So my car battery was dead this morning. A little frustrating, but I have a handy-dandy battery jump starter in the trunk.
I did as instructed and attached the positive to the battery and grounded the black clamp. Nothing happens. The battery is just not generating enough power.
I called a friend to ask him if I was using the device correctly, since he convinced me to buy it in the first place. He replied that I was doing everything right. But after I told him that the car still wasn’t getting enough power, he told me to attach both clamps to the battery.
He assured me that the car would not explode. And it worked. The car started in a matter of seconds.
So what kind of damage would I do to my car if I jumped it again using the same method? Is this an extreme measure only or are the people who tell me to ground the negative all wet? Did I mention that I know nothing about cars?
Grounding is the same as attaching to the negative terminal. They are the same electrical connection. But, you may have grounded to something with a high resistance path back to the battery, due to corrosion, etc., or you may have grounded to a non-conductive surface.
Going directly to the battery eliminates these possibilities, but is frowned upon since any sparking around the battery could potentially ignite gases coming from the battery. Mind you in 30-odd years of working with cars and batteries I have yet to witness this, and I’ve yet to hear any first-hand accounts of it happening.
If you ground something then you are, electrically, attaching it to the battery -ve. (assuming -ve earth).
The difference is probably solely down to making a better contact on the battery terminal than you did on whatever you used as a ground point before. (Was it rusty?)
The reason it’s suggested to make the final connection with a ground cable to the engine or frame of the car is to minimize the chance that a spark (from making or breaking the connection) will ignite hydrogen being generated from the battery and cause an explosion. Battery explosions are not terribly common but they do occur, and they can do a lot of damage – not so much to the car, but to a human standing next to the battery.
In your case it appears that either the cable clamp was not making a good connection to the grounding point you used, or there’s a poor connection between your car’s negative battery terminal and the engine. I suspect the former, as the latter would likely cause starting problems even when your car’s battery was not dead.
the metal engine parts and metal body parts of a car act as a wire (in USA type cars the negative). attaching the negative clamp to jump/assist in starting the car to a metal engine part is a safety action to prevent a spark (which could ignite flammable vapors if present). people have attached that clamp to the negative battery terminal for decades. there is much debate on the issue.
where or how you connected the clamp originally wasn’t making a good connection and making a complete circuit. attaching directly to the battery made a complete circuit.
I’ve seen it. Startling, but not disasterous - This was an older battery, with the kind of caps you can remove to replenish electrolyte. Basically, one of the caps popped off rather briskly, and cracked. No real harm done, short of a few gray hairs.
What would happen if I grounded the black clamp to my brother’s hand, while I started the car? The voltage is low, right, but the amperage would give him quite a jolt? Or do I have that backward?
12 volts is not enough to travel through intact skin so he would not get a shock. no current would flow over skin either so nothing would happen. yes you might get current if he had conductive goo on his skin and the wires a millimeter apart but not enough likely to start the auto.
First person account from me - exploding battery back in 1970. Blew a corner of the battery cover off. I got lots of little red burn specks on my face [wearing glasses thankfully]. Snow got the rest of the acid/electrolyte off. Coat [an old merchant marine pea coat] had dozens of small burn marks. I did get the car started - drove directly to an auto parts store for a new battery. Car ran with part of the battery cover opposite the post blown off.
Of course it hurts. Otherwise there would be no reason for the KGB agents who are secretly aiding the interrogation to hook up the car battery to the scrotal clamps in order to get Sylvester Stallone/Jean Claude Van Damme/Chuck Norris/Don Knotts to give up information. I mean come on… It’s right there in the movies.
There are two reasons to make the last connection to the frame rather than the battery itself. One is the aforementioned spark issue. The second is that if you hook up something wrong (like get the wires backwards) you can get a heck of a lot of current to flow, and this can cause the electrolyte in the battery to boil. The battery case can’t contain the pressure and again you end up with a battery explosion.
Battery explosions from sparks or an accidental short are pretty rare. Our car pro dopers have probably seen quite a few but I’ve only seen one in my entire life. They do happen though. Basically the idea is that in the admittedly rare occasion when the battery does explode, do you want it to explode in your face or do you want to be as far away from it as possible when it goes? Better safe than sorry.
I’d like to know the exact circumstances of that as well. I’ve grabbed the positive and negative terminals of a car battery simultaneously to prove to someone that the voltage is too low to shock you. Generally you need about 50 volts or so to overcome the skin’s insulating properties.
This has been my experience, too.
Many years of jumping batteries (It’s pretty common in Minnesota winters), often connecting directly to the battery terminals for the best connection, and never an explosion.
In fact, I don’t understand the explanation at all. Supposedly there is explosive gas generated by the battery, which could be set off by a spark. But the battery is dead! It isn’t generating any gas, isn’t charging, it’s just sitting there dead. Where is this gas supposed to be coming from, on a dead battery?
Possibly after it’s been jumped (charged) there would be some gas around, but then the risk would be when you disconnect the jumper cables – but that is not what is mentioned – the warnings always refer to connecting the cables. Besides, you don’t disconnect the jumper cables until after you have started the car, so then the engine fan would be running and should quickly dissipate any gas generated by the battery charge. (Heck, here in Minnesota, the 30-below wind chill blowing across you & the cars will probably have done that already.)
I’ve blown up a battery before, but it wasn’t gas. I was jumping a dead battery and somehow the cables were on wrong (I let the guy with the dead car hook them up. Big mistake.) When I started the car the terminals on my battery made a loud POP and a flash and when I looked they were melted. I don’t know how it happened, I’ve never wanted to experiment with batteries to find out how.
I still have those jumper cables, with bits of melted lead in them.
A lead acid battery is a combination of lead and lead oxide plates in an electrolyte of water and sulfuric acid. As the battery discharges, both the lead and lead oxide plates get converted into lead sulfate, and the sulfuric acid gets converted into water, and the reverse happens when it charges.
Since there is water in the electrolyte, as current passes through the electrolyte some of the water gets electrolyzed into hydrogen and oxygen. Hydrogen + oxygen + spark = BOOM.
Current flows through the electrolyte while the battery is providing power, but also goes through the electrolyte when the battery is charging. So it is definitely possible to have an explosion of a dead battery.
As I said above, there’s also the possibility of hooking up something wrong and essentially shorting the battery, which causes the electrolyte to boil from the heat (generated by the current flowing through it) which causes a physical explosion (release of pressure) instead of a chemical explosion. Either way you end up with battery acid and bits of plastic sprayed up into your face at high velocities, which is generally regarded as not a fun thing to do.
ETA: The second type of explosion (melted lead and boiling electrolyte) is what happens when you get too much current flowing through the battery. This is what happened to EvilTOJ.
I re-read t-bonham@scc.net’s post and I think this needs a bit of clarification.
If the battery is dead, chances are it has been sitting still in the car while current has been flowing into the car (because you left the lights on or whatever). While the battery has been providing current, some of the water in the electrolyte has been electrolyzing into hydrogen and oxygen, and may be concentrated in the engine compartment. You hook up the jumper cables and a spark can ignite these gases.
When you charge the battery, especially if you leave the jumper cables connected for a few minutes to give the dead battery a good charge, you can also be generating hydrogen and oxygen, and a spark as you disconnect the cables can also cause an explosion then. You should disconnect the cables in the reverse order that you connected them (i.e. the frame connection first when disconnecting, since it was last when you connected it).