I have a small electric diaphragm pump that I would like to control the speed of. It is 12VDC and has a max current of 19 watts.

I have a device that outputs a pulsed voltage signal (12VDC) that I would like to use for the speed adjustment. The device outputs the voltage in one polarity for more speed and reverse polarity for less speed. i.e. the two wires from the controlling device are + and - for faster and - + for slower. I believe that if the pump is running at the desired speed there would no voltage output. The controlling device is attached to a flow meter and outputs the signals until the flow stabilizes at a desired setting.

What sort of circuit would be necessary to perform this type of control? (Please speak slowly and use small words. I can solder, but I'm not an electronic engineer.) Is there an inexpensive off the shelf unit that will do what I need? I know that there are speed controls that use a potentiometer, but that won't allow me to control it with my voltage signal.

 

See a 555 PWM such as this http://www.discovercircuits.com/DJ-Circuits/simplepwm2.htm
Or they are about $5.00 on ebay.
Max.

 

Thanks for the reply. All of the ones I see on ebay have a potentiometer. How would I make this work with my pulsed control signal?

 

I have a device that outputs a pulsed voltage signal (12VDC)

Pulse rate? Pulse width?

 

Not really sure. It was originally designed to run a servo valve. It has a small DC motor with a gear train hooked to a ball valve. It bumps the valve open or closed to maintain a set flow. I want to use it to control a pump instead of a valve.

 

The manual for the controller says it outputs a PWM frequency of 150 Hz. Does that help?

 

I have a small electric diaphragm pump that I would like to control the speed of. It is 12VDC and has a max current of 19 watts.

I have a device that outputs a pulsed voltage signal (12VDC) that I would like to use for the speed adjustment. The device outputs the voltage in one polarity for more speed and reverse polarity for less speed. i.e. the two wires from the controlling device are + and - for faster and - + for slower. I believe that if the pump is running at the desired speed there would no voltage output. The controlling device is attached to a flow meter and outputs the signals until the flow stabilizes at a desired setting.

What sort of circuit would be necessary to perform this type of control? (Please speak slowly and use small words. I can solder, but I'm not an electronic engineer.) Is there an inexpensive off the shelf unit that will do what I need? I know that there are speed controls that use a potentiometer, but that won't allow me to control it with my voltage signal.

If your pump is a DC motor you need a way to control pump speed based on feedback from the flow sensor. What you are after is a flow controller which looks at a flow rate from a flow sensor and then in turn controls the pump speed. Control of pump speed can be a PWM (Pulse Width Modulation) circuit or even as simple as varying the DC voltage to the pump. I doubt the pump motor is designed to run in reverse so there would be no polarity reversal.

You will need to know what the flow sensor signals look kike? For example some flow sensors output a DC signal like 1 to 5 volts, 2 to 10 volts, 4 to 20 mA or even pulses with the output signal proportional to the rate of flow. There is also the matter of flow range as in 0 to something GPM or LPM. Anyway it sounds to me like your goal is flow control at a set rate.

Ron

 

Not really sure. It was originally designed to run a servo valve. It has a small DC motor with a gear train hooked to a ball valve. It bumps the valve open or closed to maintain a set flow. I want to use it to control a pump instead of a valve.

That is how it is typically done with the valve using either a voltage or current range to set it at a given point for a set flow rate. You need to make sure your pump is designed for variable speed control.

Ron

 

The controller takes the flow input and performs the logic. It outputs a signal that controls the position of the valve. I would like to intercept that signal and control the pump. The pump is able to be speed controlled.
The controller output has 2 wires for the DC volts.
Basically trying to emulate this module.
https://micro-trak.com/documents/12...ic-motor-drivers/8-40-amp-pwm-emd-manual/file

 

The unit you linked to is a PWM 40 Amp motor driver module. As shown it requires a PWM input from a controller. Does your controller have a PWM output to drive the large motor driver? The link is just a motor driver which needs a PWM input. The fact that the pump can be speed controlled is great. Your actual controller, not the pump driver, needs to have a PWM output to supply the motor driver. Unless the original pump controller has a PWM output to run to the motor driver it won't work. Whatever the input was to the original ball valve is likely what your controller output was.

