Battery Connecting Causing Damage?
Burning Brakes
Joined: Oct 2003
Posts: 1,106
Likes: 1
From: Foresters Falls(near Ottawa) Ont
I have been involved in the automotive service industry since 1961, under no circumstances have I received a shock from handling 12 volts, even from terminal to terminal.
I'm not a welder by trade, but I have done a fair bit of welding using a "stick" arc welder. Again, I have never received a shock from the electrode when accidentally prodding myself with the rod, a burn maybe, but no shock. I understand that because of the electrical shock danger when electric welding, the open circuit voltage of an electric welder is limited to 26 volts and we know the type of amperage involved. Someone more knowledgeable than I may correct me on this.
I'm not an electrical engineer, but I have survived a few years of practical application .....
RonJ ...
I'm not a welder by trade, but I have done a fair bit of welding using a "stick" arc welder. Again, I have never received a shock from the electrode when accidentally prodding myself with the rod, a burn maybe, but no shock. I understand that because of the electrical shock danger when electric welding, the open circuit voltage of an electric welder is limited to 26 volts and we know the type of amperage involved. Someone more knowledgeable than I may correct me on this.
I'm not an electrical engineer, but I have survived a few years of practical application .....
RonJ ...
Pro
Joined: Oct 2007
Posts: 679
Likes: 4
From: TremontonUT UT
The reason you install the negative last and take it off first is to prevent arching. I just did an amp test to see what load a battery has on it with everything turned off. I had my hood light unplugged. My meter was in series with the positive post and cable. When I first hooked up the meter I could hear a relay energize. The load was 1.25 amps. After a few seconds the relay dropped out and the load went down to 80 MA. A minute or so later the load went down to 40 MA and stayed there. Later! Frank
Team Owner
Joined: May 2003
Posts: 23,480
Likes: 9
From: East Meadow NY
St. Jude Donor '12
It only takes a few milliamps across the heart to kill someone ... but it also takes higher voltage to achieve current through the heart path. If shocked while wet by a 12v battery, the current would probably take the path of the wetness along the outside of the body and not put any across the heart. But of course, if you were naked, wet and hooked your feet to the + terminal and your head to the - terminal it might put some amps through your heart. In high voltage electrocutions, the earth is always the negative plane, so at least with a battery you'd have to try pretty hard to setup the right electrical path for a major damage shock.
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Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
It's current through the heart that stops it. Voltage is needed to drive the current through the resistive path - ie, your body. Every electrocution situation is different. If there is enough voltage, and the resistance path through the heart is low, then you can be killed with lower amounts of voltage - meaning you can generate the few milliamps with lower levels of voltage. To be killed with just 30v, the conditions of the electrocution would have to be very special to drive enough current. Not saying it's impossible, but just rare.
But, if the resistance path through the heart is high, then it will take a much higher voltage to drive the same small amount of current through the heart. Ohm's law applies to human electrocution scenarios.
But, if the resistance path through the heart is high, then it will take a much higher voltage to drive the same small amount of current through the heart. Ohm's law applies to human electrocution scenarios.
Thread Starter
Racer
Joined: Mar 2000
Posts: 315
Likes: 0
From: Escondido CA
This raises this question: Is the negative battery terminal more positive or negative relative to the ground cable until the cable is connected?
Don
Burning Brakes
Joined: Oct 2003
Posts: 1,106
Likes: 1
From: Foresters Falls(near Ottawa) Ont
Hmm... Even so, it still arcs. There has got to be a difference of potential between the negative battery post and the ground cable in order to have the arcing and sparking.
This raises this question: Is the negative battery terminal more positive or negative relative to the ground cable until the cable is connected?
Don
This raises this question: Is the negative battery terminal more positive or negative relative to the ground cable until the cable is connected?
Don
If your interior lights or radio are on when you disconnect, there will be a very noticeable arc. A battery switch in series with the terminal and cable eliminates most of that ragged arc and I think is easier on the electronics. This is also why the ignition should be "off" when disconnecting the battery. Just the key being in the switch increases current draw.
If you were to be disconnecting the positive terminal first and accidently let the wrench touch a grounded part of the car, there would be a major short and arcing when the positive wrench touches a negative ground. By taking the negative cable off first, you eliminate that danger!!
RonJ ...
