Custom Monostable Solenoids

Current through the coil magnetizes the frame and pole, pulling the steel plunger into the coil against a return spring. The plunger stays there only as long as current flows. Remove power and the spring returns it to rest, every time, with no electronics involved. That built-in return is why monostable solenoids are the default whenever a mechanism must fall back to a known state.

Pull-type solenoids draw the plunger into the body; push-type designs drive a pushrod out through the pole to move the load. Both are monostable; the difference is which direction does the work.

Solenoid force rises steeply as the air gap closes, so force is lowest at the start of the stroke, often exactly where the load needs it most. Pole and plunger geometry change that. A flat-faced pole gives very high force over a short stroke; a conical pole trades some end-of-stroke force for a flatter curve over a longer stroke. We tune pole geometry, spring rate, and coil design together so the curve stays above your load across the full stroke, with margin.

Monostable linear solenoids typically fall within these ranges. Force drops as the stroke lengthens, and a continuous-duty rating gives less force than an intermittent one from the same size, so the extremes do not occur together. Every design we build is custom to your specification across this range.

• Force: about 0.1 N to 500 N or more.
• Stroke: about 2 mm to 50 mm.
• Supply: mostly DC, 3 V to 48 V; AC versions exist.

Because a monostable solenoid needs current to stay actuated, holding produces heat. How long it can stay energized, its duty cycle, is set by how fast that heat leaves the coil and how hot the insulation and materials may run. A solenoid rated for brief pulses can deliver far more force from the same size than one rated for continuous holding.

Peak-and-hold drive changes that trade-off. Pulling in takes a lot of current, but holding a closed air gap takes much less, so the drive applies full current to actuate and then drops to a reduced holding current. That cuts heat and power substantially and often lets a smaller solenoid do the job. We design the coil and the drive together to take advantage of it.

Actuation speed depends on how quickly current builds in the coil, which its inductance resists; drive voltage, coil design, and overdrive at pull-in all shorten it. Release speed is often overlooked. A simple flyback diode protects the switch but keeps current circulating in the coil, which noticeably delays drop-out. Where fast release matters, we specify suppression such as a Zener or TVS clamp that collapses the field quickly.

The spring return makes a monostable solenoid naturally fail-safe: on any loss of power or control signal, it returns to its rest position. For locks, valves, interlocks, and safety mechanisms, that defined state is often a requirement, not a preference, and it is why monostable remains the right answer even where a bistable design would save power.

We develop the drive in-house alongside the actuator: peak-and-hold or PWM current control, overdrive for fast pull-in, suppression for fast release, and diagnostics where the product needs them. The coil is then optimized for the drive it will actually see, instead of for a generic supply.

Development starts from your force, stroke, duty-cycle, envelope, and power requirements. We model the magnetic circuit, then build prototypes in our own shop and characterize them on the bench: force versus stroke, response and release time, temperature rise, and duty-cycle behavior. Prototypes are built in-house in two weeks, so iterations turn around fast, and once the design is approved we manufacture production units ourselves under our ISO 9001:2015 quality system.