----- Original Message ----- From: "Russell McMahon" To: Sent: Saturday, July 31, 2004 9:09 AM Subject: Re: [OT] high temp (>85C) microcontrollers > Capacitors were mentioned in passing by soemone as a possible source of > trouble.. You really don't want any aluminium "wet" electrolytics on that > board at those temperatures. Even 105C parts can be expected to have > lifetimes of under a year at 85C operating (depending on rated life at 105C. > Typically lifetime halves for each 10C rise. So even a 10C rise from > previously (and it sounds like yo have more than that in reality if > processors are failing now but note before) will halve your capacitor life. > I reality you might expect a reduction x 4 times with the new all improved > design.. > > Note very well that if you do have electros there you NEVER want it hot with > the board powered down. Electrolytics die far quicker when heated with power > off. If the board spent a fair part of its life at 85C with no power you > could expect capacitor failures in months. > > Russell McMahon > No electrolytics present. One item I don't think I made clear was the frequency of failure. It isn't every system, every time. About one in one hundred exhibits the problem. And the problem can be traced to changes in the airflow around the controller due to a change in the chassis. Because of the change in the chassis, the mechanical guys should have made a change in the required minimum clearances around the outside of the system to allow a larger dead-air space. They didn't do that so if one of these "new" chassis units is installed according to the original minimum clearances, there is a chance the controller may overheat. Rob Young rwyoung@ieee.org -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics