I thought that I might weigh in on this one: As someone mentioned previously, the big hazard involved in jump starting an automobile is the risk of a spark igniting hydrogen gas vapors from the battery. This causes the battery to explode, which sends dilute sulfuric acid and pieces of the battery case flying everywhere. A local service garage still has holes in the plaster ceiling from one such event. Whenever working around an automobile battery EYE PROTECTION SHOULD BE WORN! Many service centers now require technicians to wear full face shields around batteries.
Service manuals advise connecting positive leads first, and then making the final negative connection (at the jumped vehicle) to a good ground AWAY from the battery. Any heavy bracket bolted to the engine should do. This is the last connection made and the first to be removed. There is always some sparking when jumping a battery and the idea is to keep it away from those vapors. There is a second hazard with modern vehicles. Suddenly breaking the connection may cause the voltage to spike which can damage electronics. This is because solid- state regulators have a much faster loop response than the older mechanical ones, especially when mounted on the alternator. A wise precaution is to place some loads such as headlamps on high beam before removing the jumper cables. I have done it this way many times without problems. The sulfuric acid in batteries is dilute enough that getting splashed will not cause immediate harm EXCEPT TO THE EYES. When gotten on the skin the first symptom is an itching sensation that quickly gets worse. The skin starts to redden as it begins to hurt. Rinsing with water will prevent injury. Any water, even from a mud puddle, is better than letting the acid remain. Even spit may be resorted to if nothing else is available. "Creepage" does exist around automobile batteries. There are three major sources: 1) Intentional low current circuits such as clocks, etc. These draw some current even when the vehicle is not running. 2) Dirt and conductive salts on the battery case. If not cleaned periodically they can drain a battery over time. 3) Faulty wiring or defective circuitry. These can cause huge current drains and may be the cause of some accidents when jump starting a vehicle. I always like to connect a test light in series with the last connection when the cause of the dead battery is unknown. If it glows brightly the load is too severe to take the risk. I apologize for being so wordy but I hope that sharing my experience may save fellow listmembers from vehicle damage or serious injury. Scott Lacey ORIGINAL MESSAGE > > > > This is because when you double the voltage the > > power is proportional to a quarter of the current > > > > Very high voltage circuits hardly creep at all > > whereas low voltages creep the most. That is why > > you should never join the two negative terminals > > when you jump start a car, the car battery > > charging circuits have so much creepage they can > > melt the battery. > > > > I though everybody knew that........... ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
