Jumper cable question

[CL8]

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]

Gauge and length as well as quality of materials used.

[CL8]

Thanks mavrick14.

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

[Mavrick14]

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]

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]

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]

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]

Originally Posted by CL8

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]

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]

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]

Originally Posted by curtis73

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]

Originally Posted by MagicRat

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]

Originally Posted by CL8

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]

Originally Posted by MagicRat

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]

Originally Posted by CL8

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.