Water pump motor running slowly with L298 H-bridge at 80% PWM

[cyeokpeng]

Hi,

The motor drive circuit in the document attached use the L298 H-bridge driver switch to control the direction and speed of the dc motor, and the free-wheeling diode bridge (L6210) is connected across the motor to protect the transistors from the induced back emf of the coils in the motor.

I have tested the circuit on breadboard, but the water pump seems to be driving slowly, even though I use 80% duty cycle PWM of the ENABLE input, which is already quite high. For the 12 V volatge source, I use the 12V acid battery, while the 5V is provided by passing the 12V through a voltage regulator. The Rsa sense wattage resistor I have used is 0.15 ohms, 3 watts.
What can be the possible problem causing the slowless of the water pump motor?

Thanks,
if you need me to provide some info so as to lead light to the problem, kindly ask me.

 

[NoTime]

Why the fancy circuitry?
According to your attachment the requirements are to pump one direction.
This seems to be a change from the original plans, so it might be time to change the circuitry as well.
And if you are going to assume that there will be an outboard pump to empty the tank, why wouldn't there be an outboard pump to fill the tank?

Also why 80% PWM?
The H-Bridge circuits I am familiar with will go 100% (or simply on/off).
Running at 80% pwm will make the pump run slow, as you seem to have noticed.