I would like feedback on the following circuit design please. I am powering a solenoid using a 3S LiPo battery but want to increase the voltage to 35v. I am using an XL6009 module to boost the voltage from roughly 12v to 35v. The voltage booster specs say it can safely output 4A. Do you see any problems with the following approach?
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The LiPo battery is connected to the voltage booster input, of course.
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The voltage booster output is connected to a 10,000u capacitor. (The solenoid, which has about 3Ω resistance, is firing for only a fraction of a second.)
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I am using a resistor to limit the current running from the voltage booster to the capacitor. I need to keep it under 4A to prevent damaging the voltage booster, especially if something goes wrong like the solenoid is engaged for longer than a pulse. I plan to use a 100W 13Ω (or greater) resistor at 35V, which will allow 2.8A going through the line.
I plan to use a relay between the capacitor and the solenoid to control the firing. I also use a mosfet to engage the relay’s coil from a microcontroller and have tested this circuit. I am using a relay that can handle 10A of current. I gather I might need a relay that can handle about 12A to be safe but figure if I am only firing the solenoid intermittently and for only 50ms, I should be ok. I will use a flyback diode to try to protect the relay from the reverse voltage spike cause by the solenoid’s inductive load.
Does this approach makes sense?
Thanks for the help!
Best Answer
This approach will work fine and is widely used for latching solenoids. Remember that the voltage on the capacitor will start to drop when the solenoid is energized, and you must reach the solenoid rated current (not voltage) to get full force. This means you must consider the inductance of the solenoid coil. The catch diode must be capable of handling the full solenoid current. Make sure the diode is in close proximity to the coil.