Power Supply Unit outputting 29V

Hi to everybody.
I own an A5 printer and following some  videotutorial on youtube I decided to replace all the orignal steppers of my printer (with the TMC22088 + additional cooling fan) in order to make it quiter it during printing.
The replacement was a sucess and know my A5 it's really quiter.. :)
Wiling to make it quiter I decided to replace the two fans on the hot-end with two Noctua 12V 40 mm fans (https://www.amazon.it/gp/product/B009NQLT0M/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1). After opening the A5 case just for my curiosity I've checked tha MKS Gen L board connection in order to find where the cables of the two fans (those placed over the hot-end) are placed. After I found the connectors just for curiosity I've checked the MKS board main power pins and I found that instead of 24V the PSU of the printer provides 29.7V open_mouth:!!!
I double check the output of the PowerSupply Unit of the printer and I found that 29.7V comes out form the unit...I've tried also to adjust the outpup voltage with the trimmer on the PSU but I can only down the output to 27.9V...
I don't know if it's a problem of my PSU unit or if every PSU units provides 29V (out of the box) to the A5.. Is it safe to power the MKS and all the other devices of the A5 with 29V (or at least 27.9V that I obtain acting on the adjust trimmer)? 
As additional question, do the two fans on the hot-end work at 12V? Or are they powered with the same voltagecoming out from the PSU??
Thanks a lot for any kind of info.


  • Samuel PinchesSamuel Pinches Posts: 2,628Administrator
    Welcome @lenny1972

    Yeah, that ain’t right. Contact JG to ask for a replacement one. While a high voltage will mean you can heat up the bed more easily, if the spec is 24 V then I think 27 volts as a minimum adjustment is crazy high .... sounds like the power supply is faulty ....  Unless theyre modifying it at the factory to “over clock“ it like this... 🤔

    All the fans on the printer run at 24 volts
  • Stephen ToddStephen Todd Posts: 281🌟 Super Member 🌟
    Yes, definately faulty PSU

    There is a chip on the PSU board that monitors the secondary voltage generated and adjusts the duty cycle of the oscillator, which increases or decreases the generated voltage - likely the factory has put the wrong value components on the board, or one of the components has failed or gone out of spec
  • Stephen ToddStephen Todd Posts: 281🌟 Super Member 🌟
    edited March 24
    The maximum input voltage of the MKS Gen L board is 24v - I don't know what the breakdown input voltage is, but you will be putting the board under strain, so I would expect an early failure if you continue to input an out of spec voltage - but it depends on how much leeway is designed into the board
    Post edited by Stephen Todd on
  • buklbukl Posts: 8Member
    Might sound strange, but before you contact the manufacturer, have you checked, that your multimeter is reading correct values? Have tried to measure a known voltage or checked with an other multimeter?
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