I have a HP server power supply that has a DC output of 12 volts, 75 amps at 900 watts off of a 110 AC input. How can this be modfied to increase the output voltage to 13.8? Attached are 2 pictures. 1 picture is of the contacts on the power supply that plug into a server. The second picture is off the same model power supply that has be modified to give the 13.8 volts output Im looking for. Can anyone help me identify what was done in picture 2 that may be what's increasing the voltage?

1 2

The resistor in picture 2 on the left side contacts is used to complete a connection to turn on the power supply with it being not plugged into a server. The 2 wide contacts are the negative and possitive contacts. In picture 2 there is something between the negative and possitive contacts and I need help identifying what it is and what it does so I can duplicate it on more power supplies.

Thanks in advance for help.

 

It would help if you could gives us the numbers on the device and maybe a clearer picture to show what it is attached to.

 

This is the label on it.

These are being converted from used servers to be used to power HAM radios

 

It would help if you could gives us the numbers on the device and maybe a clearer picture to show what it is attached to.

I do not have any other pictures that are clearer.

 

I saw some cases used the switching power to modified it became a adjustable power, I think you need to open the case and check the main IC number, and find the datasheet, maybe could find out the method.

 

I do not have any other pictures that are clearer.

Ooops , I meant the numbers on the little black square that spans the positive and negative connectors.

 

I have a HP server power supply that has a DC output of 12 volts, 75 amps at 900 watts off of a 110 AC input. How can this be modfied to increase the output voltage to 13.8? Attached are 2 pictures. 1 picture is of the contacts on the power supply that plug into a server. The second picture is off the same model power supply that has be modified to give the 13.8 volts output Im looking for. Can anyone help me identify what was done in picture 2 that may be what's increasing the voltage?

I don't see anything in picture 2 that would be increasing the output voltage; all I see is the addition of a pair of screw terminals for output connection, and what I'm guessing is some sort of overvoltage protective device like a TVS.

There's probably a trimpot somewhere inside the enclosed part of the device that adjusts the output voltage, and my guess would be that was what was done to unit #2 to raise the voltage.

 

I found the trimpot but it will only adjust to 12.7

 

I don't see anything in picture 2 that would be increasing the output voltage; all I see is the addition of a pair of screw terminals for output connection, and what I'm guessing is some sort of overvoltage protective device like a TVS.

There's probably a trimpot somewhere inside the enclosed part of the device that adjusts the output voltage, and my guess would be that was what was done to unit #2 to raise the voltage.

I wish I had another picture. I was hoping somebody could make out what it is and what it's doing.

 

You need to find out the datasheet of IC and modify the resistor, the manufacturer will set up and limited the range of adjustable voltage to be adjust.

 

12.7 V is 5% plus some margin, and almost certainly is the intended max. adjustment range of the design. A straight-on view of the end of the supply might show more clues inside. Also, most high-current supplies have remote-sense inputs (probably on some of the narrow fingers). You can manipulate the output of the supply by injecting a small current into the remote sense. If you're very lucky, the main control loop is designed such that this extra current can be derived from the main output voltage so that the supply regulates at the new. higher output voltage.

If these are used and out of warranty, rip off the lid and lets see inside.

ak

 

12.7 V is 5% plus some margin, and almost certainly is the intended max. adjustment range of the design. A straight-on view of the end of the supply might show more clues inside. Also, most high-current supplies have remote-sense inputs (probably on some of the narrow fingers). You can manipulate the output of the supply by injecting a small current into the remote sense. If you're very lucky, the main control loop is designed such that this extra current can be derived from the main output voltage so that the supply regulates at the new. higher output voltage.

If these are used and out of warranty, rip off the lid and lets see inside.

ak

The female bullets are where I connect my devices to be powered which I added.

 

I think I found a solution for what Im trying to do. It's here if anyone wants to see and offer some comments. http://www.rcgroups.com/forums/showpost.php?p=25149870&postcount=2238

 

Or, just run the radios off the 12V it supplies.

 

Or, just run the radios off the 12V it supplies.

Where's the challenge and fun in that?

 

Looks like they added a resistor on the connector (output) which I would guess is a sense pin. Look at the connector in the second image. Look at the left side and there looks to be a small resistor in there. My guess is like many supplies there are sense leads used and that resistor figures into things.

Ron

 

Looks like they added a resistor on the connector (output) which I would guess is a sense pin. Look at the connector in the second image. Look at the left side and there looks to be a small resistor in there. My guess is like many supplies there are sense leads used and that resistor figures into things.

Ron

What that thing is and does is what I was trying to figure out

 

It looks to be a resistor used to "trick" the sense lead for the - supply side. My guess is a low value resistor. What are the colors on it? The band colors? This is a typical way to "trick" the supply into sensing a lower output voltage than there is and outputting a higher voltage.

Ron

 

It looks to be a resistor used to "trick" the sense lead for the - supply side. My guess is a low value resistor. What are the colors on it? The band colors? This is a typical way to "trick" the supply into sensing a lower output voltage than there is and outputting a higher voltage.

Ron

That's what it is doing.

 

That's what it is doing.

Just add a like resistor to the second supply you want to modify. That should do it. If you are unsure of the resistor value just lift one leg of the resistor on the modified supply and measure it.

Ron