Jumper cable question


CL8
08-13-2009, 10:11 PM
I was comparing jumper cable price and quality and found one 6 gauge jumper cable will hold 400 amps, another 6 gauge cable holds 350 amps, and yet another 6 gauge holds only 200 amps.
And one 8 gauge cable holds 600 amps!

I thought the thicker the cable, the more current it would hold.
What other factor determines the amperage a set of jumper cables will carry?

Also what is the logic in the lower the number gauge, the thicker the cable?
Shouldn't it be a higher number the thicker it is?

Mavrick14
08-13-2009, 10:29 PM
Gauge and length as well as quality of materials used.

CL8
08-14-2009, 01:39 AM
Thanks mavrick14.

So how does a consumer determine the quality of materials and if the length is what they need?

Mavrick14
08-14-2009, 10:25 AM
If you want long cables, then get the bigger gauge (smaller numberically). If you want normal 6 foot cables, then 6ga will be fine, even 8. For anything 4cyl or 6cyl, youll be fine with just about anything. The real expensive ones are for bigger engines like diesels which take more juice to turn over.

tomj76
08-14-2009, 03:25 PM
As for the origin of wire gauges, read this: http://en.wikipedia.org/wiki/American_wire_gauge

A wire's current handling is first based on the diameter, but there are other issues as well in a jumper cable. Current handling is driven by the maximum allowed temperature of the cable in operation. Factors affecting this are: the electrical resistance of the cable, the temperature capablity of the insulation, and the quality of the connections at the cable ends. Different grades and alloys of copper contain other materials to enhance and optimize certain characteristics of the metal. This can be for easier drawing into a wire, for lower resistance, more flexibility, or reduced cost. In addition, different insulation materials will have similar choices, one of which is the melting temperature of the insulation. Additionally the type of connection at the end of the wire to the cable clamps will impose a resistance, which can often be a hotspot of a jumper cable.

A cable made from small wires could handle more current if the insulation choice allows a higher temperature, if the wire is a high conductivity copper, or if the cable clamps and connections are of a higher quality.

These details are not easily descerned, especially the electrical characteristics of the wire and the temperature rating of the insulation. I'd say the manufacturer's data current handling is your most reliable summary of this information.

I've found that a good set of jumper cables uses a reasonably heavy wire with an insulation that doesn't get too stiff at low temperatures (I have one pair with cracked insulation from bending the wires while cold), and has good strong clamps.

curtis73
08-14-2009, 10:03 PM
Advertising is also a big factor. You can put 600 amps through an 8 gauge wire for about a half a second... but you can advertise them as handling 600 amps.

I have a set of 1-gauge 20-foot cables that cost me about $120, but being a mechanic they get used about 5 times a day at the shop to jump start everything from a Toyota to a Kenworth, so they're worth it.

I would say that for emergency cables to keep in the car, a set of shorter 8ga cables would suffice. It might take a while to get enough juice into the dead battery to start, but it will do the trick for an emergency. I have a set of 12' 4ga cables in my truck that I got at WalMart for $36 a couple years ago and that is all you would ever need for most situations.

CL8
08-15-2009, 12:03 AM
Thanks for the input Curtis and Tom.

Would using jumper cables that can carry 600 or 800 amps on a small vehicle
that only needs 200 cranking amps possibly cause damage to that vehicles electrical system because of the high amperage it carries?

If the answer is no, would that be because the battery will only draw what it needs and no more?

(is it best to use lower amp/higher gauge cable on a small vehicle, or does it even matter?)
Thanks
cl8

MagicRat
08-15-2009, 07:51 AM
If the answer is no, would that be because the battery will only draw what it needs and no more?

The answer is no, and yes, your suggestion is correct.

Note, when you are discussing the gauge required to carry a current, you must also consider the length of the cable.

Cars use DC (direct current), not AC (alternating current, like the kind found in your house.)

DC current grows less efficient as your circuit or wires grow longer. Therefore, a set of short (6 ft) cables are more efficicient at transferring power than a longer set.

Shorter cables can use smaller gauge wire for the same effect. For regular auto use, a set of 8 ga. 6 ft cables are adequate. But, if you want a 10 or 12 ft long set, you have to move up to a 6 ga. set to get a similar ability to transfer power.

Also, usually, when you jump start a dead battery, you can hook up the cables, then let the dead battery charge up for a couple of minutes before attempting to start the car. This allows you to use a lighter gauge jumper cable set, yet still start a vehicle.

I have found that even cheapo small gauge cables work fine for gasoline engines. But, diesel engines in light and heavy trucks as well as construction equipment NEED a heavy gauge cable set.

IMO you should get the longest, thickest cable set you can afford. But don't worry if all you can afford is a cheapo set. They will still work fine.... it will just take a bit longer to get a jump, since you may have to partially charge-up the dead battery before you start the car.

curtis73
08-15-2009, 04:09 PM
Right. Amperage is how much the appliance its trying to suck through the wiring. If you have 200 amps potential from a battery, and a 200 amp appliance and you try to operate it using 16ga wire, it won't happen. You'll burn the wire. But if you have that same 200 amp battery, same 16ga wire, and a 1-amp appliance, no worries. What determines the amperage is how much juice the appliance demands.

