Need help with a project/product not running in Industry. - Page 1
Forum section: electronics / general

author: Jayy
author_rank: Contributor
timestamp: February 27, 2016, 01:08:45 pm
content: Hi,I have a project/product PCB built. It works fine in my home environment. But when i take it to the factory it does not run well.Controller - ATMega88with MAX 705 supervisor ic. -https://datasheets.maximintegrated.com/en/ds/MAX705-MAX813L.pdfI have three relays - connected to lamp ballast, and 2 solenoid valve.Now when the relay is turned on the controller is reset by the MAX705.I know this because if i don't use the MAX705 the controller works fine in the industrial environment.I have connected a 100uF and 0.1uF close to the pins 2 & 3 the power supply pins of the MAX705 ic .The Atmega88 has a regulator close by and has 100uF and 0.1uF across its output. Also i have soldered 2 0.1uF cap on the supply pins ofATMegA88.If a stabilizer is used and then the board is connected to the stabilizer output then everything works fine.What i don't understand is if the mains line is noisy should it not create a reset randomly and why only when i turn on the relays or load.any help will be appreciatedThanks,Jai.

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 27, 2016, 01:21:24 pm
content: You have diodes over the relay coils?Does the same happen when the relais are not switching anything?Can you post the pcb layout and schematics?

author: Jayy
author_rank: Contributor
timestamp: February 27, 2016, 01:43:09 pm
content: yes i have diodes for relay coils.it only happens when the solenoid valve contacts are connected to solenoid valve load

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 27, 2016, 04:34:53 pm
content: Are the tracks to the relay contacts inducing current on nearby tracks?Can you show the pcb?

author: janoc
author_rank: Super Contributor
timestamp: February 27, 2016, 06:38:06 pm
content: It is either some sort of inductive spike from the coils triggering the supervisor or your power supply is sagging under load when the relays switch, triggering it.ATMega alone can work down to 2.5V, so a minor brownout will not affect it but the supervisor you are using is more strict - 4.6V threshold voltage. I would hook up a scope and check the power rails when the relays are being switched.

author: SeanB
author_rank: Super Contributor
timestamp: February 27, 2016, 06:38:43 pm
content: There is a long lead to the solenoid? That can induce a pulse on the wiring which will be coupled through. Wire a MOV across the load, rated for the supply voltage, and add some RC snubbers across the relay contacts to reduce switching noise on the long leads which causes your issues. You can also use a line filter on the supply to the controller on the mains side, to reduce the high frequency noise that is coming in on the supply line. Make sure the filter earth lead is connected to a good mains earth, and that the equipment being controlled is also properly grounded as per local codes.

author: Jayy
author_rank: Contributor
timestamp: February 29, 2016, 01:11:41 pm
content: I figured out the problem.There is a capacitor required between pin PFI and GND. The voltage divider is sensing the 12 Volt power rail for detecting power off.Without the capacitor the device was functioning erratically due to noise.Thanks all for your response.