Jumping a car battery argument

[bryanW1995]

I'm pretty sure he meant that the wrong colored cables were used for neg/positive and that was the source of confusion, not that positive was hooked to the frame.

Btw, never buy a BMW. Not because they are bad cars...just...you shouldn't drive one.

You know, I never asked him about it, but I would also assume that he just got the cables mixed up. The hardest part was not laughing too uproariously b/c the potential customer was stalking about outside the showroom.

The salesman who did this had some bad moments at work. Another time he was trying to take a customer and his wife on a test drive in a regular cab ranger. The manager jokingly told him to "ride in the back". He was a new salesman so he did it. Unfortunately, one of those sudden Texas rainstorms blew in while they were test driving...

 

[ShawnD1]

A battery that is being used or charged produces hydrogen gas. They're not producing anything if they're not powering a load or being charged, especially if it's dead...lol

http://www.uwsa.edu/oslp/em/compliance/battery_leadacid.htm

Lead-Acid battery Basics:

The electrolyte is a solution of sulfuric acid (35%) and water (65%). This solution can cause chemical burns to the skin and especially to the eyes.
During normal operation, water is lost from a non-sealed (or flooded) battery due to evaporation.
During charging, lead acid batteries produce hydrogen and oxygen gases (highly flammable/explosive) as electrolysis occurs.
Many lead acid explosions are believed to occur when electrolytes are below the plates in the battery and thus, allowing space for hydrogen/oxygen to accumulate. When the battery is engaged, it may create a spark that ignites the accumulated gases and causes the battery to explode.

When a battery is low on water, this create a space at the top of the battery where hydrogen and oxygen can accumulate during the regular charge cycle. It's not a big deal when it's connected to the alternator because that's a fixed connection and it never sparks. Eventually the battery's electrolyte could get low enough that the battery just doesn't work worth shit anymore because it only generates power where electrolyte and plates are touching. When you try to jump start this dead battery, a spark at the terminal of the dead battery can make it explode.


You'll notice that every guide explicitly says not to connect to the dead battery last for this reason.

http://www.wikihow.com/Jump-Start-a-Car

Connect the jumper cables in the order described below:
(step 1)
(step 2)
(step 3)
step 4:
Connect the other black clamp to a piece of grounded metal on the dead car. Look for shiny metal (not painted or oily) that is attached to the engine. Usually a nut, bolt or other protruding shiny metal will work. You may see a small spark when you connect to a good ground. As a last resort, you may connect to the negative (-) post of the dead battery, but this risks igniting hydrogen gas coming off the battery.

Ideally the last connect should always go to the frame of a car (doesn't matter which one), but this is impractical because every metal part of my car is painted. The parts not painted are rusted. Paint and rust are terrible conductors.

I won't jump anyone, a battery can have some charge on it but not enough to start the car OR be so dead it won't even light a bulb, in the second case your putting an extreme load on YOUR alternator and risking toasting it, fuck that..

You're not going to kill the alternator in 30 seconds. It will only kill your alternator if you get a bit too nice and try charging the other guy's battery for 5 minutes.

 

[sleep]

if you guys don't know already, ask a professional about it.

google/

 

[Mike Gayner]

Attach positive of working vehicle, then positive to dead vehicle. Negative of working vehicle to negative of dead vehicle. Do not start either vehicle, wait a minute, disconnect opposite order then start dead vehicle

I told him that puts both of the batteries in parallel and will cause damage to the good battery.

The stupid is strong in this one.

 

[LTC8K6]

Call AAA and let them do it.

 

[BUTCH1]

http://www.uwsa.edu/oslp/em/compliance/battery_leadacid.htm


When a battery is low on water, this create a space at the top of the battery where hydrogen and oxygen can accumulate during the regular charge cycle. It's not a big deal when it's connected to the alternator because that's a fixed connection and it never sparks. Eventually the battery's electrolyte could get low enough that the battery just doesn't work worth shit anymore because it only generates power where electrolyte and plates are touching. When you try to jump start this dead battery, a spark at the terminal of the dead battery can make it explode.


