Damage from jumping someone else's battery

[copcarguy]

Originally Posted By: OneEyeJack
A lady with a toddler in the parking lot asked me for a jump late one night at work while I was driving the company Prius. She was working as a night janitor in a nearby office building. I was uncertain about possible problems so I called a friend that had an older pickup and we got her started. His battery tester appeared to indicate very low voltage, possibly a dead cell(?). It was Christmas time so I had her follow me to an AAP store and bought her a new battery and gave her the phone number of a local independent mechanic to catch up on her maintenance. She was a single mother working 2 jobs and paying for daycare that ate up a big chunk of her paycheck. It cost $300 to catch up and we split it 3 ways, the shop, the pickup driver and me. So, being concerned about jumping with a Prius led to me having a better Christmas, a much better Christmas.


God Bless You for spreading some positive energy and Holiday Cheer!

You'll be rewarded for your kindness.

 

[The motor guy]

Originally Posted By: DrRoughneck
Originally Posted By: motor_oil_madman
The thing I've always wondered about is why they always want that last connection to be connected to the engine block vs just connecting it to the negative post.

If there is a chance of spark it is when the second wire is connected. By making this second connection be negative wire to chassis, you make the possible spark happen on the chassis away from the battery where hydrogen gas was possibly generated.
That's the only reason.


That's what I thought, but I thought that only happens when people connect them in the wrong order. I used to not pay attention and most times if I attached the positive terminal last it would spark, but not so if I attached the positive first and the negative last.

 

[Wolf359]

Originally Posted By: ecotourist
Here's what I do:

Hook the batteries together as usual.

Run the donor car for a few minutes to charge up the recipient battery a little.

Turn off the donor car, but leave the batteries connected.

Start the recipient car, and take off the donor car's negative clamp as soon as it starts, then the positive.

Done.

Neither car is running while hooked up to another running car. I assume that would reduce the risk of damage to either car. And the risk of explosion is reduced because there is no sparking near the recipient battery while it's charging fast (ie when its producing a lot of hydrogen).


As mentioned earlier, the way to jump start it is to hook the cables up to the donor car first, then hook up the positive cable to the dead battery, and then the negative cable to a ground on the dead car away from the battery. That's so the sparks don't detonate the hydrogen that may be venting from the battery. Injuries from battery explosions are supposed to be quiet common so it doesn't really get reported that often so people think it's safe when it's not. And your supposed to be wearing safety goggles too when doing this (last set of pro type jumper cables I bought came with a set.). Normally you just leave the donor car running, the alternator would put out higher voltage and more current to charge the dead battery. I think the real danger to the electrical system is if you hook up the wires incorrectly and end up giving your system a 24 volt jolt. Starting a car also drops the voltage in a battery so the electrical system should be able to handle a voltage drop just like starting up the car.

 

[mjoekingz28]

Ive heard or experienced (I dont remember which) that after removing the cables, the one who needed the jump will go dead almost instantly. Like it is stumbling to stay running.



What's that all about?

 

[ecotourist]

Originally Posted By: spasm3
Originally Posted By: ecotourist
Here's what I do:

Hook the batteries together as usual.

Run the donor car for a few minutes to charge up the recipient battery a little.

Turn off the donor car, but leave the batteries connected.

Start the recipient car, and take off the donor car's negative clamp as soon as it starts, then the positive.

Done.

Neither car is running while hooked up to another running car. I assume that would reduce the risk of damage to either car. And the risk of explosion is reduced because there is no sparking near the recipient battery while it's charging fast (ie when its producing a lot of hydrogen).


Thats basically what i do, with one added step. I turn off the switch on the donor car before unhooking the cables. Protects my alternator if something gets shorted or fumbled.

I have the donor car's ignition off while the recipient car is starting. The recipient car is starting using the bit of charge it just got, plus the donor car's battery.

I have the impression that the donor car's battery acts as a kind of damper against whatever bad stuff the recipient car's alternator might produce. I'd appreciate comments on that point.

 

[Garak]

Originally Posted By: chunt
Some police departments will not allow their officers to jump start a car with their police vehicle due to the possibility of damaging the electronics in the police vehicle.

Same with taxis. Of course, the police and taxi vehicles have other sensitive electronics, too. But, as I mentioned in the other thread, it's an emergency service. Things can probably go wrong, but there's only so much you can worry about in life. If you need a boost every day or give a boost every day, then you might have valid concerns.

 

[supton]

Originally Posted By: mjoekingz28
Ive heard or experienced (I dont remember which) that after removing the cables, the one who needed the jump will go dead almost instantly. Like it is stumbling to stay running.



What's that all about?


No idea what you are talking about. Only if the recipient car has a dead alternator would this happen--if their battery shorted, it wouldn't have cranked over (might have stalled out the donor car in the process); and if the battery was kaput the alternator would still power just fine.

 

[supton]

Originally Posted By: Garak
Originally Posted By: chunt
Some police departments will not allow their officers to jump start a car with their police vehicle due to the possibility of damaging the electronics in the police vehicle.

Same with taxis. Of course, the police and taxi vehicles have other sensitive electronics, too. But, as I mentioned in the other thread, it's an emergency service. Things can probably go wrong, but there's only so much you can worry about in life. If you need a boost every day or give a boost every day, then you might have valid concerns.

Sensitive electronics is one thing. But I have to wonder if the policy is more in line with "we didn't train you to fix car, we trained you in how to drive". And "we don't want the liability of you screwing up."

As we've been hashing out in the other thread, we're not quite sure where the big voltage spikes are from, just yet.

 

[supton]

One thing I find interesting about jumping cars is how many different methods there are: engine on, engine off, battery pack. About the only variation I haven't heard is turning the dead car off before disconnecting the booster.

Makes me wonder if it's really all that big of a deal.

 

[DrRoughneck]

Originally Posted By: motor_oil_madman
Originally Posted By: DrRoughneck
Originally Posted By: motor_oil_madman
The thing I've always wondered about is why they always want that last connection to be connected to the engine block vs just connecting it to the negative post.

If there is a chance of spark it is when the second wire is connected. By making this second connection be negative wire to chassis, you make the possible spark happen on the chassis away from the battery where hydrogen gas was possibly generated.
That's the only reason.


That's what I thought, but I thought that only happens when people connect them in the wrong order. I used to not pay attention and most times if I attached the positive terminal last it would spark, but not so if I attached the positive first and the negative last.

The only positive stop is on the battery. So if you connect the positive last, the spark will happen at the battery positive terminal, close the possible H2 gas leakage.
I don't know if sparks are more likely one way or the other although I'd guess they are equally likely because it's based on the surface contact between the claw and metal, and the potential difference but don't take my word for it.

 

[Garak]

Originally Posted By: supton
Sensitive electronics is one thing. But I have to wonder if the policy is more in line with "we didn't train you to fix car, we trained you in how to drive". And "we don't want the liability of you screwing up."

As we've been hashing out in the other thread, we're not quite sure where the big voltage spikes are from, just yet.

I don't know where the spikes are from, either.

There certainly is the liability issue, but some of the strobe lights in the early days could be pretty sensitive, and there is nothing more annoying than alternator whine in a taxi radio. Additionally, police and taxi aren't there to compete with auto clubs and tow truck drivers. When I drove, I didn't give boosts. If you want a ride, hop in, I'll run the meter. If I wanted to play with booster cables in -40, I'd be a tow truck driver.

 

[ecotourist]

Originally Posted By: supton
Originally Posted By: Garak

Some police departments will not allow their officers to jump start a car with their police vehicle due to the possibility of damaging the electronics in the police vehicle.


.... Sensitive electronics is one thing. But I have to wonder if the policy is more in line with "we didn't train you to fix car, we trained you in how to drive". And "we don't want the liability of you screwing up."

Too true. I know a female DIY kind of person who reversed the poles when installing a new battery. I don't suppose that was even easy to do. I understand there was some ... ahem ... expense afterwards. Come to think of it I never heard about her doing any more DIY auto mechanics.

 

[javacontour]

Originally Posted By: bioburner
Blew the fusable link in a friends old Corolla. No good deed goes unpunished. My Xterra can activate theft deterrent system. Nothing like being in the cold and hearing the doors lock when your keys are in the ignition.


I've had this sort of thing happen before with a rental car.

So anytime I'm leaving a car run with the doors shut, I open a window....

It only has to happen to you once to be gun shy from then on.

 

[Garak]

Originally Posted By: ecotourist
Too true. I know a female DIY kind of person who reversed the poles when installing a new battery. I don't suppose that was even easy to do. I understand there was some ... ahem ... expense afterwards. Come to think of it I never heard about her doing any more DIY auto mechanics.

That would be fun.

It always pays to be cautious and think a little about what one is doing. Red and black and + and - aren't always enough. My battery cables on the F-150 have been replaced enough times that the cables are all black and blue, simply by virtue of what I've found. If it's leading off to the voltage regulator and so forth, it's probably a good bet to hook that up to the positive.