Does"over volting" a brushless direct drive motor result in

[ebikedelight]

Thanks for all the info guys,.


For upgrading the 5 phase wires and 3 sensor wires , coming directly out of the AXLE , to take 72 volts - 40 amps wouldnt 14 gauge wire be thick enough ? The wires they use now, is very thin...

Use 12AWG Silicone or PTFE for better "Punch". On my MXUS 3000W Hub Phase wire upgrade I am actually using 8AWG, and the performance boost is nice.

does it matter if it is stranded or unstranded wire ? I assume it has to be stranded so it is flexible enough to wrap the individual insulated wires tightly around each other in a braid style to reach the controller ?

is this the stuff I need

http://www.ebay.com/itm/12-2-AWG-Gauge-Marine-Grade-Wire-Boat-Cable-Tinned-Copper-Flat-Red-Yellow-40ft-/131447270276?pt=LH_DefaultDomain_0&hash=item1e9ade2b84


also, if i just attach the thicker wires at the exit point of the axle, wont the thinner wires that are still inside the ehub/ axle, be at severe risk of burning up with 72 volts - 40 -60 amp ?

 

[MadRhino]

It does matter if it is stranded, and the more strands the better. Insulation type does matter too, to stand heat and friction.
If the phase wires off your motor are 10 ga, even 12ga, you can keep them. Splicing a better wire not too far, their short length will not make too high resistance, and can stand higher power than you plan to feed. Smaller than 12, it is much better to open the motor and updrade them.

 

[John in CR]

Doing a wire upgrade the lazy way (outside of the motor) has an added benefit in addition to the lower resistance of the larger wire run. That is that it will also act as a heat sink for the short run of thinner wire thru the axle to the termination of the phase windings inside the motor. The larger wire outside will always be cooler, and since copper is such a good heat conductor it will "suck" significant heat out of the short run of thin wire keeping it notably cooler than it would be with thin wire all the way to the controller.

We I do it that way, I leave an appropriate length or the original harness outside the axle to make the splice end up within the drip loop where the transition is easy to hide.

 

[MadRhino]

is this the stuff I need

http://www.ebay.com/itm/12-2-AWG-Gauge-Marine-Grade-Wire-Boat-Cable-Tinned-Copper-Flat-Red-Yellow-40ft-/131447270276?pt=LH_DefaultDomain_0&hash=item1e9ade2b84

Nope, this one, and 8 ga would be much better if you plan higher power upgrade eventually.
http://www.hobbyking.com/hobbyking/store/__9672__Turnigy_Pure_Silicone_Wire_10AWG_1mtr_BLACK.html

 

[ebikedelight]

Thanks for all the help...

not sure how accurate this is :

8AWG 200 amps
10AWG 140 amps
12AWG 90 amps
14AWG 60 amps
16AWG 35 amps
18AWG 20 amps
20AWG 12 amps
22AWG 10 amps


if correct, then 12 gauge should be plenty for my upgrade . I will also mount the controller very close to the motor allowing me to shorten phase wires considerably .

 

[Punx0r]

Those ratings are very optimistic - the usual RC hobby grade ratings. Applicable to short lengths of wire if you don't mind them getting very hot.

 

[MadRhino]

The less current lost in the wiring, the more current fed to your motor and the lower the heat as a bonus. Big wires, big connectors, are making a bike that you can upgrade at will in the future. Then, what a wire is rated for, is not the optimal. There is a short time accelerating from a standstill, when the controller does feed much more than it is set to. Lower resistance is giving full benefit of hard acceleration.

 

[ebikedelight]

The less current lost in the wiring, the more current fed to your motor and the lower the heat as a bonus. Big wires, big connectors, are making a bike that you can upgrade at will in the future. Then, what a wire is rated for, is not the optimal. There is a short time accelerating from a standstill, when the controller does feed much more than it is set to. Lower resistance is giving full benefit of hard acceleration.

sounds logical...upgrading wires is a simple and inexpensive process, so it only makes sense to go with a thicker wire like 8 -10 gauge , which will make a less powerful setup run more efficently and allow a major upgrade in power down the road , without having to redo the wires.

10 gauge should be more then enough to handle 100 amps especially if the wire length is 3 feet or less ?

 

[friendly1uk]

Watts is power. VA=W

Actually... No.
VI=W
VA is a different measurement.

W can be higher than VA, while VA does more work.

 

[wesnewell]

I don't know where you went to school, but Volts times Amps equals Watts, thus VA=W. Always has, always will.

 

[John in CR]

The less current lost in the wiring, the more current fed to your motor and the lower the heat as a bonus. Big wires, big connectors, are making a bike that you can upgrade at will in the future. Then, what a wire is rated for, is not the optimal. There is a short time accelerating from a standstill, when the controller does feed much more than it is set to. Lower resistance is giving full benefit of hard acceleration.

I think you mean voltage not current. There's greater voltage drop with higher resistance. That will cause a decrease in top speed, and will to some extent shift the torque curve, which is created by phase current, but it's root cause is the controller behaving differently due to the decrease in voltage not because higher resistance eats up the current.

 

[chilledoutuk]

People need to remember that Current the flow of electron holes is the result of EMF (Voltage) overcoming the electron flow Resistance.

Outside of superconductors they cant exist independent of each other.

What that means in the same circuit if you want to increase the current you would have to increase the voltage or decrease the resistance or both.

The real key is to check to see if your controller is actually limiting your current as some low KV motors themselves at certain voltages will not hit the current limit of the controller and using a higher voltage will have more substantial gains in this situation.

Experimentation is key really and keep an eye on temperatures to be sure to not fry your controller or motor.

As much as increasing voltage increases power i wonder that if you were to run a relatively low current limit say 25 amps with 72 volts or higher if the motor may be forced to run at too low of an rpm causing it to be very inefficient and get hot.

 

[ebikedelight]

On the subject of resistance, conductivity and overall efficiency when using wires , its interesting to note that there are benefits not only to gauge of wire , and length of wire used , but also in specific material of wire . Not all copper is the same of course.

annealed copper wire having a density of 8.89 g/cm3, 1 meter long, weighing 1 gram, with a resistance of 0.15328 ohms is considered to have 100% conductivity , which is the standard others are measured against . Id imagine most copper wire sold to us consumers for our home projects, may not be of this high grade of copper, therefore we are not achieving 100% conductivity . Silver wire is rated highest with 105% conductivity.

 

[John in CR]

As much as increasing voltage increases power i wonder that if you were to run a relatively low current limit say 25 amps with 72 volts or higher if the motor may be forced to run at too low of an rpm causing it to be very inefficient and get hot.

Using current limiting in that manner generally isn't an issue at all for the motor unless the load bogs it down too much, like on too steep a hill. Acceleration suffers of course, but the efficiency curve ends up very broad and flat. With speed wind motors where that approach is the most effective, it's the controller that is put under stress.

Efficiency is power output divided by power input, and heat created in our is comprised of 2 components, copper losses and iron losses. While iron losses increase with rpm, they're generally low enough to be ignored in this kind of analysis, because copper losses dominate and our motors shed more heat at higher rpm. Copper losses increase by the square of current, ie current squared times resistance. If you're putting 50A through a motor it doesn't matter whether you're getting 200W output at the wheel due to low rpm during the early stages of acceleration, or 2,000W output at higher rpm, that 50A of current will create the same amount of heat in the copper. Hubmotors get hot from the resistance of copper and the current flowing through it. The efficiency % isn't directly related.