10awg vs 12awg wire

Garrick_s

Garrick_s

100 W
Joined
Oct 13, 2010
Messages
109
Location
Ventura CA
I need to re-do most of my battery wiring to better meet my new configuration.
Everything is now 10ga Silicone wire.
I have a local Hobby shop that has 12ga.

Should I stick with 10ga?
Is there that much of a difference between 10 and 12?

Thanks

G
 
I run 15S divvied as 3 x 5S, and use 12-AWG to mate each cluster together (matching the same gauge coming from the batteries). However the harness from this clustering is 10-AWG all the way to the controller and again back to the motor connector. This early “upgrade” was most noticeable for my initial capacities of 15Ah and generally worked quite well to assuaged sags on dead-starts and hill climbs where the momentary current draw was close to 40 A. The wire I chose was mil-spec Teflon-lined 36-strand silver-plated10-AWG, though it is stiff to work with. I think the silicone noodle wire would be perfect for the high-flexibility joins, and the mil-spec better suited for the straight runs if one had such favorable options. :)

~KF
 
Garrick_s said:
Is there that much of a difference between 10 and 12?
Click to expand...


It depends on the current you're drawing, as YPedal has said. Here are a couple of examples that (hopefully) show the difference you might see. First, let's assume you have 4ft of wire (2ft + and 2ft -) between the battery pack and controller.

First, let's look at 10g wire:
For a current of 40A, the voltage drop across 4ft of 10g wire will be about 40 x 0.004 = 0.16V. The power lost in the wire will be 40 x 0.16 = 6.4W

For a current of 80A, the voltage drop across 4ft of 10g wire will be about 80 x 0.004 = 0.32V. The power lost in the wires will be 80 x 0.32 = 25.6W

Now, let's see what happens with 12g wire:
For a current of 40A, the voltage drop across 4ft of 12g wire will be about 40 x 0.0065 = 0.26V. The power lost in the wires will be 40 x 0.26 = 10.4W.

For a current of 80A, the voltage drop across 4ft of 12g wire will be about 80 x 0.0065 = 0.52V. The power lost in the wires will be 80 x 0.52 = 41.6W

You can scale the figures above for different wire lengths; if the wire length is double (4ft + and 4ft -), then the values above will double.

You want to lose as little power in the wires as you can, so generally the bigger the wire (the smaller the gauge number) the better.

Jeremy
 
Jeremy Harris said:
Garrick_s said:
Is there that much of a difference between 10 and 12?
Click to expand...


It depends on the current you're drawing, as YPedal has said. Here are a couple of examples that (hopefully) show the difference you might see. First, let's assume you have 4ft of wire (2ft + and 2ft -) between the battery pack and controller.

First, let's look at 10g wire:
For a current of 40A, the voltage drop across 4ft of 10g wire will be about 40 x 0.004 = 0.16V. The power lost in the wire will be 40 x 0.16 = 6.4W

For a current of 80A, the voltage drop across 4ft of 10g wire will be about 80 x 0.004 = 0.32V. The power lost in the wires will be 80 x 0.32 = 25.6W

Now, let's see what happens with 12g wire:
For a current of 40A, the voltage drop across 4ft of 12g wire will be about 40 x 0.0065 = 0.26V. The power lost in the wires will be 40 x 0.26 = 10.4W.

For a current of 80A, the voltage drop across 4ft of 12g wire will be about 80 x 0.0065 = 0.52V. The power lost in the wires will be 80 x 0.52 = 41.6W

You can scale the figures above for different wire lengths; if the wire length is double (4ft + and 4ft -), then the values above will double.

You want to lose as little power in the wires as you can, so generally the bigger the wire (the smaller the gauge number) the better.

Jeremy
Click to expand...

very interresting calculation but what that mean the 0.0065 and 0,004 , thank you
 
r
 
lifepo4ever said:
very interresting calculation but what that mean the 0.0065 and 0,004 , thank you
Click to expand...

As LFP as (perhaps a little cryptically) said, it's the cable resistance in ohms. In this case 0.004 ohms is about the resistance of 4ft of stranded 10g wire, 0.0065 ohms is about the resistance of 4ft of stranded 12g wire (these figures are rounded, and come from one manufacturer, in practice the resistance varies slightly from one wire to another depending on the strand count etc).

The point to watch is that the cable power loss increases in proportion to the square of the current, so doubling the current means four times the lost power in the wire. This is one very good reason why cable sizes need to increase fairly dramatically once you start pulling more than 20 or 30 amps from a system. I'd not want to see more than about 10 to 20 watts wasted in the wiring on a high power bike. As the phase current to the motor will often be two or three times the battery current it's worth taking that into account when sizing cables.

