[SOLVED] Problem With "Power Line Disturbances"

[MB.ESK]

I have a question about "Power Line Disturbances"
Is the last methode for suppressing Power Line Disturbances using "ups" ??
I USED ISOLATED TRANSFORMER AND LINE FILTER IN MY DESIGNING BUT WHEN I TURN ON SINGLE PHASE MOTOR(start/run capacitor) BY CONTACTOR (MANUALLY) MY BOARD (STM32F4-DISCOVERY BOARD) RECEIVE AN INTERRUPT !!!
It's suprising. because it happens eventhough I DISCONNECT IT FROM MY DEVICE AND I USE LAPTOP USB PORT FOR it's POWER SUPPLY8-O. IT MEANS THAT BOARD RECEIVE NOISE FROM AC POWER LINE .
I observe all the rules in my designing .
power and controlling parts are isolated by seperated power supply and optocouplers.
as I said, I used isolated transformer for each part.
one stage line filter used befor trnsformers.
but all motors connected directly to 220v ac power line.
I used mosfet for turning on contactors and i used 1n4005 as free-wheeling diode in parallel with cantactor bobbin.
THANKS.

 

[treez]

Years ago I was testing offline power supplies plugged into the lab socket.

Into a totally different socket was plugged a HV test chamber which had a safety contactor which acted to turn the mains supply off to that chamber (only) when someone opened the door.

Whenever this contactor switched, the power supply that I was testing would go into a fault mode.

Im afraid that very often even lawful and regulation passing isolation and filtration measures just cant stop this kind of thing.

You can do all the usual stuff like reducing size of current loops on pcb, etc

 

[D.A.(Tony)Stewart]

If Radiated large CM interference couples to long wires as a conducted noise. Then large CM ferrite chokes are needed.

If not grounded properly then line filter will not work well.

You can simulate the noise with any small relay with power from a battery to Normally closed contacts thru the coil and use the wire loop as a large antenna to test your new filter.

CM Chokes both on interfering source and load ( your IO cables and power source) will improve EMC...ie. compatability.
Suitable RF caps to a good ground from each line then provide the low shunt reactance for the series 50~ 500 Ohm CM chokes to attenutate incoming signal disturbances. CHoose high permeability lossy ferrite. Similar to DC power cords and VGA video cables ( clamshell type)

Both high impedance series CM Choke with absorption loss and shunt RF caps are best for attenuation of CM noise which gets translated into a differential signal from unbalanced lines. like Reset. So add an RF cap to Reset while you are at it and beware of ground shift impulse noise.

Consider all long paths as antenna from source to CPU.

transformer isolation is poor at HF and VHF RF impulse frequencies, but maybe OK at AM band and down. Generally only for line frequency safety.

Ethernet is pretty immune due to well balanced lines and CM choke.

 

[MB.ESK]

Thanks for your answer.
But i considered rf impulse in my design . So i used ferrit bead and emi filter (blm41pg102sn1 and nfm41pc204f1h3) befor and after swiching and linear regulators or in the entrance of board's powre supply.
I used separated ground plate for noisy part and also for digital part like microcontrollers and it cause that eliminate ground loops.digital analog and noisy power parts are completely separated form exclusive trsnsformer and regulator (power supply).
But i don't have problem with my designing power supply only, as i said i recieve interrupt from ac power line ! In this way usb cable is very short and standard and suprising thing is that what adaptor and mother board are doing ??? These are designed by asus company and aren't my design !!!

 

[D.A.(Tony)Stewart]

Laptops are having floating battery chargers for safety reasons in case a transformer fault makes the metal case on the laptop live and the user gets a shock. But the coupling capacitance is enough to get a shock already of about a few hundred uA when the user is grounded and can feel the current on their wrist or bare knee. Similarly an external high impedance microphone that is unbalanced can pick up noise from CFL pulses and all these disturbances can be removed by adding more capacitance between floating ground and earth ground to suppress the impulse.


most likely your interfaces are unbalanced and differential noise is generated somehow from poor RF isolation or poor grounding.

Interfaces must be optically coupled for better isolation otherwise a star or mesh ground for everything is required or if balanced differential like USB then CM chokes with LC filters need to be considered.

