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How to convert a HP HSTNS-PL18 psu to 13.8V ?

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rjmusto:
Thanks eblc1388 for that. Really nice to see a schematic.

Reading through that other post, it seems my experience with the PL18 is just the same. Staying at 13.4v or lower gives no problems, going higher does.

The pot I have tweaked to get rid of the issue for me is shown in the photo.  With no values on the schematic and no component designations on the board, it is hard to be sure what I'm looking at. Could it be this pot is VR120?  In which case, what is 'IAC Detecting'? (The schematic does not say what IC160 is.)

eblc1388:

--- Quote from: rjmusto on October 17, 2021, 12:24:05 pm ---The pot I have tweaked to get rid of the issue for me is shown in the photo.  With no values on the schematic and no component designations on the board, it is hard to be sure what I'm looking at. Could it be this pot is VR120?  In which case, what is 'IAC Detecting'? (The schematic does not say what IC160 is.)

--- End quote ---

No. IC160 is UCC3818, which is responsible for PFC function at the primary side. On the schematic, if you look carefully at the ground pin of that IC, you will see a small letter 'p' inside the triangle symbol. This side is HOT, has no isolation to the mains, means it can electrocute if one touches it.

This ground on the low voltage side is a different one, which has a normal ground symbol without 'p'.

IAC detecting is the detection of line current signal after the PFC inductor used by IC160 to provide the PFC function.
 

jbuszkie:
Hello!  I've got a bunch of these supplies that I've modded with an external pot to adjust the voltage.
I'm using 4 in series to make a 48V charger.  I have to keep fiddling with the pots to make the the current "constant".
I was hoping to use some digital pots instead to have it be MCU controlled.  The problem is the  200ohm digital pot.
Has anyone played with other solutions?  Maybe a isolated voltage source to fool the feedback pin?

serisman:
Sorry for resurrecting an old thread, but I modded an HP HSTNS-PL14 (460W variant) today, and have a few additional details that might help someone else out.

So, I traced a few other resistors, and it looks like there are three resistors on the high side of the voltage divider feeding the Vref.  One is 4.42k, another is 10 ohm, and another is 39.2 ohm, for a total high side resistance of about 4.4692k.  On the low side, there is the 1k resistor, the 100 ohm resistor, and a 100 ohm potentiometer, for a total low side resistance of 1.1 k up to 1.2k.  Back calculating gives a plausible 2.5Vref as output of the voltage divider (I could have just measured this in hindsight).

So, knowing the Vref, total high side resistance, and low side resistance we can use a calculator to adjust the resistors/potiometer to fit our needs.

By default the 1.1k - 1.2k low side resistance gives a (calculated) adjustment range of ~ 11.81V to 12.66V.
By bridging the 100 ohm fixed resistor, we change it to 1k - 1.1k for a (calculated) adjustment range of ~12.66V to 13.67V.

I went a slightly different route, and replaced the 100 ohm fixed resistor with a 16 ohm, and the 100 ohm potentiometer with a 1k.  This gives me 1.016k to 2.016k for a wider (calculated) adjustment range of about 8.04V to 13.5V.  I added the 16 ohm to lower my upper bound to about 13.5V since it seems like anything greater might require other mods for stable operation at > 10A.

In practice I have also found that anything under about 8.6V isn't very stable, and the power supply shuts down, probably due to an undervoltage condition.

After making these changes, I used my load tester and verified that my power supply is stable at 9V up to at least 17A, and at 13.5V up to at least 11A (that is about the limit I can test with my 150W load tester).

pienari:
Hi.
Can you upload few pictures of your mod?

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