"proper" use of jumper cables
 

I've wondered about this for a while. I was reminded of it this morning when I found I had left my car keys on in the "accessory" position overnight, resulting in a call to my local auto club.

If you read the instructions for using jumper cables (read the instructions? BWAHAHAHA http://www.barks.org/misc/rotflmao.gif) you'll find that you are supposed to attach the black clamp from the cables onto some grounded part of the car's frame, NOT to the negative terminal of the battery. Why is this recommended? And if it's so important, how come nobody ever does it?

Because if you fuck up, the battery can explode, leaving you with battery acid in your eyes.

It's to prevent the hydrogen cloud from exploding when jumping the dead battery. The cables on the end of the live battery need to contact both posts, but the dead end needs to contact the positive post and a ground of the car (engine block, frame, etc) to prevent arcing.

In more English terms, the last contact you make is probably gonna spark. Better for that to happen away from the battery, where an explosive hydrogen cloud could conceivably exist.

I'd bet the reason almost no one does it is that red to red, black to black is easy to remember. Live red to dead red, live black to dead ground is not as easy.

Considering how well-made today's batteries are, I'd say the likelihood of the battery blowing up is far lesser than the likelihood of your average driver forgetting which color goes to ground.

It's not a matter of the quality of manufacture. It's a function of lead/acid batteries to outgas hydrogen. Even the "sealed", never add water models do it. The "gel" batteries don't, plus they can't spill and don't corrode anything. But, "gels" cost almost twice as much.
I've seen batteries explode. It ain't pretty.:eek:

I once dropped a wrench on to the hot terminal of a bettery that already had the ground hooked up. Welded the thing to the car frame and blew up the battery after three seconds or so.

Made a heck of a mess., as well as making me use up four boxes of baking soda to clean it all up.

Sheesh

I'm more careful now.

That's kinda what I thought. But what I don't understand is, why do people like tow truck drivers do it? I've jumped maybe half a dozen cars in my time. Surely somebody who answers roadside assistance can do several per day. I'd assume they understand the risks, and that they don't want to "get lucky" and have the battery blow.

Oh, yeah. Most people are dumb as posts. I forgot. Never mind. :cool:

So, you just hook the ground up to the car frame?

The best place is where the cable from the neg post attaches to the engine or frame. Unfortunately that's quite often on the engine near the fan, which is a hazard to cables and hands. When you hook the cables up the engine's not running, but hopefully it will be when you're done. It also helps if the car doing the jumping, is running.
One other caution. Some older foreign cars are POSITIVE GROUND. It's rare, and if you have one you're probably aware of it. BUT, if someone offers you a jump, be aware of their car.:eek:

The only time I ever had a problem jumping my car (postive to postive, negative to ground is a mantra for me) was when some "helpful" man connected the battery cables for me.

Nice guy, dumb as a post. As I was yelling, "You're doing it wrong" he cross-wired the cables, and blew a fusible link (only, thank goodness) in my car.

Dumbass.

Gel batteries (and AGM) CAN outgas, particularly during overcharge. They don't in normal operation, though.

As for the connect-to-ground advice, I've tried it. On most cars I've tried, it doesn't work; battery to battery is the only way to do it. Positive on good to positive on dead, negative on dead to negative on good, in that order.

Connecting to the starter housing or other well-grounded thing should work too, but getting to those parts is more of a hazard than a possible spark.

How so? I thought these were completely sealed, hence safe to use in the trunk or passenger compartment, even upside down?? :confused:

Hydrogen gas problem is but another minor reason why a spark is not desireable adjacent to a battery. (Where is hydrogen concentrated when fans and engine move so much air?) But if the battery connection is via a frame, then a possible short circuit is not really a short circuit. That wire (battery to frame) slows the battery discharge meaning that battery is either less likely to explode or that the explosion would not occur as immediately - human having time to correct his mistake.

Also connecting a black wire to chassis makes it difficult to short two batteries negative to positive - making destruction of vehicle electronics less likely due to jumper leads reversed.

