spacemart wrote:these look pretty worthless. I've had trouble starting a car with bigger copper cables. Twice I've doubled up jumper cables and gotten it to start. If your battery won't hold a charge thin cables like these won't do it. As someone said earlier, do not skimp on jumper cables.
All discussion of gauge, amps, and so forth aside, there are only two categories of jumper cables: those able to turn over the engine of a car with a flat dead battery (or NO battery at all), and, those that NEED to have a fairly decent (but dischaged) battery in the car that's being jumped.
In the former case, you can start a car with a battery that's gone to that great landfill in the sky (assuming that the vehicle has an alternator in good working order, to KEEP it running once you remove the jumper cables). In the latter case, you can start a car with a good battery that's been run down by too much hard starting, or by having left the headlights on, etc.
Cables of the first type will cost you dearly. Basically HEAVY duty COPPER welding cables, capable of carrying a couple HUNDRED amps without heating up (and, HEAVY duty COPPER clamps, too).
Cables of the second type (the VAST majority of those on the market) can be afforded by mere mortals, but, will NOT be able to start a truly dead vehicle. You will NEED to connect to the target vehicle, and then sit there for a while running YOUR engine, so that YOUR alternator can charge the other car's battery.
Then, when you start the other car, you're starting it with it's OWN battery.
To recap: HEAVY copper "welding cable" jumpers are STARTING cables -- but the vast majority of "consumer grade" cables are CHARGING cables.
Edited to add: The reason I emphasized COPPER is because I've never seen aluminum cables of sufficient gauge that were intended for other than fixed applications (i.e., strung between two poles, rather than looped up and carried in your trunk).
The difference is that a cable that is intended for this sort of application will need to be flexible. A good welder cable will have MANY strands of fairly SMALL gauge copper wire, whereas a cable designed to be set in place and left alone (i.e., power distribution) will have relatively FEW strands of very THICK wire.
Obviously, the total amount of metal will determine the carrying capacity of the cable (unless you're talking about RF applications where stuff like "skin effect" comes into play), but, at the extreme, a single "strand" of wire (AKA "a bar") will carry enough current, but be IMPOSSIBLE to work with (picture everyone you know trying to horse a metal bar into shape to fit between two cars, and then trying to bend it back into a loop to stow back in your trunk when done).
If someone does make aluminum cables with enough FINE strands, then they might work, but I'm skeptical, since aluminum lacks copper's ductility, and IMO if it was thin enough to be flexible (with enough diameter to carry the necessary current), the strands would not be robust enough to endure actual use -- they'd break after flexing a few times. So, we're generally left with consumer grade aluminum cables with a few strands that are thick enough to endure flexing, but NOT thick enough to carry starting current.
BTW the big problem with aluminum (that causes house fires) is that unlike copper, it will readily compress (when you tighten a screw terminal), but NOT expand later on. Due to thermal effects, the pressure is constantly increasing and decreasing (at each terminal). With aluminum wire, each time the pressure increases, the wire compresses, but, when the pressure decreases, the wire does NOT expand again.
This causes poor conduction (AKA resistance) which in turn causes more heat, increasing the compression (and the problem), and, eventually, causing enough heat and sparks to cause a catastrophe.
Connectors designed for aluminum are spring-loaded, so that they will maintain firm contact regardless of the aluminum wire's one-way compression behavior.
