14 gauge wire current limit.

[mvly]

What is the maximum continuous current limit on a 14gauge wire about a one foot in length with 48V input and Teflon coating insulation?

doing online research on this topic, I came across this site that provides a pretty detail description of what is expected.
http://www.zetatalk.com/energy/tengy10s.pdf

If I assume a 3% loss voltage loss (really it's a lot less). I should be OK up to 45Amps if the wires are only 1 foot. The graph does not show it, but you can extend and it should come out to be around 0.3Amps for 12V with 3% V drop at 45Amps. But since I am running it at 48V, it should be really 4*0.3 or 1.2 feet. Now that is probably max.

here is the quick math on the voltage drop. If I have 1 foot, resistance is linear so from wiki on AWG wire, it should be 2.525Ohms/1KFT or 0.002525Ohms and at 35A, V=IR = 0.088375

Vres/Vsys = 0.088375/48V = 0.00184 or 0.18% loss. Of course this is ideal, so it should be really 1% just to be conservative.

So here is my real question. Since I plan to run at 35A, I should be pretty much on the clear right?

other notes are: Amps should not exceed ampacity, but since I am only running this at 1 foot, I might be able to ignore this fact or at least fudge it a bit?

 

[liveforphysics]

A billion amps would be fine for a billionth of a second.

A single amp would mean certain failure in an insulated enviroment or a vacuum.


In other words, it depends strictly on the application. On an Ebike, 14awg could do OK with a 90amp controller, or smoke on a 30amp.

 

[dogman dan]

This is the last foot that goes into the motor right? I've run 5 ah through similar wire at 3000w with no particular problem. You just gotta make the ride short. Melting stuff may be more related to the actual temp of the axle than the wire resistance with just one foot of it. In any case, you need short duration, or less watts.

 

[bigmoose]

Perhaps this table is what you gentlemen are looking for:
View attachment 1

Now if you want more, everything you need to ever know about wire ampacity is in the following graphs from MIL W 5088L, those old mil standards had a lot of good in them if you know where to look!

 

[grindz145]

I run about that on a 16 gauge wire to the hub. I only give it bursts to 40a here and there though, for the most part I'm under 20A (battery current of course) That seems to work just fine. I'd say you're OK unless you ride the current limit.

 

[mat h physics]

An electrician once told me, "If you can keep it cool enough, the current can be infinite".

Increase in temp, will cause an increase in resistance, which will cause an increase in temp

I think what you are trying to ask is, at what temp will the wire insulation remain intact. Or somewhere along the lines of what amount of energy can be radiated at what current.

The density of copper is an asset relative to aluminum. Though the aluminum has less resistance, silver has even less.

Anyone ever find silver clad copper magnetic wire? 8)

Good insulators usually hold in heat as well as electrons.

 

[auraslip]

You can use my spreadsheet to see how much power you are losing by using 14 awg.

People often talk about how much power a wire can HANDLE, but IMHO the real issue with a battery powered electric vehicle is how much power you are losing. Battery capacity is expensive. Thick cables aren't.

 

[liveforphysics]

You can use my spreadsheet to see how much power you are losing by using 14 awg.

People often talk about how much power a wire can HANDLE, but IMHO the real issue with a battery powered electric vehicle is how much power you are losing. Battery capacity is expensive. Thick cables aren't.

Yep, this is the truth. It's really really stupid to waste your pack's energy in heating up wires. All the wire heating in the world doesn't make your bike go any further or any faster, but it does drain your pack.

If you use good supple cables, you will NEVER regret over-sizing the wiring.

 

[mvly]

Thanks for all the reply. And thanks for the spreed sheet. The reason why I ask is because if I run too much current through the 14 guage wires while the motor is hot, it might melt the insulation and screw up the motor. It has happened to me before, but there is many factors that might screw the motor so I can't say for a fact that it was the current going through the wires that destroyed my first motor. It was probably a contributor, but probably not the sole source.

both motors are the same, BMC V3
First motor: 35A at 48V - died due to melted insulation between wires. Currently in the procress of being fixed with silver coating copper core with telfon coating 14 gauge wires. These I know are rated at 35A for short running. Probably < 3 feet in length.
Current motor: 30A at 48V - still going strong. Opened it up after 2 weeks of full throttle at 30A and no sign of melting insulation that I can see.

Essentially what I am getting at is I want to know the max current that I can push through these wires without the resistance causing the wires to heat up too much to melt the insulation (Teflon insulation). Moreover, I would like to run it at that current for essentially until the battery is drained.

I have tested 35A through the motor before and essentially until battery is drained and everything still worked. But that was mostly on flats. However when going up a hill, which probably put a lot more heat out vs kinetic energy, the motor died.

 

[gensem]

+1 for the spreadsheet... Very nice.

You can use my spreadsheet to see how much power you are losing by using 14 awg.

People often talk about how much power a wire can HANDLE, but IMHO the real issue with a battery powered electric vehicle is how much power you are losing. Battery capacity is expensive. Thick cables aren't.

 

[mvly]

On the topic of silver wires. Is there any benefit in running silver coated copper core wires vs full silver core wires? My guess is the solid silver core wires will be better, but how will they do under heat and high current.

