Modern Vespa

Hi all

I have bought some what I think is 18 awg wire for rewiring a PK stator for my et3 for 12v conversion and for adding extra wires for indicators.

I bought 2 sets of wire from 2 sources. Both claim to be 18 awg but the amount of insulation on one of set of wires is much thinner. Both are sold as automotive wire.

There seems to have a similar cross section of wire. The thicker one has 18 awg printed on the outside.

Does the thickness of the insulation matter as it will be in a pvc sleeve so will be protect from rubbing. The thinner wire is easier to route through tights spots.

Is there an easy way to see what current the wire will put up with.

The 18 AWG refers to the wire itself, not the jacket. That can be different thickness, different material, etc. - as you are finding out. Some jacket materials are suitable for automotive/scooter use, some are more suited for speaker or doorbell wire.

Current capacity will depend to some degree on how long the wire is and whether it's part of a multicore cable. There are numerous online references. In general, for a scooter application, 18 AWG should be good for 7A max. I don't run more than about 5, just because I like to be on the more conservative side.

So in practice if I have a short 1-2 foot run from the stator blue wire to the regulator is 18 awg going to be enough?

Google search txl vs gxl wire. It doesn't mean that you have either of those wires, but you will find an explanation on the insulation thicknesses.

Most stuff sold in Aus will give you the cross-sectional area in mm2. Google says 18awg is 0.75mm2.

Calculate the voltage drop over the length of the wire (there and back), should be <0.5 volts max.

https://www.rapidtables.com/calc/wire/voltage-drop-calculator.html

Thanks.

More questions, what sort of output in amps would a pk stator have from the blue wire? All I can find is that they may be 90-120 watts so at 12v that's about 7.5 -10 amps ? So the blue wire to the regulator at 18 awg over about 0.8 m would drop 2.5% in voltage. I think for this wire will use the thicker insulation.

I am assuming for the indicator wires that go to low voltage LEDs that the amps would be very low so I am free to use the thinner 18 awg as it will get through the headset easier.

The thickness of the insulation will have essentially no effect on the current capacity of the wire. If the wire will carry up to 10 A, I personally would go with 16 ga - or more likely just run two 18 ga in parallel, if that's all I had on hand.

Also remember that while we refer to these systems as "12 V", pretty much nothing actually runs at 12 V. I don't have direct personal experience with scooters that have batteries, but these systems typically run anywhere from 13.5 or so up to 14.6 V. A fully charged battery will measure 12.7 (give or take, depending on battery chemistry) and charging voltage will be higher than that. So your max current is probably more like 8.5A.

If the thinner insulated wire you have is "modern thinwall cable" I'd say the opposite. Although thinner the insulation is lighter and more abrasion resistant than pvc.
And contrary to an above post, the insulation does affect the current carrying capacity of the wire. Modern thin wall is rated for a much higher current than pvc for the same size conductor (0.75mm^2 thin wall will carry a max of 14A).

You are correct that the thinner one is higher quality. It's a TXL cable with a higher heat range than the thicker one (125 c vs 105 c).

I think I may go belt and braces and use 16awg from the engine terminal to the regulator for that short 80 cm run on the blue and black wires.