This has now become the Hummie vs Devin (Volts conversion to amps) - #142 by SimosMCmuffin - General Discussion - Electric Skateboard Builders Forum | Learn How to Build your own E-board topic.
But all in all it can be summarised in this
[quote=“devin”]
See how those values flip in the steady-steady example but stay the same in the pulsed-pulsed. The terminology confuses people.
If you have the same battery energy capacity and the power stays the same, it will empty that battery in the same time without care for the amps if the power is the same.
Then I guess we’re assuming variable power as well. The main point of stating that higher voltage leads to less amps is so people don’t burn out their components with heat. This is something I still believe.
Ok. This is only applicable with the MOSFETs heat loss and not the motor’s heat loss. The ESC will run cooler with a high voltage battery and low kV motor. If you don’t change the motor’s kV, but up the voltage then you also increase the amperage and increase the I^2*R power losses in the MOSFETs because your load resistance stays a constant.
All in all, I don’t understand why people don’t use math to prove they’re right… I am a student at a university in Finland, studying for my bachelor’s degree to become an electronics engineer. I also have a long time of electronics hobbying under my belt so I know how to use the math to prove my points.
yeah @SimosMCmuffin is right. a lot of people throw around the “more volts is less amps” line around here and its not entirely true.
in most of our cases more volts does work out to be less amps because we also run lower kv motors with the more volts. and that is not to be overlooked.
I mean, I did mention that it is somewhat of a misconception way earlier in the thread.
the equations become incredibly complex once you add variable throttle and wave duty cycle into the mix.
but it is safe to say as far as our build are concerned you can use the rule of thumb that more volts will lead to less amps.
Then why did you still use flawed examples, which I proved to be wrong?
I fully admit to being a dick, but I’m the good kind.
If you have false understanding of how things work and you go ahead to a practical testing, you will not get the results you expect to get. I’m here to explain why you’re wrong and I use example calculations to prove it. It’s a dickish thing to do, but it will save you from unwanted monetary/time investments when you then have to buy the right components to get the expected results, or use time to setup your gear in the right way.
I’m being a dick, for your own good. If you can’t think rationally and analytically enough and when someone argues with the correct math behind him/her. Do you get angry or do you thank the person for saving you from useless purchases or needless work?
YES, higher voltage can = lower current! But just increasing voltage and ignoring other factors doesn’t guarantee lower current or less heat.
Because high current/heat in the motor is determined by increasing load. So you must consider that the voltage, motor kv and gearing together decide what current you need for a given amount of torque. Higher gearing reduction mechanically amplifies torque, which reduces load & current & heat.
So actually what is most important is to design a drive system optimized for your desired max speed, which should be the maximum speed the motor can reach with the available battery voltage. Also, it’s worth noting that simply running high voltage and only using half throttle doesn’t help.
if you gear for high top speed (or use high kv hub motors) the losses will be higher even at low speed since current is what causes the heat, and at low speed you will have higher current and lower motor voltage for a given torque than you would with gearing for lower top speed.
People need to start thinking about esk8 system not as sperate unrelated components, they must design and build complete system that are designed for optimal performance & ideally aesthetics and practicality too
Couldn’t have said that better myself! For example, 8s and 245 kv with 14 and 36 teeth and 83mm wheels will give you the same top speed as a raptor (10s, 190kv, 15 and 36 teeth, 83m wheels) but at the cost of higher rpm. High rpm is inefficient and therefore the raptor would be the better setup. The only benefit to the 245kv setup would be that you would have the benefit of having a much higher top speed is you when 12s but again there is high rpm. In the end, the raptor is more efficient than the 8s 245kv setup.
Exactly!
It’s too bad that people get confused with this stuff.
For example my current board specs are: 4S, 149kV, 19T MG, 30T WG and 80 mm diameter tires and I get about 21 km/h on flat at 100% duty
I have a metal MG (motor gear) planned with only 15T, so I would expect my top speed to drop to: v = (15T / 19T) * 21 km/h = 16.6 km/h or a bit higher due to more mechanical torque due to higher gearing, but because ~17 km/h is too slow even for me, I’m going to upgrade the battery to 6S to get more top speed.
And then accounting the new battery voltage my new top speed would be: v = (6S / 4S) * 16.6 km/h = 24.8 km/h or a bit lower as the needed torque increases. So I’ll be using more power in total to run, but at higher speed.
If that is true then that means 12s is not efficient for the VESC cause the difference in in efficiency because of heat dissipation is around 15-18%(only 65% efficient) slower speeds. It was off by 3 miles from what you said you got with 10s(this with 80% efficiency cause of load).
You will be fine if you have low enough KV. I ride a 12s everyday on the om5065 200kv motors but they are actual 200kv windings. I have seen a lot of other motors with higher kv values than advertised so be sure your erpm does not get too high.
Yes mine says it’s a sk3 149kv or I could use the motors I got from you. Thanks
I don’t think anyone makes a BMS for 11s
bestech does! http://www.bestechpower.com/407v11spcmbmspcbforli-ionli-polymerbatterypack/BMS-D163.html
You posted this chart previously based on the Vesc having a 60000 erpm limit. 8570 RPM ---------------/50v = 170kv - 12s ---------------/42v = 200kv - 10s ---------------/33v = 260kv - 8s ---------------/25v = 340kv - 6s What changed?