The downside is that heavy gauge cable is expensive and harder to hide on the bike, but if you also remember that cable length is every bit as important as cable gauge, and arrange things so that all of the high power cable runs are as short as you can possibly make them, that will help.

Jeremy
 
Thanks for the numbers. Helps me understand why my 12 guage 24" of wire doesn't get very hot at 40 amps. And why it might at 100.

I assume that my race bike can stand to lose less than 10 watts when it runs at 90-100v at 40 amps. But 50 watts heating the wire could get kinda warm, especially on a flaky connector.

Does this change much with voltage? Like 90v vs 72? I get the impression that the amps is what matters.
 
dogman said:
Does this change much with voltage? Like 90v vs 72? I get the impression that the amps is what matters.
Click to expand...

You're right, voltage doesn't have an effect on the wire losses, it only affects the insulation rating that the wire needs. Not really a problem for ebikes, where we're not likely to get over 100V or so, but insulation ratings do get to be a potential problem at the higher voltages used in bigger EVs, both for the cable and the connectors.

Jeremy
 
Yeah, I can see why you'd want thicker insulation for more voltage. Even at 24v, it's pretty spectacular when some bit of wire chafes through and shorts out.
If you did get a short at 100v, thin low melting point isulation would melt in a jiffy.
 
I remember an old electrician joking about the difference between 250V and 600V fuse - about 2 inches... 600V can jump air more easily so they make the fuses physically longer.
 
Jeremy Harris said:
dogman said:
Does this change much with voltage? Like 90v vs 72? I get the impression that the amps is what matters.
Click to expand...

You're right, voltage doesn't have an effect on the wire losses, it only affects the insulation rating that the wire needs. Not really a problem for ebikes, where we're not likely to get over 100V or so, but insulation ratings do get to be a potential problem at the higher voltages used in bigger EVs, both for the cable and the connectors.

Jeremy
Click to expand...


i have 8 gauge wire from my motor and 10 gauge for my controller but i have 6 gauge for the on/ off switch i took the wire from from car booster cable
but i want to know if i need bigger wire for my 100 volt set up also the breaker is not the best thing i lose maybe some heat there

here the wire : http://www.youtube.com/watch?v=JkZpQ2iLODU
 
If you have 10ga now then going to 12ga would be a downgrade, something I'd discourage. I've had 12ga phase wires get pretty hot. While those were long runs, I'm staying away from 12ga except for portions of battery packs that won't see full current, and the interior of motors which aren't easily reharnessed or will see 40A max.
 
Thank you all for your input.
Mr Harris, you laid it all out quite nicely. Thank you.
10awg it is.

Anyone one know of a competent and reliable supplier of 10awg Silicone wire?
that goes for a good PWR switch and connectors too.

Thanks again.

G
 
I get mine here:
3 foot of black and 3 foot of red, 6ft total $8.95
http://www.rcdude.com/servlet/the-1511/10-AWG-Silicone-wire/Detail

HobbyKing has 2 different kinds of 10AWG wire, the price is a little bit less but you have to wait 2 weeks for normal shipping.
 
RCdude had what I needed and got it to me in two days.
Randy was helpful and communicated well.

Thanks for the hookup TMaster.
 
Yep he's on the ball! You're welcome! 8) 8) 8)
 
I had a similar question to you. In my case I wanted to find the right gage wire to make up by lipo pack and to install remotely my Watt meter.. http://endless-sphere.com/forums/viewtopic.php?f=2&t=23474&start=0

knowing the max Amps my controller draws and the total cable length needed for the installation I use the info bellow to determine that I would need wire gage 10-12 to make my battery and watt meter harness.


TAKEN FROM

http://www.epanorama.net/documents/wiring/wire_resistance.html

FROM A CAR AUDIO PERSPECTIVE. IT DOES CERTAINLY APPLIES TO EBIKES

Car audio cable recommendations
This info in from rec.audio.car FAQ (orognally from IASCA handbook). To determine the correct wire size for your application, you should first determine the maximum current flow through the cable (looking at the amplifier's fuse is a relatively simple and conservative way to do this). Then determine the length of the cable that your will use, and consult the following chart:
CURRENT_WIRELENGHT_GAGE.png