You'll notice that every guide explicitly says not to connect to the dead battery last for this reason.

http://www.wikihow.com/Jump-Start-a-Car


Ideally the last connect should always go to the frame of a car (doesn't matter which one), but this is impractical because every metal part of my car is painted. The parts not painted are rusted. Paint and rust are terrible conductors.


You're not going to kill the alternator in 30 seconds. It will only kill your alternator if you get a bit too nice and try charging the other guy's battery for 5 minutes.

And guess what, if his battery is totally flat it'd NOT gonna start in 30 seconds, I jumped my neighbor once for about 3 minutes and my atl was too hot to touch, last time for me..

 

[ShawnD1]

And guess what, if his battery is totally flat it'd NOT gonna start in 30 seconds, I jumped my neighbor once for about 3 minutes and my atl was too hot to touch, last time for me..

Was your car idling or were you revving it? I'm just curious.

 

[Bartman39]

Just a thought but why even consider jump starting with another auto...? Our company has a strict policy of not doing this and for a reason... We have had a few to many batteries blow up and even hurt a few people... We either remove the cables and charge the dead battery with a charger or just replace the battery or batteries... The only approved method of jumping is with a jump box that has a switch to turn it on or off after you have connected the cables...

So you say just put it on the positive post and the neg on the frame or engine in your own order...? Did you know you were introducing very high current back through the weak or dead battery which can fry its plate connection causing a big spark which does what to hydrogen...? Think you know that one...:hmm::thumbsdown: (why do you think you see a melted post sometimes but what you dont see is the plate connection inside )

If you have no choice but to jump with cables then as some have said connect your positives first then the neg to the weak or dead battery and the final connection to the running charging system... For 3 reasons first off the fan is turning with the running auto and is circulating the air in the engine compartment so any build up of hydrogen is dissapated so very little danger of an explosion (unless its in the frick`in trunk uh BMW)... Second it makes it alot easier to know if your connection is good by hearing the alternator of the running car load up and the engine slow down just a bit (just removed the cables in the reverse order rather quickly)... Third if you try and start the car your jumping with after you connect then your dropping the voltage down possibly to low, even to a point of damaging something on that car namely the alternator its taking a big hit right off the bat but if its already producing it is less likely to fail... Also modern computer cars have voltage spike protection built into the ECM`s but other systems are not so lucky like your antitheft systems, radios and other sensitive componets so just remember this when you think about jumping another car or if you need a jump (as they say)

Batteries are cheap compared to most anything else including yourself...

 

[KentState]

I've always done left testicle then right. Otherwise the guy doesn't take you seriously.

 

[ShawnD1]

So you say just put it on the positive post and the neg on the frame or engine in your own order...? Did you know you were introducing very high current back through the weak or dead battery which can fry its plate connection causing a big spark which does what to hydrogen...?

One can tell whether or not a battery is low (safe to jump) or if it's completely dead (not safe to jump). All you need to do is check if the weak battery can do anything. If the weak battery can turn over the engine or almost turn over the engine, then it's good to charge. It's not dead, it's just low. You can parallel it to your own battery and the other guy's car should start without issue. If the battery is so weak that it can't turn over the engine or run the headlights or any of the accessories, then it's totally dead and should not be jumped.

Your car's alternator (and most battery charging systems) only look at voltage. If it's connected to something that has no voltage at all (completely dead battery), it will put an enormous load on the alternator. That's bad. If it's connected to a battery that has a low 11.5V, the alternator only supplies a small amount of current to charge it.

 

[DaTT]

Here's how I do, and have done it for as long as I can remember. No explosions, no wrecked batteries, only success.

1) Car running
2) + and - to either one first
3) + and - to other one (yes, I use neg post on dead battery)
4) try and start car right away to determine if you have to wait for a charge or not
5) If car started, remove + then - from either battery, then the other.
6) If no start, wait and go back to step 4
7) Again if no start, remove battery and use the running vehicle to go to the battery store and buy a new one.

 

[DaTT]

One can tell whether or not a battery is low (safe to jump) or if it's completely dead (not safe to jump). All you need to do is check if the weak battery can do anything. If the weak battery can turn over the engine or almost turn over the engine, then it's good to charge. It's not dead, it's just low. You can parallel it to your own battery and the other guy's car should start without issue. If the battery is so weak that it can't turn over the engine or run the headlights or any of the accessories, then it's totally dead and should not be jumped.

