Thermal Fuses, PTCs and Thermostats Inside Transformers: Choosing and Positioning Protection
When a Transformer Needs Its Own Protection Most transformers are protected by the fuse on the primary side, and that is usually enough for a fault in the load. It is not enough for a fault inside the transformer: a shorted turn, a partially collapsed insulation, or a winding that heats slowly under a sustained […]
Wire Gauge and Current Density in Transformer Windings: What a Winding Can Actually Carry
Rules of Thumb That Hide the Physics Every magnetics engineer has heard “4 A per mm² for natural cooling, 6 for forced”. The numbers are useful starting points and dangerous when treated as limits, because the permitted current density is an outcome of the thermal design, not a property of the wire. Two windings at […]
Ferrite vs Powder Core for Switching Inductors: A Practical Decision Table
The Two Candidates For a switching converter inductor there are two mainstream material choices: a gapped ferrite core, which has high permeability and low loss but saturates sharply, and a distributed-gap powder core (iron, sendust, or a moulded composite), which has lower permeability and a soft saturation curve but higher core loss at high frequency. […]
Why Magnetic Component Lead Times Change, and What a Buyer Can Do About It
Lead Times Do Not Move Randomly A supplier that quoted 35 days last quarter and now quotes 60 has usually not become less efficient. Something upstream moved: a core grade that is allocated, a magnet wire size that is on a rolling mill schedule, a varnish batch that is shared across the plant, or a […]
DC Fast Charging Module Magnetics at 800 V: Isolation, Loss and Liquid Cooling
What Changed When Chargers Went to 800 V A 350 kW DC fast charger module is a different magnetics problem from an on-board charger. The DC bus moved to 800 V, the switching frequency rose to shrink the passives, the module is liquid-cooled at 60–70 °C coolant temperature, and the isolation barrier now carries a […]
How to Compare Three Quotes for the Same Transformer: Normalising Before You Decide
Three Quotes, Three Different Parts When three suppliers quote the same drawing at 1.08, 1.24 and 1.45, the instinct is to treat the lowest as best value and the highest as overpriced. In most cases the three are not the same part: they differ in core grade, insulation system, test scope, tolerance, and what is […]
Medical Isolation Transformers and IEC 60601-1: What the Standard Requires of the Magnetics
IEC 60601-1 Changes the Magnetics, Not Just the Product Medical equipment is not a harder version of industrial equipment with more paperwork; it is a different insulation problem. IEC 60601-1 divides the patient circuit from the mains by two means of protection, defines working voltages that include the applied part, and imposes leakage and insulation […]
Audible Noise in Transformers and Inductors: Finding the Cause Before Changing the Design
The Complaint That Never Appears in a Datasheet A power supply that hums at 8 kHz is a commercial problem long before it is an engineering one. The customer hears it in a quiet room, the product gets returned, and the magnetics supplier is asked to “make the noise go away” without anyone having established […]
Ferrite Core Gapping: How the Gap Decides Inductance, Saturation and Cost
Why Ungapped Cores Are Almost Never the Answer Ferrite has a high permeability and a low saturation flux density. An ungapped ferrite core stores almost no energy before it saturates: the permeability that makes it good at coupling flux is exactly what makes it unsuitable for storing it. Gapping the core trades permeability for energy […]
The Cost of Poor Quality in Magnetic Components: What the Quotation Does Not Show
The Number That Is Never on the Quotation Two suppliers quote 1.10 and 1.18 for the same transformer. The procurement decision usually goes to 1.10 and is recorded as a saving. Eight months later there is a rework line at the contract manufacturer, a scrap rate nobody budgeted for, and a field return that costs […]