Wire gauge and allowed current?

[Bigbikebob]

Hello I am in a process of building my ebike and one aspect I never noticed in the past is the wire gauge, mostly because my previous kit was 500W 36V and was purchased from one supplier.

Now that I enter to the 1000W club and would like to overclock to about 2000W, things like "pipe size" become important.

So, is there a wire gauge table with different wire sizes that is relevant to ebikes, which shows the allowed current via each wire gauge?

I also know that if you put too much current via a wire you would damage it, my question is after how long,
is there a formula or a table that shows that (for example) 14 gauge wire is rated for up to 15A if you put 20A via the wire you would damage it after 10 hours and if you put 40A you would damage it after 2 hours....?

Thanks

 

[Ykick]

Many of these type questions can be answered here:

http://www.endless-sphere.com/w/index.php/Main_Page

Scroll down to - Wire Gauges / Types vs. Power Usage

forum link:

http://endless-sphere.com/forums/viewforum.php?f=32

I run 2kW peaks with average power consumption between 500-1000W. 12Ga wire battery/controller for years and well over 10k miles.

 

[gwhy!1]

just use 10awg this is a good safe size to use for lowish power <3kw

the only real thing you need to keep a eye on is how hot the wire or connectors get when pulling a lot of power, silicon wire will be the safest and most flexible as the insulation will not melt off or burn upto around 180c, it is the heat that will damage the wire but if the wire/connector do not get hot then it will last for a very long time.. the wires or connectors should not get remotely warm when in use if they do then there is a problem.

 

[Drunkskunk]

No, we don't have a good simple formula table like that. The wiki gives you some helpful links, but we don't have anything that explains it the way you're looking for it. We need it.

But it's complicated. You can run far more power through a wire that's air cooled and exposed than to a wire buried deep in a bundle of other wires, stuffed into the frame of your bike. And those ratings are for 100% duty cycle, where you will rarely meet your maximum amp draw for more than a moment, and few bikes carry enough battery to pull full amps for more than an hour. To correctly size your wire, you need to be an engineer. There's an @$$load of math involved. No one bothers with this for an ebike, as we start with a good thick wire, and make it thicker if it gets warmer than we like.

2000w is fine on 12g wire for most ebikes, unless you're doing something unusual with the wire. 14g would probably work in many cases. However, thinner wires resist more and you should go with the thickest wires you can practically use. 8-10g in most cases.

 

[Bigbikebob]

Ykick,
Thanks for the WIKI, very useful to know it is around.
Sadly the wiki doesn't answer my question,
from this link
http://www.solarhome.ru/en/basics/batteries/sizing_cables.htm

under "Conversion of American Wire Gauge to Metric"
you can see that a 10AWG can handle 40A

in this link:
http://www.powerstream.com/Wire_Size.htm

under "Maximum amps for power transmission"
you can see that a 10AWG can handle 15A

Plus this doesn't take into account for how long and by how much you can "overclock" your wire.

gwhy!,
I Already ordered a 10AWG wire from HobbyKing. the thing is I want to know for sure what I can and can't do.

Drunkskunk,
Math is no problem, and so is engineering , but every good engineer knows to look around and copy before starting to work hard the internet is a big place...

You are right, almost no one is putting 100% of his current all the time, and most of the batteries will last less then an hour if you do. that is why I asked my question about "overclocking" a wire.
I am already going with the 10awg wire, just want the science behind it (will probably buy a 3.5KW kit in the future).

And from personal experience, 14awg and 2KW will burn slowly

 

[Ykick]

My reluctance to use 10ga wire is that it never seems to fit APP connectors I use.

 

[Bigbikebob]

I use bullet connectors with a crimping tool , and plenty of space in magic pie 3 motor for the 10awg wires, don't need to bring them via the axle

 

[amberwolf]

Well, the obvious answer to that is to use bigger APP's or a different connector.


And that's actually what I stopped in to point out, is that upping hte wire gauge to not heat up often doesn't fix the problem some poeple have, of using too small a connector or one not designed for a really good connection at a high current.

So when you do use bigger wire, make sure that you're alos using a bigger connector.

Yeah, it's a PITA because now they don't fit in wher eyou want them too, or they'r emore expensive, or a host of other little or big problems resulting from the size, but at least you won't have ot deal with the problem of either fitting the bigger wire (or it's thicker insulation) into the housing for a smaller ocnnetor, and you won't have the contact heating or failure problems, etc.

 

[wesnewell]

The wire itself can handle a lot more than you may think, but the insulation may melt. Just fro a test I used 24awg plastic insulated telco wire drawing up to ~30A for my battery connection. Don't recall exact time it took to melt the plastic insulation off, but it was under a minute iirc. The biggest problem besides melting the insulation is the voltage drop for thinner wire. I found the chassis wiring values of the chart here to be a good guideline for the minimum wire gauge you should use for battery to controller wiring.
http://www.powerstream.com/Wire_Size.htm
Of course the bigger, the less voltage loss. You can get that value from the app at the bottom. As for phase wires to the motor, well I've never changed the original wiring and have never had a problem. I'm not sure just how much it would improve performance, but I don't image it would be a lot. But if you're looking for maximum performance, every little bit helps.

 

[Bigbikebob]

amberwolf ,
It is a good point about connectors, many people miss that. I already got bullet connectors for 10awg-12awg wire.

wesnewell,
if the insulation start to melt then the efficiency of the system is going in the wrong direction and you are not getting the most out of your current. and that is beside the fact that heat is not good for electronics.

Ff I go by "Maximum amps for chassis wiring" as a guideline then my battery (20Ah 40A 48V) to controller
12awg should be fine, my phase wires are currently 14awg and should be upgraded to handle the current.