CL8
08-15-2009, 11:38 PM
Thanks MagicRat for the good info on cable length and on charging the battery with "cheapo" cables. I will use that info on my
"jump starting a car" page on my website.
Thanks Curtis for the good description of amperage.

Another question, if you don't mind, In my research, more than one person has said not to rely on your alternator to recharge your battery after a jump, because the alternator is made to maintain a charged battery, not charge a discharged one.
They therefore say to use a battery charger.

I have always just drove around on a freeway or highway for a good ten minutes after my battery has been jumped, and have never had an alternator problem. How valid is the advise to use a charger, not your alternator?

thanks,
cl8

CL8
08-15-2009, 11:49 PM
Advertising is also a big factor. You can put 600 amps through an 8 gauge wire for about a half a second... but you can advertise them as handling 600 amps.


I take it you meant "can't" here?

CL8
08-16-2009, 12:37 AM
Also, usually, when you jump start a dead battery, you can hook up the cables, then let the dead battery charge up for a couple of minutes before attempting to start the car. This allows you to use a lighter gauge jumper cable set, yet still start a vehicle.

Would this work for even a Ford F150, needing 500 cranking amps?

MagicRat
08-18-2009, 07:41 AM
Would this work for even a Ford F150, needing 500 cranking amps?

This will work for any battery in any vehicle. Often, just a few minutes is necessary.

It is also temperature-related. The warmer the battery is, the quicker it will charge up. Therefore, a dead battery in the summer time may need just a couple of minutes to charge up. During a frosty winter, the same battery may need 5-10 minutes.

Some years ago, I jump-started a Cummins 855 cubic inch diesel in the middle of winter with my Bonneville. This diesel had 3 huge 12-volt batteries, all pretty much dead. My car was hooked up to the batteries, running for 1 hour before the diesel would start.

CL8
08-18-2009, 10:42 PM
This will work for any battery in any vehicle. Often, just a few minutes is necessary.

It is also temperature-related. The warmer the battery is, the quicker it will charge up. Therefore, a dead battery in the summer time may need just a couple of minutes to charge up. During a frosty winter, the same battery may need 5-10 minutes.

Some years ago, I jump-started a Cummins 855 cubic inch diesel in the middle of winter with my Bonneville. This diesel had 3 huge 12-volt batteries, all pretty much dead. My car was hooked up to the batteries, running for 1 hour before the diesel would start.

What gauge cables did you use?
And did you run out of gas?

The owner of the diesel must have been very thankful!

MagicRat
08-19-2009, 07:08 AM
What gauge cables did you use?
And did you run out of gas?

The owner of the diesel must have been very thankful!

Actually, the diesel truck was my own. It was a really frigid Monday morning and for some reason, the batteries were pretty low.

The wires were probably 6 gauge, but the alternator was probably putting out only about 30-40 amps at best, at a fast idle, so even the cheapest jumper cables would have handled that.

CL8
08-21-2009, 02:14 AM
Actually, the diesel truck was my own. It was a really frigid Monday morning and for some reason, the batteries were pretty low. Were you concerned about jump starting a frozen battery, and would there be a danger of a frozen battery exploding by letting it charge first without turning on the vehicle?

The wires were probably 6 gauge, but the alternator was probably putting out only about 30-40 amps at best, at a fast idle, so even the cheapest jumper cables would have handled that.

MagicRat
08-22-2009, 08:02 AM
Were you concerned about jump starting a frozen battery, and would there be a danger of a frozen battery exploding by letting it charge first without turning on the vehicle?

In my experience, batteries only freeze when they are completely discharged. Then, when they freeze, they are completely dead. :(

Also a frozen battery will have broken or distorted lead plates inside, so imo any frozen battery is damaged and useless, and cannot be recharged, even when thawed out.

The truck's 3 batteries still had some signs of electrical output.... just not enough to star the engine... so I knew they were not frozen.

If the truck had no sign of any electrical activity, then I would assume they are frozen and I would not try to charge them up until I checked them out.

CL8
08-25-2009, 10:30 PM
Here is my "Jump starting a car" page, any suggestions?

www.drivingtips.org/jump_starting_a_car.html (http://www.drivingtips.org/jump_starting_a_car.html)

thanks, Cl8

MagicRat
08-26-2009, 08:23 AM
Here is my "Jump starting a car" page, any suggestions?

www.drivingtips.org/jump_starting_a_car.html (http://www.drivingtips.org/jump_starting_a_car.html)

thanks, Cl8

Very nice job :)

two points:

1. Your pictures indicate it's okay to place the negative clamp on the car body (your pic shows a strut tower to be used). This is actually a bad idea.

Most cars have a relatively thin wire (called a 'ground strap') that connects the body/chassis with the engine. Clamping the cable to the body means all the power to crank the engine is going through this thin strap, which impedes current flow.

Therefore it is much better to place the clamp on part of the engine itself. Usually a bolt or bracket for one of the accessories (alternator, power steering pump etc) presents itself.

