...

    Besides the way it is running right now, I can't think of anyway either... :(

    Thinking out loud again... What if I put a capasitor before the psu? Might be enough to 'regulate' the voltage...
     

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