G'day Rod,



14 Mar 97 06:33, Rod Speed wrote to Paul Edwards:



 PE> Can you tell this from the fact that it's hot?



 RG> Can we tell it is a faulty contact from the fact it's

 RG> getting hot? Sure we can - a good contact doesn't get hot.



 RS> Why just one ? Thats the give away, indicates its not as good a

 RS> contact as the other one. Both obviously have the same current going



What is it with you Spood...   To PaulE you say this, yet in the msg

to me written less than 1minute before, on the very same topic, you

wrote..



 RG> Can we tell it is a faulty contact from the fact it's

 RG> getting hot? Sure we can - a good contact doesn't get hot.



RS > Thats not necessarily true either if its been cranked over for



Fucking amazing eh...  To the VERY SAME COMMENT, to me, you say "not

necessarily true" yet to Paul you are agreeing with me by

saying "Thats the give away.... "



What colour did you say that White picket fence was?



RG> The reason it gets hot is all related to Ohms law...  a bad contact

RG> = high(er) resistance, and for any given amount of current being

RG> drawn this increases the power dissipated by this resistance..

RG> the more power dissipated (ie, the greater the resistance) the

RG> more heat will be generated. A good connection has a theoretical

RG> resistance of zero ohms, meaning no heat will be generated at all.



RS> Pity that no real battery connection is ever like that and that



Fuckwit.. I said A THEORETICAL RESISTANCE of zero ohms. I never said

that 'real' battery connections are like that. Heck a straight peice

of wire doesn't even have zero resistance  - and as far as I know,

nothing on earth does (unless super cooled - but even then I'm not

sure if zero resistance has been achieved)



RS> engine cranking current for long enough to flatten a normal

RS> battery may well produced a quite hot terminal,



Regardless how much current is drawn - with a theoretical resistance

of zero Ohms there will be NO heat generated - such is the beauty of

super conductors.



 RS>  even if its nothing special corrosion wise.



With a perfectly clean terminal, with a good contact, the contact

itself would have roughly equal resistance as the earth wire itself -

in such a case, even when cranking the starter for a long time, the

terminal would get no hotter than the wire itself - if it does it can

only be due to one thing - the connection has a higher resistance than

the actual wire - This is dictated by Ohm's law - not Speed's law.

Ergo, what I originally told Paul holds true - if the terminal gets

hot (not the wire) then there can only be one possible cause - poor

contact.



 RS> The main flaw in his argument is that while it may well not be as low

 RS> a resistance as the other terminal and connection to it, it may well

 RS> not have a damned thing to do with the fact that the battery was

 RS> flat.



I wasn't talking about flat batteries, nor was I discussing the

resistance of one terminal compared to the other. I was talking

about ONE of the two terminals (and nothing else) getting hot.

A flat battery won't generate any heat anyway.



 RS> That may well just have been a long time at the massive

 RS> currents seen when the starter motor is cranking the engine, with it

 RS> not starting.



In which case, the entire wire/cable to the starter motor would get

hot, not just the terminal.



Rod



___ QWKRR128 V4.50 [F]



--- FMail 0.94