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he unscrews his car's battery from the mounting, then flips it over and presses the contacts directly to my car's battery. is that safe? Electrically, it's

by manarth 10y ago

he unscrews his car's battery from the mounting, then flips it over and presses the contacts directly to my car's battery. is that safe? Electrically, it's not all that different from using jump leads - there's the same risk of sparks, the same voltage and load involved. There is a risk of battery acid leakage from flipping the source battery, but that depends on the type of battery - a sealed unit is unlikely to leak. There's also a risk of injury from being so close to the engine bay when it's started - say, if your hand came into contact with a moving part like a belt or a fan - but again, that's dependent on the layout of the engine bay, and those risks are generally clearly visible and obvious. It's certainly not "normal" practice for the western world, but there isn't really all that much risk in it. And it turns out Americans do it too! https://www.youtube.com/watch?v=dcYjJcEZuOA https://www.youtube.com/watch?v=dcYjJcEZuOA

scrumper 10y ago
Also there's some potential for damage to electronic components like the ECU by connecting terminals in the wrong order (i.e. not +ves first). And sparking. Lots of chance of that, more than jump leads which (unless you're incompetent) aren't going to be making and breaking contact several times while you wiggle the battery around trying to make it fit.
- MertsA 10y ago
  The order in which you connect the terminals has nothing to do with preventing electrical damage. The reason why you're supposed to connect jumper cables in a particular order is for safety. When you connect just the positive, it doesn't matter if you accidentally brush the other end of the cable against the body or ground of the other car. Then the only thing left to connect is ground and if you accidentally brush the ground lead up against the body then it isn't going to matter as you're trying to connect that lead to ground. Also, the reason why you connect the last lead to a well grounded part of the engine away from the battery on the god car is because that's the only connection that creates sparks. Sparks around a bad battery are a bad idea. Batteries regularly create some Hydrogen and Oxygen gas, normally it doesn't produce that much at all and it gets vented out of the battery but with a bad battery it might have very little electrolyte left and it might have multiple cells filled with a bit of acid and a lot of explosive gas. If that spark ignites any explosive gases in the battery it will probably crack apart the plastic casing and shower you with battery acid.
MertsA 10y ago
There's the same amount of sparks but now instead of the sparks being on a grounded part of the engine away from the battery the sparking occurs right at the terminals. The problem with bad batteries is that it might not just be dead, batteries will vent hydrogen and oxygen and on batteries that lost most of the electrolyte in a cell they might have enough hydrogen in them to blow the battery apart and throw acid over the person jumping the battery. Also, the risk of battery acid leaking is probably a good bit better than you might think. If you just grab a run of the mill car battery there's a very good chance that it's just a regular old wet cell battery with an open vent so it'll leak acid if you turn it upside down.

by manarth 10y ago

scrumper 10y ago

Also there's some potential for damage to electronic components like the ECU by connecting terminals in the wrong order (i.e. not +ves first). And sparking. Lots of chance of that, more than jump leads which (unless you're incompetent) aren't going to be making and breaking contact several times while you wiggle the battery around trying to make it fit.

MertsA 10y ago
The order in which you connect the terminals has nothing to do with preventing electrical damage. The reason why you're supposed to connect jumper cables in a particular order is for safety. When you connect just the positive, it doesn't matter if you accidentally brush the other end of the cable against the body or ground of the other car. Then the only thing left to connect is ground and if you accidentally brush the ground lead up against the body then it isn't going to matter as you're trying to connect that lead to ground. Also, the reason why you connect the last lead to a well grounded part of the engine away from the battery on the god car is because that's the only connection that creates sparks. Sparks around a bad battery are a bad idea. Batteries regularly create some Hydrogen and Oxygen gas, normally it doesn't produce that much at all and it gets vented out of the battery but with a bad battery it might have very little electrolyte left and it might have multiple cells filled with a bit of acid and a lot of explosive gas. If that spark ignites any explosive gases in the battery it will probably crack apart the plastic casing and shower you with battery acid.

MertsA 10y ago

There's the same amount of sparks but now instead of the sparks being on a grounded part of the engine away from the battery the sparking occurs right at the terminals. The problem with bad batteries is that it might not just be dead, batteries will vent hydrogen and oxygen and on batteries that lost most of the electrolyte in a cell they might have enough hydrogen in them to blow the battery apart and throw acid over the person jumping the battery. Also, the risk of battery acid leaking is probably a good bit better than you might think. If you just grab a run of the mill car battery there's a very good chance that it's just a regular old wet cell battery with an open vent so it'll leak acid if you turn it upside down.