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12 volt power supply

Discussion in 'Power Electronics' started by rnovia80, Nov 7, 2012.

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  1. rnovia80

    rnovia80

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    Nov 7, 2012
    I am making a 12 volt power supply for my rc lipo charger. I need to get a solid 12v or above for the charger. i am using a load resistor connected to 5v and ground. what would be the best resistor to use. how high can i go. 10ohm 10 watt.
     
  2. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    For about $5 you can purchase a commercial laptop power brick on Ebay that will give you a solid 12+ Volts at a decent Amp load...

    As for the rest of you comment about a load resistor, what exactly are you trying to do?
     
  3. rnovia80

    rnovia80

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    Nov 7, 2012
    i am making a power supply from my old computer. It is 12v 25 amp so i can power my lipo charger.
     
  4. CocaCola

    CocaCola

    3,635
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    Apr 7, 2012
    Original
    Well not being psychic (but trying to get better every day) and you not stating much in the original post, I like most have no idea what you are attempting to make or use...

    If you are attempting to just force the power supply to think it's under load, from the post I have seen it doesn't take much, certainly not a 10 Watt resistor... A 1/4 Watt should be sufficient...
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Ah, no. He needs to place a load on the 5V rail to make it regulate the 12V rail.

    Some (PC) power supplies don't need this, I assume the OP has checked and found his does.

    I would say 10 ohm 5 watt should be fine, but get two just in case you need a greater load. If you do, place them in parallel.
     
  6. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Gotcha the load required on the 5V side is generally proportionally to the load drawn from the 12V side if I remember correctly...

    Most people that I have seen that want to maximize the output simply use a few automotive brake lights because they are cheap and put a decent load...
     
  7. rnovia80

    rnovia80

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    Nov 7, 2012
    The power supply i have now is 12v 25amp. and without a dummy load resistor its like right under 12v like maybe 11.75v. I tried 2 10ohm 10 watt sandbars and the 12v rail went up to like 12.30v. and then i tried a 1ohm 10watt sandbar and the 12v rail was like 12.60v which was nice but that resistor heated up so fast to like 230 degrees. I was wondering how many 10ohm 10 watt resistors i could use in parallel to get it up there higher. Like what would a single 50ohm 10 watt or a 100ohm 10 watt do. would it be good for it or bad for it.
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I would stick with the two 10W 10R resistors.

    Then check the 12V rail under load (is it rated for up to 30A?)

    If it droops, try adding additional 10W 10R resistors in parallel. a 1 ohm resistor would be dissipating 25W, and I would recommend a 50W resistor for this. But that load is way too high.

    Stick to what I suggested (even 1 of the 10R resistors may be OK)
     
  9. rnovia80

    rnovia80

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    Nov 7, 2012
    ok sounds good. the 12v rail is max 25 amp. one of the chargers i was looking at was the hitech x2-400 multicharger. it can charge 2 lipo packs charge current rate is 1.0 - 20 amps per channel which is nice but it says that it the required input amperage is 60amps. so i dont know what my power supply that only puts out 25amps is gonna do. I def wont be able to charge 2 seperate packs at 20 amps each.
     
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