I am looking into an inexpensive circuit that would allow me to activate a linear solenoid at 24VDC and then almost instantly decrease voltage to 12VDC. This would allow the solenoid to run continuously without overheating. I figured out how to get control and power to the circuit; I just need assistance with changing the voltage.
what about a large inductor in series with the coil. it should allow a large current to initially flow and then taper off. im not sure what size you would need though. oops, does the opposite.
Well the term 'linear solenoid' is not real clear. A 'standard' solenoid is more like a digital device, it's either fully on/open or off/closed when applying or removing it's rated coil voltage. There are linear actuators that can move in position between fully open or fully closed depending on the amount of voltage or current supplied to it.
Now for standard DC solenoids there is sometimes additional circuitry either build into the solenoid or in the driving circuit to allow full pull-in current to flow, but after a time fall back to a lower holding current. This saves energy if power consumption is important for the application.
Lefty
what about a large inductor in series with the coil. it should allow a large current to initially flow and then taper off. im not sure what size you would need though.
Nope, that's not what inductors do. That's what capacitors do! Also the solenoid is already a large inductor,
I presume you want a high initial current for rapid action, then a minimum current to hold position thereafter.
Just used analogWrite(), starting with 255, and back off as necessary a suitable number of milliseconds later.
If the 1kHz PWM of the arduino is too low a frequency (buzzing noisily!) there are ways to increase this by manipulating one of the timers on the ATmega.
Don't forget a free-wheeling diode or something will fry.
Here's a tutorial on solenoids that may be relevant to what you need:
http://www.arduino.cc/playground/Learning/SolenoidTutorial
To reduce holding current, I would keep voltage at 24V, but use PWM (pulse width modulation) to control current. Use 100% duty cycle when switching on and 50% or less when holding. You may need to experiment to find the minimum holding power needed and the time you need at full power.