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Old 04-11-2017, 03:12 PM   #241 (permalink)
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I believe it is much more complicated than that as our electric motors are not linear in behavior and the pick efficiency spot changes with voltage and amp.
Probably most ESC's throttle is not linear as well...not sure

You can play a bit in this calculator to learn more:
http://www.bavaria-direct.co.za/constants/

Play with the efficiency calculator
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Old 04-11-2017, 04:00 PM   #242 (permalink)
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It's not the efficiency that I'm concerned with but the actual strain on the ESC. I just want a simple way to estimate what kind of mid-throttle amperage I can have without blowing the ESC for a given amp rating.
Say I have a 150 amp-rated ESC... Would this be able to handle half throttle at 100 amps or would that go over the limit so it'd risk damage due to it becoming 200 amps for some reason(that I don't quite understand)?
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Old 04-11-2017, 04:42 PM   #243 (permalink)
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No that high amp cannot happen at low throttle:
First if you lower the V you lower motors rpm and lower the speed so the power goes down.

Second way to look at it is ohms law:
V= I*R hence I= V/R
R is a constant of your system so if you use lower V max I will also go down, and so does total power.

Power goes up with more throttle giving more V and therefore more I and P.

And finally to be specific - working at lower throttle is harder on the esc especially is it doesn't have active free wheeling. It mainly produces more heat. If yours can take it or not depends on ventilation , heat sink, esc rating and build, ambient temp etc.
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Old 04-11-2017, 07:12 PM   #244 (permalink)
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I get that half volts= half speed and half power but what I'm not sure of is how many amps a 100 amp ESC can handle at half-throttle. Is 50 amps the limit at half throttle for a 100-amp ESC?(ignoring burst, I just mean continuous usage)

The problem with that motor calculator is that it wont let me set the battery voltage and then test varying throttle amounts.
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Old 04-12-2017, 02:10 AM   #245 (permalink)
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I am sorry but there is no straight answer to your question it's hard to tell how much amp it can suffer at partial throttle.
I agree regarding the calc they have changed it recently but it can still be done by playing with the input v
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Old 04-12-2017, 09:23 AM   #246 (permalink)
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Not knowing what your application is, I would simply say that running any setup at low throttle continuous is slightly foolish and you should really either re-gear it or switch to a lower kV motor.
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Old 04-12-2017, 01:06 PM   #247 (permalink)
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Quote:
Originally Posted by prototype3a View Post
Not knowing what your application is, I would simply say that running any setup at low throttle continuous is slightly foolish and you should really either re-gear it or switch to a lower kV motor.
I think its for E-bike so he wants full speed range with the ability to use low throttle when needed, without a gear.

It can probably be done with the right ESC: either a very high over-kill amp ESC, or one which has free- wheeling like YGE/yep/scorpion/HW.

I believe I have seen some of my friends do that. but they ride fast most of the time.
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Old 04-12-2017, 01:13 PM   #248 (permalink)
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For e-bike, you want that open source ESC (I've completely forgotten what it's called) as it supports sensored and sensorless FOC which is ideal for low rpm starting and stopping.
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Old 04-12-2017, 03:53 PM   #249 (permalink)
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An E-Bike is what I'm trying to do and I've seen some DIY E-Bike setups from Endless-Sphere forums doing things as simple as putting sandpaper on the can of an outrunner and putting that directly on a tire but that wont work for me because I have lots of hills where I live. I'm currently looking at Leopard motors and thinking about using a 1" friction drive roller that's sold as part of an ICE motor bike conversion kit.

The problem is that I also wanted a 20mph top speed and that requires 175kv at about 40volts but to go up hills without amp overkill I'd have to gear it to 4/1 rpm for 5mph up the hills, assuming no greater slope than 23 degrees.

If an ESC could just let me go up hills at 25% throttle with 80 amps instead of the 20 amps I'd use for topspeed(probably less) then I would have just gotten a HV 160Amp ESC but it seems that would cause 200+ amps to be drawn or something crazy like that.

I was also wondering about continuously variable transmissions, maybe that could solve my problem if I use a V-belt?

And another concern of mine is the Lipo VS LiFe battery situation. I found some LiFe battery packs with BMS from Bioenno Power but I can't find Lipos with them and the LiFe ones have horrible 40milliOhm resistances that drop the efficiency by 15% or more the higher your amps are. I just found this out messing with that motor calculator posted in this thread.
I like the safety of LiFe but the LiPos can be 3milliOhms or less resistance making a significant efficiency difference.

Pretty big mess here, feel free to take a jab at any part of it. Much appreciated.
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Old 04-12-2017, 07:21 PM   #250 (permalink)
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I think the point you're missing is that from kV you can calculate kT and the units for kT are torque per amp. There is no way to get around the fact that a certain amount of torque is going to require a certain amount of amps reguardless of the "throttle" or equivalent average voltage.
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Old 05-04-2017, 01:51 PM   #251 (permalink)
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Quote:
Originally Posted by prototype3a View Post
Not knowing what your application is, I would simply say that running any setup at low throttle continuous is slightly foolish and you should really either re-gear it or switch to a lower kV motor.
Theres an exception to this when running an active freewheel esc governed.

my yep esc ungoverned would be too fast at 80% throttle for my needs but with goberner enabled 80% throttle brings it down to 3200RPM (non goverend above 3600)

my lowest throttle is 65% for 2800RPM and the esc is barely warm, flight times go up.

with non freehweeling esc's from what ive read should be run in the 80% abvoe range otherwise there not efficient
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Old 05-04-2017, 04:45 PM   #252 (permalink)
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The 80+ percent is not about efficiency. It's about heat.
AFW esc produces less heat at low throttle, where non AFW might fail especially if stressed.
But if your throttle is in the range you wrote lowering your gearing will increase your times. You are not in the efficient range regardless if you have AFW or not
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