I looked into how fat the wire going from stunt batteries to motor speed controllers needs to be.  Results are interesting, but not too astonishing. I'd assumed that AWG 20 wire would suffice to carry the current with acceptable resistance loss, and that people are using AWG 12 or 14 wire for some Eli-the-ice-man* reason. However, it appears that inductance (the pertinent Eli-the-ice-man component) is a function of wire length, rather than thickness, and is maybe not a big deal even for length.. 

Is weight reduction from smaller wire worth the resistance penalty?  Ideally, one would cipher airframe change due to weight and other esoteric stuff, but I took an easy way out.  The upper left table in the attachment shows properties of three comparable battery species: 1) five Molicel P50B 2700-size LiIon cells, 2) six Molicel 18650-size LiIon cells, and 3) good old Thunder Power 2800 mAhr six-cell LiPos.  The upper right table shows a trade between the latter two.  Name-brand stunt fliers have decided that batteries of LiIon cells are better than those of LiPos.  To wit, it's worth  .066 ohms of internal resistance to lose 61 grams of battery: .00108 ohm/gram.  The lower right table shows trades between 18-gauge wire and 14-gauge wire and between 20-gauge wire and 14-gauge wire.  From 14-gauge to 18-gauge costs .00111 ohm/gram, so if it's worth changing from the LiPo battery to the LiIon battery, it's worth changing from 14-gauge wire to 18-gauge wire.  Returns diminish for 20-gauge wire.

There are other considerations, e.g.  1) For a given connector, which size wire would require more solder?  2) It's easier to deal with thinner wire in a narrow fuselage.  3) Heat could be a problem with thin wire.  At 20 amps, the average current for my Impact with a six-cell battery on a cool day at 200 ft. altitude, 18-gauge wire dissipates 2.6 watts/foot.  20-gauge wire dissipates 4.1 watts/foot.  Peak current is more than 20 amps, and remembering the nursery rhyme, "Twinkle twinkle little star, power = I squared R," one might worry about melted insulation or charred paint.  Even worse would be on a multi-motor airplane with high-kV motors and fewer cells.

*E = L dI/dt, I = C dE/dt

Actually when I make up my 6S Li-Ion packs, I use Castle creations 13 AWG wire.  I figure the 14 AWG wire is about the minimum AWG wire we should be using.  I would never consider using 18 or 20 AWG wire.  If you're looking at saving weight by using thinner wires, just build lighter and use the 14 or as in my case 13 AWG wire.

Electric planes tend to fly better nose heavy.  No idea why but weight in the nose is not the big deal weight in the tail is. I use the same gauge wire that comes with the motor and ESC which, since I am mostly into 28xx and 35xx which means nothing smaller than 14(.). 

Ken

Quote from: Ken Culbertson on February 17, 2025, 06:08:29 PM
...weight in the nose is not the big deal weight in the tail is.

Especially if you build your airplane with too short a nose, as I do.

I tried to convince a local full-scale airplane builder that weight is a bigger deal some places than others. 

I drew some pictures.  The first one shows the trade between wire mass and resistance.  Remember we are willing to pay .00108 ohms per gram of mass reduction for the change from Thunder Power 6s 2800 batteries to 6s 18650 LiIon batteries.  That's the slope of the red line (-.00108, actually).  That slope is about the same as the ohms per gram of switching between 14 and 18 gauge wire, or the ohms-per-gram slope at 16 gauge wire.  Considering only the mass-resistance trade, if you would switch from Thunder Power 6s 2800 batteries to 6s 18650 LiIon batteries, you wouldn't want to use any wire fatter than AWG 16.  As for thinner wire, you can see the diminishing returns.  Bob Carver, an electrical person, was at the house Saturday.  I asked him about battery wire gauge.  He said he'd use 22 gauge, but he likes to fly Nelson .36-powered combat planes on .012" lines.

The second picture shows how much power goes into heating the wire for various currents.  Heating is proportional to the square of the current.  The third picture shows voltage drop.  This could be a concern toward the end of a flight with LiIon cells if current or battery internal resistance increases.

Please tell me if I missed something or ciphered wrong before I rewire my dogs.

Unless basic electric doctrine has changed recently, you could run higher volts and lower amps and deliver the same watts through a thinner and lighter wire.

But I learned that in school 65 years ago just before they said I couldn't be an electrical engineer. 

The people who taught me that still use really BIG wires to connect 12 volt batteries to car starters. 

Quote from: Paul Smith on February 18, 2025, 07:36:04 AM
Unless basic electric doctrine has changed recently, you could run higher volts and lower amps and deliver the same watts through a thinner and lighter wire.

I think we do and we can.

22AWG is used as a fusible link rated at 30A, should be interesting. Nobody ever tried to save weight in wire gauge, even back in the NiCd days of electric RC. Competitive electric RC models keep wire lengths to an absolute minimum, just enough to make the connection.

Quote from: spare_parts on February 18, 2025, 12:04:35 PM
22AWG is used as a fusible link rated at 30A, should be interesting. Nobody ever tried to save weight in wire gauge, even back in the NiCd days of electric RC. Competitive electric RC models keep wire lengths to an absolute minimum, just enough to make the connection.

Interesting since our local electric code requires a 15A fuse/breaker on 14 gauge wire.

Ken

I lived over 30 years in a 60 amp house and used an electric stove, air conditioning, lights, television, home computers and power tools.  I was amazed to read that for some people 60 amps is not enough to fly a model airplane.

This might have to do with that 110/220 VAC stuff compared to 15 volt Lipos. 
I am an interested spectator in electric stuff, like the Indy 500.  I don't inhale the stuff but I watch it on TV.
If you see something with wires, put your hands in your back pockets and slowly back away.