Thread Starter
Racer
Joined: Mar 2000
Posts: 315
Likes: 0
From: Escondido CA
Ok RonJ,
Thanks to you, my lightbulb just got lit.
The arcing doesn't happen while connecting the ground cable, it happens during the momentary DISCONNECTION(s) when you are trying to hold the connector on the terminal while turning the wrench. My over-40 brain cells sometimes have a similar problem, but that's another theory I have. 
Don
Thanks to you, my lightbulb just got lit.
The arcing doesn't happen while connecting the ground cable, it happens during the momentary DISCONNECTION(s) when you are trying to hold the connector on the terminal while turning the wrench. My over-40 brain cells sometimes have a similar problem, but that's another theory I have. Don
Racer
Joined: Mar 2002
Posts: 399
Likes: 0
From: Mtns of Western NC & SW FLA
Hmm... Even so, it still arcs. There has got to be a difference of potential between the negative battery post and the ground cable in order to have the arcing and sparking.
This raises this question: Is the negative battery terminal more positive or negative relative to the ground cable until the cable is connected?
Don
This raises this question: Is the negative battery terminal more positive or negative relative to the ground cable until the cable is connected?
Don
This is the 2nd new battery, (in 9 yrs), and I don't recall the first swap out producing that kind of sparking...in 50 yrs of battery changing, I have never seen any sparking, on cars, m'cycles, etc.
Pos is on correctly, and tight...should I just suck it up and push this sparking neg cable on, and start the tightening process? Pretty damn weird, imo.
Thanks, mD
Tech Contributor
Joined: Jan 2007
Posts: 19,401
Likes: 1,141
From: Dyer, IN
To resurrect an old, but informative thread...I am swapping out the battery, and as I push the neg cable toward the threaded receptacle on the battery, there is a lot of sparking and click, click, clicks.
This is the 2nd new battery, (in 9 yrs), and I don't recall the first swap out producing that kind of sparking...in 50 yrs of battery changing, I have never seen any sparking, on cars, m'cycles, etc.
Pos is on correctly, and tight...should I just suck it up and push this sparking neg cable on, and start the tightening process? Pretty damn weird, imo.
Thanks, mD
This is the 2nd new battery, (in 9 yrs), and I don't recall the first swap out producing that kind of sparking...in 50 yrs of battery changing, I have never seen any sparking, on cars, m'cycles, etc.
Pos is on correctly, and tight...should I just suck it up and push this sparking neg cable on, and start the tightening process? Pretty damn weird, imo.
Thanks, mD
Tech Contributor
Joined: Jan 2007
Posts: 19,401
Likes: 1,141
From: Dyer, IN
1) Pull every fuse, and isolate every circuit on the battery buss, then connect the cable.
2) Have it towed to a shop, and let them connect the cable.
3) Connect the cable, with an understanding that modern vehicles have many systems drawing current(with the vehicle off)....besides just the clock.
Team Owner
Joined: Jul 2006
Posts: 22,162
Likes: 4,171
From: Kannapolis NC
It's simple, just disconnect the positive terminal. Then the negative terminal won't spark when you connect it. Then when you're ready to connect the positive terminal, disconnect the negative terminal first. That way the positive won't spark either. If you follow these simple directions, neither positive nor negative will ever spark.
Pro
Joined: Aug 2010
Posts: 545
Likes: 4
From: Calgary Alberta
Okay, here's the thing. Negative off first on last. If the positive is done first and a wrench slip occurs resulting in a grounded wrench you have just effectively shorted the battery. The high current can and has lead to a rapidly heated battery that ruptures its case. This means hot acid flying around. The short circuit situation also creates a significant fire hazard.
If you are uncomfortable with the sparking or touching the live electrical parts consider hiring a professional.
For those that are willing to do the work consider wearing gloves to avoid shocks and burns.
As for current required to stop a heart, Class A GFCI's, the ones you use in your home, are required to trip at .006 amps. The voltage required to flow that amount of current through the human chest cavity is entirely dependant on the conditions.
If you are uncomfortable with the sparking or touching the live electrical parts consider hiring a professional.
For those that are willing to do the work consider wearing gloves to avoid shocks and burns.
As for current required to stop a heart, Class A GFCI's, the ones you use in your home, are required to trip at .006 amps. The voltage required to flow that amount of current through the human chest cavity is entirely dependant on the conditions.
Intermediate
Joined: Apr 2011
Posts: 36
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