I was thinking to make a pair of cables for jump starting cars, using silicone wire and some clips. Because silicone wire it’s soft, fluffy and can bend a lot, so it would be easier to stuff somewhere in the car.
I would buy the wire from China. They say it has tinned copper inside.
What gauge should I get ? Is 8 AWG enough ?
In the specs they say that 8 AWG can drive up to 190 amp current.
Jumper cables are usually 6 or 8 awg I believe. I’m not sure how much softer they would be with a silicone coating. The copper metal the wire is made of is probably going to matter the most. You could get 8 awg with maximum strand count to soften them. I think strand count will be more effective than silicone coating at making them more bendable.
Have you checked for welding cables? They tend to be flexible and well insulated.
Its more important how fine the copper leads are, the higher count and finer the more flexible is the cable
on 30 or 50mm² the insulation does not matter much, silicone is less robust than other materials
I use this 2 AWG cable for arc welding. Very flexible with a nice thick EPDM jacket. The jacket seems very durable, but I must admit that I have only used the cables about a half dozen times so far over the past few years.
Agreed. What makes my spaghetti noodle wires notable is not just the silicone insulation, but the very high strand count as well.
What would be the optimal strand count?
The chinese one has listed 1650 strands for the 8 AWG wire. And sectional area is 8.29 mm^2
Careful with wire-gauge buying from Chinese suppliers, as they sometimes (if you’re lucky) say “not equivalent to American gauge” or somesuch. Ie, you’ll buy 10ga but get 12ga or so in the wraps. Worse, it won’t be contiguous wire strands, but various loose strands just twisted together. Bad, bad, bad.
Eg, just goggled on AX for 18ga wire, and one entry at random had this review:
Compared with awg18 wires from the speed controller, the wire turned out to be a smaller section, similar to awg20. The parcel came quite quickly, the claimed 5 meters correspond, even a little with a margin. Insulation silicone. so who need awg18 wires order on,, size,, more. Seller recommend. There were no problems with the order. 21 Aug 2019
Might wanna upsize the wire you order, then.
The gauge to use is dependent upon what you are starting and where you are located. For a sub-compact in Florida, you could get away with 10 gauge. For a big block or a diesel in Manitoba, I would want nothing less than 4 gauge, maybe 2 gauge.
What kind of clamps are you planning on using? The best jumper cables use clamps that are heavily insulated to help avoid accidents. Also color coded of course, lots of red insulation on the + and lots of black on the neg. Mistakes blow up lead acid batteries and are dangerous.
As was mentioned it is the fineness of the individual strands of copper wire that make for more flexibility. The best purchased jumper cables use insulation that remains flexible in cold temperatures. I have seen some otherwise good jumper sets that use plastic insulation that gets very stiff in winter weather. Welding cable insulation is also tough to cut. Welding cable has tough insulation as they are dragged on the floor and get snagged on things all day as one works. I have welded for decades and don’t think I have ever abraded a cable to the point where the insulation was degraded to the point of being dangerous. I am not sure that silicone insulation is as tough.
For car cables, if you want something cheap, high current, and you don’t care about volume, you should just get extreme high gauge aluminium wire.
At 60% the conductivity the copper, and 1/3 of the density, it’s still a very good alternative.
The clamps have to be nickel/gold plated copper for low contact resistance.
Just for s&g, I priced out some wire, clips, etc., and quick-goggled for jumper cables. Even 22bux at Amazon for a 20’ set (ie, 40’ of wire) looks pretty damned good vs DIYing it, no?
Then there’s soldering/crimping cable-to-clip, weatherproofing the junctions, etc.
Sure you don’t want to reconsider? I’m as cheap thrifty as the next guy, but I’d rather just buy the damned things and be done with it (and have it all not look like taped-together nerd-glasses). 
Nightmarish information, considering what else is being build in China these days.
As blueswordm mentioned get good quality copper clamps. I made a heavy duty 4m set and used stainless steel clamps these didnt work properly so i had to buy the clamps again.
From the networking world, CCA (Copper Clad Aluminum) is looked down on because of the aluminum’s tendency to break from being flexed. Is this different in the large gauge power world?
it’s not about the price. I am sure it will cost me way more to make them. Silicone wire is very expensive too, that’s why I was thinking to get it from Aliexpress, but it is still quite expensive compared to pvc-insulated wire.
The reason I wanted to make them is because I am always hearing people say that home-made jumper cables are the best and that commercial ones suck. I already have a set of cheap jumper cables that I only had to use once, and they did their job…
I see no reason why a 50mm² commercial jumper wire will suck, the clamps of mine are very solid
they are well enough flexible with at least 100 strands, Insulation is OK
Silicone insulation is mainly used on high flex cables, talking of >100 strands per mm², they are expensive mainly because of the copper
or for wiring that gets hot
extreme high flex you need for daily use item like professional welding cables
I have purchased welding lead wire from my local tractor supply before, nice and flexible for the heavy guage.
But for the amount you would need, I’m pretty sure you could buy a already made good quality heavy guage set of jumper cables for less than making it yourself.
https://www.amazon.com/Energizer-1-Gauge-Jumper-Battery-Booster/dp/B017O8JZP6
MANY years ago,mw Dad bought a 25 foot set, made with 2 gauge welding cable…
best way to go. Flexible, Durable, and can handle some amps.
No idea what it would cost today, but it was $50 then… Warshawsky brothers !