Problem; cars provide no good point to clamp that ground wire. Either good clamping point does not exist or jumper wire gets tangled up with fan belts, etc.

Batteries have an interesting design. Built so that batteries tend not to explode up. Instead weaker points are on the side where an explosion is less likely to take out a human face.

If you have two cars with metal bumpers, you can hook up the positives and make the final connection from your drivers seat. Saftey first kiddies!

If the fan was running we wouldn't have to jump it, would we.
Not so. That wire is larger than most jumper cables so it's not the limiting factor.
Nope. See above or better yet weld one yourself.
What explodes is the hydrogen gas which above the liquid level. It blows the top off. I've witnessed it twice and seen the aftermath of many more.
The problem with clamping to the frame or even through metal bumpers is that the resistance can be to great. If the battery is marginal it may work but if the battery is way low, part of the juice is trying to charge the battery and part is trying to start the engine. The low battery provides the path of least resistance thus starving the starter.
Quite often the reason the battery is discharged in the first place is corrosion between the battery and the cable ends which prevents charging. This corrosion can also prevent jumping. I had to needlessly buy a starter to learn that one.:(

Wouldn't the most important safety aspect of jumper cables be prevent a complete short, as BrianR did with the wrench?

That's highly recommended.:D

Originally, battery terminals were exposed. In mid-1970s, GM introduced Freedom battery with terminals on the side and mostly protected (more difficult to jump start). However Japanese created what is now defacto standard on cars - the plastic cap over + terminal. Installed just so the bouncing wrench does not cause battery explosion. Previously the bouncing wrench could result in you signing words usually known only to angels.

IN response to previous post:

BTW, hydrogen is a danger when the fan is moving - because that is when the battery is finally under strong recharge. A running engine is required to create enough current so that battery might release significant amounts of hydrogen.

When talking about current necessary to cause a battery explosion, then yes - those heavy cables from battery to car frame do restrict current flow making battery explosion less likely or slowing down the time to explosion.

True but with the fan running and probably the hood up the gas doesn't accumulate. A stream, even a strong one, could ignite and scare the hell out of you. But it would not explode and would not backtrack into the battery setting it off.
Even a dead short should not cause an explosion because of the internal resistance of the battery becomes current limiting. The danger is at the contact points of the short. Arcing causes heat, flame, molten metal, etc. A friend of mine arced a 24 volt system with a wrench in his left hand and lost his ring finger by melting his wedding ring. Another danger of marriage. :D

Battery explodes because internal battery resistance dissipates the entire short circuit. In a car battery, that resistance may be on the order of hundreths of ohms. In a short circuit, all battery electrical power would be dissipated by that internal resistor - resulting in a battery explosion.

However if shorted by a circuit that also includes a battery cable, then the short circuit would have more fractional ohms to also dissipate the power - outside the battery. Granted, that cable is still too low to provide full protection. But the additional resistance of battery cable will at least slow down the 'time to explosion'. Gives a human time to correct his mistake.

Returning to the original question - probably the most important reason to ground to chassis - one cannot confuse which is positive and negative. Therefore someone will not blow out car's entire electrical system. In can't tell you how many times the black electric cable was replaced by a red one. Mechanic was more concerned with what he had rather than doing it right. Then when someone jumpered the battery, they hooked positive cable to the red wire. Sparking is well after damage has been done.

The rest of the circuit is another battery and cables that are smaller in diameter (more resistance) and 8 to 10 times as long as the ground cable. Therefore I can't see the ground cable helping very much.

Most modern cars, trying to jump them backwards will just blow the main fuse and not damage anything else. Not that this is a good thing!

Gel and AGM batteries will outgas if mistreated -- normally they are sealed but there's normally a controlled weak spot in the enclosure which will blow out under overcharge.

Just a side thought.
I needed my pickup the other day so I started it for the first time since 3 days before the "BIG SNOW". February, wasn't it?. Anyway, start it and idle for 4 or 5 minutes, the gel battery was completely recovered according to the gage. Sweet.:D

Color of cables matter?
 