Your car's alternator (and most battery charging systems) only look at voltage. If it's connected to something that has no voltage at all (completely dead battery), it will put an enormous load on the alternator. That's bad. If it's connected to a battery that has a low 11.5V, the alternator only supplies a small amount of current to charge it.

I have jumped countless "dead" batteries. Some work, some don't. And yes, dead to the point of no accessories will light up/work.

 

[exdeath]

Leave it to ATG to have 10 pages of debate over the proper way to change a lightbulb :awe:

 

[jlee]

Leave it to ATG to have 10 pages of debate over the proper way to change a lightbulb :awe:

If your alternator is the size of bulk beef, does it really matter? :awe:

 

[BUTCH1]

Was your car idling or were you revving it? I'm just curious.

I held it at around 2K RPM..

 

[DaTT]

If your alternator is the size of bulk beef, does it really matter? :awe:

You raise a good point.

 

[JCH13]

If your alternator is the size of bulk beef, does it really matter? :awe:

It's true... your cruiser will jump-start anything. Yay for 200A alternators :awe:

 

[Zenmervolt]

...dead batteries can sometimes leak hydrogen gas.

Actually, batteries release hydrogen gas during charging, not from being dead.

So basically there's just a few things to keep in mind
1 - your car should be running before you start hooking stuff up

Wrong. The car should be turned OFF.

2 - connect the jumpers on the dead battery first

Wrong. Connect the two positive leads first (doesn't matter what order), then connect the negative lead to the GOOD battery, then, LAST OF ALL, connect the negative lead to a chassis ground point to avoid excessive arcing and the potential to ignite hydrogen when removing the leads after the stricken car has been started.

3 - give a tap test when connecting to the good battery. if there's a large spark, that's a good sign the dead battery is internally faulted and you should NOT try to boost it!

Wrong. As mentioned above, the last connection should be to a CHASSIS GROUND ON THE STRICKEN VEHICLE. Additionally, this mythical "tap test" (that I've never heard of in 2 decades of working on cars) won't prove anything other than that you've completed a circuit. If someone followed the incorrect instructions you've given they would always get a spark doing what you suggest. There's no way to judge the condition of the weak battery based on a spark. That's simply ridiculous.

4 - if there is only a tiny spark or no spark, clamp it and start the other guy's car

Wrong. See above.

5 - immediately disconnect the jumpers from the good battery

No need for such a sense of urgency. You can remove the cables at your leisure. 5-10 minutes isn't going to hurt a damn thing.

The last part is to protect your alternator. We went over this in the last thread. Alternators are not intended for charging dead batteries. Using your alternator to charge a dead battery is a great way to burn out your alternator. Let the other guy burn out his own alternator.

Bullshit. While very extended periods at full output can indeed shorten the life of an alternator, 5-10 minutes hooked up to a "dead" battery sure as hell isn't going to have any meaningful effect. An average passenger car alternator will deliver between 100 and 200 amps at full output. A charging system will limit the amperage to the battery to, at most, 12 amps. A weak battery isn't somehow going to magically suck every available amp from the alternator, if the charging system allowed that the battery would get fried from charging too fast.

Look, kid, just let the adults who have actual experience working on cars answer these sorts of questions. All you do is provide bad information and confuse people who are looking for reliable advice.

ZV

 

[ShawnD1]

Actually, batteries release hydrogen gas during charging, not from being dead.

They generate hydrogen gas when charging. It can leak hydrogen at any time. It's more of a problem with dead batteries because dead batteries are often low on electrolyte and this allows gas to accumulate at the top of the battery. I even posted a link explaining this if you care to read the whole thread.

Wrong. Connect the two positive leads first (doesn't matter what order), then connect the negative lead to the GOOD battery, then, LAST OF ALL, connect the negative lead to a chassis ground point to avoid excessive arcing and the potential to ignite hydrogen when removing the leads after the stricken car has been started.

Good luck finding anywhere to connect this on a modern car. A car in 1980 had a steel bumper you could clamp to. My car and your car are all plastic. The bumper is plastic, the doors are plastic, the bottom of the car is coated with foam to reduce noise, and the entire area under the hood is painted. The only part of the car you can connect to is either the battery itself or the ground wire connected to the battery. Trying to clamp it onto one of the painted areas will result in a whole lot of nothing.

Wrong. As mentioned above, the last connection should be to a CHASSIS GROUND ON THE STRICKEN VEHICLE. Additionally, this mythical "tap test" (that I've never heard of in 2 decades of working on cars) won't prove anything other than that you've completed a circuit. If someone followed the incorrect instructions you've given they would always get a spark doing what you suggest.

This is absolutely wrong. I parallel car batteries every year when I go camping and they never spark. If it sparks, that means you connected it backwards. You tap test it to make sure the polarity is right. Most battery related incidents are directly caused by people getting the polarity wrong. Even good batteries can explode when you connect them wrong.

No need for such a sense of urgency. You can remove the cables at your leisure. 5-10 minutes isn't going to hurt a damn thing.

As stated above by BUTCH:
"And guess what, if his battery is totally flat it'd NOT gonna start in 30 seconds, I jumped my neighbor once for about 3 minutes and my atl was too hot to touch, last time for me.."
Trying to be a super nice guy and charging both batteries for 10 minutes could end up costing you a new alternator. Let the other guy's car do all the work.

Bullshit. While very extended periods at full output can indeed shorten the life of an alternator, 5-10 minutes hooked up to a "dead" battery sure as hell isn't going to have any meaningful effect. An average passenger car alternator will deliver between 100 and 200 amps at full output. A charging system will limit the amperage to the battery to, at most, 12 amps.

I want you to go to your car right now and look at how it's connected. On every car I have owned to date, the alternator has a single pair of wires going to the battery, then everything is connected to the battery. There isn't some magically controlled circuit for charging the battery. All the alternator sees is a voltage. The alternator doesn't know the difference between you charging a dead battery vs you trying to run the headlights and the fans and cigarette lighter and the rear window defroster all at the same time. It's not limited to anything. If you put a completely dead battery on your alternator, the alternator will run as hard as the voltage difference allows it to run.

A weak battery isn't somehow going to magically suck every available amp from the alternator, if the charging system allowed that the battery would get fried from charging too fast.

Actually that does happen. This is exactly why people buy “trickle chargers” for batteries instead of jumpering them to their car and letting it run for 10 minutes. Trickle charging is easy on the battery. Doing a fast 10 minute charge at 50amps will screw up the battery and it can take out the alternator as well if the alternator gets too hot (edit: driving the car provides extra cooling to everything, so running it full blast when you're on the highway might not overheat but running it like that on your driveway can).

Look, kid, just let the adults who have actual experience working on cars answer these sorts of questions. All you do is provide bad information and confuse people who are looking for reliable advice

I'm an electrical engineer and much of my job is battery backup systems for vital circuits. Most of the stuff I deal with is 12V DC coming from a battery system very similar to that found in cars. Most of the stuff I've posted is stated in manuals that come with the battery systems I order. Things like when hydrogen gas is made (during charging), when it can be a problem (any time), when it accumulates (when electrolyte is low), doing a tap test before strapping batteries together, how chargers only look at battery voltage, and how batteries can explode if you hook them anti-parallel for even a couple seconds.

 

[Zenmervolt]

They generate hydrogen gas when charging. It can leak hydrogen at any time. It's more of a problem with dead batteries because dead batteries are often low on electrolyte and this allows gas to accumulate at the top of the battery. I even posted a link explaining this if you care to read the whole thread.

Hydrogen gas, being lighter than air, dissipates relatively quickly. It only vents while being generated because that's the only time it creates enough pressure.

Good luck finding anywhere to connect this on a modern car.

Try connecting the negative lead to the engine. Engines are still metal. There are plenty of unpainted surfaces on the engine where you can connect a lead.

This is absolutely wrong. I parallel car batteries every year when I go camping and they never spark.

Bullshit. There is always a load on the battery of a modern car. There's a spark when replacing a battery as well. There's a spark when connecting a bench charger (if you're fool enough to have the charger plugged in before connecting the leads). When connecting a battery to a live circuit, there's always going to be a spark

As stated above by BUTCH:
"And guess what, if his battery is totally flat it'd NOT gonna start in 30 seconds, I jumped my neighbor once for about 3 minutes and my atl was too hot to touch, last time for me.."
Trying to be a super nice guy and charging both batteries for 10 minutes could end up costing you a new alternator. Let the other guy's car do all the work.

Wow. Something under the hood of a car, next to the engine, was too hot to touch with the engine running. What a shock. I've yet to come across a car where the alternator was cool when the engine was running.

I want you to go to your car right now and look at how it's connected. On every car I have owned to date, the alternator has a single pair of wires going to the battery, then everything is connected to the battery. There isn't some magically controlled circuit for charging the battery. All the alternator sees is a voltage. The alternator doesn't know the difference between you charging a dead battery vs you trying to run the headlights and the fans and cigarette lighter and the rear window defroster all at the same time. It's not limited to anything. If you put a completely dead battery on your alternator, the alternator will run as hard as the voltage difference allows it to run.

If it weren't limited, the battery would never stop charging and you'd have an overcharged and destroyed battery after a single road trip. You also seem confused about voltage and amperage. A car's electrics are regulated to a nominal value of 13.5 volts. Extra load will pull more amps, but it won't mess with the voltage unless the voltage regulator is malfunctioning.

Actually that does happen. This is exactly why people buy “trickle chargers” for batteries instead of jumpering them to their car and letting it run for 10 minutes. Trickle charging is easy on the battery. Doing a fast 10 minute charge at 50amps will screw up the battery and it can take out the alternator as well if the alternator gets too hot (edit: driving the car provides extra cooling to everything, so running it full blast when you're on the highway might not overheat but running it like that on your driveway can).

No, it doesn't happen. If it did, I'd kill a battery every week because my 40-minute commute would be overcharging my battery every time I drove. People buy float chargers (not trickle chargers) because they want to be able to let the car sit for a long time without the battery dying and a massive bench charger isn't well suited for that job.

I'm an electrical engineer and much of my job is battery backup systems for vital circuits.

Please do us all a favor and tell us where you work so we know not to buy shit you've mucked about with.

how chargers only look at battery voltage

You just claimed that the charging system in a car doesn't have any intelligent circuitry... And now you're claiming that "chargers only look at battery voltage"? Which one is it? Chargers "look at battery voltage" to determine the battery's state of charge and then adjust the current flow (amperage) supplied to avoid overcharging. Chargers "look at battery voltage" because they have regulation circuitry to accomplish that task. They don't simply supply a fixed current, at least, they haven't done so for quite a long time.

and how batteries can explode if you hook them anti-parallel for even a couple seconds.

Show me where anyone has suggested that hooking up the battery backwards is a good idea...

ZV

 

[KentState]

One thing that wasn't mentioned in this thread is cars with batteries in the trunk/rear seat should be jumped used the remote posts under the hood. It's the same steps, except easier since you don't have to find something to ground against.

 

[LTC8K6]

Yeah, I noticed the new Grand Cherokee has an AGM battery under the front pax seat with remote posts under the hood.

Incidentally, with the Trailer Tow Group IV, you get a 220A alternator.

 

[KentState]

Yeah, I noticed the new Grand Cherokee has an AGM battery under the front pax seat with remote posts under the hood.

Incidentally, with the Trailer Tow Group IV, you get a 220A alternator.

I wonder how hard of a job it is to replace the battery. Do they have a lot of room under the seat?

 

[LTC8K6]

I wonder how hard of a job it is to replace the battery. Do they have a lot of room under the seat?

You have to move the pax seat all the way forward. After that, it's pretty straight forward.

http://www.wk2jeeps.com/wk2_battery.htm

 

[jlee]

Show me where anyone has suggested that hooking up the battery backwards is a good idea...

And even then, most of what I run across on forums is that someone will fry an ECU, blow a fuse, or melt a fusible link before the battery explodes.

I'm not afraid to jump a car with my personal car, but I'm not letting someone else hook up the cables.