siemens sitop 24 vdc Smps outputs higher voltage 33 vdc

[PedroGG90]

Hi everybody.

I have two 3 phase 400 vac smps siemens sitop 24 vdc giving red light overload and higher output 33 vdc.

The switching is controlled from micro controller.

Is it micro controller or transformer ? Or else pls ,?

[CapLeaker]

Open it up and have a look and take some measurements??? If the PWM is bad, you wouldn't get anything at all. Same thing with the transformer and you get like 33V on the output. What is the full spec of this PSU?

[PedroGG90]

Open it up and have a look and take some measurements??? If the PWM is bad, you wouldn't get anything at all. Same thing with the transformer and you get like 33V on the output. What is the full spec of this PSU?

Specs : Siemens 6EP1437-3BA00 SITOP Modular DIN Rail Power Supply 24VDC 40A 960W 3-Phase



This power supply mosfets gets pwm signal from a microcontroller not generic IC.

So maybe that microcontroller is faulty ?

here is a video describing how the power supply behaves .

[CapLeaker]

wow... it's transformer is squealing like a little piggy! Interesting... what is the micro controller? Compare the AC power draw with a good power supply. Check how much volts you get on the main filter capacitor. I suspect there is something wrong on the primary side. I guess you have to do more dismantling of the PSU.

[PedroGG90]

wow... it's transformer is squealing like a little piggy! Interesting... what is the micro controller? Compare the AC power draw with a good power supply. Check how much volts you get on the main filter capacitor. I suspect there is something wrong on the primary side. I guess you have to do more dismantling of the PSU.

Do you think it's maybe capacitor ?

I will to check them in my bench .

[CapLeaker]

Dunno. Could be. But that's where I would start.

[PedroGG90]

Dunno. Could be. But that's where I would start.

Can an lcr meter do the job ?

it can measure dissipation factor "D" of capacitor .

[CapLeaker]

A proper LCR that actually tests the cap under high voltage, yes. Basically a leakage test. The little battery operated LCR's are junk on high voltage capacitors.
for now, just test the Dc voltage on the cap, then switch your DMM to AC and see how much AC you get. This gets you at least on a ballpark.

[PedroGG90]

A proper LCR that actually tests the cap under high voltage, yes. Basically a leakage test. The little battery operated LCR's are junk on high voltage capacitors.
for now, just test the Dc voltage on the cap, then switch your DMM to AC and see how much AC you get. This gets you at least on a ballpark.

Hi , i checked the primary capacitor and it gives low Dissipation factor and good capacitance.

I also checked the secondary capacitors, and its all good , also all semiconductors are good. So power side is not faulty i think.

I still suspect bad PWM signal , i mean the output is there "33 volts dc " but it should be 24 volts dc. maybe the modulation is bad or the output sense regulator inside the microcontroller is faulty .


Note : One thing i am sure of is that all controls are inside a small pcb containing 2 optocouplers and a microcontroller. There is a separate uc3845 PWM ic but it controls PFC (power factor correction) circuit

[CapLeaker]

PedroGG90
With high voltage caps you got to do a leakage test in order to be sure the cap is fine.Any other test is pretty much useless there. Been there and done that. Yes, I agree that there is something wrong with the switching, since the transformer squeals like a pig.
Make sure you measure the DC voltage on the primary cap. I wonder if something isn't right with the feedback rather than anything else, since it kind of does work and you get 33v instead of 24vdc. Things can get messed up if that PSU has a PFC, but the PFC isn't working. So make sure the PFC works if it has it first.

[PedroGG90]

PedroGG90
With high voltage caps you got to do a leakage test in order to be sure the cap is fine.Any other test is pretty much useless there. Been there and done that. Yes, I agree that there is something wrong with the switching, since the transformer squeals like a pig.
Make sure you measure the DC voltage on the primary cap. I wonder if something isn't right with the feedback rather than anything else, since it kind of does work and you get 33v instead of 24vdc. Things can get messed up if that PSU has a PFC, but the PFC isn't working. So make sure the PFC works if it has it first.

Ill let you know next week

[sam_sam_sam]

I would agree and add something like if I were repairing this drive and especially if the drive is over 10 years old and they are not brand name capacitors I would just go ahead and replace all of the capacitors and see if it behave like normal I have repaired several VFD and servo drives that were over 10 years old and were showing over current with no motor or servo motor hooked up or squeaking not as bad as yours but it did sound weird when it would run

[PedroGG90]

I would agree and add something like if I were repairing this drive and especially if the drive is over 10 years old and they are not brand name capacitors I would just go ahead and replace all of the capacitors and see if it behave like normal I have repaired several VFD and servo drives that were over 10 years old and were showing over current with no motor or servo motor hooked up or squeaking not as bad as yours but it did sound weird when it would run

Hi , I checked all the caps , they are good and high quality " rubycon" its less likely that they are faulty.

I still havent checked optocouplers from feedback loop.

But i still posit on the idea that the pwm signal is not correct or not sensed very well eather from logic side or analogue side.

[PedroGG90]

PedroGG90
With high voltage caps you got to do a leakage test in order to be sure the cap is fine.Any other test is pretty much useless there. Been there and done that. Yes, I agree that there is something wrong with the switching, since the transformer squeals like a pig.
Make sure you measure the DC voltage on the primary cap. I wonder if something isn't right with the feedback rather than anything else, since it kind of does work and you get 33v instead of 24vdc. Things can get messed up if that PSU has a PFC, but the PFC isn't working. So make sure the PFC works if it has it first.

Ok i have replaced primary and secondary capacitors with fresh ones , and the red light of overload has gone and i only see green light .

But i still hear that transformer squealing and still got 33 vdc not 24 volts ,

Any ideas ?

[harp]

Test optocouplers to see if inside led/foto transistor worked,

Like this video Off power opto testing
https://m.youtube.com/watch?v=U3qYXnbVhuo

and test full feedback path to see if it switching led on 24v threshold.
What element drive optocoupler? Tl431, zener, comparator, else...?

[CapLeaker]

Sounds to me that it is still not regulating. Look at the whole feedback circuit on the primary and the secondary.

[PedroGG90]

Sounds to me that it is still not regulating. Look at the whole feedback circuit on the primary and the secondary.

I will check and let you know .

[CapLeaker]

Maybe take some high resolution, straight shot pictures, so we can see something.

[PedroGG90]

Maybe take some high resolution, straight shot pictures, so we can see something.

This power supply is a hell to disassemble.

Ill try my best.

[PedroGG90]

Test optocouplers to see if inside led/foto transistor worked,

Like this video Off power opto testing
https://m.youtube.com/watch?v=U3qYXnbVhuo

and test full feedback path to see if it switching led on 24v threshold.
What element drive optocoupler? Tl431, zener, comparator, else...?

I need to open this thing to tell you , ill be back !