 

[bigmoose]

For info: Silver or tin plating is used to protect bare copper from heat and chemical accelerated oxidation. Silver is used instead of tin for high temperature applications. In aerospace we use crimp connections as they are more reliable than soldered, when vibration is considered. For high temperatures silver coated copper makes a "nice," stable, low ohm crimp connection.

 

[auraslip]

Those BMCs had lots of problems with the wires. Best bet is to due 8awg as close as you can to the hub, and large 8mm or 5.5mm bullets. Hopefully that'll be enough of a heat sink to keep the wires in the axle from melting.

 

[mvly]

Those BMCs had lots of problems with the wires. Best bet is to due 8awg as close as you can to the hub, and large 8mm or 5.5mm bullets. Hopefully that'll be enough of a heat sink to keep the wires in the axle from melting.

well that is the problem with putting 8 gauge wires at the opening in the axles is that while it does allows a lot of current to be pushed to the small 14 gauge wires, it doesn't take away the fact that you still have 14 gauge wires to the motor.

Think of it in analogy with a highways. You have a one lane highway in each direction, but it's only for a few blocks. Then you have a 3 lane highway in each direction a few miles in length connected to the one lane highway in each direction. Even though you have the 6 lane highway, cars eventually you end up at the 2 lane highway. There will be traffic at the 2 lane highway if you push too many cars on the 6 lane highway. However, that grid lock might be really short (3 blocks only) but it might be enough to destroy the 2 lane highway.

The goal is to find the most number of cars to push through the 6 lane highway such that it does not cause a grid lock in the 2 lane 3 block length highway.

 

[vanilla ice]

42amps.

 

[auraslip]

well that is the problem with putting 8 gauge wires at the opening in the axles. It allows a lot of current to be pushed to the small 14 gauge wires.

oh man, luke is gonna have a blast with this one :?

 

[mvly]

42amps.

Have you extensively tested this fact?

 

[vanilla ice]

Yes. And my supercomputer comes up with the same.

 

[vanilla ice]

Hrmmm it also gives me 42 for the question of 16awg wire amp capacity.. but seriously for short bursts 14 will handle it.

 

[mvly]

Hrmmm it also gives me 42 for the question of 16awg wire amp capacity.. but seriously for short bursts 14 will handle it.

Well I am looking for a current that I can run continuously until the battery is drained. I know 14 gauge can handle this current in short burst. Do you have the max continuous current for 14 gauge wire? I have ridden at 30A continuous and no problem so far. So i know it has to higher than that.

 

[liveforphysics]

Hrmmm it also gives me 42 for the question of 16awg wire amp capacity.. but seriously for short bursts 14 will handle it.

Well I am looking for a current that I can run continuously until the battery is drained. I know 14 gauge can handle this current in short burst. Do you have the max continuous current for 14 gauge wire? I have ridden at 30A continuous and no problem so far. So i know it has to higher than that.

#1. Why do you not want bigger wire?

#2. If it's the phase lead going through the axle of a hub motor that you're talking about here, keep in mind battery current is NOT phase current. Motor phase current can be 100amps while battery current is 10amps. Your controller can not see phase current, only battery current.

 

[amberwolf]

As LFP says, the phase currents you're seeing at that 30A (battery current, presumably) continuous is probably a lot higher than 30A.

Remember also that if you are talking about the phase wires into the motor, the capacity will change as the motor heats, because the wires themselves can then dissipate less and less heat from themselves into the motor and axle, and must then conduct the heat to the outside before it can be shed. At some point, the motor itself is probably hotter than the wires, and they begin *absorbing* heat from the motor, rather than radiating/conducting any of it into the motor.

Then the only way the wires can shed heat at all is to conduct that heat outside the axle, into the flow of air past the bike. The more concealed those wires are, covered in layers of insulation jacket/sleeve/heatshrink/etc., the less of that heat they can shed in that airflow. That's the point at which the wires inside the axle and/or motor are more likely to suffer insulation failure.

Hrmmm it also gives me 42 for the question of 16awg wire amp capacity.. but seriously for short bursts 14 will handle it.

I'm pretty sure it would work even better with your towel. Especially when wet.

 

[mvly]

Hrmmm it also gives me 42 for the question of 16awg wire amp capacity.. but seriously for short bursts 14 will handle it.

Well I am looking for a current that I can run continuously until the battery is drained. I know 14 gauge can handle this current in short burst. Do you have the max continuous current for 14 gauge wire? I have ridden at 30A continuous and no problem so far. So i know it has to higher than that.

#1. Why do you not want bigger wire?

#2. If it's the phase lead going through the axle of a hub motor that you're talking about here, keep in mind battery current is NOT phase current. Motor phase current can be 100amps while battery current is 10amps. Your controller can not see phase current, only battery current.

1) axle diameter will not allow for larger wires.

2) thanks for making it clear that phase current is not the current controller sees.

If the phase current is likely to be much higher than battery current then i am going to say that 14 gauge wires can handle much higher current than 42a.

I guess to really answer the underlying question, I will need to try it out myself.

 

[amberwolf]

i am going to say that 14 gauge wires can handle much higher current than 42a.

Yes, they can... but as has been pointed out more than once, it depends on the thermal conditions around them, as far as how *long* they can handle that current.