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The variables when buying jumper cables seem to be:

  • length
  • cable thickness
  • amps
  • engine cc

Length obviously determines how far it can go.

What affect will cable thickness have?

Is amps simply the amount that can travel through so the higher the quicker charging so there is no harm in buying a lower amp cable if you don’t mind slower charging?

Cc is obviously related to engine displacement. I notice the packaging on some cables say ‘suitable for up to 1.9’ cc. Are these designed for 2.0l cars or is it 1.9 and below? Some cars are considered 2l but then elsewhere I see the cc listed as 1.95 etc perhaps by convention. Is the 1.9 on jump start cables a convention or is it literal and shouldn’t be used on anything above 1.9l car?

Also What will happen if you used a 1.6 cc cable on a 2.0 car? What is it about the cable that has been constructed that in differentiates between an engines cc?

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  • Resistance varies as a function of thickness and length. Ideally you want short thick cables. If the battery has a bad cell or other internal problems, small cables may never be able to start the car, because the battery will never charge. Here is a good article explaining the things to look for. myknowledgeguy.com/how-to-choose-quality-jumper-cables – the_storyteller Sep 21 '20 at 17:59
  • If you use small cables to jump start a large engine, they may get hot, melt the coatings, and potentially catch fire...which is very exciting, but not ideal in most situations. – the_storyteller Sep 21 '20 at 18:01
  • There is also the matter of the metal clips which contact the battery. Cheap leads can have poor quality metal which can bend or snap against the force of the spring. The connection of the cable to the clip can be dodgy on a cheap set too. I now have a pair of heavy duty leads... – Weather Vane Sep 21 '20 at 19:59
  • Jump cables are not exactly meant for charging. Any case, I don't see much of an issue in using cables "designed for an engine of up to 1.9L" on a 2.0L car. – EᑎOT Sep 21 '20 at 20:42
  • Jump cables aren't meant for charging, more like conducting enough current to start the car. Too thin cables either get hot or won't allow enough current to successfully start a car. Also some thick, but surprisingly cheap jumper cables are mostly fakes as they merely have a very thick insulation and some thin copper conductor – Martin Sep 21 '20 at 21:48
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I would modify the criteria used for jump starting cables. These are important characteristics:

  • Length
  • Cable thickness
    • This determines the amperage and how big engine the cables can start and how rapidly they can charge the flat battery, so no need to specify amperage and engine capacity separately. A given mm2 of copper always conducts the same. There is no difference between copper from mine 1 and copper from mine 2. There is however difference in how cable vendors calculate the amps and engine capacity, and those differences can cause you to select a low-mm2 cable that provides 1000 amps (perhaps, but only for few seconds or else it overheats) and can start a 10 litre engine (perhaps, but only after a long charge of the flat battery) over a high-mm2 cable whose manufacturer has a huge safety margin in amperage rating and engine displacement rating.
  • Whether the insulation is flexible even in freezing temperatures
  • How high quality the clamps are.
    • Low-quality clamps are not pure copper but rather only copper plated. These should be avoided as they cause additional resistance. High quality clamps are pure copper. Of course quality costs more so don't expect to find cheap cables having pure copper clamps.

What affect will cable thickness have?

It's the determination of amperage. This in turn determines how quickly you can start a big engine and how big engine exactly.

Is amps simply the amount that can travel through so the higher the quicker charging so there is no harm in buying a lower amp cable if you don't mind slower charging?

Yes. Lower amp cable is less expensive and has lower weight. Also it is always a good strategy to charge the flat battery, remove the cables and only then start the engine that you couldn't previously start.

If you start the engine prior to disconnecting the cables, and the battery is dead, it will happily start. Then when you disconnect the cables, engine running, the destination car just lost its only buffer in its electrical system (the battery of the source car) and lots of expensive electronics damage will result. This has led to some car manufacturers recommending that cars not be jump started. At your own risk, you can ignore the recommendation, but if there's even a bit of suspicion about the health of the battery (not just its state of charge), you should charge the battery with the jumper cables, disconnect the cables and only then try starting the engine.

Cc is obviously related to engine displacement. I notice the packaging on some cables say ‘suitable for up to 1.9’ cc. Are these designed for 2.0l cars or is it 1.9 and below? Some cars are considered 2l but then elsewhere I see the cc listed as 1.95 etc perhaps by convention. Is the 1.9 on jump start cables a convention or is it literal and shouldn’t be used on anything above 1.9l car?

I don't know of any car with smaller than 1.9 cc engine!

Joking aside, this is the cable manufacturer's idea of how big engine you can start. It has no rigorous basis. Even thin cables can start big engines if you slowly charge the flat battery with them. It just takes a lot of time.

Also What will happen if you used a 1.6 cc cable on a 2.0 car? What is it about the cable that has been constructed that in differentiates between an engines cc?

It might start. Try it, it could even work!

If not, then just wait and try again.

As I said, there is no rigorous basis for the engine cc rating. Different cable manufacturers may have different rating criteria. You can always ignore these ratings, but thin cables with big engines means it won't start immediately. After a bit of wait, it will start.

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