When buyers request an electromagnet, they usually begin with magnetic field strength:
“We need 0.5 T.”
“We need 1 T at a 40 mm pole gap.”
“We need the highest field possible.”
But one of the most important questions is often missing:
How long must the electromagnet maintain that field, and how often will the operating cycle repeat?
An electromagnet that produces the required field for 30 seconds is not necessarily capable of maintaining the same field for eight hours.
A system designed for occasional short tests may use different coils, cooling, power supply capacity, temperature protection, and operating limits from a system intended for continuous production testing.
This operating pattern is generally described as the electromagnet duty cycle.
For buyers, defining duty cycle is not a minor operational detail. It directly affects:
- Coil temperature
- achievable continuous field
- air cooling or water cooling
- power supply rating
- field stability
- system size
- safety interlocks
- operating cost
- equipment lifetime
- quotation price
This article explains how to define electromagnet duty cycle correctly before requesting a quotation or issuing a purchase order.
1. What Electromagnet Duty Cycle Means
Electromagnet duty cycle describes how the magnet will be energized over time.
At its simplest:
Duty cycle (%) = ON time ÷ total cycle time × 100
For example:
- 5 minutes ON and 5 minutes OFF = 50% duty cycle
- 10 seconds ON and 50 seconds OFF = approximately 16.7%
- continuously energized = 100%
But this percentage alone is not enough.
The following two operating patterns are both 50% duty cycle:
- 10 seconds ON, 10 seconds OFF
- 30 minutes ON, 30 minutes OFF
They can create very different peak coil temperatures because the heating and cooling periods are different.
A useful duty-cycle specification must therefore state:
- ON time
- OFF time
- number of cycles
- operating current or field
- ambient temperature
- cooling method
- allowable temperature rise
- whether the pattern repeats continuously
2. Why Field Strength Alone Is an Incomplete Specification
Magnetic field strength tells the supplier what the electromagnet must produce.
Duty cycle tells the supplier how the electromagnet must survive while producing it.
The same field may be offered under very different conditions:
- Maximum short-time field
- maximum intermittent field
- maximum continuous field
- continuous field with air cooling
- continuous field with water cooling
- field available only below a specified ambient temperature
- field available after thermal equilibrium
- field available with a particular pole gap
A quotation stating “maximum field: 1 T” is incomplete if it does not explain whether that field is available for 10 seconds, 10 minutes, or continuous operation.
3. Continuous, Short-Time, and Intermittent Operation
A practical electromagnet RFQ should distinguish among three main operating patterns.
Continuous Operation
The electromagnet remains energized long enough to approach thermal equilibrium and continues operating without a planned cooling interval.
Typical examples include:
- Long-duration Hall measurements
- automated production testing
- overnight material experiments
- continuous sensor calibration
- extended optical measurements
- long temperature sweeps
Short-Time Operation
The electromagnet operates for a defined limited period and then remains off long enough to cool substantially before the next run.
Typical examples include:
- One-minute high-field exposure
- short magnetic characterization runs
- occasional peak-field tests
- brief sample switching experiments
Intermittent Periodic Operation
The electromagnet repeatedly alternates between energized and non-energized periods.
Typical examples include:
- 2 minutes ON, 3 minutes OFF
- repeated sensor qualification cycles
- magnetic exposure sequences
- automated test batches
- periodic field reversal experiments
IEC 60034-1, although written for rotating electrical machines rather than laboratory electromagnets, provides useful engineering vocabulary by distinguishing continuous running duty, short-time duty, and intermittent periodic duty. Buyers can use the same basic distinctions when describing electromagnet operation, without implying that an electromagnet is certified to that motor standard.
4. “100% Duty Cycle” Still Needs Operating Conditions
Saying “100% duty cycle” is better than saying nothing.
But it is still incomplete.