*I am not an electrician nor an electrical engineer.*  From many of the things I've read, wire amp ratings are safety factor rated for enclosed spaces with little to no ventilation or cooling.  In our planes, we generally have some reasonable air exchange happening.  We generally use heat resistant silicone jacket wires, but there is probably a best practice for heat related efficiency loss.  Use what makes you feel safe, but it seems like we might have a tendency to over spec.  The attached silicone wire manufacturer chart is certainly an interesting read for max current ratings. 

Brent:  What your chart tells me is that for our purposes we are probably safe with 14gauge on most CL applications using a 6s battery.

Ken

Having flown electric since '97 or so I've selected quite a few power systems and well beyond. I can't recall ever being concerned about wire size supplied by an established mfg ever being excessive or inadequate. I always kept things as short as possible, and almost never used a connector between the ESC and motor.

When comparing batteries, I always look at watthours. I don't understand why 5S p50B would be compared to 6S P30B when 7 still weigh less the the P50B pack.

Fusible links aren't really rated like fuses. However, I want video if an attempt is made to fly a 30A setup on 22AWG wire. If my power supply was in the garage, I'd demonstrate it myself. I burned up a Toolkit M6 charger yesterday, did that smell. Don't push these to the limit.

Keeping wires short is more important than wire gage.  Short wires weigh less and have lower total resistance. 

Quote from: John Rist on February 19, 2025, 09:29:50 AM
Keeping wires short is more important than wire gage.

Can you show me quantitatively?

QuoteI don't understand why 5S p50B would be compared to 6S P30B when 7 still weigh less the the P50B pack.

It was another trade: my effort vs. clarity. I started with a spreadsheet I made for something else and worked on it until I thought it sufficed to show a mass vs. resistance trade. I deleted most of the chaff on the spreadsheet, but not enough to get my point across. I am a poor communicator, as my high school English teacher told me.

The great automotive engineer, Charles "Boss" Kettering invented, along with many other things, the electric starter.  Previous engineers and inventers concluded that (like with model engines today) the electric starting system needed to be bigger and heavier than the car engine itself.

Kettering made a smaller and lighter starter based on the fact that you could overload an electric circuit for a short time but not all day long.  Likewise, a modeler can eliminate the safety factor in order to gain advantage while only risking a model airplane.

On paper, the lost voltage in small wiring doesn't look terrible. You'll lose maybe 100RPM at full throttle. and pull 0.1A more at governed speed. Using a small connector with the small wire might double that. At 18-22V, voltage is already high compared to the early days of electric with ~8V batteries. I'd exhaust all means of weight saving prior to reducing wire size. Changing from one cell type to another, or one cell up or down is a bigger factor overall in mass and energy.

You see relatively small batteries for drones with huge wiring, but they are 75C rated packs and the flippity floppity types do pull it. 850mAh Tattu come with 14AWG and XT60 connector.

Electric cars existed before electric starters for engines. Motors could move a car, battery, and passengers, let alone turn over an engine. Looking at Kettering's patent (1,150,523), it was for a system including starter, generator, ignition, etc. Electric starters existed prior to this, Clyde J. Coleman patent 745,157 in 1903.

Quote from: spare_parts on February 21, 2025, 09:16:30 AM
I'd exhaust all means of weight saving prior to reducing wire size.

I did, except for paint, of course.  Nontautening dope shrinkage crushed the hollowed four lb/cubic ft ribs on my current dog.  That got me to wondering about all that copper in the nose.

John Hart-Smith told me that his previous company, a now-extinct California airplane maker, was willing to increase primary structure weight by a pound to save $50, while paying $1000 per lb for weight reduction elsewhere in the airplane. (I forget the exact numbers, but those are close.)

While I was typing this, Amazon delivered my 18-gauge wire.

Not that MY opinion is worth much...I've been using 16ga (Castle Creations stuff) since early on in MY electric endeavors.  I use MOSTLY Castle Talon 35A ESC in my various stunt ships and they use 16ga on the battery wire with it.  I figured IF CC uses it at up to 35A, heck I can use it at 28! Most of my Li-ion packs use 16ga wire with XT30 connectors now.  Weight savings secondary...Space is the primary reason.

Quote from: spare_parts on February 21, 2025, 09:16:30 AM
Using a small connector with the small wire might double that.

If connectors are bad, why don't they get hot?

I am switching from Deans to Spektrum IC3 connectors, but for reliability, rather than resistance.  Igor recommends something-Jet connectors, which have super low resistance and are made of good stuff, but I haven't seen any that come in pairs. 

Quote from: Crist Rigotti on February 17, 2025, 05:23:01 PM
Actually when I make up my 6S Li-Ion packs, I use Castle creations 13 AWG wire.  I figure the 14 AWG wire is about the minimum AWG wire we should be using.  I would never consider using 18 or 20 AWG wire.  If you're looking at saving weight by using thinner wires, just build lighter and use the 14 or as in my case 13 AWG wire.

Crist, I think you need some trip strips and vortex generators to give you the aerodynamic oomph you need to carry that extra weight. 

Quote from: Howard Rush on February 21, 2025, 05:01:20 PM
Crist, I think you need some trip strips and vortex generators to give you the aerodynamic oomph you need to carry that extra weight.

Touche'

Bottom line:  I use the wire size that comes on the batteries, motor, and ESC.  I would think the factories that manufacture these items would use the smallest wires that will work safely.  It's a cost thing.   

The lightest connectors I've ever seen were Kontronic, I believe solid silver even. When it matters, I use a bullet type with heat shrink.

Even double of a very low value might be acceptable, just the point you're making. I've measured connector resistance and equated it to wire lengths. If optimizing to this point, you'll have to make the call on mass vs. loss. This application is not high current or power.