I am testing a motherboard that has short to ground.

I want to use a ATX psu
So in this order PSU 12v rail to - mosfet on mobo tells the board it needs to be at 12v
ground on board -to positive end of (something that draws 5 10 or 15 amps)
ground wire of ---the something
back to the PSU ground. The motherboard will be the middle man.
I need to be able to put a demanding load on the output of ground wire on the motherboard. I should be able to feel the heat where it's shorting to ground ie GPU
The led strip I have is too small I need something more demanding I need something 12v that will draw the type of amperage.

 

Lightbulb? I use an old auto headlight. It'll draw ~4A at 12V.

 

Lightbulb? I use an old auto headlight. It'll draw ~4A at 12V.

So the ground on mobo to positive bottom of bulb and the wire to the side of bulb ground back to psu ground?
I 've seen this done before with a Whole bunch of LED strips on the output of the ground on motherboard I think it has be something load demanding to inject the 12v through the board. I don't have a whole bunch of leds.

 

Parallel or serial configuration is up to you, depending on what you want to accomplish.

 

Does the power supply need to see 2.4ohms to draw 5amps? so it needs to go before the motherboard? The bulb is actually a current limiter so its not shutting off the PSU when it sees the shorts and wants to shut down right?

 

I think utimatley I'm need a way to have it where the ATX psu 12v does not want to shut down when it sees the short on the board. I need it to feel stay hot where the short is. So I think i'm needing something with alot of resistance on the output of the board right?

 

Borrow an auto battery tester from a mate in a garage.

But beware some (the lorry type) can draw a frightening amount of amps.

 

Really need to use a variable current limited supply. Set volts to 12v or so, connect and slowly raise current limit to required level. You may be able to track voltage drops on tracks to determine short location or if possible use a current tracer(if available). Other option if is to use calibrated fingertip to feel for hot parts.

 

Really need to use a variable current limited supply. Set volts to 12v or so, connect and slowly raise current limit to required level. You may be able to track voltage drops on tracks to determine short location or if possible use a current tracer(if available). Other option if is to use calibrated fingertip to feel for hot parts.

There is no idea to get variable current limiting from the 12v psu I have?

 

In series, lightbulbs of different wattages will limit current to the amount the bulb uses at 12V. Placing an identical bulb in parallel to the first will double that current. Not elegant, but cheap if you already have the bulbs.

You could certainly build yourself a constant current supply from a computer PSU but it's not the easiest project for a newbie because of the power involved.

 

In series, lightbulbs of different wattages will limit current to the amount the bulb uses at 12V. Placing an identical bulb in parallel to the first will double that current. Not elegant, but cheap if you already have the bulbs.

You could certainly build yourself a constant current supply from a computer PSU but it's not the easiest project for a newbie because of the power involved.

The Psu I have is 12v @9.2amps I need to bring it down to 1 amp or little higher can I use a resistor?

 

Well, a 12W bulb will allow 1A thru itself.

A resistor will sort of work. Suppose you want to drop 12V at 1A. That means a 12Ω resistor. The power it will dissipate is I^2 x R, or 1 x 12 = 12 watts. To keep it from overheating, you'll want one rated to at least 24W.

Neither of these simple solutions is the same as a constant current supply, which will self-adjust the voltage (up to a limit) to reach the current target.

 

Well, a 12W bulb will allow 1A thru itself.

A resistor will sort of work. Suppose you want to drop 12V at 1A. That means a 12Ω resistor. The power it will dissipate is I^2 x R, or 1 x 12 = 12 watts. To keep it from overheating, you'll want one rated to at least 24W.

Neither of these simple solutions is the same as a constant current supply, which will self-adjust the voltage (up to a limit) to reach the current target.

Thanks for all your input greatly. I will try with a 10w 1.0hm resistor first.

 

It will overheat. Be careful.

 

It will overheat. Be careful.

What the psu ? it will shut itself off right ?

 

The resistor is not rated to handle the power and will get very hot, and then fail.

 

The resistor is not rated to handle the power and will get very hot, and then fail.

I can't handle all this i'm going to buy a long led strip off amazon overnight and connect the the positive to the ground on board and the negative from led to the psu and I should be in business.

 

Why don't you spend your money on two 5 ohm 10 watt resistors. I think you may instead of .

 

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Why don't you spend your money on two 5 ohm 10 watt resistors. I think you may instead of .

I've seen this done before actually the two mosfets on the board one has 18v and the other turns it into 12v the board can use to boot , by making the board the middleman the load of the led strips will continuously pull the 12v need to find the shorted component by heat.

 

Use a milli-ohmmeter or and audible one. No high currents involved.