I'm using a BTS7960 module with an Arduino to adjust the voltage for my DC motor.
When I check efficiency there is a problem. PWM efficiency is supposedly about 90% but mine is only about 50%.
I have a 7S3P 29V li-ion battery and a 12V DC motor. While I was using it 50% PWM mode, I calculated the efficiency of power consumption and I realized that I almost lost half power in PWM.
How I measured the efficiency:
- I put a clamp meter between the battery and the BTS7960 and I have check voltage "B +" and "B-" terminals. Voltage is 29V and current is 11 amperes so my battery is giving 320 watts.
- Then I checked the consumption of the DC motor. I put a clamp meter between the BTS7960 and the DC motor and I measured voltage "M+" to "M-" terminals. Voltage is 13,6 and current is 13,8 amperes so as I understand my DC motor consumes 187 watts.
Either my PWM module efficiency is very bad or I'm doing something wrong.
The BTS7960 module became really hot while testing.
If you ask why I dropped 29 volts to 13 volts and drive the DC motor, it is because I have a 7S3P li-ion battery and I have a 12 volt Dc motor. If I can overcome the problem, I will drive a 24 volt DC motor with a 7S3P battery.
What is the reason for the high power loss?
(edit)Additional information:
My clamp meter is Unit UT210E. Also you can reach datahseet this link:
Also I measured current with multi meter(Unit UT39C)
Lastly I made same circuit with dc-dc convertor. The energy loss in the measurement was very low and I saw this as normal aslo With dc-dc converter, the battery and cables was not very hot, but in pwm modulation, the battery, cables and bts7960 integrated was very hot.
Best Answer
Your multimeter and your clamp meter are both not meant to observe PWM going through an inductive devices.
You need an oscilloscope with a high-bandwidth method of sensing current. I don't know your PWM frequency, but rule of thumb: estimate how fast the transition from fully on to fully off has to be, take the inverse of that time (yielding a frequency), and take 5, better at least 7 times that frequency as minimum bandwidth if you really want to see what happens on that cable. It's not DC, by any meaning of that word.
Current measurements can be quite tricky, so you might end up getting a hall effect sensor IC with something like 400 kHz or 1 MHz of bandwidth, and just live with current components that you cut off through that not-really-sufficient bandwidth.