Continuous operation should be linked to:
- Required magnetic field
- coil current
- pole gap
- ambient temperature
- cooling-water temperature
- cooling flow
- maximum coil temperature
- operating altitude, when relevant
- power supply configuration
- expected operating duration
A magnet might support continuous operation at 0.4 T but only short-time operation at 0.7 T.
Another magnet might support 0.7 T continuously only when connected to a specified chiller.
The continuous-duty rating must therefore be tied to a defined operating point.
5. Why Electromagnet Coils Heat Up
An electromagnet produces magnetic field by passing current through its windings.
The windings have electrical resistance, so they dissipate heat.
A basic expression for resistive heating is:
P = I²R
where:
- P is power converted into heat
- I is current
- R is coil resistance
This relationship matters because heating increases with the square of current.
If current rises by 20%, resistive heating does not rise by only 20%. Assuming resistance initially remains the same, it rises by approximately 44%.
That is one reason a modest increase in requested field can create a much larger thermal-design problem.
6. Coil Resistance Changes as the Magnet Heats
Copper resistance increases as temperature rises.
As the coil warms:
- Coil resistance increases
- required voltage changes
- power-supply operating point changes
- heat distribution changes
- mechanical dimensions may shift
- magnetic field stability may be affected
A GMW electromagnet manual notes that coil resistance depends on temperature and states that voltage across the coils is not a good direct measure of field. It recommends constant-current operation for stable field performance and describes temperature-related resistance changes during operation.
This creates an important purchasing lesson:
Cold-start electrical values are not the same as hot continuous-operation values.
7. The Maximum Field May Be a Cold-Coil Value
Some field curves or performance tables may be based on a cold magnet.
The magnet begins near room temperature, reaches the target current, and produces the stated field.
During longer operation:
- Copper resistance rises
- the power supply may need more voltage
- coil temperature continues increasing
- thermal protection may activate
- cooling demand increases
- field stability may change
Buyers should ask whether the published field is:
- Cold-coil field
- thermally stabilized field
- short-time peak field
- intermittent operating field
- continuous water-cooled field
A maximum-field number should never be separated from its thermal condition.
8. Why Constant-Current Control Matters
For most electromagnet applications, magnetic field is primarily controlled through coil current.
A stable current source helps maintain a stable field even as coil resistance changes with temperature.
A voltage-controlled supply may allow current to drift as the coil heats.
This can produce:
- Field drift
- inconsistent calibration
- changing measurement conditions
- different results at the beginning and end of a test
- poor repeatability between cold and warm operation
A matched excitation power supply should therefore be evaluated not only by maximum current, but also by:
- Current stability
- voltage headroom
- continuous power rating
- cooling
- protection
- ramp control
- readback accuracy
- communication interface
9. Duty Cycle Affects Power Supply Selection
The power supply must support the same operating duty as the electromagnet.
A supply capable of delivering a high peak current briefly may not be capable of maintaining it continuously.
The supplier should check:
- Maximum output current
- continuous output current
- output voltage at hot coil resistance
- continuous power
- internal thermal derating
- cooling-air requirements
- ambient temperature rating
- overload duration
- protection behavior
- inductive-load compatibility
A magnet described as continuous-duty is not a complete continuous-duty system unless the power supply and cooling equipment are also rated for that operation.
10. Short-Time Field Is Not Automatically Unsafe
Short-time operation is not inherently inferior.
It may be the correct design choice when the experiment only needs brief field exposure.
A short-time system may offer:
- Higher peak field
- smaller magnet
- lower cooling demand
- lower cost
- reduced water use
- simpler installation
For example, a laboratory may need maximum field for only 30 seconds while collecting one measurement point.
Designing that system for eight-hour continuous operation may add unnecessary cost and size.
The problem is not using short-time duty.
The problem is purchasing a short-time magnet while assuming it is continuous-duty.
