Help! Motor-ESC extension wire gauge recommendation?

[JozMk.II]

Hi,

Fairly specific question here. I’m scratch-building a 10-ft-wingspan semi-scale B-25 Mitchell, primarily out of foamboard. I plan to mount the batteries in the fuselage or nose, and run wiring from there to the 1500w motors in the engine nacelles. Per recommendation of my local hobby store’s long-time owner/RC enthusiast as well as several threads I’ve found on RCGroups, my plan is to avoid using long battery leads and instead mount the 100a ESCs near the batteries in the fuselage, with extension wires running from the ESCs out to the motors in the wings.

I may be able to keep the wires as short as 2ft, but without modification to the nacelles and wings they’ll have to be at least 4ft, and possibly up to 6ft if the batteries are all forward into the nose. I imagine I’ll likely be making these wire extensions myself, and so am interested in selecting a type and gauge of wire that would result in the lowest voltage drop possible over such a long length. I would imagine I would want them to be considerably thicker than normal to reduce the overall resistance. Could anyone give me recommendations for a type and thickness of wire?

And any other relevant input is welcome, too - This is the largest electric RC plane project I’ve worked on to this date.

ESCs: 2X Hobbywing 100a V2
Motors: 2X DIAMONDDYNAMICS Hobbyhh D5065 400kv 1500W (Amazon)
Connector: 4.0mm gold bullet connector
Power: 6S 22.2v Lipo (3 or more parallel sets of 2 3S 2200mah 11.1V lipos in series)

 

[Merv]

Some say to extend the wires between the ECS & motor others say to extend the wires between the battery & ESC. I'm not sure it matters, I have always extended the battery wires, 2 wires rather than 3. I would use a similar size wire that came with the battery.

 

[joelspangler]

You are right to extend the wires to the motors rather than the batteries. There's reasons that are hard to explain, but it sounds like you already know that based on your post. You should be able to find recommendation for DC wire size based on length of the wire plus the amperage running through them. I've always used 1/3 of the ESC's rating because the load is spread over 3 wires. I'm often surprised at how thick the recommended wire is. I've dropped to smaller gauges since it'll still work - just with creating some heat. My thought process is that with most planes you only run full throttle for a small period of time to take off, and possibly for a few full throttle passes. The time in-between those spikes will give the wiring time to cool down.

 

[joelspangler]

here's a page with a good chart - https://www.bluesea.com/support/art...oosing_the_Correct_Wire_Size_for_a_DC_Circuit

Based on this, it seems like they are recommending 10guage for 30 amp at short lengths, but I'd probably drop that to 12 or 14 unless your model will be a hot-rod that you'll be flying at full throttle a lot.

 

[quorneng]

It is not just the loss of power wire resistance creates but also the heat it generates.
Electric planes work because the LiPo is providing lots of power likely several hundred watts in many cases. Also note that most of the wire used is covered in a thick layer of silicone so is well insulated thermally too. This means even a modest amount of heat energy generated in such a wire will raise the temperature quite quickly. Copper is good heat conductor so resistance 'wire heat' can get to and soften solder joints!

It is one reason I use "magnet" wire, similar to the wire used in motor windings, for really long ESC to motor lengths. With its "varnish" insulation only a few microns thick the wire stands a chance of dissipating the heat to air rather simply getting hotter and hotter.
One further point. For the same amp capacity magnet wire is only half the weight of flexible silicon coated!