Case Study: Choosing a 24 V Solenoid for Medical Bed Adjustment, Sample Passed Customer Testing
Selecting a Solenoid for Medical Bed Adjustment
A medical equipment manufacturer needed an electromagnetic actuator for a bed adjustment function. They had already discovered that the small solenoids they were evaluating did not behave the same way on the bed as they did on a bench. We supplied a DC24V electromagnet specified against the real working conditions, they tested the sample on their own rig, and it passed — with clear satisfaction from their engineering team.
This case is written as a selection guide rather than a product description, because the same questions come up in every hospital bed project we handle.
Three Bed Functions, Three Different Requirements
Not every actuator on a medical bed is doing the same job. Getting the selection right starts with being honest about which function the solenoid serves:
| Function | What the solenoid must do | Dominated by |
|---|---|---|
| Position locking / release | Hold a set position against load, release on command | Holding force at working gap, release reliability |
| Backrest or legrest adjustment assist | Actuate repeatedly during adjustment, often held by the operator | Force at stroke, tolerance to extended energisation |
| Emergency or quick release | Fail to a safe state, work after long idle periods | Reliability after inactivity, spring return behaviour |
In this project the requirement sat in the middle column: a part that works at a defined stroke, tolerates being energised longer than the nominal duty cycle suggests, and keeps its force after hundreds of thousands of operations.
The Specification That Was Supplied
| Item | Specification |
|---|---|
| Application | Medical bed electromagnet (medical device / DC micro solenoid) |
| Rated voltage | DC 24 V (working range DC 24 V ±10%) |
| Rated power / coil resistance | 18.48 W at DC24V, coil 31 Ω ±10% |
| Operating cycle | ON : OFF = 0.05 s : 0.15 s; continuous energisation permitted up to 300 s |
| Force | ≥ 300 g at 5.8 mm stroke |
| Operating temperature | -20 °C to +45 °C |
| Insulation resistance | DC 500 V, ≥ 50 MΩ (coil to bobbin) |
| Dielectric strength | 700 V, 50/60 Hz, 1 s, leakage ≤ 1 mA (coil to case) |
| Service life | Over 500,000 cycles under normal use |
Four Selection Rules We Applied
- Quote force at the working stroke, not at contact. A solenoid rated at 300 g on contact can deliver a small fraction of that at a 5.8 mm gap. Every specification we issue for a bed application states the force at the stroke the mechanism actually uses.
- Design for the worst-case energisation, not the nominal duty cycle. The 0.05 s / 0.15 s duty is the normal pattern; the specification also permits continuous energisation up to 300 s because that is what happens when a nurse holds an adjustment. The coil has to survive the real-world case, not the datasheet case.
- Treat electrical safety as a first-class requirement. Insulation resistance at DC500V and dielectric strength with leakage within 1 mA are specified and tested, because on a patient bed these checks — not force — are what device approval hinges on.
- Size the life expectancy for the service life. 500,000 cycles for a component in a bed that actuates a few times a day means the solenoid should not be the reason a field service visit happens.
What the Customer Tested
- Force at stroke, repeated across samples to check consistency rather than a single favourable reading
- Extended energisation, observing heat build-up inside the housing against the 300 s allowance
- Insulation and dielectric performance, the data their device approval file needs
- Cyclic operation, confirming force does not decay and release stays clean
- Workmanship — no damage, cracking, rust or surface staining
The sample passed the test and the customer confirmed their satisfaction with the part.
If You Are Selecting an Actuator for a Bed or Chair
Send us four things and the selection becomes straightforward: which function the solenoid serves, the required force at the actual stroke, the longest time it may stay energised, and the safety standard the device must meet. We will propose a specification, state clearly what we will commit to in writing, and supply samples for your own rig rather than ours.
Contact our engineering team with those four details — we will respond with a specification and a sample plan.
