


Thread OP

Discussion
how to calculate correct AWG
Hi!
I do actually have above average knowledge about current and cables and how to calculate this, but not in the model/rc field. When I see the cables on a 20A or 40A ESC, or on my motors I know something is way off with how I would calculate my cables if I do this my self they are SO thin!! So therefor I would like some help.. Please fill out this: 5A = AWG 10A = AWG 20A = AWG 30A = AWG 40A = AWG 50A = AWG 60A = AWG 70A = AWG 80A = AWG 100A = AWG 150A = AWG 200A = AWG 250A = AWG I do not know how to ask the next question, because I can't find the right English words, but I would like to know ruffly what I should multiply the total Amp with when I calculate the main power cables from power board or cable harness from battery.. 





Thread OP

No one?? This has to be basic build knowledge...??
Maybe it's the list that make people go away? Then drop the list, because I really need to know how you calculate this! In my head, with 16A you need 2.5 mm2 or about 12 awg, 25A is 6mm2, about 64 awg.. This is with 220v, and I know that you normally would go UP in awg with lower volt, because of the voltage drop, but as I said, when I look at the cables that is used on the gear I have from factory there is something strange here.. 





Quote:
http://www.engineeringtoolbox.com/am...uged_730.html 






Also your numbers are for 220V AC and single wire, with the RC hobby its DC current and multiwires cables.
AC current flows outside of the wires, DC is using the whole surface, AC single wire is a waste of good copper And the silicon insulant is quite resistant to heat, and not inside plastic tubing, so it allows warmer conditions. 





Quote:
12 VDC is a good base for 3S and 4S cable section calculation Since power between ESC and motor run on 3 wires I think it is OK Heat = lost of power 





Thread OP

The last thing that no one mention here is the voltage drop.
Lets use papajef's post in the "Fake Cinestar frames on GoodLuckBuy" thread (he has the same motors as me). Quote:
Volts= Length x Current x 0.017 Area Volts= Voltage drop. Length= Total Length of wire in meters Current= Current (amps) through wire. Area= Cross sectional area of copper in square millimeters. The frame they discuss in this thread I think is about the same as size as mine, arms= 1000mm. So, the current needs both "+" and "", so the length has to be x2. From Stefan1204 earlier post, we can see that 18 awg is 0.82 mm2. 2 x 16 x 0.017 = 0,66 volts dropped to the motors. 0.82The table in the other Stefan1204 link about maximum current through a 12V electrical wire, size (AWG) and length of cable has no shorter length then 15 feet. 2 meters is about 6.56 ft. If we double the length in the table, we can see that it goes from a 10 AWG to an 8 AWG cable with 15 amps (with this note: Note! The wire size is required for a 3% voltage drop in 12 Volt circuits. Oversize the wire if the voltage drop is critical.). So if we go the other way, we go down 2 awg sizes because our wires is 6.5 feet, and ends up with 12 AWG wire (12 awg = 3.31 mm2) 2 x 16 x 0.017 = 0,16 volts dropped to the motors. 3.31a 0,5 volts difference. So if watts = amps × volts and battery is 12 volts 18 awg = 12V  0,66 V = 11.34 V = 16x11.34 = 181.44 watts 10 awg = 12V  0,16V = 11.84 V = 16x11.84 = 189,44 watts 189,44  181,44 = 8 wats lost power from each motor. BUT we also get a much heaver cables, I do not know the weight of the kind of cables used in rc, but found a table showing that Weight lbs/ 1000 ft for the 18 AWG is 4.91, and 10 AWG is 29.89. That defiantly add some gr. to each arm.. I do not know how to calculate how much watts you need to lift one gram. 






Quote:
Your calculation is done for the maximum power (full throttle) but hovering will be at +/ 50%, in the winter the lost will be less than in the summer (cables will be cooler) 






https://www.rcgroups.com/forums/show...24&postcount=2
Every hk ESC uses way too thick wires for both battery and especially motors 

Last edited by timecop; May 12, 2013 at 05:07 AM.




Not sure if i saw it referenced but the insulation temperature rating is what allows the higher amp rating , that and some other factors, but the insulation is the big one for RC users.
the cut and past job below, the last column is the gauge, the number to the left of it is amps at 200 C insulated wire. I tried to break them out for easier reading, but the formatting didn't stick, I also think this list is a tad conservative as its industry related and we leave margins. Insulated Conductor Temperature Rating at 80°C at 90°C at 105°C at 125°C at 150°C at 200°C AWG SIZE 0.33 0.49 0.55 0.6 0.71 0.78 40 0.47 0.68 0.77 0.84 0.98 1.1 38 0.63 0.91 1 1.1 1.3 1.5 36 0.87 1.2 1.4 1.5 1.8 2 34 1.2 1.7 1.9 2.1 2.4 2.7 32 2 2.2 2.5 2.8 3.2 3.6 30 3 3 3.4 3.7 4.3 4.8 28 4 4 4.6 5 5.7 6.4 26 5 5.5 6.2 6.7 7.7 8.7 24 8 10 11 12 14 16 22 10 13 14 15 18 21 20 15 18 20 22 24 28 18 19 24 26 28 31 35 16 27 35 39 42 46 54 14 36 40 51 55 60 68 12 47 55 67 72 80 90 10 65 80 90 97 106 124 8 95 105 121 131 155 165 6 125 140 160 172 190 220 4 145 165 180 194 214 252 3 170 190 215 232 255 293 2 200 220 247 266 293 344 1 


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