Battery voltage in relation to controller and motor voltage

[leakimc]

Hello,

If my setup has a 36V 15A controller and a 36V rear hub motor, is it recommended to also have a battery unit rated 36V (20Ah)? Are there issues that could arise from using a 48V 15Ah battery with a 36V controller and motor? Also, if I were to choose a 36V 20Ah battery, the 20 amp hours aren't a problem with the 15 amp controller right?

Thanks.

 

[lnanek]

Ah is the battery capacity. A 20Ah capacity battery will last longer under use at the same current than a 15Ah capacity battery. E.g. 20Ah / 15A = 1 hour 20 minutes vs. 15Ah / 15A = 1 hour.

A is the max current. The Ah capacity isn't really related to A max current of the battery pack. It could be made of low max discharge cells or high max discharge cells. There could be more or less cells in parallel to add both capacity and max current.

The controller's max discharge rating in A should be less than the battery pack's max discharge rating in A, otherwise the Battery Management System will turn off the battery pack when you go full throttle.

 

[docw009]

"Are there issues that could arise from using a 48V 15Ah battery with a 36V controller and motor?"

Yes, you could kill the controller. There are components inside it that are voltage sensitive. These include the electrolytic capacitors, the can shaped objects in the pictures. They come in various ratings, but 63V capacitors are in 48V controllers and 50V capacitors are in 36V controllers. They save a few pennies using 50V caps. A 48B battery is 54.6V at full charge. Running a 50V cap that high will shorten its life.


Sometimes, they use 63V caps in a 36V controller. Then you can overvolt it w/o the capacitors failing. Something else might fail though. These designs often have parts that overheat with time even with the design voltages.

If you're willing to experiment, blow things up, and replace them, then you might overvolt your controller. Long term, if you're building an ebike, or simply replacing the battery on an existing bike, I'd suggest staying within the original design intents,

 

[fill]

Hello,

If my setup has a 36V 15A controller and a 36V rear hub motor, is it recommended to also have a battery unit rated 36V (20Ah)? Are there issues that could arise from using a 48V 15Ah battery with a 36V controller and motor? Also, if I were to choose a 36V 20Ah battery, the 20 amp hours aren't a problem with the 15 amp controller right?

Thanks.

If you have a dual voltage controller- no problem, simply pulling one battery and inserting another will cold reboot the system and it should recognise the new battery voltage straight away, just ensure you allways charge the 48v battery well over 42v to avoid confusing the controller, and i may take a couple of resets on occasion..

your controller label will have 36v/48v in large print and at the top of the information it provides if its a dual voltage controller.

If its a single voltage 36v only controller as most pre fitted to bike controllers are.. Its easy enough to source a dual voltage controller as long as its the standard silver box format. More compact formats such as down tube options or within battery slide housing formats tend to be single voltage however, due I assume to space limitations.

dont confuse the batteries charge capacity measured in amp hours with its max drain rate measured in Amps, Just ensure your selected controller will require LESS amps at peak power, than your battery/BMS can accommodate. (Max drain, while a battery cell property, its also a cap limited by the BMS so is often published as a BMS metric)