11. Air Cooling: When It May Be Enough
Air cooling may be suitable when:
- Current is moderate
- field demand is modest
- ON time is limited
- OFF time is sufficient
- ambient temperature is controlled
- high long-term field stability is not critical
- fan vibration is acceptable
- system size permits airflow
Air cooling can reduce system complexity because it may avoid:
- Chiller procurement
- cooling-water connections
- flow interlocks
- filters
- leak management
- condensation concerns
However, air cooling has practical limits.
As the thermal load rises, coil temperature may continue increasing faster than the surrounding air can remove heat.
12. Why Air Cooling Can Affect Field Stability
Even when a magnet can operate safely without water cooling, thermal variation may still affect measurement quality.
A GMW electromagnet manual states that operation below a certain current can be safe without water cooling, but also notes that coil temperature varies with power dissipation and that resulting dimensional changes make air cooling unsuitable when high field stability is required.
This distinction is important:
- Safe operation means the magnet is not expected to exceed a protection limit.
- Stable measurement operation means the field and geometry remain sufficiently consistent for the experiment.
A magnet can be thermally safe but still too unstable for precision measurement.
13. When Water Cooling Becomes Necessary
Water cooling is commonly considered when the application requires:
- High continuous current
- high continuous field
- long operating periods
- compact high-power coils
- stable thermal conditions
- reduced cooldown time
- repeated high-duty cycles
- controlled coil temperature
- low drift after warm-up
A water-cooled electromagnet may include:
- Cooling channels or plates
- inlet and outlet connections
- flow requirements
- temperature requirements
- pressure requirements
- flow switch
- overtemperature thermostat
- chiller
- filter
- leak-resistant fittings
In one documented laboratory electromagnet example, the manufacturer specifies cooling-water temperature, flow, pressure, thermal interlocks, and different chiller capacities depending on the power-supply configuration. This illustrates why “water-cooled” is not a complete specification by itself.
14. Water Cooling Must Be Specified Quantitatively
A buyer should not write only:
“Water cooling available.”
The useful information is:
- Inlet water temperature
- allowable outlet temperature
- minimum flow rate
- pressure or pressure drop
- water quality
- available chiller capacity
- facility water or closed-loop chiller
- ambient dew point
- flow-interlock availability
- hose connection size
Cooling performance depends on the complete cooling circuit.
A magnet designed around 18°C water may not perform the same way with warm facility water.
15. Cooling Below the Dew Point Creates Another Risk
Very cold cooling water may appear beneficial because it removes heat more effectively.
But if magnet surfaces fall below the ambient dew point, condensation can form.
Possible consequences include:
- Electrical leakage
- corrosion
- insulation damage
- short circuits
- water accumulation
- unsafe terminals
Electromagnet documentation commonly warns against cooling below the ambient dew point for this reason.
The cooling target should therefore balance thermal performance and condensation risk.
16. Duty Cycle and Pole Gap Are Connected
Pole gap affects the field that an electromagnet can produce for a given current.
If the buyer increases the pole gap, the magnet may require more current or a different design to maintain the same field.
More current can mean:
- Higher coil heating
- higher voltage requirement
- larger power supply
- higher cooling load
- reduced continuous-duty field
- shorter allowable ON time
A quoted duty cycle should therefore be linked to the agreed pole gap.
“0.8 T continuous” at a 20 mm gap does not imply “0.8 T continuous” at a 60 mm gap.
17. Duty Cycle and Pole Diameter Are Also Connected
Pole diameter affects:
- Uniformity region
- magnetic efficiency
- sample access
- required magnet size
- saturation behavior
- thermal demand
A larger pole may support a larger uniform region but can require a different magnet structure and power level.
When buyers change pole diameter, uniformity volume, or pole gap, the original duty-cycle rating may no longer apply.
18. Duty Cycle and Field Uniformity
Thermal changes can affect more than coil resistance.
They may also change:
- Mechanical dimensions
- pole alignment
- frame temperature
- sample position
- field-center location
- mapping repeatability
For routine exposure testing, small thermal shifts may not matter.
For calibration or high-precision material measurements, they may be important.
