Go to Post Keep in mind that words can be harsh and people do not forget what is said against them. Please, for your teammates sake, keep your egos in check and try to use some tact and consideration. - Andy Baker [more]
Home
Go Back   Chief Delphi > Technical > Electrical
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
 
 
Thread Tools Rate Thread Display Modes
Prev Previous Post   Next Post Next
  #17   Spotlight this post!  
Unread 12-02-2009, 11:10
Russ Beavis Russ Beavis is offline
Registered User
no team
 
Join Date: Nov 2005
Location: Manchester, NH - DEKA R&D Corp.
Posts: 341
Russ Beavis has a reputation beyond reputeRuss Beavis has a reputation beyond reputeRuss Beavis has a reputation beyond reputeRuss Beavis has a reputation beyond reputeRuss Beavis has a reputation beyond reputeRuss Beavis has a reputation beyond reputeRuss Beavis has a reputation beyond reputeRuss Beavis has a reputation beyond reputeRuss Beavis has a reputation beyond reputeRuss Beavis has a reputation beyond reputeRuss Beavis has a reputation beyond repute
Re: Solving static electricity problems by grounding the frame

The cRIO isn't ESD sensitive - the Driver Station is. Have you ever caused the cRIO to "fail" with an ESD event?

The auto industry is ALWAYS doing safety vs. cost analyses. There are plenty of single-point failures that can result in dangerous situations but they've done everything "reasonable" to ensure that such events are unlikely. Imagine, for example, that your steering rack snaps or your brake pedal becomes disconnected. Automobiles are NOT fail-safe under every circumstance.

I don't agree with the rationale provided in Section 8 regarding the need for chassis isolation. Collisions would need to have multi-point/multi-differential voltage contact to get really exciting. For example, birds don't seem to mind sitting on high tension wires. Current needs to have a return path in order to flow.

I do, however, agree with the FIRST isolation rule for this very specific reason - if the chassis is grounded and ANY cable touches it, current will flow.

The chassis current will be limited by the breakers in most such failures but there are arcs that can be struck and maintained at < 40 amps. I've personally experienced this in non-FIRST applications. This is one of the primary reasons why UL often limits low-voltage devices to 8 amps.

The most dangerous instance, by far, is when the battery shakes loose and its positive rail touches the chassis. Now THAT'S exciting - a dead short on a 12V/18AHr lead acid battery!! The 120A main breaker won't help you then.

The second most exciting failure is when the output from the 120A main breaker is shorted to the chassis. That breaker takes a while (relatively speaking) to open since the short circuit current for the battery is "only" a few hundred amps. That's a lot of damage before the breaker opens.

The auto industry and PC industry have obviously weighed the pros and cons. I would NEVER consider shorting my car battery's positive output to the chassis to test for isolation and breaker operation but, if you care to try this on your own car, please post the video on Youtube for everyone to watch.

Russ
 


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Lunacy Wheels Static Electricity nilesenator Kit & Additional Hardware 18 05-01-2009 23:19
Math genius rejects attention after solving problems Andy Baker Math and Science 14 24-08-2006 01:47
Static Electricity JeffO Championship Event 5 19-04-2004 11:04
Stupid Question about Static Electricity Novice100 Electrical 5 04-02-2004 05:15
Static Electricity archiver 2001 12 24-06-2002 00:34


All times are GMT -5. The time now is 19:40.

The Chief Delphi Forums are sponsored by Innovation First International, Inc.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi