Jumping a Battery

[mainebrokerman]

lots of good info on here

I jump my riding lawnmowers battery from my car

it works

[tickyul]

I can charge a 12v, 800 CCA, automotive battery with a little 12v, 500ma wall-wort charger. If you have a very discharged car battery and only lightweight booster-cables......you can gradually
bring-up the voltage of the discharged battery before attempting to start just by making a connection between the 2 vehicles..........run the charging vehicle for faster charging.

[Ultrarunner]

And that is why some cable sets are called "Booster" and others are "Jumper"

The Booster Cables have less current carrying capacity...

[belovenow]

Originally Posted by RosemaryT

A friend asked me to jump start her car with my 2015 rental car. I politely told her, "I'm sorry, but these electronics are pretty delicate and I don't want to do anything to damage this vehicle."

She was pretty ticked with me.

Conversely, my daughter allowed a boyfriend to jump HIS car from her minivan and it fried the electronics.

PS. A mechanic friend with 40 years experience is the one who initially advised me that "jumping" could wreak havoc with automotive electronics.

Your mechanic friend has made you overly paranoid about jumping automobiles. Unless your vehicle has something specifically written in the manual about never jump starting it or other cars, your car will be fine if you hook up everything properly (and... do it yourself vs allowing a stranger to do it). Most people get the order of the connections wrong and I've even seen people mistakenly think to prove a good connection they should even spark the ends of two clips (either of those things will potentially mess up electronics on a vehicle). Done correctly however, you won't experience any issues helping out others in need.

How to hook up Jumper Cables is simple
dead battery - red cable to positive terminal
good battery - red cable to positive terminal
good battery - black cable to negative terminal
dead battery - black cable to grounded connection (Unpainted bolt or other part of vehicle as far from the battery as possible to avoid a hydrogen spark when the connection is made - the reality is that you can connect this to the negative terminal but if a spark occurs on a damaged dead battery you risk an explosion. I've used the negative terminal many times over the past 20 years without issue, but it only takes one time to get a nasty explosion so if you can find a good grounded connection instead)

Start the good battery vehicle and run for 5-10 minutes (revving the RPMs a bit vs idling will send more electricity and speed up the charging process)

Then start the bad battery vehicle. The driver of that vehicle should then drive it/leave it running at least 10 minutes (but longer is advisable) to allow their alternator to charge up the battery. For some reason a lot of drivers don't seem to know about or do this part.

Once started - disconnect the cables in reverse order they were connected.

[Mike From NIU]

Originally Posted by burdell

With engine off

1) Red cable to dead battery's + terminal
2) Other end to booster battery's + terminal
3) Black cable to booster battery's - terminal
4) Other end to a bare metal ground on dead vehicle

Start booster vehicle and after a few minutes start dead vehicle

5) Disconnect black cable from dead vehicle's ground
6) Disconnect other end from booster battery's - terminal
7) Disconnect red cable from booster battery's + terminal
8) Disconnect other end from dead battery's + terminal

Originally Posted by mbuszu

How to hook up Jumper Cables is simple
dead battery - red cable to positive terminal
good battery - red cable to positive terminal
good battery - black cable to negative terminal
dead battery - black cable to grounded connection


Once started - disconnect the cables in reverse order they were connected.

Interesting. I knew the +/+/-/ground order for hooking up (and the reverse for unhooking cables), but I thought you started with the booster battery ("A") and not the dead battery ("B"), thus my order has always been +A/+B/-A/-B and then reversed. Good to know the correct order (Start with the dead and end with the dead).

A question about the grounding, though. Given modern engines and electronics, how do you know that a particular ground is safe to attach the - clip? Can you fry the boostee electronics if the negative cable is attached to a bolt that happens to be connected to the car's computer?

[belovenow]

Originally Posted by Mike From NIU

A question about the grounding, though. Given modern engines and electronics, how do you know that a particular ground is safe to attach the - clip? Can you fry the boostee electronics if the negative cable is attached to a bolt that happens to be connected to the car's computer?

You have asked the thousand dollar question! You need to be smart/knowledgeable when attaching the grounding clip. I think using a multimeter (on the ohm setting) searching for zero resistance is your best bet. If you do not have a multimeter, having knowledge of where standard factory grounded connections are in engine bays is a good backup idea (there are diagrams online and standard locations to use/or test).

Here's a good Youtube on using a multimeter and testing for ground locations in an engine bay:
https://www.youtube.com/watch?v=BCZeBx84ZFY

When I have been doubt because I don't have a multimeter and the engine bay has no good grounding locations that I can see to attach the clip AND the dead battery looks good physically, I do the negative terminal (I've done this many times in the past 10 years with no issue). It's a risk, I know it is, so I try to minimize with gloves, glasses, and turning my head when I make the final connection, but I have thankfully never had a dead/damaged battery explode due to a gas leak (and spark). In most cases it would seem that the vehicles I have jumped successfully have "died" because of excess energy drain due to an interior light being left on, a door left open, accessories left on, etc.

So all that stated, now you can probably understand why I don't let anyone connect up jumper cables with me or for me... I insist on making all the connections myself. Most people don't know where the standard grounding locations under the hood are, what a multimeter is, and then those that do haven't the foggiest how to properly connect (in what order) jumper cables. I've seen people do ridiculously dumb things (such as making the connections on a vehicle and then "checking" it by sparking the cable ends they are holding) and I have zero interest in having my electronics fried by such stupidity.