Turnigy nano-tech power leads

[Nick Jackson]

Turnigy nano-tech 3S 850mAh 45-90C discharge Lipos from HK UK: I was surprised to see that the latest batch of these cells, bought for F5J models pulling on launch c 40A for c 25 secs, has thinner-than-usual power leads; marked as '18AWG'.

Has anybody else come across this? A quick Google suggests much lower current limits for this sort of thickness.  Where should I be on a scale of zen / afraid / very afraid?

Obviously I can try them on the ground before risking anything but thought I'd ask first.

[wookman]

I'd have thought 40 amps going through 18 awg cable for 25 secs is going to warm those cables quite nicely.

I would suggest at least 'very afraid' possibly bordering on petrified. 18 awg is servo cable isn't it?

Remember, don't let the smoke out!

[Gary B]

I have four of those batteries, two bought a year ago, two bought this month, the power leads are all the same (18 AWG).

I have one 'A-Spec' 850 where the wire gauge looks thicker but I can't read it.

I use the four nano-techs quite heavily, pulling 42 Amps without problems, they can do two 150 metre/30 second launches safely.

Oddly I had an LVC cutout with the A-Spec after one launch from full charge so I don't try another with it.

The wires look thin to me as well but I suppose the manufacturer should have done their homework and used an appropriate gauge for the rating.

90 x 0.85 is 76.5 amps, this is for a burst but they never say what a burst is exactly!

Silicone is a good insulator and can take higher temps (it's used on IC engine exhaust extensions) , if the wires are getting hot you wouldn't necessarily be able to tell.

I would keep an eye on things as I'm doing.

   Cheers

      Gary

[satinet]

Bear in mind the wire is coated in high temperature silicone. The sort of stuff you could put in an oven. 

The other factor to bear in mind is the length of the cable is also probably very short (<30cm?), so there is less of it to be resistant.

Also the wire is likely cooled by the motor/holes in the fuselage. And the other main factor is that you will only run the motor for 25s not with a continuous current supply, which is what your AWG/amp table will be talking about. 

 

Personally I would not be very afraid.

 

[RustyKnee]

18 AWG is about 21miliohms per meter. for 40A in 15cm leads (30cm total out and back) equates to about 10W dissipated in the cable...should warm it up quite well.

 

[Nick Jackson]

Thanks for the various observations. With some trepidation in the light of the more pessimistic ones, I soldered one of the packs up, charged it and gave it a whirl - ran it full throttle for 25 secs, which I guess is working it a bit harder than in the air, when it will unload a bit. Everything seemed to survive OK and though, as usual, the pack got a little warm the leads did not heat up noticeably (though I take the points about the silicone insulation). I should probably have stuck a meter on it to compare the current draw with one of my older 850mAh packs with thicker leads but it didn't feel like it was giving less urge than usual.

I was sufficiently reassured to be prepared to give it a go in the air - maybe tomorrow if not too windy.

[Nick Jackson]

Two launches with the pack yesterday. Not easy flying with your fingers crossed but all seemed well.