I've only heard that one needs to hook up the red cable to positive and the the black cable to negative. But if they're just cables, why couldn't you hook up the black cable to positive and the red cable to negative? So long as you're consistent with placing black on positive for both cars and red on negative for both cars, I don't see why red needs to be on positive and black on negative. Do the cables have some sort of diode to block current going in a particular direction?

A diode in that circuit would be immediately destroyed. It's true, as long as you're consistent and have the same hookup on both cars, the color doesn't matter. It's just convention and simpler to instruct.

I typically use the bumper mount on older cars and the towing point for newer cars for jump starting. You'll have to bend down to find the tow point, but it gives a good earth to the body!

Can I still put one on each nipple?

Has anybody EVER had a car start by following the POS-POS, NEG-Engine Block/frame?

Yes. :)

Yepper!

Then what the hell am I doing wrong?

Sure, if that's what it takes to get you started...:shock:

Vroom, baby... vroom-vroom!:drool:

I learned about cars due to attitudes by so many others. Some cars (with cables replaced) even had black to the positive terminal and red to negative. If you matched jump cable colors to battery cable colors, the results were destructive.

Yes, match colors. And then like anyone must do, have some other method to confirm your assumptions. So include following that battery cable to what it connects to. Find the + and - markings on the battery. Use a meter. But you must always have some separate confirming method even when only jumper starting a car. Nothing new. It goes right back to lessons learned by doing things and constantly asking why. An educated human never does something catastrophically dangerous without some separate confirmation.

It's also called a parking brake. Same concept.

I bet you're clamping to something that looks like it is bonded to the block but isn't. Do you see any arcing when you make the last connection (always on block so no boom boom)? If not at least one connection is bad.

It could also just be crappy jumper cables. They can wear out after a few years.

Once cables have been attached, then move / shake the clamp on engine block. If cables are making a sufficient connection, then that movement will create some sparks. If the block has some sealer or paint, or if one of those connections on the battery is not sufficient, then no sparks when the cable is moved.

That sparking will also 'clean' the electrical contact.

Most of the cheap cables I see on the market are of limited value at best. :(

Sick.

Welcome to the Cellar, Kacgekcad. :D
Could you please expand on, "sick", a little?
Just enough so we can figure out what you're talking about, ya know.

Or, was that just the prerequisite post to spam in your second post?

I was thinking the same thing. :-)

That spark exists if connecting direct to a battery or indirectly via a chassis. Hydrogen has nothing to do with it.

Positive is connected first so that either + terminal does not accidentally connect to most everything else. 'Everything else' is connected to the - terminal. Firmly attaching those red clamps before making any other connection makes an accidental short less likely.

Connecting to a chassis - not battery - is so that an accidental short circuit is less likely to cause a battery explosion. An explosion not due to ignited hydrogen. A battery that is shorted can get so internally hot as to explode.

Why do I know? We learn this stuff from experience (mistakes).

I've always connected negative first on both ends. Just because I figure hooking up the ground isn't going to put any current into the cable. If I have the positives connected, and one neg, what if I drop the other end of the negative, and it touches a grounded surface? bzzt. I've never hurt myself or the battery.

Something new to learn about cables.

:):):)

cables for jumpers?

I wasn’t sure if that was a UK English word that you yanks wouldn’t understand .....


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Why are they called jumpers, anyway? I'm talking about what we call a sweater...

cuz we want girls to jump when they wear them. mmmm... sweater puppies....

The original jumper was a guy hiding in the bushes who jumped out when he saw the right kind of girl.

Everything is phallic in electricity. That is why connectors are male and female. And couples talk abut the right kind of electricity in their relationship.

Sometimes we want to resist her charms.

5 foot 2. Eyes of blue. Six transistors in each shoe. Has anybody seen my gal.

Bender on a bender is cute

Don't forget to reverse your battery cables in the spring so the A/C works instead of the heat. :haha:

Thanks for the reminder. :dunce: