A few years ago I decided to build a golf trolley that had cruise control. The objective was that the golf trolley could be set at walking speed and it would maintain this speed regardless of the terrain or gradient and therefore did not require constant manual speed correction. To achieve this I learnt about Pic microcontrollers and how to program in assembly language. More as a hobby I have refined the program over the years and recently decided to increase the frequency of the PWM to reduce the groaning noise at low speed from the 12volt 150 watt Lemac brushed DC motor. I am using a Pic 16f873a with the oscillator running at 6MHz. The PWM frequency is currently 366Hz and although noisy does work perfectly.
Increasing the PWM frequency to around 5400Hz by reducing the Timer2 prescaler from 1:16 to 1:1 results in a significant reduction in the level of noise and seems to make the trolley more responsive to speed adjustments.
My problem is that I am using a Tracer Lipo 30A battery and as soon as I put the trolley under any sort of load the battery BMS turns off completely. I then have to disconnect the battery and reconnect it for it to come back to life.
If I return the PWM to 366Hz everything works perfectly and it is impossible to turn the BMS off by putting the trolley under severe stalling load. The same cutting out problem occurs if I increase the frequency to only 1400Hz.
The output stage uses 3 x IRL540n in parallel. There is a diode across the motor to prevent a back emf if the trolley is pulled backwards.
I am interested to understand what is going on here and is there anything I can do with the circuit design to prevent this happening? May be a smoothing capacitor of some sort?
I obviously don’t have access to the BMS in the battery.
I do have a second Lipo golf battery which does not suffer from the same problem and works perfectly.
Any advice would be welcome. Thanks for taking the time to read through this.
Increasing the PWM frequency to around 5400Hz by reducing the Timer2 prescaler from 1:16 to 1:1 results in a significant reduction in the level of noise and seems to make the trolley more responsive to speed adjustments.
My problem is that I am using a Tracer Lipo 30A battery and as soon as I put the trolley under any sort of load the battery BMS turns off completely. I then have to disconnect the battery and reconnect it for it to come back to life.
If I return the PWM to 366Hz everything works perfectly and it is impossible to turn the BMS off by putting the trolley under severe stalling load. The same cutting out problem occurs if I increase the frequency to only 1400Hz.
The output stage uses 3 x IRL540n in parallel. There is a diode across the motor to prevent a back emf if the trolley is pulled backwards.
I am interested to understand what is going on here and is there anything I can do with the circuit design to prevent this happening? May be a smoothing capacitor of some sort?
I obviously don’t have access to the BMS in the battery.
I do have a second Lipo golf battery which does not suffer from the same problem and works perfectly.
Any advice would be welcome. Thanks for taking the time to read through this.