Are the led STATUS INDICATORS doing anything?

Ron

 

The manual for the controller says it outputs a PWM frequency of 150 Hz. Does that help?

That doesn't sound consistent with the reversing polarity signal you describe in post #1. Most PWM signals are uni-polar. Is this 'controller' the 'device' you mentioned? Can you post a link to the spec/manual of the post #1 'device'?

 

Sorry, I posted the incorrect unit. The controller output isn't a PWM signal.
This is the correct type of unit.
https://micro-trak.com/documents/12...rivers/10-40-amp-pwm-emd-w-enable-manual/file
I'll see if I can find a manual for the controller.

 

The Pump Driver Module (EMD) replaces the servo valve. System flow is controlled by regulating the pump speed via a PWM signal to the EMD. NOTE: This unit will ONLY work with PWM (Pulse Width Modulated) Control drives. Set the PWM frequency of your controller to 150 Hz.

That is telling you that the motor driver is designed for a 150 Hz PWM input. The second page of the link clearly shows a PWM Input to the module and the module output to the pump. The module does not create a PWM signal, it is merely a big amplifier capable of driving 40 Amps. So what you have is power to the module and a PWM in and PWM out. Unless the original controller has a PWM output this will not work. Got a part number or link to the controller manual so we can see what the outputs were or are?

My thinking here is your controller which originally drove the ball valve has a scaled DC output as I originally mentioned of 1 to 5 VDC, 2 to 10 VDC or 4 to 20 mA which are very common. Should that be true you will need to get from what you have (any of those three or another) to what you need which is PWM to drive the motor driver module.

Ron

Ron

 

Sorry, I posted the incorrect unit. The controller output isn't a PWM signal.
This is the correct type of unit.
https://micro-trak.com/documents/12...rivers/10-40-amp-pwm-emd-w-enable-manual/file
I'll see if I can find a manual for the controller.

That makes all the difference in the world. The controller should work using the old servo out from your original controller when setup as in the link. Your controller out to the servo input. What are the status lights showing?

Ron

 

I don't have the motor controller in the link. That is what I want to try and build. I have the box that controls the box in the link. It reads the flowmeter and outputs a signal to this box. I don't need the LED's.

 

Manual for the controller.
https://www.micro-trak.com/documents/discontinued-products/140-mt-3000-manual/file

 

In the OP should be 19 amps not 19 watts.

 

It would seem the servo value signal is generated by a bridge circuit from the controller to generate a floating output of either plus or minus polarity, or zero to the servo valve.
Each output to ground is thus likely either 12V or 0V depending upon the polarity.

Conceptually you could convert this into the required PWM signal by:

• Use one of the servo outputs to cause a digital counter to count up, and the other output to cause the counter to count down. For zero output the counter stays at its previous count.
• The counter output goes to a D/A converter that outputs a DC voltage proportional to the count.
• This voltage controls a voltage controlled PWM modulator.

That could also be done with some analog circuitry including an analog integrator but that would be more problematic to get working properly.

A simpler way would be to use the two signals to control a microprocessor such as an Arduino to generate the PWM signal, but that requires learning how to write a simple program.

 

I looked through the manual. This entire system was designed as a system for apparently farm use. They do not make mention of what the original controller output actually was. My best advice here is to call the manufacturer because unless we know what the original control signal was there is no way we can begin to build an interface and new motor driver. I have seen servo valves operate on any of the signal types I mentioned. Maybe someone else will get something out of the controller manual but there is nothing I can see.

Ron

 

crutschow I believe you are correct in your thinking.

I thought about using the Arduino. I have experimented a little with them, but this is way beyond what I could design. Would that be an easier method to build a circuit.
What would I need to interface with the pump motor?