The problem is finding wire.. I found this on another forum

FROM (http://www.rcuniverse.com/forum/m_7952172/anchors_7952172/mpage_1/key_/anchor/tm.htm#7952172)
---
[XXT-CRer ]
go to the home depot electrical department and ask to look at their s-o, s-j, s-j-o, or s-o-e-w, type copper wire. its multi-conductor so if you want 10awg you need to ask for 10/3 or 10/4. this means that if you buy 3 ft of 10/4 you actually get 12 ft of wire. it would be 3ft of black, 3ft of red, 3ft of white, and 3ft of green. it very closely mimics the wire we use in rc at a fraction of the cost. it has a very high strand count with very fine strands, and it solders very well.

any combonation of s-o is rated for 600 volts and has a very high strand count and a little thicker and softer insulation. anything starting with s-j will still do fine and much more closely resemble hobby wire than standard building, but will be a little stiffer than s-o types.


---
[hnasdad ]
The "AWG" is a standard for the size of the wire itself. The insulation is the difference in what we are talking about. Solid, stranded wire has a slightly different Outside Diameter. Obviously Solid wire is not what you looking for. Home Depot, lowes, or major stores like this are going to carry mostly THHN wire. These four letters are used to explain the makeup of the insulation of that wire. Not what you are looking for. If you go to an electric supply store that specializes in selling all electrical supplies is your best bet. I dont know the insulation off the top of my head but ask for a wire for Panel makeup. The wires used in making up electrical panels is a high strand count with a very flexible insulation. THHN has an outer jacket of nylon the last N, in THHN. You should be able to pay cash at any supply house and they will hook you up. Much better prices than Home Depot. Ask them to take you in the back and you can check out the wire that they carry and find exactly what your looking for. I know that you have already found a wire that suited you needs. Just wanted to put in my two cents.
just tell them you want to see the 10awg rubber cord. they will cut it for you, to the length that you want, even 1 ft.

the rubber cord that you want should fall into the s-o, or the s-j category. you will be impressed with its construction and softness.

im an electrical contractor and we build machines that use this cable and rely on its ability to move freely to allow for proper automated movement of the equipment.

bryan.
 
Garrick S,
I would not be using booster cable wire unless you know that it has had very little use and is less than 2 years old, old boosters should be recycled and will have alot of resistance because of corrosion or being cooked from the high amperage required to start cars.
 
Not sure about Booster cable.
I purchased 10awg, high strand, silicone wire from RCdude up in Oregon.
It's brand new.
Went with all new Anderson connectors too.

Thanks for everyone's input.
 
My HD has some nice double 12awg cable IIRC for outdoor low voltage lighting. Flexible high strand count and reasonably priced. It was the only desirable 10-12awg option they had in the whole wiring section and I checked everything. All the other ones were too stiff. I have used 16 and even some 18awg lamp cord on my 30 amp currie bike without any problems. What ever I could find. Works fine, only thing is like Jeremy says you lose watts! Got to put that 12 on there one of these days.. :)
 
Wire thickness is one of my main worries with bikes. At the moment on my personal bike I have the stock 12awg wire from the Infineon controllers (bikes.ca) going to the 3 phase wires.....I have cut the motor wires back to about 3 inches of the very thin Teflon coated (14 or 16 awg?) that comes with the 9c and magic pie motors.

My worry is that I am pumping on average 25amps at 60 to 66volts with peaks on pull away and short hills at 40amps, the wires do not seem to get worn but fatigue of the wires is a concern.

I have been given some 12 wag (looks awfully thin though) Teflon Aircraft wire, very stiff.....but after showing it to an aircraft engineer he warned me that they have had a few fires because of this wire due to breaking of the coating and the wire breaking down.

Have ordered a load of 10awg and 12awg from Hobby King but it is taking it's sweet time to get here for these two builds I am doing grrrr.
 
I used some Mil spec 12awg teflon wire (has white insulation) for my phase upgrades. Like you said, very stiff, but very tough. I had it in below zero weather (the garage) and was flexing it, and didn't get any cracking. Also, I laid my 40W soldering iron right on the insulation for a long while, and it doesn't even leave a mark. Seems like good stuff.
 
Spacey said:
Have ordered a load of 10awg and 12awg from Hobby King but it is taking it's sweet time to get here for these two builds I am doing grrrr.
Click to expand...

If you want some 10g silicone wire from a local source (Southampton...........) then look here: http://www.technobotsonline.com/cable-and-accessories/cable/silicone-insulated-cable.html Their 6mm² is the same size as 10g and is £1.21 a metre, plus postage (less if you buy a 100m roll). It's not as flexible as the HK stuff, but I've found it to be pretty good.

Jeremy
 
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