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12 volt PWM Control with Toggle Switch
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Posted 3/13/2019 11:29 (#7377654 - in reply to #7377495)
Subject: RE: 12 volt PWM Control with Toggle Switch

Southern Minnesota Between Freeborn & Wells
TS79 - 3/13/2019 10:05

working on controlling a 12volt PWM valve that's a Danfoss PVEP, I can control it with Ag Leader no problem as they are sending a 12volt PWM signal to the valve. I need to be able to control the valve with a toggle switch as well, I can't send straight 12 volts to the valve as it will only accept a PWM signal. I'm looking for a PWM driver that could convert a 12volt signal to a PWM signal to the valve, I see lots of PWM drivers and controllers online but I need a little help on what I need exactly to make it work or if such a thing is possible. TIA

First of all it's definitely possible. As you are likely aware, a PWM signal consists of short "shots" of electricity followed by a gap of no electricity. This ON/OFF pattern happens very rapidly. This is called the frequency. You can learn a little or a lot about PWM by doing a Google Search.

In your Ag Leader system, the control module calculates your applied rate and compares that to the target rate you have entered. If the calculated rate is not within tolerance to the target rate, the system changes the duty cycle which will cause the valve to open or close a bit. The Duty cycle is the ratio of the ON time versus the ON + OFF time. It can vary from 0-100%. This changes the oil flow and ultimately affects the applied rate. It does this constantly while application is taking place.

I assume this works fine for you but you want to do this manually without the use of the Ag Leader system. A simple toggle switch would open the valve fully when ON and allow the valve to go fully closed when the switch is OFF. I assume this is not acceptable as you probably want the ability to be in between these two extremes. I'm not sure what you mean when you say "as well". This could cause complications if two systems are trying to run the valve. If you want to temporarily take over but let the Ag Leader run it most of the time, there may be some other options.

To run the valve without the Ag Leader you need a PWM controller. Some of these have an ON/OFF switch and a knob that you can use to manually adjust the duty cycle of the output. Other models are setup so the knob is turned fully counterclockwise to stop. One consideration is the electrical load that is involved. The Ag Leader systems can only handle a 1 amp load as I recall. This means your load must be less than 1 amp since it works with the Ag Leader. Otherwise an inline driver might be needed although some of the models shown can handle some hefty loads. I doubt that this is a problem for your situation. This can come up when trying to control the speed of a fairly large 12V motor.

If you do a search you can find lots of information on PWM. There are lots of possibilities. My guess is you want to purchase something that is already assembled and ready to go. This link shows several possibilities.

This folowing looks promising to me. The price is right. You would connect 12V and ground to the input terminals and connect the output terminals to the valve. Turning the knob should cause the valve to open partially or all the way.

There are more expensive models some have a digital readout which might be nice to return to a certain value.

Edited by tedbear 3/13/2019 16:10
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