Buyers requiring strict uniformity or field repeatability should ask whether performance is specified:
- Immediately after startup
- after a warm-up period
- at thermal equilibrium
- throughout the full operating cycle
- at maximum continuous current
19. Warm-Up Time Should Be Part of the Test Method
Some electromagnets require a warm-up period before the field becomes thermally stable.
A practical operating sequence may be:
- Start cooling.
- Energize the magnet.
- Allow temperature and resistance to stabilize.
- Verify current and field.
- Begin the measurement.
If a buyer requires immediate high-accuracy measurements after cold startup, that should be stated.
Otherwise, supplier and buyer may evaluate stability under different conditions.
20. OFF Time Must Allow Real Cooling
In an intermittent-duty system, OFF time is not only “time without field.”
It is the cooling interval.
The required OFF time depends on:
- Peak current
- ON duration
- coil thermal mass
- cooling method
- airflow or water flow
- ambient temperature
- starting temperature
- maximum permitted coil temperature
- number of previous cycles
Ten minutes of OFF time may be sufficient after a short low-current pulse.
It may be insufficient after a long high-current run.
The OFF interval should be defined through thermal evaluation, not chosen arbitrarily.
21. Repeated Cycles Can Accumulate Heat
A magnet may survive the first operating cycle but become progressively hotter over repeated cycles.
Consider this sequence:
- 5 minutes ON
- 2 minutes OFF
- repeated for 50 cycles
If two minutes is not enough to remove the heat generated during five minutes of operation, the starting temperature rises with each cycle.
Eventually, the magnet may reach:
- Thermal equilibrium at an acceptable temperature
- a protection threshold
- an unsafe temperature
- a temperature that causes unacceptable field drift
Duty-cycle evaluation should therefore cover the complete repeated pattern, not only one ON/OFF cycle.
22. Peak Coil Temperature Matters More Than Average Percentage
Two systems can both be described as 50% duty cycle but reach different peak temperatures.
The temperature profile depends on:
- Cycle duration
- thermal time constant
- cooling performance
- current
- ambient conditions
- starting temperature
This is why a supplier needs the actual sequence.
Weak Requirement
“Duty cycle: 50%.”
Better Requirement
“Operate at 0.6 T for 10 minutes, then at 0 T for 10 minutes, repeated continuously for four hours, in a 25°C laboratory.”
The second statement can be evaluated.
The first cannot.
23. Field Ramping Also Adds to the Operating Cycle
Duty-cycle discussions often assume only two states:
- Full field
- zero field
Real experiments may include:
- Ramp up
- dwell at field
- ramp down
- reverse polarity
- dwell at negative field
- return to zero
- wait for measurement
Current during ramps still produces heating.
A complete cycle should include all energized periods, not only the full-field dwell.
For frequent bipolar sweeps, the magnet may have little real cooling time even though it repeatedly passes through zero.
24. Field Reversal Does Not Reset the Thermal Load
Changing from positive current to negative current reverses the magnetic field.
It does not make the coil cold.
From a heating perspective, +I and −I produce similar resistive losses because heating depends on the magnitude of current squared.
Therefore, a sequence such as:
- +50 A for 5 minutes
- −50 A for 5 minutes
is effectively ten minutes of high thermal loading, not five minutes ON followed by five minutes OFF.
This is a frequent misunderstanding in bipolar magnet projects.
25. Zero-Current Dwell Is the Real Cooling Period
A system cools most effectively when current is reduced substantially or turned off.
A low-field dwell may still generate meaningful heat if the current remains high relative to the coil rating.
Buyers should provide the full current or field profile, including:
- Positive field
- negative field
- zero-field dwell
- ramp periods
- standby current
- cycle repetition
This allows the supplier to estimate the real thermal load.
26. Duty Cycle for Hall Measurement Systems
Hall measurements may use:
- Positive field
- negative field
- current reversal
- field sweeps
- temperature sweeps
- long stabilization periods
- repeated sample measurements
A Hall experiment may appear intermittent because the field changes frequently.
