I got this from Rew on Vedder’s forum. I always wondered what volts were doing in a motor…turning into amps
"Say the example of my friends… They had a motor doing 50V, 10k RPM. at 200A. 10kW. When they run it at 2500RPM, the motor effectively sees only 12.5V, and assuming the 200A max still holds, the maximum power is only 2.5kW. If the battery is still 50V, the motor fries after a while at 50A battery current (200A through the motor). And the motor will tolerate 300A for a while, but you blow up the 300A ESC after a few seconds of 75A battery current. "
So, what your saying is that less throttle is less voltage and more throttle is more voltage to the motor, not amps?
If thats true, then we need a gear ratio that allows us to run at full throttle most of the time.
And, assuming that neither voltage or amperage are constant, and the throttle determines the esc’s output voltage,
what determines the 3 phase amp draw, load on the motor?
I have a clamp volt/current meter. I’m gonna do some testing on the 3 phase side of the Esc and get back later with my findings.
I’d like to know what u find on that side of the esc and look forward to reading what you find. Does ur meter record? It would be good to get a recording of the results under load. Supposedly lots of spikes and a large difference from what goes in.
The basic thing I’m finding which seems to be widely misunderstood is that increasing your battery voltage doesn’t mean you will run the motor or the esc cooler. You will have a higher top speed, have the ability to kick amps to the motor really quickly. These are the benefits. But when it comes to efficiency the closer you are running to the max speed of the motor (volts x kv) the better. Efficiency means cooler. Cooler means greater continuous power
This is exactly what onloop has been saying all along. gear ratio and voltage so that full throttle=cruising speed.
This can be difficult to achieve because sometimes I like to go 25-28 mph but not always.
I will do some testing and try to post my findings later today or this evening.
Ok, ran some tests using my clamp meter to read voltage and current on the 3 phase going from the Esc to the motor.
What I discovered is that the throttle does indeed control the amount of voltage that goes from the Esc to the motor.
More throttle=more voltage Less throttle = less voltage
With no load on the motor, the current draw form Esc to motor stays mostly constant regardless of the amount of voltage fed to the motor.
I ran these tests with 6s and 12s.
To my surprise, the no load current from Esc to motor was slightly higher with 12s.
1.3 amps at 6s
1.7 amps at 12s
There were momentary spikes in current during rapid acceleration.
And the current did increase substantially as I applied load by squeezing the wheel with my hand.
It did also seem that I was able to ramp up the current more when testing with 12s than with 6s.
Afterwards I went out for a road test, 12s vs 6s.
Climbing the same 10% grade
6s at full throttle went up the hill without slowing down
12s at maybe ½ throttle went up the hill with power to spare( 12s could have gone up faster but I was trying to keep same speed)
Checking the temp of the Esc heat sink, the 12s run made it warmer than the 6s run.
Also to my surprise while going down the hill, the brakes seemed more effective and controllable with 6s
I decided to run the road test again with an inline meter between the battery and dual Esc’s. The results are as follows:
6s:
Esc’s heat sink temps 84deg
Peak Amp draw from battery 37.38
Peak watts 863
Watt-hour use 1.9
12s:
Esc’s heat sink temp: 94deg
Peak amp draw from battery 18.4
Peak watts 898
Watt-hour use 2.1
All road tests where performed with dual TB 12s Esc’s and dual TB 6355/230kv motors 16/36 gears and 90mm wheels
After running these tests, I’m not so sure that 12s is such a good idea even with dual motors. Although higher voltage = less amps on the battery side of the Esc, it’s appears to be a different story on the motor side.
I was not able to test current on the 3 phase during road tests but it did seem evident during bench tests that more voltage = more current, not less. Guess thats the difference between DC current and 3 phase AC current.
This could very well be the source of our problems with overheating Esc’s
Double amp draw from the battery with 6s but I’m not so sure about the amp draw from the esc to the motor.
I need to extend one of the 3 phase wires so I can measure the amperes while riding to get a real comparison.
This is excellent…This is the start of finding a good standard for what Voltage, ESC and Motor combo would be most ideal under various riding conditions.
Now that I know for a fact that the Esc regulates the amount of voltage to the motor. I think that we have the right battery voltage when we can go full throttle confidently. I have not been able to do that with 12s.
With my setup I should be running 8s or 10s
Seems like handing the Esc 50 volts and then only allowing it to pass 20-30 volts on to the motor causes it to overheat. This is a whole new train of thought for me.
I’ve got some 14t motor pulleys coming tomorrow. I’m gonna swap out my 16t with them so I can feed more voltage to the motors and spin them faster to create more hp without having to go faster. During my bench test it seemed that the faster the motors turned, the more load I had to put on them to make the amps go up.
