150 watt power supply question

Discussion in 'PowerPC Macs' started by poiihy, Feb 25, 2015.

  1. poiihy, Feb 25, 2015
    Last edited: Feb 25, 2015

    poiihy macrumors 68020


    Aug 22, 2014
    I have a 150watt power supply from my beige G3.

    And I have a 10 watt 12 volt halogen bulb that I have connected to it.

    When I have the bulb connected in it the fan increases speed quite a bit (the fan varies speed according to load).

    My question is, what percentage of the max draw does this 10w halogen lamp consume? Does it consume 12% or does it consume more? If it consumes 12% then a 150watt power supply should be enough for nearly any regular PC, but I see that 400 watt is minimum today and even that is not always enough.

    P.S. A little story about the halogen bulb: When I first plugged it into the PSU and played around with it a bit I soon broke off a pin. The pins cannot tolerate bending so if you bend it at all then it may break easily. So I had to dig into the glass base of the bulb until a stub of metal sticked out, then I dumped a blob of solder and a wire to make contact with the stub. Also soldered a wire to the good pin (that was the easy part) Then I used e.tape to wrap it up so the wires dont rip out. Problem is that after using the light for a while it starts to roast/melt the e.tape and make a smell.
    That's the short story of the halogen bulb. :p
  2. LightBulbFun macrumors 68000


    Nov 17, 2013
    London UK
    a 10W restive load like ur halogen Bulb will draw 0.8333333333A at 12V. check the 12V Bus rating on the PSU I know early PSUs don't have many amps on the 12V rail BTW the reason your Halogen bulb is melting tape is it heats up to about 300C (572F) to make the halogen cycle to work and start depositing the tungsten back onto the filament if u run the lamp on a Lower Voltage the temp will be too low and the Halogens will eat the filament and the Quartz glass bulb will blacken rapidly due to tungsten not being returned to the filament
  3. poiihy, Feb 25, 2015
    Last edited: Feb 25, 2015

    poiihy thread starter macrumors 68020


    Aug 22, 2014
    This is a reflector bulb and so the halogen bulb is inside a reflector casing. A bare halogen bulb would get very hot and there must not be any fingerprints or dirt on it or it will shorten the life of the bulb. Reflector bulbs don't get very hot because of the case and the e.tape doesn't exactly "melt" it just gets hot and soft.
    I knew halogen lamps return tungsten to the filament but I didn't know that process doesnt work at lower voltages so thanks for that
    The PSU says Max 5 amps for the 12 volt rail. The 5 volts rail has max 20 amps or something like that.

    My main question is why most PCs today use minimum of 400 watt power supply when a 150 watt power supply would be plenty? And then they say that even 400 watts may not be enough and you may need 750 watts for a powerful gaming PC. Do modern PCs really use that much electricity (internally)?

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