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May 11, 2013, 03:49 PM
Registered User
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..
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May 11, 2013, 04:49 PM
Registered User
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 6-4 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..
May 11, 2013, 04:56 PM
Registered User
Quote:
Originally Posted by tormodnt
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 6-4 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..
http://www.engineeringtoolbox.com/aw...uge-d_731.html

http://www.engineeringtoolbox.com/am...uge-d_730.html
May 11, 2013, 05:04 PM
Registered User
Thread OP
Perfect Stefan!

I still think that the cable used from factory is to small, but then again it's short too :-)

Now I can keep building my hexacopter into the night :-P
May 11, 2013, 10:37 PM
Registered User
Be aware, those links are at 12V, if you're not using 3S they aren't really accurate
May 12, 2013, 12:39 AM
Since 1902. Maybe.
Olivier_C's Avatar
Also your numbers are for 220V AC and single wire, with the RC hobby its DC current and multi-wires 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.
May 12, 2013, 03:02 AM
Registered User
Quote:
Originally Posted by Olivier_C
Also your numbers are for 220V AC and single wire, with the RC hobby its DC current and multi-wires 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.
From battery to ESC is DC
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
May 12, 2013, 03:56 AM
Registered User
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:
Originally Posted by Papajeff
These HL 48-22 490kv pancake motors, that I got from HiModel, are quite different from
any other outrunners that I have ever used. They look like they are extremely well made
and powerful, but the proof is in the test flights so we shall see.

The motor wires are 18 AWG so I used the same guage for the boom extensions eventhough
the Castle ICE 50's have 13 AWG motor wires. My pal, Greg Covey the AMP'D Man, suggested
doing this and I always follow his suggestions.
The voltage drop here is:

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.
0.82
The 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.
3.31
a 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.
May 12, 2013, 04:31 AM
Registered User
Quote:
Originally Posted by tormodnt
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).



The voltage drop here is:

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.
0.82
The 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.
3.31
a 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.
You have to make a compromise, even the biggest AWG will lose power.
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)
May 12, 2013, 05:00 AM
Suspended Account
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.
May 15, 2013, 12:42 AM
Registered User
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 80C at 90C at 105C at 125C at 150C at 200C 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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