XPost: alt.home.repair, sci.electronics.repair   
   From: rod.speed.aaa@gmail.com   
      
   On Thu, 19 Jan 2023 03:21:25 +1100, Peter   
    wrote:   
      
   > micky  wrote:   
   >> It had to do with accidentally ....aha it had to do with   
   >> accidentally touching both cables to the frame of the car.  Say you've   
   >> hooked it up to the car with the good battery, and then you connect the   
   >> negative first.  Then while you're trying to connect the positive (and   
   >> sometimes that's not easy. It has a cover or it's tucked away, or you   
   >> can see it but can't get the clamp on, you touch the metal body or   
   >> engine or frame of the car.  Now you have both cables touching the frame   
   >> while at the other end, at the car you are using to jump your own, they   
   >> are connected to a good battery.   Big spark.   
   >   
   > Well. That makes sense. So maybe my initial reasoning was wrong that the   
   > last cable attach will spark, and you want that spark away from the   
   > battery, so that would have to be the negative cable.   
   >   
   > However, you also said that the DISCHARGED battery is the one with all   
   > the   
   > hydrogen,   
      
   That's wrong. You don't get hydrogen when attempting   
   to start the car with a battery that is flat or can't deliver   
   the current the starter motor requires to turn the engine   
   over fast enough.   
      
   > so that means that you want to put the donor battery cable on   
   > last (because that's where the spark will be and the donor battery is   
   > presumed to have less hydrogen outgassing).   
      
   > But then you made a good point that if you put the positive on first,   
   > then   
   > anything any negative touches by accident, will spark where it touched.   
   >   
   > So now we have one good reason to put the negative on last and   
   > specifically   
   > the negative on the DONOR car on last by one line of reasoning, and by   
   > another line of reasoning, we have the positive going on last, presumably   
   > also on the donor car because it's going to spark.   
   >   
   > Which is the correct line of reasoning?   
   >   
   > (A) Put the negative on the donor car last because that spark is least   
   >     likely to ignite hydrogen gases from the discharged battery   or   
      
   Yes, but thats not because of the hydrogen.   
      
   > (B) Put the positive on the donor car last because you have less chance   
   >     of accidentally shorting the circuit   
      
   More chance of accidentally touching part of the body of the donor car   
   with the positive lead clamp.   
      
   & the donor has less outgassing   
      
   > Which is more logical?   
      
   A, but for a different reason.   
      
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