Thermally, however, the electromagnet may remain energized for hours.
Buyers should state:
- Maximum positive and negative field
- sweep rate
- dwell time
- zero-field time
- number of cycles
- total experiment duration
- temperature environment
- required field stability
For automated Hall systems, the realistic duty may be much closer to continuous operation than the user initially expects.
27. Duty Cycle for Optical and MOKE Experiments
Optical and MOKE measurements may require long dwell periods for:
- Camera exposure
- signal averaging
- laser alignment
- polarization adjustment
- sample scanning
- temperature stabilization
- repeated hysteresis loops
The electromagnet may remain at one field while the optical system collects data.
This can create a high thermal duty even when the magnetic sweep itself is slow.
The buyer should estimate the full experiment duration, not only the sweep time.
28. Duty Cycle for Cryostat-Integrated Electromagnets
Cryostat integration introduces additional thermal and mechanical concerns.
Long magnet operation may heat:
- The magnet frame
- nearby air
- cryostat supports
- optical components
- cables
- sample environment
The magnet’s cooling system is separate from the cryostat’s cooling system, but thermal interaction may still affect alignment or stability.
For cryogenic projects, buyers should define:
- Magnet ON duration
- sample stabilization time
- total low-temperature run
- field sweep profile
- expected continuous operation
- allowable heat near the cryostat
- vibration limits from cooling equipment
29. Duty Cycle and AC Magnetic Fields
AC operation requires a different thermal review.
Important parameters include:
- Frequency
- waveform
- peak current
- RMS current
- DC offset
- duty cycle
- continuous duration
- driver losses
- core losses
- eddy-current effects
A square-wave or fast alternating field may create different losses from steady DC operation.
A DC continuous-duty rating should not automatically be applied to AC operation.
AC capability must be assessed at the required frequency, amplitude, waveform, and duration.
30. Duty Cycle and Ambient Temperature
An electromagnet operating in a 20°C laboratory has more thermal margin than the same magnet operating in a 35°C equipment room.
Relevant environmental information includes:
- Minimum ambient temperature
- maximum ambient temperature
- enclosure or open-air installation
- ventilation
- nearby heat sources
- altitude
- direct sunlight, where applicable
- cooling-water temperature
If the room becomes warmer, the magnet starts closer to its temperature limit and cooling becomes less effective.
Continuous ratings should therefore state the assumed environment.
31. Thermal Interlocks Are Not Optional Extras
A high-power electromagnet should normally include appropriate thermal protection.
Possible protective elements include:
- Coil thermostat
- temperature sensor
- cooling-plate sensor
- water-flow switch
- chiller fault input
- power-supply inhibit
- overtemperature shutdown
- alarm output
- emergency stop
Documented laboratory electromagnets may include multiple coil thermostats and door or cooling interlocks to prevent operation under unsafe conditions.
Buyers should ask:
- What temperature is monitored?
- Where is it measured?
- At what threshold does protection act?
- Does the system ramp down or shut off immediately?
- Is manual reset required?
- Is the fault recorded?
32. A Thermal Cutoff Is Not an Operating Target
If a thermostat opens at 80°C, that does not necessarily mean the magnet should routinely operate at 79°C.
A thermal cutoff is usually a protection boundary.
The recommended operating temperature may be lower to support:
- Longer insulation life
- better field stability
- lower resistance
- safer surfaces
- improved reliability
- margin for cooling variation
Buyers should distinguish between:
- Normal operating temperature
- maximum recommended temperature
- alarm threshold
- shutdown threshold
- insulation limit
33. Duty Cycle Affects Reliability and Service Life
Repeated operation near maximum temperature can stress:
- Winding insulation
- adhesives
- connectors
- cable terminations
- cooling seals
- temperature sensors
- mechanical supports
The IEC’s reliability vocabulary defines reliability in terms of performing as required for a stated interval under stated conditions, emphasizing why operating duration and conditions should be explicitly defined.