Because the motor spinning faster does not increase amp draw. Only applying load does.
U have so much info it’s easier for me to do this:
Ok, ran some tests using my clamp meter to read voltage and current on the 3 phase going from the Esc to the motor.
What I discovered is that the throttle does indeed control the amount of voltage that goes from the Esc to the motor.
More throttle=more voltage Less throttle = less voltage
if u hold the throttle till the motor fully spins up does the voltsge reading go down or stay the same?
With no load on the motor, the current draw form Esc to motor stays mostly constant regardless of the amount of voltage fed to the motor.
I ran these tests with 6s and 12s.
To my surprise, the no load current from Esc to motor was slightly higher with 12s.think that’s normal as its a higher speed with the 12s right?
1.3 amps at 6s
1.7 amps at 12s
There were momentary spikes in current during rapid acceleration.
And the current did increase substantially as I applied load by squeezing the wheel with my hand.
It did also seem that I was able to ramp up the current more when testing with 12s than with 6s.
Afterwards I went out for a road test, 12s vs 6s.
Climbing the same 10% grade
6s at full throttle went up the hill without slowing down
12s at maybe ½ throttle went up the hill with power to spare( 12s could have gone up faster but I was trying to keep same speed)great test isolating the voltage
Checking the temp of the Esc heat sink, the 12s run made it warmer than the 6s run.which test first? Maybe leftover heat? Actually this makes sense as esc work less on full throttle
Also to my surprise while going down the hill, the brakes seemed more effective and controllable with 6s setting could change this right?
I decided to run the road test again with an inline meter between the battery and dual Esc’s. The results are as follows:
6s:
Esc’s heat sink temps 84deg
Peak Amp draw from battery 37.38
Peak watts 863
Watt-hour use 1.9
12s:
Esc’s heat sink temp: 94deg
Peak amp draw from battery 18.4
Peak watts 898
Watt-hour use 2.1
It it makes sense that the 12s would use a bit more watt hours as it’s riding at a much lower percent of the no-load
All road tests where performed with dual TB 12s Esc’s and dual TB 6355/230kv motors 16/36 gears and 90mm wheels
After running these tests, I’m not so sure that 12s is such a good idea even with dual motors. Although higher voltage = less amps on the battery side of the Esc, it’s appears to be a different story on the motor side. **. its the trade off giving up low speed efficiency for the possible high speed and quick power. it’s worth it to me. Nice to see its not that inefficient considering how much higher the no-load is with the 12s than 6s. I’ll gladly give up a bit of range for the much greater top speed. **
I was not able to test current on the 3 phase during road tests but it did seem evident during bench tests that more voltage = more current, not less. Guess thats the difference between DC current and 3 phase AC current.
This could very well be the source of our problems with overheating Esc’s
The greater watt hours to get up the hill was pretty insignificant on 12s and the esc heating is likely the fact it’s being held to half throttle
would this explain why running those 190kvs at 12S unloaded on my bench gets the motors so damn hot but hauling ass down the trail doesn’t get them quite so hot? I’m going purely based on touch, i still need to invest in an IR thermometer, but the fact that i can keep my hand on them probably means they’re fine.
also one easy way to get your VESC to drive your board at grandma’s bicycle speed is to limit your current to something low, it will accellerate slowly and the top end will be slower.
and NOT limiting your current to something reasonable is a great way to make a board almost unridable do to the never ending accelleration issue, but that’s also tied into proper throttle signal tuning as well.
I prefer my boards to have a smooth and predictable acceleration curve as well as the same for braking, and in my experience this means tweaking the current limiting for each board’s battery and motor configuration. ITs possible to have some crazy top end without launching into a tree the minute you stand on the damn thing, and its possible to have it set up to where you can easily cruise at half throttle and have that be your fun/cruise speed and still have plenty of throttle left so you can floor it and harass the cyclists by getting into the low 30’s mph wise.
Weird they’d get hot on the bench. There should barely be any amp draw on the bench regardless of the voltage. The amp draw should be a bit more with no-load at 12s but still as namasaki showed its not much.
For some reason whenever I try to do a no-load test using the vesc on the pc by choosing an rpm on the right side of the screen it spins quickly and then stops. Maybe try duty cycle or something?
Namasaki how’d you get such detailed no-load amperage?
I run 12s with 90kv and amps set to 60 on FOC. It’s great but there’s the overheating risk but it’s worth it
Both 6s and 12s 3 phase amperage bench tests where conducted at full throttle.
But remember that the current stayed constant regardless of the amount of throttle or Rpm
it only spiked momentarily if throttle was increased quickly. Once the rpm leveled out, the voltage returned to the constant.