Hi guys,

Not sure if this question was asked before. I have a 12 volt water pump that waits for a PWM signal for two seconds, then goes to full power if it does not get that signal. I want to send the PWM signal and power to the pump at the same time to bypass this problem. In other words. I want to use the PWM signal to turn the pump on. I was thinking a bistable 555 timer circuit? Some kind of latching relay? I will be using an analog circuit for this. It will have relays. What are my options?

Thank you

 

Just peak rectify and filter the PWM signal to control a transistor driving a relay to apply 12V to the pump.
I can supply a schematic if needed.

What is the PWM voltage and frequency?
How much current does the pump take?

 

Thanks for the reply. It is 12 v, 100 Hz. Pump is rated for 5A

 

Seems like something is missing in the description of the pump operation. How does the pump know when to wait for the pwm?
If the pwm is used to activate a relay is the pwm a continuous signal while the pump is running?

 

This is a car water pump. I want to use it in a different circuit.

This is from the manufacturer:

If PWM Speed Control *is* Used

If there is no PWM signal within 2 seconds of power-on, the default mode of full speed operation will be used.

If there is a valid PWM signal, a speed-proportional response to a commanded 15-90% duty cycle will be delivered.

+12V PWM controlled,

Recommended PWM frequency: 50Hz to 200Hz (nominal = 100Hz)

Recommended PWM Duty range: 15 - 90%

The water pump operates at its minimum speed when the PWM duty cycle is 15%, and it reaches its maximum speed when the PWM duty cycle is greater than 90%.

 

One version using PWM to power a 12 volt relay. Operation verified at 100hz, 10% duty cycle.

 

One version using PWM to power a 12 volt relay.

That works only if the PWM amplitude is the same as the power supply voltage (here 12V).

 

TS said the pwm was 12v at 100hz in post #3.
Schematic indicates 12v pwm.

 

It is 12 v, 100 Hz.

Where is the PMW signal coming from?
So its amplitude is always equal to the battery voltage?

 

Sorry for the late reply. The PWM signal will be coming from an industrial board. The pump should only be turned on when the signal is outputted by the board. The pump will have a different 12 v power supply to supply power to it. I want to put a relay between the power supply and the pump, and have the pwm signal trigger it somehow to start the pump.

 

If the PWM signal is 12volts as you stated earlier then the schematic in post #6 should work.

 

If the PWM signal is 12volts as you stated earlier then the schematic in post #6 should work.

The relay coil ON voltage will be about two diode drops below the PWM peak signal voltage, but that likely is okay.

 

I was able to use a simple low pass filter, then a voltage divider to lower the voltage. I programmed my arduino to trigger a relay when voltage is detected. It works. Thanks for the help guys!