Off-the-shelf toroids cover the common voltages, but many projects need something specific. Examples are an unusual secondary, several windings, a size limit, or special leads. Toroids are easy to customise because the core and each winding can be sized independently. Here is what to decide before you ask for a quote.
The specification checklist
| Parameter | Example | Why it matters |
|---|---|---|
| Primary voltage and frequency | 230 V, 50 Hz (or 2 × 115 V for export) | Sets the primary turns. A 60 Hz design run on 50 Hz runs at higher flux and may saturate. |
| Secondary voltage(s) | 30-0-30 V, plus 15 V | State whether it is at full load (usual) or no load. |
| Secondary current(s) | 5 A, 0.5 A | Sets the wire gauge. Say if the load is a rectifier and capacitor, since that raises RMS current. |
| VA rating | 320 VA | Sets the core size. It is the sum of all secondary V × A. |
| Maximum dimensions | ≤ 110 mm Ø × 50 mm high | Very important in 1U/2U cases. |
| Mounting | Centre bolt kit / potted centre / PCB | Affects the finished shape and hole size. |
| Leads | 200 mm, sleeved, specific colours | Saves rework in production. |
| Electrostatic shield | Copper foil between primary and secondary | Reduces mains noise coupling, useful for audio and medical equipment. |
| Thermal protection | Thermal fuse or cut-out | Required by some product standards. |
| Insulation class | Class B (130 °C) or F (155 °C) | Sets the allowed temperature rise. |
| Regulation / inrush targets | ≤ 8% regulation, low-inrush design | A special request can trade size for performance. |
| Hi-pot (insulation) test | Primary–secondary test voltage you need | Should match the safety standard your product must meet. |
| Quantity | 2 prototypes, then 200/year | Affects price and lead time. |
Tips that avoid a second prototype
- Specify voltage at full load. If you need a particular DC rail, state the rail and the load current and let the manufacturer work backwards. Rectified rails are about 1.414 × the AC voltage. See the amplifier guide.
- State the real load type. A capacitor-input rectifier draws peaky current, so the transformer needs a larger RMS rating than the DC current suggests.
- Give the mechanical limits first. If the diameter or height is fixed, say so up front. It is the one thing that cannot be changed later.
- Mention the environment. High ambient temperature, vibration or an enclosed case all influence the design.
- Ask for a sample first. Test it in your actual equipment, on your actual mains, before ordering in volume.
An example specification
Primary: 230 V AC, 50 Hz
Secondary 1: 30-0-30 V AC at 5 A (full load), feeding bridge + 20,000 µF
Secondary 2: 15 V AC at 0.5 A
Rating: ~310 VA
Size: max 115 mm dia × 55 mm high
Mounting: centre bolt, rubber pads, steel washer
Leads: 250 mm, colour-coded, labelled
Extras: electrostatic shield (earth lead), Class B insulation
Quantity: 2 samples, then approx. 100 pcs
Ready to request a quote?
Send your specification through the Vaani custom transformer request form. Vaani designs and winds toroidal transformers in India.
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