question about gauge wire?

[lildjloop]

so i am building a new heli and have a CC 120HV with 8awg wire for the batt connection. my question is for my wire Y harness that i intent to make to connect to my batts in line, does that y harness need to by 8awg as well? or can i make it out of 10awg? my 6s batts all have 10awg wiring..

[pctomlin]

Although harder to work with since it is 8 awg, I like to stay with the wire gauge on the ESC when making a Y harness etc..

[pilot10]

you should stay with 8 awg but you might be fine with 10awg wire

[Dennis Everett]

You could try the 10 , after flying check to see if its hotter than the 8 , if not , your good to go , if hotter, go to 8 , all that being said , 8 would be better

[prototype3a]

8awg is only recommended if you're planning to pull 200A continuous. Otherwise 10awg is sufficient. Frankly, 8awg on a 120A esc is overkill.

[cycled]

Is there a list of recommended amp draws for each size wire? There seem to be different ratings everywhere, for example 12AWG recommended for 60A where many batteries and ESCs use 14AWG.

[prototype3a]

I think one reason we can get away with smaller wire is the distances are short, there is generally good airflow and we don't really pull a lot of current for much more than a few seconds at a time.

I do however know that if you use 12awg for 200A continuous (a minute or two) things tend to desolder themselves.

[jharkin]

Originally Posted by cycled

Is there a list of recommended amp draws for each size wire? There seem to be different ratings everywhere, for example 12AWG recommended for 60A where many batteries and ESCs use 14AWG.

The problem is that if you look up wiring ampacity charts online you are going to find numbers that either come from the NEC (for AC house wiring) or DC charts meant for boats and RV's - like the Blue Sea systems website. These charts assume enclosed wiring, longer runs and bigger safety factors than modellers are probably running.

For example, a 12 volt boat wiring chart calls for 2 guage wire on a 120amp circuit, even over short distances. NEC tables would be specifying 0 or even 00.

What you might try is plugging some number into a voltage drop calculator like this one
http://www.calculator.net/voltage-drop-calculator.html

[lildjloop]

the whole reason i ask if i can get away with using 10awg instead of 8awg is just cause of the thickness of the cable. ill be using the castle connectors for my esc and batts. this 8awg is pretty hefty and i was thinking i hope these fit into the castle connector without issue.. they are rated up to 6awg.. does anyone else use these connectors? ill be using the ec3 connector for my rx batt to the split leads into the Rx..

[lildjloop]

quick question, i will be going with the pulse 3700 or 4100 45c 6c batts, does anyone know what the gauge thickness of the power leads are? if they are 8 i will go with full 8awg, if they are 10 i will make my harness from 10awg..

thanks

[prototype3a]

As far as I know, no one puts 8awg leads on their packs. Most larger packs use 10awg or 12awg. Revolectrix used 8awg for a while but people complained as they didn't fit basically any connector out there.

[mba83]

Would be good to have a chart here on HF somewhere of max current for each AWG for helicopter application.

8awg 200A
10awg 150A
12awg 100A
14awg 70A
16awg 40A
18awg 20A
20awg 10A

Does this look like a good start?

Edit: also found this thread: http://www.rcgroups.com/forums/showthread.php?t=320240

[prototype3a]

That looks reasonable. Maybe a bit high at the smaller gauges. FWIW, an increase of 3 wire gauge sizes is equal to two in parallel of the smaller. IE 2x 20awg = 1x 17awg As such, the current rating shouldn't quite double for every 2 size increases.

That said, by my maths, if 8awg was 200A then that would mean 20awg would be 12.5A

On the other hand, I suspect we're less tolerant of voltage sags at the lower end of the scale which might explain why I would probably use 18awg for a ~12A load and why I have 2x 22awg leads on all my ESCs for the BEC.

[bradg]

I would use wire no smaller than the battery leads, the current will be same. I would like to think that the battery manufacturer put in a lot of thought about its decision of wire size and I'll trust them.

Brad G

[lildjloop]

Originally Posted by bradg

I would use wire no smaller than the battery leads, the current will be same. I would like to think that the battery manufacturer put in a lot of thought about its decision of wire size and I'll trust them.

Brad G

Yeah that's probably what I'm gonna do which is 10awg.

[prototype3a]

Originally Posted by bradg

I would use wire no smaller than the battery leads, the current will be same. I would like to think that the battery manufacturer put in a lot of thought about its decision of wire size and I'll trust them.

Brad G

Frankly, they don't put as much thought into it as you might think. Testing has shown that some manufacturers choice to use 12awg leads on big packs or 12awg connections on split packs are downright foolish.

[LinusLarsson]

Originally Posted by prototype3a

Frankly, they don't put as much thought into it as you might think. Testing has shown that some manufacturers choice to use 12awg leads on big packs or 12awg connections on split packs are downright foolish.

Agree to some extent. However, the packs are made to be light, nobody wants heavier equipment than necessary for the task at hand. If you have special needs (like emptying a pack in 2.5 minutes) you should be more careful when selecting packs. Most normal packs do work for the intended purpose even with what can be considered to small wire.

I just bought 6S 3650Mah hyperion batteries to be used in an R5, these have 12Awg wire. I will definitely "ramp up" the amperage on those to see that everything checks out.

To the op, 10Awg is definitely enough.

[jhamel]

Originally Posted by prototype3a

As far as I know, no one puts 8awg leads on their packs.

They may have changed by now, but when I purchased the blue Turnigy 6S 40C 5,000mah packs back in 2011, they came with 8 AWG wires. Way overkill.

[Staub]

I'd also like to point out that some of the wire/current calculators on the internet can be a bit misleading, they assume 110 volts. Plus I'm guessing they are rating the wire for constant amps and continues use, a 120 Amp ESC in a heli is not going to pull 120 Amps for 4 hours.

Here's a good site that gives the ability to adjust parameters. http://www.rapidtables.com/calc/wire...calculator.htm

Assuming their calculations are right, 2 feet of 10 gauge wire will drop the voltage by .47 volt at 120 Amps and 45 volts, about 1%. .47 volt x 120 amps is 56.4 watts. So I'm figuring 2 feet of wire would be dissipating about 56 watts of heat.

[PhenixFord]

Like some of you have noticed, most ampacity charts are designed for continuous current ratings. To complicate things even further, DC wire gauge ampacity ratings can be "de-rated" depending on circuit length.

For those of you who plan on pushing the limits of their electrical systems, there is no such thing as "overkill" when it comes to selecting wire gauges for custom circuit designs. However, there are a few things to consider. Bigger wires are harder to work with. Also, if your battery has smaller gauge wires, switching to larger size wires after the ESC wouldn't help the electrical system.

Having said all that, with the overall circuit lengths that are used on these models being very short, just about any size wire will handle the ampacities seen by the systems for a very short duration. what you should be more concerned with instead of conductor size is: The conductors resistance rating and heat carrying capacity. Larger conductor sizes always do better in those areas.