A magnet can be technically capable of reaching a field while still being poorly matched to the intended long-term operating pattern.
Reliability depends on how the equipment is actually used.
34. Duty Cycle Affects the Quotation
Two buyers may request the same field and pole gap but receive different quotations because their duty requirements differ.
Buyer A
- 0.8 T
- 40 mm gap
- 30 seconds ON
- 10 minutes OFF
- five tests per day
Buyer B
- 0.8 T
- 40 mm gap
- continuous eight-hour operation
- strict field stability
- automated control
Buyer B may require:
- Larger coils
- better cooling
- more powerful chiller
- higher continuous-duty power supply
- thermal sensors
- flow interlock
- more robust cables
- longer FAT
- continuous-run testing
The price difference reflects a different delivered system, not merely a different commercial strategy.
35. Why a Cheaper Quote May Hide a Duty-Cycle Assumption
A lower quotation is not automatically wrong.
But buyers should check whether the supplier assumed:
- Short-time operation
- low ambient temperature
- external cooling supplied by buyer
- limited current duration
- no long-term stability guarantee
- maximum field only from a cold start
- no continuous-run FAT
- no cooling interlocks
If another supplier includes continuous operation with a chiller, temperature protection, and endurance testing, the two quotations are not directly comparable.
Compare the operating basis, not only the maximum-field number.
36. What Should Be Included in FAT
For a duty-critical electromagnet, Factory Acceptance Testing may include:
- Cold coil resistance
- cooling-water flow
- flow-interlock function
- temperature-sensor function
- current ramp
- target field
- continuous operating period
- coil or cooling-plate temperature
- hot coil resistance
- power-supply voltage and current
- field drift after warm-up
- overtemperature protection
- controlled shutdown
The test duration should be long enough to represent the agreed duty.
A two-minute field test does not verify eight-hour continuous operation.
37. Define the Temperature Measurement Point
“Coil temperature” can refer to different locations:
- Winding interior
- winding surface
- cooling plate
- pole
- yoke
- frame
- cooling-water outlet
- thermostat location
These temperatures will not be identical.
The acceptance document should state:
- Sensor type
- sensor position
- test duration
- ambient temperature
- cooling condition
- pass/fail threshold
Without this information, two temperature measurements may appear contradictory even though both are correct at their respective locations.
38. A Practical Duty-Cycle RFQ Checklist
Before asking for an electromagnet quotation, provide the following.
Magnetic Requirement
- Required field:
- pole gap:
- pole diameter:
- uniformity region:
- field direction:
- bipolar or unipolar:
- DC, sweep, or AC:
Operating Cycle
- ON time:
- OFF time:
- number of repeated cycles:
- total daily operating time:
- maximum continuous run:
- ramp duration:
- positive and negative field dwell:
- zero-current dwell:
- expected standby condition:
Thermal Conditions
- Ambient temperature:
- allowable coil temperature:
- field-stability requirement:
- warm-up time allowed:
- air or water cooling preferred:
- facility water available:
- chiller available:
- inlet water temperature:
- flow and pressure available:
Electrical Requirement
- Local input voltage:
- power supply required:
- current stability:
- remote control:
- ramp control:
- interlock requirement:
- emergency stop:
- data logging:
Acceptance Requirement
- Continuous-run FAT duration:
- temperature measurement point:
- field verification:
- field drift limit:
- cooling-flow test:
- thermal interlock test:
- report required:
This information allows suppliers to design and quote on the same basis.
39. Better RFQ Examples
Weak RFQ
“We need a 1 T electromagnet with a 50 mm gap.”
This does not define how long the field is required.
Better RFQ: Continuous Operation
“We require 1 T at a 50 mm pole gap for continuous operation of up to eight hours per day. Laboratory ambient temperature may reach 28°C. Please include the matched power supply, water-cooling requirements, chiller recommendation, temperature and flow interlocks, warm-up time, and continuous-run FAT.”
