Acceleration at 72v vs 36v?

[SHARKBITEATTACK]

I got a 2808 motor, a 40 amp Infineon controller and a 36v 10ah nimh battery pack. Will acceleration improve when I double the voltage to 72v? Obviously it will go twice as fast. I know with a brushed DC motor when you double the voltage then the motor will draw twice the current. However I'm not exactly sure how the brushless setup works and I think the controller supplies the current and can only provide a max of 40 amps.

 

[Ykick]

Do the Watt math (VxA=W) to see "power" figures.

72V @ 40A = 2880W

36V @ 40A = 1440W

You'll definitely experience power, thus acceleration using 2880W as opposed to 1440W.

 

[Ypedal]

http://ebikes.ca/simulator/

8)

 

[SHARKBITEATTACK]

Do the Watt math (VxA=W) to see "power" figures.

72V @ 40A = 2880W

36V @ 40A = 1440W

You'll definitely experience power, thus acceleration using 2880W as opposed to 1440W.

The thing is I don't think power and acceleration our directly correlated. The way I look at it is horsepower = torque * rpm. So for a given wattage it would be possible to have a lot of rpm but very little torque. For example a 2880v system with a 1 amp controller would also be a 2880 watt system. Idk, could be wrong, just my take

 

[Ypedal]

click on the SIMULATOR above and look at the startup torque at 0 rpm from each setup.

higher voltage = better acceleration, and top speed.

 

[friendly1uk]

If the controller is limiting current then more voltage would not increase current so there would be little gain. What there was would come from the current climbing from nothing (Or back emf) to the limit quicker, but that is a small part of the duty cycle. In my own setup the controller is always limiting current, so I certainly wouldn't see twice the wattage from doubling my voltage until I actually got to the newly found velocity's. Only then would I notice any real difference.

My case is not the norm, but hopefully you can relate to what I'm saying.

 

[speedmd]

I do not know how your controller works exactly to limit the current, but it will most likely also let more amps through when voltage is raised, assuming the battery can supply it. Only way to find out for certain is to pour in the juice.

 

[Ypedal]

but it will most likely also let more amps through when voltage is raised, ...

wrong.

all hub motor , brushless controllers i know of.. are fixed current limited.. regardless of voltage. ( but you do need to have the right controller, that can take the higher voltage )

 

[Ykick]

Maybe compare it to a heater element used to boil water on a stove? Regardless how you get there, Volts/Amps - 3000 Watts applied to heater element will boil a given amount of water much quicker than 1500 Watt element.

Obviously, motors and vehicles present different losses and efficiencies compared to resistive heater elements but the fundamental principle of power still applies. The eBike simulator takes all this and more into account which allows us to enjoy accurate projected performance data.

 

[speedmd]

I looked at the simulator and a bunch of the scenarios are showing most of the 36 v batteries not coming close to reaching the 40 amp limit. Same controller is showing above 40 amps at higher battery voltage. Is the simulator wrong also. My limited experience, the higher the supply voltage, will also sneak through slightly more current also. I would be interested in some real world current limiting you could expect to see with these types of controller.

 

[SHARKBITEATTACK]

click on the SIMULATOR above and look at the startup torque at 0 rpm from each setup.

higher voltage = better acceleration, and top speed.

I will look into it. On a mobile device right now

 

[d8veh]

You get the same current going in to the controller, which is what is limited, but the voltage is twice as high, so twice as much energy goes into the controller. It has to go somewhere. If you look at the commutation pulses on an oscilloscope, they're twice as high, so each pulse has a bigger kick, so surely the torque must be higher, otherwise where does all that extra energy go.
I've done lots of tests on a little hill next to my house. Most of my bikes have 36v batteries. Some cant get up the hill on their own, but when I put a 48v battery on with the same controller, they easily climb it. One bike with a 500w Xofo motor could just make it without pedalling. I increased the voltage to 64v, and it didn't stop accelerating all the way up. These tests show that there is definitely more torque at higher voltage.

 

[lbz5mc12]

I have 36V and 48V going to my rear hub. My bike accelerates faster when I have it switched to 48V. Same controller for both packs. Also more toque.

 

[hjns]

110Nm versus 80Nm is almost 1.5-fold increase in torque. You will definitely feel the difference in acceleration.

 

[dogman dan]

Ai chihuhahua. Hell yeah you will accelerate faster. You don't need the simulator to know, just do it and you will see it is so.

You may not reach top speed in less time than before, but only because the top speed is faster. You'll for sure reach 20 mph fast.

 

[Chalo]

To be clear for the benefit of those who may be perplexed by the apparent conflict with a fixed current:torque ratio of electric hub motors, this increase is the result of increased motor phase current on the output side of the controller, right?

That is, higher energy from increased voltage on the input side of the controller gets translated by the controller into higher current in the motor phases?

 

[hjns]

Probably both. The motor sees the higher voltage as well, and the controller feeds the motor with more phase current, translating in many more Watts. Combination is a 40% increase in torque.

 

[parajared]

I have played with 6s 12s 18s and 24s lipo (22, 44, 66 and 88 volts) and slow speeds 1000 watts at high voltages seems twitchy, but boggier than 1000 watts on low voltages. I'm not sure why this is.