Correct. However, if that higher voltage requires that you run your controller at a much lower pulse width to achieve the same winding current, then you will see higher losses in your controller (specifically higher peak currents and higher switching losses.) So your controller will tend to run hotter if you keep the same motor and go to a higher battery voltage.
I run 4110 mosfets above 100v when my battery is fresh charged, because I charge them lipo 4.25v per cell, sometimes as high as 4.35. I’ve been doing so for years. 18 X 4110 controllers running 24 s up to 105v, and seeing short 25+ Kw acceleration bursts daily. Of course I have had controllers damage, and sometimes they need mosfets replaced a few times before I have a reliable set that last. Yet, once I have one reliable, it is usually good pretty long. I always have a few on the shelves anyway, like all other components and service parts for all of my bikes. That is a basic requirement to ride performance bikes, with strict maintenance schedule of course.
Agreed. I akways have a bike that is more conservative for comfortable long range, reliable transportation. Sport is another story, where components are pushed to the limits and frequently modified or replaced. Performance always have a high cost in parts and maintenance. It is the same with any other kind of motor sports. Yet, when I was riding motorcycles, the inventory was much more expansive and the labour much longer.
Motor heating primarily comes from the current flowing through the motor (phase amps). At different battery voltages, if your controller is limiting motor current to the same amount, the motor heating will be the same.Sunder wrote: ↑Sep 11, 2018 2:46 amAlright, either I'm taking crazy pills here, or some eminent experts in the field have replied, and have failed to noticed that to get his simulation to work, he throttle limited both bikes.
Higher voltages do not cause motors to heat up faster when you're throttle limiting them.
72v @ 12% throttle = 8.64v
48v @ 18% throttle = 8.64v
Coincidence? I think not. The motor is seeing exactly the same "resultant" voltage from PWM because of the throttle setting. From the motor's point if view, it can't tell what battery is attached.
Try the same thing with a load that exceeds the capability of the controller (with throttle at 100%), and see which motor heats up faster:
Correct. For a fixed load (Same speed, same weight, same incline, etc), the controller must maintain speed. Since motors are locked to a KV, to maintain the same speed, they must reduce the effective voltage through PWM.Addy wrote: ↑Sep 11, 2018 10:48 amMotor heating primarily comes from the current flowing through the motor (phase amps). At different battery voltages, if your controller is limiting motor current to the same amount, the motor heating will be the same.
If your higher voltage setup allows you to feed more current to the motor, it will heat up more, but you're also getting more torque.
That's because you are driving the MOSFETs far past their limits. You are eventually ending up with MOSFETs that do not fail immediately under that abuse. Like most components, their failures under overload will fall within a bell curve; you are seeing the small end of the bell curve.
You are pushing this at tad too far, with ‘poor design’ and ‘constant failures’. First, I leave everyone in the dust in the mountain here, and the failures are always the bikes trying to follow me. Once I have a bike tuned and set up, it does require frequent maintenance but it does the ride everytime. If that is poor design, what about all those who didn’t succeed keeping behind me, or didn’t complete the course? That is, all of them who tried.billvon wrote: ↑Sep 11, 2018 6:49 pmThat's because you are driving the MOSFETs far past their limits. You are eventually ending up with MOSFETs that do not fail immediately under that abuse. Like most components, their failures under overload will fall within a bell curve; you are seeing the small end of the bell curve.
Poor design is not "a basic requirement" to ride performance bikes. Indeed, it is something to be avoided by people who value performance over constant failures and degradation.
Exact. Test laps are expansive, when the race is going to be perfect. But, what a feeling when the machine is perfect and you fly with ease and confidence.dustNbone wrote: ↑Sep 11, 2018 8:45 pmIt's just the nature of high performance anything. If you're not breaking stuff, you can probably be going faster.
Race vehicles aren't generally designed with reliability as a priority, sure it's a factor, the thing needs to make it around the track at least occasionally, but there's always a balance somewhere between going fast and avoiding failure.
Finding that balance wins races.