Hacking Power Supply

Any more schm of this looks smiler to i have build from a old AT PSU b4 ATX LULZ  to power my sega Game Gear 12v to 9v  10 yrs  ago  but a more detailed Schm on this

The one I have is HP part  number  5187-1098.  The OEM label says HIPRO HP-D2537F3R, 250 watts max. and there is a new part that replaces it designated HP part  number 5188-2622.  Mine has no burn smell and I only gave $1.10 for it.    Hope it is fully functional.

I am thinking 22 ohm 10 watt (Newark Part Number 40M8806 @$0.55 each has NO Stock, I could go with 40M8183) might be the right fit.  Justification: (12 volts / 22 ohms) * 12 volts = 6.55 watts

Of the dozens of PC ATX-type power supplies I've used in analog, digital, and electrochemical circuits, I've never needed to add a "stabilizing" resistor.

Basically, ground out the green wire, and the fan comes on.  You get +12V on the yellow, +5V on the red, and GND on the black wires.  The whole setup requires one paper clip and about fifteen seconds with pliers.

The thing I really love about PC power supplies is if you overload or short them, the crowbar circuit just kills the power with a quiet "zoop" sound.  It self-resets after about a minute, giving you time to reflect on electrical safety!

The resistor isn't to stabilize the PSU, but rather give the system a dummy load on the 5v that helps "pull up" the 12.

Taking the green wire to ground will still turn it on, but then messure the voltage with a meter. It will most likly be under 12 volts, something like 11.7 volts instead. Also you will notice that about an amp of draw on the 12 volt will trigger the crowbar and shut it down with no load on the 5v rail.

The resistor isn't "needed", but it is suggested.

Here's mine,

http://www.jassper.com/other/project.pdf

Power resistors are hard to find. Just use a 12V Automotive tail light / side light bulb on the 5V supply.

It will be bright enough to function as a "Pilot light" and will last almost forever at 5V... 

...works on every AT / ATX supply I've used....

12v automotive tail light iv never thought of that terry king il do that to my project and give it old tube circuits feel as well

Q:  What is the normal range (or average) for current draw on a vacuum tube heater element.

I am trying to determine if there is a potential of using the VTs in lieu of power resistors.

A:  Wikipedia states that tubes like 12BA6, 12BE6 are 12.6 volts.

Here is a fun Vacuum Tube site that indicates the heater of  12B4A draws 12.6/6.3 V, 0.3/0.6 A.

Conclusion: I would need 2 vacuum tubes and sockets to put the approx. 0.6 amp load on the  12 volt rail of  my "Steam Punk" power supply.

( I have plenty of tubes; so I will have to find some new/nos sockets for them.)

Hooray for Harbor Freight and Ryobi Power tools!

I finally used my Ryobi DP120 drill press and knock out punch kit.

First I had to drill a 1/2" hole in the power supply lid, then knock it out

to 3/4", then dremeled down the rough edge.  It is perfect.  Looked thru my TV repairman's collection of V-tubes to find a good looking Tung-Sol (even says Made in the USA) 9 pin 12xx7.  I am only going to hook up the heater.  It will light up when the switch is on!

New Question:  The inrush current for the 12xx7 valve heater is too large and the PC power supply is shutting itself down.  I have some NTC thermistors (100 ohm, 450mW max.) which (according to my understanding of the data sheet) cannot handle the power when the heater is full on:  12.6V @ 150mA.

I have two options that I know of:

Opt A:  Replace with a 6.3V @ 300mA valve and series resistor ~20 ohms (three 60 ohm 5 watt in parallel)

Opt B:  Purchase something like a 3 watt 10 ohm NTC thermistor and put it in series with the heater.

Exactly what use is made of these low power thermistors?  Please tell me there is a way to use it with a power transistor to accomplish my goal and describe that circuit if you please.  Maybe the only answer is use as a temperature monitor.

P.S.  While attempting to work this out for myself I came up with the following:  low power thermistor with series 1/4 watt resistor feeding the base of a PNP transistor which controls the current thru the heater coil.  Let's assume the power PNP (has to deliver 2 watts Max.) has an  gain factor of only 10 then the most current that needs to come up thru the base is 15 mA. Thus, the base leg  would have a minimum resistance of about 800 ohms.   Do I want the starting resistance to be 900  or 1800 ohms (using 1K thermistor)?  I cannot imagine 15mA heating the thermistor up very quickly ( I could be wrong about that and it would be a good thing.) and find it even harder thinking that 7 mA would have any effect at all.  Seems like a good time to experiment! 

P.P.S. Found some interesting thermistor application notes here.