Boost regulator to power a solenoid

#1

I am powering a solenoid using a 3S LiPo battery but want to increase the voltage to 35v. I am using an XL6009 module available on Amazon to boost the voltage from roughly 12v to 35v. The voltage booster specs say it can safely output 4A. I would love feedback on the following approach (I realize a drawing of the circuit would be ideal but I am hoping the following makes sense):

1. The LiPo battery is connected to the voltage booster input, of course.

2. 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. This size capacitor works well in tests. I didn’t do the math to calculate the minimum size capacitor but if anyone wants to share, please do!)

3. I am using a resistor to limit the current running from the voltage booster to the capacitor. In need to keep it under 4A to prevent damaging the voltage booster. This is in case something goes wrong (e.g., a programming error) and the solenoid is engaged for longer than let’s say 50ms. If I use a 100W resistor at 35V, I calculate I can have 2.8A going through the line. At 35V and 2.8A, ohm’s law dictates that I use a 13Ω or greater resistor.

4. 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.

So, I am wondering whether this approach makes sense.

If there is a better approach, please do tell!

Thanks for the help!

#2

Hi.

Your general plan seems okay. However, I recommend double checking the current rating of your regulator. Generally, step-up regulators are rated by the amount of input current they can handle since that will be higher than the output current. Outputting 4A while converting 12V to 35V would mean an input current of over 11A.

-Claire

#3

I checked the regulator datasheet and it’s 4A input voltage as you noted was probably the case. Thank you for the help!