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I am working on solving a problem that we generally deal with in a mechanical fashion. We have a hydraulic system with a dumb controller and a dumb valve stack. We can change the valve stack solenoids to a type in which you can vary the current. From here we would like to able to vary the current, set the flow proportions using a potentiometer and a MOSFET, then lock the box containing the potentiometer and related electronics. The solenoids draw a max of 3 amps, the current shouldn't need to go lower than 1 amp, and the entire system runs on 12 volts. I am wondering if control in this nature is not only possible, but is it wise?

I'm aware that a diode should be installed with the solenoid to protect the MOSFET.

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    \$\begingroup\$ solenoids to a type in which you can vary the current .... what is the result of varying the current? .... in which manner is the current being varied? ....analog value or PWM? ........... you really need to explain clearly what you are asking ..... your actual question is unclear ... what do you mean by control in this nature and wise \$\endgroup\$
    – jsotola
    Commented Jan 18, 2019 at 3:58

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It is not unknown technology to simply switch the hydraulic solenoid valve on and off in full switching manner. If the drive waveform is a variable duty cycle PWM signal at the proper frequency you can thus cause the valve assembly to float at a controlled position.

Note that there are certain types of hydraulic valves that are designed for this type of operation as opposed to others where it would not work at all. So make sure to check this detail with your valve supplier first.

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  • \$\begingroup\$ As the fluid heats or cools, or as the solenoid heats or cools, or as the MOSFET heats or cools, why do you expect the rate-of-fluid--flow to remain constant? \$\endgroup\$ Commented Jan 18, 2019 at 9:44
  • \$\begingroup\$ The fluid rate change with things such as temperature and load are simply ignored. Once the flow rate is proportioned, small variations are acceptable \$\endgroup\$ Commented Jan 18, 2019 at 14:15
  • \$\begingroup\$ And, I don't have a way to generate a pulse without adding extra parts to the circuit. I was trying to avoid going this route, but if there were no way without it then I'd have to go that route... \$\endgroup\$ Commented Jan 18, 2019 at 14:18
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current can be varied by using the PWM signal for MOSFET using variable duty cycle. Yes diode is necessary to protect the mosfet from the back EMF of solenoid.

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