Better RFQ: Intermittent Operation
“We require 1 T at a 50 mm pole gap for five minutes, followed by at least 15 minutes at zero current. This cycle will repeat no more than eight times per day. Please state the required cooling method, maximum coil temperature, and whether the quoted field is available from every cycle after thermal stabilization.”
These RFQs describe two very different systems.
40. Common Buyer Mistakes
Mistake 1: Asking Only for Maximum Field
Maximum field without duration is not a usable operating specification.
Mistake 2: Writing Only “50% Duty Cycle”
The supplier also needs the actual ON and OFF times.
Mistake 3: Treating Negative Field as Cooling Time
Positive and negative current both heat the coil.
Mistake 4: Ignoring Ramp Time
The magnet still dissipates heat while current is ramping.
Mistake 5: Assuming Water Cooling Guarantees Continuous Operation
Cooling-water temperature, flow, chiller capacity, and interlocks still matter.
Mistake 6: Comparing Cold and Hot Performance
Cold-start field and stabilized continuous field may have different electrical conditions.
Mistake 7: Forgetting Ambient Temperature
A rating based on a cool laboratory may not apply in a warm equipment room.
Mistake 8: Testing for Too Short a Time
A brief FAT does not prove long-duration thermal performance.
41. How Cryomagtech Supports Electromagnet Duty-Cycle Planning
Cryomagtech supplies electromagnets, Helmholtz coils, high-precision excitation power supplies, bipolar magnetic field drivers, cooling configurations, field sensors, and custom Magnet & Field Systems for research and industrial testing.
For electromagnet projects, we help evaluate:
- Required continuous and peak field
- pole gap and pole diameter
- ON/OFF cycle
- repeated operating sequence
- maximum continuous run
- coil resistance and current
- hot-condition voltage requirement
- air-cooling feasibility
- water-cooling and chiller requirements
- temperature and flow interlocks
- continuous-duty power supply selection
- field stability after warm-up
- FAT duration and acceptance basis
- realistic trade-offs among field, duty cycle, cooling, size, and cost
An electromagnet should not be selected only by the strongest field it can produce.
It should be selected by the field it can produce safely, stably, and repeatedly under the buyer’s real operating cycle.
References
- IEC – IEC 60034-1:2022 Preview, Duty Types and Ratings
https://webstore.iec.ch/en/iec_catalog/product/preview/?id=L3B1Yi9wZGYvcHJldmlldy9pbmZvX2llYzYwMDM0LTF7ZWQxNC4wfWIucGRm - GMW Associates – Model 5453 Electromagnet User Manual
https://gmw.com/wp-content/uploads/2019/03/5453_User_Manual.pdf - IEC Electropedia – Reliability
https://ieclib17.iec.ch/iev/iev.nsf/IEVref_xref/en%3A192-01-24
Key Takeaways
- Electromagnet duty cycle must define more than a percentage.
- Buyers should state ON time, OFF time, repetition, field, ambient temperature, cooling, and total operating duration.
- Maximum short-time field is not the same as maximum continuous field.
- Coil heating increases strongly with current, and copper resistance rises as the magnet warms.
- Constant-current control is generally preferred for stable electromagnet field performance.
- Air cooling may be suitable for moderate or intermittent use, but temperature variation can limit precision field stability.
- Water-cooled systems still require defined inlet temperature, flow, pressure, chiller capacity, and interlocks.
- Positive and negative field operation both generate heat; polarity reversal is not a cooling period.
- FAT duration should represent the agreed operating duty.
- Quotes should be compared using field, gap, duty cycle, cooling, stability, and acceptance scope—not maximum field alone.
For electromagnet procurement, the key question is not only:
“How much magnetic field can this magnet generate?”
The better question is:
“How much field can it maintain safely and stably for the full duration and repetition pattern of our real experiment?”