weather and old circuits

Discussion in 'Homework Help' started by sunshine03, Dec 30, 2007.

  1. sunshine03

    Thread Starter New Member

    Dec 30, 2007
    I have a question that could deal with anything electrical.I was told that hot
    and cold temperatures can control how electricity flows through older circuits.
    Is it true that all of the plastic and metal parts of connectors,relays and other
    things can expand when hot,contract when cold and actually work themselves
    apart (or hang up as with relays) breaking the circuit-and any old grease and
    gunk can make things worse (grease getting cold and hard-stuff like that)??
    Could this be the case in colder months when there is a slight delay between
    the time you flip the switch and when the lights actually come on-its like the
    current has to punch it's way through?
    Thanks alot for your time and years of experience
  2. SgtWookie


    Jul 17, 2007
    Yes, things generally expand when heated up, and contract when cooled down.

    The problem with electronic circuits with this is that the materials have a different coefficient of expansion; that is they don't expand and contract the same amount over a given range of temperatures. Eventually, the flexing will result in crystallization of metals and their subsequent failure, just like when you bend the tab on a can of soda back and fourth too many times.

    With the light switch, it's more like the contacts are getting burned, and the switch needs to be replaced. It could be grease, but they haven't used grease in light switches for years to my knowledge.
  3. Dave

    Retired Moderator

    Nov 17, 2003
    To supplement what SgtWookie has said above about your specific query, you may also like to look at the following section in the e-book which will add some background to how temperature affects the way electric-currents flow in conductors.

    A search of the e-book for temperature will bring up many results that may also be of interest.

  4. recca02

    Senior Member

    Apr 2, 2007
    temperature can affect not only older circuits but any circuit for that matter, that is why while designing circuits(or anything in engg) temperature tolerance etc are taken as a factor.
    temperature increase/decrease can cause good conductors to increase/decrease their resistance( as is the case with most metals).
    temperature increase can decrease resistance of many material esp semiconductors.
  5. mrmeval

    Distinguished Member

    Jun 30, 2006
    At several places I've worked we test units hot and cold while operating. Some of the tests are insanely complex and the cycling is severe. Then they try and break them with a vibration and drop tests. Of course this was at a defense contractor.

    Design of the circuit can be a big factor in how hot and cold effect the expansion and contraction.

    You'll find odd bends in some components that you would think mean nothing but they are there so the part and leads can expand and contract without putting excessive force on the solder connection and so that it's not too 'stiff' allowing vibration to fatigue a lead to failure.

    There are also special lead bends that are not usually done to commercial parts, the defense contractor ordered them with the leads sticking straight out and had special machines to stamp and cut the leads to shape. Simple parts are bent by hand in many cases.

    Then there is the bonding, they'd bond large parts to the board, Hughes seemed to like 'gas tank sealant'. It's very low weight compared to other sealants and adheres incredibly well but it's one draw back is if the part overheats the resultant goo eats *everything* metal it touches.

    Oh, it's also a teratogenic, mutagenic and probably causes you to turn into a cat grrrl
    with prolonged use.

    They also used BeO substrate VLSI chips with a metal can soldered on top which was then bonded to a heat sink with a metal or alumina bearing epoxy. It had the special lead bends and was hand soldered to the board even though 'surface' mount.

    This is all 1970s - early 80s stuff, they still fix them but it's costs a LOT.
  6. sunshine03

    Thread Starter New Member

    Dec 30, 2007
    Hi Guys

    Thanks for the feedback.Sorry for not including the examples in my previous note.The first is my old Nissan car-when the weather is cold and I need the headlights,the headlights and dashlights take up to a min or more to illuminate after the switch is turned on.The second example is when its cold outside our home phone completely stops working.These problems always occur when the outside temperatures drop into the 40's and below.But when the temperatures warm up into the 50's and above-the problems disappear as if nothing was wrong.These things have been going on for so long-we have just about accepted them as normal.When I started asking around about this problem I found many people have experienced these things-but nobody can explain it.Its hard to recreate the conditions that cause the problems,so techs and repairmen can't find anything wrong when you call on them for help.The guys at Advance Auto said problems like these have baffled techs for years.These "GREMLINS" create poor performance,can burn up contacts,deteriorate components,and other bad things.They also said if a person understood what was going on-electrical maintenance and troubleshooting would be much easier on techs and the customers.Then one of the guys spoke up and said this would be a good PHYSICS QUESTION-so here I am.Aside from myself,I hope this discussion helps everyone who has had,or is having to deal with with this situation.
  7. sunshine03

    Thread Starter New Member

    Dec 30, 2007
    Its me again.So when the guys at Advance said contacts can burn up-they werent talking about an actual fire.They were talking about as the contacts are weakened and fouled from age and the expanding and contracting from temperature - current trying to get through this type of connector will just burn it to the point it cant work any more.
    Please correct me if I said this wrong
    Thanks Guys
  8. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    They make canned freeze and they make heat guns so one can subject components to some temperature variations other than normal.

    Yes, relay contacts can become pitted or other weakening effects, increasing the resistance to a point where the contact drops too much voltage rendering poor performance in the overall operation.

    The same can be said of any connection.

    Effective testing protocals can assist in identifying problems.

    I just had a TPS [throttle position sensor] become defective. It appears the TPS and the low coolant sensor are using the same chip ... and the low coolant indicator was intermittent. The mechanics said it was the same circuit ... which is crazy ... but I've seen in the past where a single chip interfacing multiple alarms trigger more than one alarm indication.

    In the old .... very old days .... we burnished the contactors that were weakened as part of our normal preventive maintenance protocals.