Without a block diagram of your power and signal connections and their grounds , it's hard to visualize.(hint)

I used to have a lab in the corner of the office with every computer you imagine in the early 80's and a few more... The metal wire cage became a nice antenna for ESD when someone walked across the carpet and touched the cage, the MOT Exerciser system, would reset and maybe a few Apples. The fix was to ground the cage properly and used carpet antistat spray

 

[MB.ESK]

You are right! but I think I have considered all the things as you said, but for being sure I put my power supply schematic for you to check it please. my device is an industrial machine with a fairly big size. as you see . https://obrazki.elektroda.pl/4684567500_1447403196.jpg
It has two metal wire cages (one for recognition part and another for controlling part) the machine has several actuator like several pneumatic jack dc motor and also has 3 single phase motor (start/run capacitor type)
actually these motors make faults in my system ...
these are controlled by contactor with controlling board as below schematic:
https://obrazki.elektroda.pl/4550416500_1447406699.jpg
https://obrazki.elektroda.pl/5146439700_1447406745.jpg
https://obrazki.elektroda.pl/4570439800_1447406803.jpg
in page 1:
there are entrance connectors. 24v for contactors & 12v (vbat1) for opto sensors (IR)
AND SOME SIGNALS TO/FROM MICROCONTROLLER THAT ARE ISOLATED BY TLP250 or separated power supply.
PAGE 2 AND 3 ARE DRIVERS FOR MOTOR'S CONTACTOR.I should explain about relays.they are safekeeping relay that prevent to active several part of machine together in error time of controllers or manually activation, illegaly.
as you see, some normaly close relay's contactors put in series with driver from another parts(another boards).

NOW IT IS NECESSARY TO CHECK POWER SUPPLY BOARDS:
At the first, AC Power Line pass from line filter as below:
https://obrazki.elektroda.pl/2783082600_1447410688.jpg

then goes to MAIN POWER SUPPLY BOARD THAT PROVIDES ALL VOLTAGES IN DEMAND :
https://obrazki.elektroda.pl/5658890900_1447408290.jpg
https://obrazki.elektroda.pl/3745015900_1447408330.jpg
as you see, there is 3 separated input transformer and output terminal voltage .
AND TWO ANOTHER POWER SUPPLY BOARDS THAT ARE DERIVERD FROM THIS BOARD .
THESE ARE PROVIDE FINAL VOLTAGE FOR MICROCONTROLEERS :
1- https://obrazki.elektroda.pl/9646797200_1447408950.jpg

2-
https://obrazki.elektroda.pl/1507475000_1447409109.jpg
https://obrazki.elektroda.pl/2140322800_1447409155.jpg
https://obrazki.elektroda.pl/1262136100_1447409183.jpg
https://obrazki.elektroda.pl/9270926600_1447409221.jpg

In general,I attempt to separate noisy part from beginning and I connected with optocoupler to these noisy parts in all parts of circuits and now surprising thing is that both Ac power line of machine and DC power output of machine's DC power supply are noisy in swiching time of motors !!!! as I said before,I receive interrupt from ac power line of machine(Ac plug) when stm32f4-discovery board is connected to a laptob through an adaptor !!!
thanks.
also I should say all the boards are isolated from metal wire cages and because of some limitations ,there is no earth !

 

[d123]

Hi,

Not necessarily so, but maybe something here will be useful to re-view how you have things set up, and if there is possibly a preferable alternative to an opto-isolator:

https://www.ti.com/lsds/ti/analog/isolation/documents.page

"Pushing the envelope with high performance, digital-isolation technology"

https://www.ti.com/lit/an/slyt649/slyt649.pdf

 

[MB.ESK]

THANK YOU. I CONSIDERED ALL OF THEM BEFORE BUT I CHECKED IT AGAIN.... :sad:

 

[D.A.(Tony)Stewart]

YOu need an earth at least coupled by RF caps on all sensitive boards or really excellent shielding and CM chokes , which by the way I did not see anywhere only single ended ferrite.

The big problem is ground shift.

Stimulate disturbances with a plastic cap discharge on NEutral to ground using LiPo battery multivibrator method or Loop antenna. anddo same with scope probe ( large loop short) to act as antenna to monitor influence.

If you have a bag of CM chokes, that would be an easy start and PU or PE Plastic Film ultra low ESR Caps for Connecting grounds using flexible copper conduit (think plumbing) this prevents DC or line ground faults.

think of it this way..
If you have a 1kV line transient and tolerate 1V on the Reset line or ground shift with logic. you need 60dB CM attenuation at 1 MHz approx., I would go for 100dB CM rejection of 1MHz injected on the line. as impulses.

 

[MB.ESK]

Thank you very much .
I'll test this way as soon as possible and report the result ...
I can use body of machine for grounding as an earth at least . am I right ??
again, tahanks my freind. :smile: