I am trying to control the force of a solenoid. My current system has a bank of capacitors connected to a relay. In order to control the force (how hard I am trying to hit the object) I am increasing or decreasing the the time the relay is on. The problem is this works but it either hits with too much force or way too much force. I can turn the relay on for 5 ms or more. If I try to turn it on for 1 ms it does not even respond. (I am using a mechanical relay.)

I would like to have more control on how much of the energy I discharge so I can control how hard/soft the solenoid moves (say discharge only 10 percent of the total energy stored so it hits slower). While searching I found out about Solid State Relays which according to wikipedia can be switched on an off way faster that mechanical relay (of the order of microseconds to milliseconds).

So my question is am I on the right track? or is there something better to achieve what I am trying to achieve?

  • $\begingroup$ You may want to consider asking a question here about how to solve your underlying problem rather asking how to solve the problem with your current solution. If we know what you are trying to hit, why, how hard and what your budget constraints are, we might be able to offer a better solution than using a relay for a purpose it wasn't really intended for. $\endgroup$
    – Mark Booth
    Mar 4, 2013 at 16:54
  • $\begingroup$ Solid state relays have no moving parts, so they won't help. If you have the budget, I would look into piezo actuators for low force, fine control. Using Lever arm amplification you may be able to make your own flexture stage with suitable force and travel. $\endgroup$
    – Mark Booth
    Mar 4, 2013 at 17:13

2 Answers 2


To clarify, you have a bank of capacitors and you want to use them to power a solenoid for a short period of time, right? I assume you are directly connected to the solenoid coil, not through a controller or anything.

In this case the variables you can alter are length of pulse, and current of pulse. Decreasing either of these will of course cause your capacitors to drain less with each pulse. The actual force from the solenoid is much more linearly affected by current than length of pulse, and the easiest way to decrease current is to simply stick a power resistor somewhere along the line between the caps and the solenoid.


You can use a MOSFET instead of relays. MOSFET replies faster so you can achieve your goal..

Here is a simple schematic of a shooting system using solenoids.

Shooting using MOSFETs

Note that the solenoid is the L1 Inductor in the schematic and I've used the push-pull mechanism for putting diodes in the schematic which are necessary for this system... You can see wikipedia for further info.

And the Optocoupler is used to translate micrcontroller's signals.. ( The microcontroller's logic one is 5v while this system's logic one (VS) is 16v.)

And surely you need to put parallel capacitors between GNDHV and VS for the shooting system to work. ( Not present in this schematic. )

Legend : GNDHV: Voltage supply's ground ( the ground that comes in to your circuit ) VS : Voltage supply GND: The low voltage ground which is used to power up the micro controller. Kick: The kick signal.

Note: This system kicks when the Kick is set to zero.


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