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partha	Posted: February 10, 2009 02:40 pm
Newbie Group: Members+ Posts: 3 Member No.: 22,473 Joined: February 10, 2009	Hello all, We manufacture instruments using Rs485 connectivity. We have connected about 30 units on a 4 wire RS485 network (multi drop configuration). The instrument that s addressed by the host (PC) only enables its transmission and sends a packet to PC. Over some time we notice the RS485 ICs becoming very hot and eventually burning off and the PCB in the area is also showing burnt marks. We are not able to fine the reason for this behavior. Can some one indicate where the proble could be? Thank you Partha

CWB	Posted: February 10, 2009 02:59 pm
Forum Addict ++ Group: Spamminator Taskforce Posts: 19,523 Member No.: 15,154 Joined: May 15, 2008	supply voltage is too high ? do you have "on board" regulation per unit ? -------------------- "Know how to solve every problem that has been solved" R. Feynman '88

partha	Posted: February 10, 2009 07:32 pm
Newbie Group: Members+ Posts: 3 Member No.: 22,473 Joined: February 10, 2009	Nope the voltage is within range - 5V Partha

SiliconBurner	Posted: February 10, 2009 10:12 pm
Forum Addict Group: Spamminator Taskforce Posts: 696 Member No.: 6,663 Joined: October 08, 2006	Show the schematic. -------------------- Theo Electricity is actually made up of extremely tiny particles called electrons, that you cannot see with the naked eye unless you have been drinking. Dave Barry (1947 - ), "The Taming of the Screw" Power corrupts. And atomic power corrupts atomically.

Colt45	Posted: February 11, 2009 06:55 am
Forum Addict ++ Group: Trusted Members Posts: 3,749 Member No.: 1,333 Joined: October 02, 2004	groundloop hell? all the RS-485 transcievers I've seen can't take more than ±5V common mode, if your grounds are out by more than that you'll need some opto-isolated modules. -------------------- >]:::\|-

partha	Posted: February 12, 2009 04:05 am
Newbie Group: Members+ Posts: 3 Member No.: 22,473 Joined: February 10, 2009	Hello Colt45, Yes the cable lengths are reasonably high. But what is this ground loops you have mentioned? We have a common ground line connecting all the devices. How can one use op-to couplers in such a case? Can post some suggestions? In our case each unit is given a unique ID and all the units are in listen mode with their transmitters in off condition. When the host addresses a particular unit only that unit will enable its transmission and send a reply. I await your reply. Thank you. Partha

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