Thermal Relief vs. Fuse

Discussion in 'General Electronics Chat' started by tindel, Nov 22, 2013.

  1. tindel

    Thread Starter Active Member

    Sep 16, 2012
    I'm being forced to make a difficult trade-off.

    Manufacturing is requesting that I add thermal relief to my power connectors... but my power connectors can provide large currents 30ADC with up to 50A surges. I argue that the thermal reliefs are really fuses at these type of currents. I calculate power densities anywhere from 20W/in^3 (best case) to 20kW/in^3 (worst-case) in the spokes of my wagon wheels (calculated using IPC2222) - a delta of 3 orders of magnitude!

    I've made many of these type of connections before and have never wagon-wheeled my high current pins before - and it hasn't been a significant problem in the past - not enough that I heard about it anyway. I'm having serious heartburn with this one despite heavy pressure from both manufacturing and my technical leads to add these fuses (ahem - excuse me - thermal reliefs).

    Anyway, does anyone have any words to the wise or experience regarding this type of power and wagon wheels? Anyone know of a software package where I can put in my connectors and the current through each pin to calculate thermal delta's in the wagon wheels? Any professional white papers, anything? My google searches haven't revealed too much.
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    If this worked in the past then present the drawing of the older product to manufacturing and say "just built this one like you built that one."

    If that doesn't work then consider revising your entire connector scheme. Make it very expensive so you get some backup from management over building it as originally intended.
  3. #12


    Nov 30, 2010
    I think that's a brilliant answer. Give them what they asked for and never leak a clue that you would rather do it the practical way. Smile ever so sweetly at being allowed to usher in the next generation of quality, and have further "improvement" options available while they choke on what it's going to cost.
  4. wayneh


    Sep 9, 2010
    My first boss was a tyrant, and all the more aggravating because he was almost always right.

    One of his top rules that he beat into us was, "always ask, WHY?" In your case, it may help you to know WHY they are asking for this change, and maybe WHO in particular might be leading the charge. It never hurts to dig a little to learn what is really going on.

    Over time I learned, as I'm sure my tyrant boss had before me, that sometimes there's next to nothing behind some requests even though they might introduce huge costs. Could be the boss walked by and said, "why aren't we doing xyz?".

    A good quality system would help discourage frivolous requests, and serves to communicate clear reasons behind manufacturing changes.
  5. ronv

    AAC Fanatic!

    Nov 12, 2008
  6. #12


    Nov 30, 2010
    I made that exact mistake. One of my friends asked me why I didn't fly on Eastern airlines. I assumed he was recommending that airline, so I tried them the next time I had to fly. They stole my guitar again!:mad:

    Every time I have flown on Easter, they stole my guitar!
    Then I found out he wasn't recommending them. He actually wanted to know why I quit using Eastern Airlines.