I am trying to replace a damaged power for a simulator at work. I order in LPT102M. Data sheet is avaible on Digi-key. The spec all meet or exceed the orginal power supply that was in the unit.
When all connected the CPU doesn't post. The voltages all measure fine 5V, +12V, -12V. I connected a different power supply. It is physically to big to fit in this simulator, but also has the correct voltages. It works. Through mixing and matching i determined that the 5V on the LPT102M was the voltage preventing the system from running.
I thought the LPT102M was maybe deffective and unable to produce the required current. I connected a 10 ohm resitor to the 5V, got 1/2 amp, then connected a 2 ohm resistor, got 2.5 amp, then a 1 ohm got 5 amps, I think the power suppy is fine.
I measured the current draw on the larger power supply while starting the simulator. it measured 1.7 amp. also checked what the max was during start up 2.4 amps.
The LPT102M only measured 1.3 amps while connected. This difference is what is probally preventing the cpu from posting.
Any ideas why the power supplies are out putting different currents?
Could i possible connect a resistor in parallel, or some other electrical compent to make the smaller power supply work?

I know this is very wordy and long, but thanks for any help!

 

Welcome to AAC!
Is the measured current the mains input current, or the current from one of the outputs?
What is the mains input voltage you are using?
Assuming the mains voltage is 110V and the 1.3A refers to the mains current then the input power is around 143W, which exceeds both the free-air 80W rating and the 130W forced-air rating of the unit. The unit has inbuilt overload protection so will go into protect mode.

 

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I am trying to replace a damaged power for a simulator at work. I order in LPT102M. Data sheet is avaible on Digi-key. The spec all meet or exceed the orginal power supply that was in the unit.
When all connected the CPU doesn't post. The voltages all measure fine 5V, +12V, -12V. I connected a different power supply. It is physically to big to fit in this simulator, but also has the correct voltages. It works. Through mixing and matching i determined that the 5V on the LPT102M was the voltage preventing the system from running.
I thought the LPT102M was maybe deffective and unable to produce the required current. I connected a 10 ohm resitor to the 5V, got 1/2 amp, then connected a 2 ohm resistor, got 2.5 amp, then a 1 ohm got 5 amps, I think the power suppy is fine.
I measured the current draw on the larger power supply while starting the simulator. it measured 1.7 amp. also checked what the max was during start up 2.4 amps.
The LPT102M only measured 1.3 amps while connected. This difference is what is probally preventing the cpu from posting.
Any ideas why the power supplies are out putting different currents?
Could i possible connect a resistor in parallel, or some other electrical compent to make the smaller power supply work?

I know this is very wordy and long, but thanks for any help!

Sounds like you are doing something wrong. Assuming you have the same load, the voltages can't be the same if the current is not the same.

 

Is the measured current the mains input current, or the current from one of the outputs?

Thought he said this was on the five volt line only.

 

What type of meter is being used to measure the (presumed) AC input current?

The LPT102M has active power factor correction, so for the same DC output power the RMS input current will likely be very substantially less than for a power supply without power factor correction. The average input currents should be roughly equal, assuming equal efficiency.

The specs on that power supply are devious. The total output power in free air is 80 W, but if you sum the individual output powers it comes to 137 W. There is nothing fundamentally wrong with this, as long as it is pointed out in big bold type in the datasheet.

 

Welcome to AAC!
Is the measured current the mains input current, or the current from one of the outputs?
What is the mains input voltage you are using?
Assuming the mains voltage is 110V and the 1.3A refers to the mains current then the input power is around 143W, which exceeds both the free-air 80W rating and the 130W forced-air rating of the unit. The unit has inbuilt overload protection so will go into protect mode.

I was using a Fluke 87V. I was measuring the 5 Volts on each different power supply. It never occured to measure the input. If the unit went into overload protection wouldn't it just shut off, although i don't know.

The mains is 120V off a wall outlet.
Thank you

 

It may not shut down completely, just limit the output.

 

What type of meter is being used to measure the (presumed) AC input current?

The LPT102M has active power factor correction, so for the same DC output power the RMS input current will likely be very substantially less than for a power supply without power factor correction. The average input currents should be roughly equal, assuming equal efficiency.

The specs on that power supply are devious. The total output power in free air is 80 W, but if you sum the individual output powers it comes to 137 W. There is nothing fundamentally wrong with this, as long as it is pointed out in big bold type in the datasheet.

Monday I can hook up 4 meters and determine what current draw is on the mains, 5V 12, -12. I don't think the total will be very high.
I will also hook an oscilloscope up. I half expect to see a fairly noisey wave form.

If i do these things, I still am not very sure what possible courses of action are.

At this point i am tempted to buy a 45W 5V power supply which is small and connect both power supplies. But I am not 100% sure that would work for me either.