Solenoid Work Notes

15 years in custom solenoid and solenoid valve design, selection, simulation and failure analysis.

Browse by topic

• Troubleshooting 17 A unit is failing now: no movement, weak force, sticking, heat, noise, leakage.
• Selection and specification 17 Choosing a topology, a winding and a set of tolerances before anything is built.
• Materials, corrosion and sealing 8 Humidity, washdown, dust, water quality and the coatings that decide service life.
• Applications 12 Vending, locks, coffee, medical, automotive, agricultural and HVAC duty.
• Fundamentals 6 Air gap, ampere-turns, saturation and temperature: the four relationships behind every number.

Latest notes

• Ampere-turns in a solenoid: why equal magnetomotive force is not equal force

  Two coils with the same 877 ampere-turns at the same 3 W can differ by 40 % in force, and the difference is entirely in the magnetic circuit rather than the winding. Wire gauge does not change ampere-turns at fixed dissipation, so choosing a gauge is a voltage decision, not a force decision. Here is the arithmetic, the saturation limit, and what actually sets the efficiency.

• Air gap vs. solenoid force: why it is closer to inverse square than linear

  Force falls roughly with the square of the gap, so the last fraction of a millimetre costs more than the whole rest of the stroke. A gap growing from 0.30 mm to 0.35 mm removes 27 % of the force, and to 0.40 mm removes 44 %. Here is how the magnetic circuit divides, how much of it the iron actually consumes, and which tolerances to attack first.

• Copper resistance and temperature: predicting hot-state solenoid force from a cold measurement

  Copper gains 0.393 % of its resistance per kelvin, which means a coil at 90 °C has 27 % more resistance than the same coil at 20 °C and delivers 61 % of its cold force at fixed voltage. That ratio also turns a resistance measurement into a winding thermometer, accurate to about 2 K without a thermocouple. Here is the arithmetic and where it stops working.

• Custom solenoid development: from specification to control plan

  A custom solenoid project fails in the order of its documents, not in its magnetics. The control plan has to come from the process flow and the FMEA; written from the characteristic list instead, it controls the 30 dimensions that are easy to measure and misses the one that decides whether the unit pulls 4 N at 3.5 mm. The sequence, with the sample sizes and indices that make it verifiable.

• Seal material selection for solenoid valves: NBR, EPDM and FKM

  The chemical compatibility chart answers the third question, not the first. Temperature and compression set decide whether a seal still pushes back after a thousand hours, and they pull against chemical resistance. Here is the order to choose in, with working numbers for NBR, EPDM and FKM, and the hot-water case where no single compound wins.

• Rotary vs. push-pull solenoids: reading a torque-angle curve

  A rotary solenoid does not have a torque, it has a torque curve, and the curve is not monotonic. It rises, peaks somewhere in the middle of the rotation and falls away again towards both ends, so a selection made on peak torque is wrong at both ends of the stroke. Overlay the return spring and the two worst points are usually not where the datasheet highlights.

Contact