Increase Meanwell Voltage Range

[Degull]

Hi everyone. I recently picked up a Meanwell SP-500-24 power supply and did not realize that it's maximum voltage is 27v. The voltage adjustment pot is 0.9 ohms when turned to the maximum 27v output. I was wondering if there was a way to increase the output voltage on this power supply. I was hoping to charge a 8s Konion pack (requires 33.6v) with it.
Any help would be appreciated. Thanks!

[heathyoung]

Two things set the maximum voltage - the over voltage protection zeners, and the voltage divider pot (ie. voltage feedback). You need to modify the ratio of the divider by changing the value of that pot.

You need to change it so that the divider ratio will get you ~2.5V at the ovp point.

[Degull]

I get that. Not sure what values I should be using but I will try fool around with different resistors in series and in parallel. Thanks!

[Degull]

I managed to get the voltage to increase by replacing a resistor in series with the voltage adjustment pot and the OVP point. A 2K resistor was swapped with a 1.5K resistor just before the OVP point. The voltage range was 17-27V before I swapped the resistor and now it is 22-29V. I don't think I can lower the resistance of the pot circuit any more because the power supply goes into protection mode higher than 29V. There are 3 zener diodes in proximity to the OVP point, any idea which ones I might try to replace in order to get the voltage adjustment to go up?

[heathyoung]

Well that sucks. I havn't messed around with this particular model, but I would say that they are probably pretty similar in the way that they do the OVP. You would think so anyway.

Sorry I cant be of much more use, a couple of photos of the top and bottom sides of the boards (not the PFC board, the power supply board) may help.

[Degull]

I'm going to get some pics up in the next couple of days. In the mean time I will try to research the forum and try to find how it's done with other models. I really appreciate the help!

[Degull]

I removed a zener diode coming off the supply output and I can now adjust to the desired 33.6V. The over voltage protection is now deactivated so I have to be careful not go over the output capacitor's rated voltage of 35V (they tend to blow up if you go over their rated voltage).

For anyone else with one of these supplies looking to do the same, I replaced the stock voltage pot with a 1K Bourns multiturn pot, replaced R95 with a 1.5K resistor and removed ZD52. Be careful not to set the output over 35 Volts with ZD52 removed!!

R95 was removed and I soldered the new 1.5K resistor to the back side of the board. The R95 spot looks empty but it is actually soldered in on the other side.

Thank you Heathyoung!

[cor]

Hi Degull,
I see that ZD53 and ZD52 are in series, so their voltages add up to give the protection voltage of 29V.
You can either take the part nr of the zener you removed, or measure its zener voltage by connecting it to your supply with about 10kOhm resistor in series.
Say that it shows it is a 12V zener diode and you want to raise the protection from original 29V to 34V (5V higher) that means that you need to add 5V to the zener voltage, either by adding a standard 5.1V zener in series or buying a zener with 5V higher voltage (for example 17V iso 12V)
You could raise the voltage to somewhere in the 34-35V so you still have a protection against accidental turning up the supply too high....

[Degull]

Hi Degull,
I see that ZD53 and ZD52 are in series, so their voltages add up to give the protection voltage of 29V.
You can either take the part nr of the zener you removed, or measure its zener voltage by connecting it to your supply with about 10kOhm resistor in series.
Say that it shows it is a 12V zener diode and you want to raise the protection from original 29V to 34V (5V higher) that means that you need to add 5V to the zener voltage, either by adding a standard 5.1V zener in series or buying a zener with 5V higher voltage (for example 17V iso 12V)
You could raise the voltage to somewhere in the 34-35V so you still have a protection against accidental turning up the supply too high....

That was what I was thinking! I replaced ZD52 with a 20V zener and now my over protection is back. When the power supply hits 34.5V it goes into protection mode. I can now vary the voltage on the SP-500-24 between 22-34.5V with no worries about blowing it up.
I also have a SP-500-48 and the boards and layout are identical to the SP-500-24. I replaced ZD52 with a 30V zener in the SP-500-48 as well and now my voltage range is 38-63V with over voltage protection.

Thanks so much Cor!

Now if I could only figure out how to keep the fan running in a quite manner.

[cor]

You could slow down the fan, but often the best way to make a noisy fan silent is to remove the noisy fan and put in a silent fan, since it is the design of the blades (mostly) and speed that causes the noise, so a quiet design is needed, not a slow-running noisy fan as that will also impair the cooling.