Battery power dependent on level of charge?

[6zfshdb]

Wouldnt it be better to just put more P in to reduce sag.
Lot of factors mainly how much you are pulling.

It isn't so much the voltage sag, but rather the loss of motor current as the voltage drops (wattage) that affects performance. As long as the battery voltage is higher than the motor rating, in theory, the buck converter will maintain both voltage and current at a constant level.

For example, a 52V battery cuts out at around 42V, which is higher than a 36V motor rating. In theory, a buck converter should be able to maintain constant voltage and current until the battery LVC cuts out.

As you say, there are many factors involved and it's difficult to know how the controllers on e-bikes would react. Hopefully, I'll get around to doing some experiments in the near future.

With a little design modification, e-bike controllers could do this internally. I know the controllers on some bikes already do, but unfortunately, most don't.

 

[Gionnirocket]

Exactly... I'd rather have a larger battery (more cells in parallel) that will also extend range than adding hardware to combat sag.
Also keep in mind having a lower voltage motor introduces other inefficiencies.

Personally I don't find sag that big of an issue...
YVMV

 

[Mr. Coffee]

...
But.....Im asking for help here...volts is speed, current is sort of torque? but it needs volts for more power.

Extremely sort of.

This is all extremely approximate but I'll try to give a simplified explanation:

Imagine if you take an electric motor and feed a constant voltage. The motor will spin at a certain speed (RPM) for that voltage. Increase the voltage and you'll get more RPMS. You haven't connected the electric motor to anything yet so it draws very little current.

Now imagine you have a wheel attached to the motor and the wheel is spinning in the air at the same RPMS but the motor is now drawing a bit more current.

Put that motor and wheel on a bike and put 100kg of rider meat on the bike and on a level, smooth roadway the wheel still spins at that constant speed but the motor is now drawing even more current.

If that whole system now goes up a steep, rough hill the wheel still turns at the same speed (given constant voltage, again) but the motor is drawing even more current. You can keep increasing the amount of work the system is doing until the motor burns out. Then you can't do any work.

And "work" is the literal technical term here. Under Newton's laws work is force times distance. You need more force to move more stuff a given distance in a given amount of time. If you want to move stuff faster you need more power, because you are doing more work in a given unit of time.