2. It is a VERY good idea to turn on the headlights of the running car before the first jumper cable is removed, to prevent a damaging voltage spike.

You see, when the good, running car is still hooked up to the dead car's battery, it's alternator is generating power because the dead battery is accepting it. When the cable is suddenly removed, that extra power has suddenly nowhere to go. It might cause a harmful voltage spike which might damage some electrical equipment.

FWIW, I have found that many people are terrified of providing a jump start because they have heard somewhere that is can be harmful. This voiltage spike reason is the cause of such fear.

However, I found that such reluctant donors cannot be convinced that switching on the headlights will alleviate the risk. Imo their ignorance means they will refuse to help out when someone has a dead battery.

shorod
08-26-2009, 12:06 PM
I don't like to consider myself ignorant, but even with my degree in Electrical Engineering I stuggle to understand how having the headlights on will filter the spike better than the battery by itself could, or for that matter, any of the filtering that is present in the PCM/ECU. Years ago there wasn't much filtering in the PCM/ECU, but the last few I have opened appeared to have pretty decent filtering.

-Rod

MagicRat
08-26-2009, 06:35 PM
I don't like to consider myself ignorant, but even with my degree in Electrical Engineering I stuggle to understand how having the headlights on will filter the spike better than the battery by itself could, or for that matter, any of the filtering that is present in the PCM/ECU. Years ago there wasn't much filtering in the PCM/ECU, but the last few I have opened appeared to have pretty decent filtering.

-Rod
Originally, this "headlights-on" suggestion was intended to protect the diode trio found in the old-style internally-regulated General Motors alternators. I first heard this in the pre-ECM days. Since then, it pops up regularly as a suggestion for jump-starting instructions.

To be more specific, Rod, (as my post suggests) this has more to do with the fears of the uninformed motorist than anything else. The 'headlights-on" suggestion may have some real value in some cases, in others, it may be just a placebo.

However, I have come across so many ill-informed motorists, friends, co-workers etc who REFUSE to provide a jump start specifically over fears of voltage spikes and damage. Any placebo to soothe their irrational fears is a good one, imo.

I have even suggested that if they are so fearful, they can provide a jump with their car actually switched off..... which would eliminate any risk. But typically. such refuseniks are so fearful and obstinate, they ignore sound advice and contine to be irrationally stubborn.

shorod
08-26-2009, 07:15 PM
This is one of the reasons I keep a charged portable jump start pack in each of our vehicles. It avoids people (or me) being stranded because people refuse to jump start a car for fear of damage. The only times I've seen damage occur is when someone connects the jumper cables incorrectly or allows them to short out. The jump start pack made me a lot of friends during my college years.

-Rod

CL8
08-27-2009, 02:03 AM
http://i327.photobucket.com/albums/k475/CLRM/bateng.png (http://i327.photobucket.com/albums/k475/CLRM/batnegsc.png) Thanks MagicRat for the tip on where to place the negative cable. My problem is, in my Echo in the picture above, the engine on the left has a plastic cover, I find no metal to connect a clamp to.

Other than that screw on the strut tower, the only other metal I see to possibly connect a clamp to, is one of three screws connected to the air filter as the one to the left in the picture below, however it seems to only wrap around the rubber of the air filter hose.
In the last picture below there is another screw near the bottom of the hose, but again it looks like it only wraps around the hose.

However to the left of that last screw by the green arrow there is a screw that appears to be more connected to where the engine and air filter meet. Though it's a tight squeeze, the clamp can connect there.

Am I wrong in thinking the first two screws wouldn't be a good connection
because they only wrap around the air filter hose, or would they work?


Thanks, Cl8



http://i327.photobucket.com/albums/k475/CLRM/batafs1.png

http://i327.photobucket.com/albums/k475/CLRM/bataifs.png

MagicRat
08-27-2009, 07:22 AM
1. Check your owner's manual for the jump-start procedure on your car. Usually, the manufacturer provides approved attachment points for jumper cables, if none are obvious.

2. Those screws are not a good idea as an attachment point. Your last pic (green arrow) seems to show a good spot for the clamp.

CL8
10-06-2009, 02:34 AM
MagicRat,

I finally got around to editing my "Jump Starting a Car" page.

Under step#4, for connecting cables, I made an addendum stating what you said MR, about not using metal parts connecting to the body as opposed to the engine block for the last negative clamp.

Does that sound correct in how I worded it?

http://www.drivingtips.org/jump_starting_a_car.html


Thanks,

CL8.

MagicRat
10-06-2009, 11:14 AM
It looks good to me. I like the conversational tone of your description where you briefly discuss the reasoning behind your actions.

I would suggest that the paragraphs showing you connecting the cable to the engine should come first in Step 4 because imo it's best to demonstrate the proper method first.

I also think you might suggest for the reader to check their owner's manual for the correct procedure for their car. Often, newer cars have an approved terminal of point where the negative cable should go.

The part showing you connecting it to the strut tower should be placed last, and shown to be a 'last resort' if nothing else presents itself.

CL8
10-06-2009, 11:30 PM
Good advice! thanks MR!

Add your comment to this topic!