24v psu problem

After a month of successful printing, with a new 24v PSU dedicated to the bed, first the power expander burnt then the PSU doubled in voltage. Without a expander i connected the PSU to the melzi ground and let the built in MOSFET do the job.
The increase in voltage seem to happen when the system is in idle i.e. no print loaded and goes away after a few on/offs. The problem still occur when disconnected from the printer.
Any ideas to what the problem could be?

For the first time i hearing this kind of problem it's better to it the service center

Some cheap power supplies don't regulate the output well when there is no load. However, I think it more likely that the PSU you have is simply faulty.

I expect the increased output voltage is what caused the power expander to fail.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

The PSU worked for a three hour print, bang bang not pwm as before. The no load problem crossed my mind hence I will add a 24v 10w bulb as load to see if it makes a difference.
Got hold of two free 575w server PSU that can be connected in series to produce 24v if the old one does not improve. The voltage or pwm probably killed the power expander although it is rated to 48v (probably not during pwm though).

Be careful about connecting those server PSUs in series - they may very likely have the 0V rail tied to mains ground.

I guess the Power Expander may not like fast PWM - I haven't seen the schematic so I can't tell. Do you know what PWM frequency the firmware was using when you had bed PID enabled?

Edited 1 time(s). Last edit at 02/19/2016 02:29PM by dc42.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks for the heads up. I have seen this particular model in series, it did however not say of there was a ground issue. PWM Hz, not sure, standardish Marlin for Mendel90 though.