XPost: alt.home.repair, sci.electronics.repair   
   From: rod.speed.aaa@gmail.com   
      
   On Wed, 18 Jan 2023 15:10:44 +1100, Clifford Heath    
   wrote:   
      
   > On 18/01/23 14:35, mike wrote:   
   >> When I looked up how to jump a car battery, they tell you WHAT to do,   
   >> but   
   >> not WHY, which is infuriating as it's harder to remember unless you know   
   >> why.   
   >> First they say the cars shouldn't touch.   
   >> Why?   
   >>  Then they said positive first.   
   >> Why?   
   >>  Once started, they say remove the negative cable first.   
   >> Why?   
   >   
   > These three questions only need one answer.   
   >   
   > In case there is any hydrogen gas that has developed in the battery and   
   > may be still concentrated enough to burn,   
      
   Don't buy that for two reasons. Firstly most cars and trucks   
   have the battery in the engine compartment and just opening   
   the hood/bonnet to get to the battery will ensure that any   
   hydrogen under the hood will be long gone by the time you   
   use the jumper leads. Secondly you will always get a spark   
   when connecting the last one anyway.   
      
   Presumably the 'logic' for connecting the negative lead to the   
   body of the car with the dead battery is that the spark will be   
   further away from the battery, but as I say, it is a pretty dubious   
   proposition that there will be any hydrogen still around.   
      
   A few cars do have the battery in the passenger comparment or   
   the trunk/boot, so many that instruction is to cover that situation.   
      
   > any spark from completing the circuit should be made at some distance   
   > from the battery. That is, but connecting the earth to some metal part   
   > of the chassis, not to the battery terminal itself.   
      
   > The chassis is (usually) negative, which is why that is the first and   
   > last contact point.   
      
   >> And what happens if you tap water instead of distilled?   
      
   > If there is any ionic content in your tap water, it is likely to   
   > precipitate as conductive salts in the bottom of your battery,   
   > increasing the self-discharge rate. Here in Sydney, our water is clean   
   > enough not to need to bother - any effect on battery life is negligible.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)