Building a PC for the first time? Read this.

By red1776 ยท 5 replies
May 6, 2011
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  1. hellokitty[hk]

    hellokitty[hk] Hello, nice to meet you! Posts: 3,448   +145

    I took out a bestec powersupply out of an emachine, and used the 12v rail to power up my hobby charger.
    I tried charging a 7.4v li-po pack at 1200mAh, and the voltage levels kept falling down below 10, where my charger would turn off. The fan audibly slowed down when the charger was charging, and the voltage on the 12v rail would not hold up until I decreased charging rate down to 80mAh.

    The charger's efficiency, I'm sure, is above 70%. It's disappointing that the power supply won't hold up, even to this. It wasn't even powering a computer. I suspect I might be doing something wrong, but I can't imagine what. It worked fine when I plugged it into my corsair 400w, which was powering a computer.
  2. Technochicken

    Technochicken TechSpot Paladin Posts: 729


    A lot of power supplies require some load on the 5V and/or 3.3V rails to start completely. Otherwise they do not fully start, which may be why it's not working properly. I recenlty converted an old ATX power supply to a bench PSU, and I had to add high wattage resistors to the 5 and 3.3V rails.
  3. red1776

    red1776 Omnipotent Ruler of the Universe Topic Starter Posts: 5,224   +164

    The resident "MacGuyver" has spoken...I would do that..:)
  4. hellokitty[hk]

    hellokitty[hk] Hello, nice to meet you! Posts: 3,448   +145

    Hey it worked. Luckily I have the perfect resistors on hand.
    For some reason though, all I had to do was turn it on with the resistors once, and it still works without them even after turning it on/off...? Ok sure whatever; I have the resistors if needed.
    Do yours get warm?
  5. Technochicken

    Technochicken TechSpot Paladin Posts: 729

    Yes, quite. I have a 5 Ohm resistor on the 5V rail, so it has to dissipate 1W of heat. I had to mount it to a small heat sink. I forgot to mention that it should probably be an under 10 Ohm resistor rated for about 10W.

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