Near Intersection of I-35 & I-90 Southern Mn. | Orfarmer - 8/29/2014 12:35
Is there an easy way to manually control a pwm valve? I was thinking some kind of 3 way rocker switch with up/down/neural. I know you can adjust the valve itself, but I want to do it from the cab. Thanks for any insight.
Are you sure that you have a PWM valve? The reason I ask is that you indicate that you can adjust the valve itself. I don't know how that could be done with a PWM valve. The following assumes that you do have a PWM valve. If you have a servo type valve then a manual switch is quite simple.
The switch you describe will not work with a PWM valve. PWM stands for Pulse Width Modulation. This amounts to sending short shots of electricity to the valve for control. This happens very fast.
If no electricity is sent out, the valve stays in the closed position and no product flows. If a constant 12 Volts were sent out, the valve would open completely and maximum product flow would occur. If short shots of electricity (sometimes On, sometimes Off) are sent, the valve tends to "hover" is a position that is partway between fully open and fully closed. Since this ON/OFF cycle occurs very rapidly, the valve doesn't have time to go fully closed or fully open and hovers partway in between. This in effect creates an average voltage some where between 0 & 12V.
If the position of the valve needs to be changed then the ratio of On time to Off time is changed. If the position is fine then the ratio remains at the present ratio.
This concept is used with motors as well as a way to crate a variable speed DC motor. Fertilizer and planter systems that use electricity for power often utilize the PWM concept.
This is in contrast to servo valves where opening requires 12V of a certain polarity and closing requires 12V of the opposite polarity. A Double Pole Double throw momentary switch can be wired to send out either polarity or none. This is in line with your thinking but would not work with a PWM valve.
You need some type of circuit that allows the operator to manually change the voltage out to the valve. A rheostat type device can be used. With these, 12 V comes in but the voltage is dropped via using a variable resistance.
This is how many older heater fans worked. Just last week I had to replace the fan speed board in my Eagle truck. The fan switch has four positions. Only high would work. The fan circuit board was corroded and the terminals in bad shape. The board had 3 coils of wire that acted as resistors. In the first 3 fan speeds, the voltage was dropped depending on the position of the switch. In the high position the board was bypassed and the fan got the full 12V. This is why I had nothing or high with the circuit board problems.
Another way to run a PWM valve manually is to obtain a circuit designed for that purpose. The manual control from Brand as indicated in the above post is such a device. This one is designed to work with the Brand PWM hydraulic valve and should be a good choice.
Some PWM generators will not have the current handling capabilities of certain valves and will simply burn out. If you would use some type of controller such as an Ag Leader system, the PWM generation is handled by the external module that is involved.
Edited by tedbear 8/30/2014 07:24
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manual control of pwm valve
