Hello, I'm new to All About Circuits and I'm hoping someone might be able to help with a battery wiring question. I have an off road mobility scooter with 4 x 750w brushed motors. They are powered by 2 x new 24v LiFeP04 batteries each capable of 50 amp continuous discharge. For everyday use this is fine but when taken on steeper slopes the scooter grinds to a halt. As far as I can tell it is the BMS on each battery restricting power output and I need more battery power. I have the space to fit one more 50amp battery but want advice on how to safely wire it in. There are separate connections to each of the 2 x existing batteries and they join together (positive to positive / negative to negative) to a single positive/negative wire powering the scooter. Could I simply wire the extra battery in parallel to one of the existing batteries so long as I balance the voltage on each battery?

 

BeforeI provide any suggestions have you investigated what actually is happening?? It might be that the drive system is reaching a shutdown limit, in which case more battery power will not help.
So what you need to do is check the specifications of the drive control system, and the drive motor specification. Consider that both the motor and the drive control also have limitations. Have you checked the battery voltage whaen the scooter"grinds to a halt"?? My concern is that it is entirely possible to supply a motor with enough power to burn it up.

 

Thanks MisterBill2, thanks for the advice. I'll go away and find out the information and add to this post.

 

BeforeI provide any suggestions have you investigated what actually is happening?? It might be that the drive system is reaching a shutdown limit, in which case more battery power will not help.
So what you need to do is check the specifications of the drive control system, and the drive motor specification. Consider that both the motor and the drive control also have limitations. Have you checked the battery voltage whaen the scooter"grinds to a halt"?? My concern is that it is entirely possible to supply a motor with enough power to burn it up.

In addition to that, I'd like to say that if the scooter is cool, full battery, and then you throttle to the maximum at the hill and it still halts, it might be the limiting power by the driver. If it's not cool (you've been riding for a while) and then you go to the hill and it halts, it might be temperature limits.
But bear in mind that as MisterBill2 said, it can be various problems.

 

BeforeI provide any suggestions have you investigated what actually is happening?? It might be that the drive system is reaching a shutdown limit, in which case more battery power will not help.
So what you need to do is check the specifications of the drive control system, and the drive motor specification. Consider that both the motor and the drive control also have limitations. Have you checked the battery voltage whaen the scooter"grinds to a halt"?? My concern is that it is entirely possible to supply a motor with enough power to burn it up.

Hello @MisterBill2, I've gathered the info. Hopefully this will give you a better idea of the scooter setup.

The motor controller is a S.Drive Series 200amp (spec sheet attached)

Key Specifications

• • Brand/Manufacturer: PG Drives Technology
  • Model Number: D51448 (S-Drive Series)
  • Input Voltage: 24V DC
  • Maximum Current Output: 200 Amps

The electric motors are Electrocraft MP36 24v motors (spec sheet attached)

Key Specifications & Information

• Series: ElectroCraft MP36 MobilePower™
• Motor Type: 4-Pole Permanent Magnet DC (PMDC) Brush Motor
• Gearbox: Right-Angle Worm Gearbox
• Key Features: High starting torque, manual release brake option, and durable design for uneven terrain.
• Operating Voltage: 24 VDC.

I took the scooter out this morning to check the voltage under load. The unloaded voltage was 26.3v. When it stalled on a steep slope the volts dipped to 25.1v

Thank you for your help.

 

So I can say it`s not a worn battery, the internal resistance is still low enough under the highest load. Just one problem cut out of the many.

 

So I can say it`s not a worn battery, the internal resistance is still low enough under the highest load. Just one problem cut out of the many.

Thank you @kiroma