Control Transformer Manufacturer in China | Wilmall
Wilmall is a control transformer manufacturer based in Yueqing, Zhejiang, China. We build JBK3 series control transformers from 40VA to 1.5KVA for machine builders, panel manufacturers and industrial OEMs who need reliable control-circuit power.
The control transformer family we supply
Our control transformer range covers the voltages most machine control circuits need: 220V to 24V, 220V to 36V, 220V to 110V and 380V to 220V, in ratings from 40VA up to 1500VA.
- JBK3 series — the standard enclosed control transformer for PLC panels, contactor circuits and CNC cabinets.
- Custom voltage builds — any input / output combination your control circuit requires, wound to order.
- Enclosure options — terminal cover, mounting bracket style and colour matched to your panel layout.
Why control transformers need to be specified carefully
Control circuits draw a high inrush current when contactors and relays energise together. A transformer sized only for steady-state load can sag under that inrush and cause the control voltage to drop below the pick-up threshold of the contactors. The standard rule is to add 20-30% margin, and to check the inrush VA against the transformer’s capability.
Sizing a control transformer
Add the VA of every device on the control circuit — PLC, relays, contactors, solenoids, indicator lamps — and multiply by 1.2 to 1.3. Example: a panel with a 50W PLC, 30W of contactors and 20W of lamps totals 100W, so a 150VA control transformer is the safe choice.
For three-phase machines with a 380V supply and 220V control circuit, we build a dedicated 380V to 220V control transformer with the same inrush handling.
Quality and testing
Every JBK3 unit is tested for winding continuity, insulation resistance, output voltage under load and dielectric strength before packing. CE / RoHS documentation is available for each model.
Installation tips for panel builders
Control transformers fail early most often because of installation mistakes, not manufacturing defects. Mount the transformer away from heat sources inside the cabinet, leave clearance for air to circulate, and make sure the primary fuse or breaker is rated for the inrush current of the transformer, not just the steady-state load. Use the correct torque on the terminal screws — loose connections heat up and can melt the terminal block over time.
For machines that run continuously, check that the transformer’s continuous rating matches the duty cycle of the machine. A transformer rated for 100% duty at its nameplate VA can run at that load all day; if your panel draws more than that, move up one size.
Common input and output combinations
| Rating | Common inputs | Typical use |
|---|---|---|
| 40-100VA | 220V / 380V | Small relays, indicators |
| 150-300VA | 220V / 380V | PLC + contactor panels |
| 500-800VA | 220V / 380V | Machine tools, CNC cabinets |
| 1000-1500VA | 380V / 220V | Larger machines and lines |
Why buy control transformers factory direct
Panel builders and machine makers buy control transformers in batches with a fixed specification. Buying factory direct means the specification is never “adapted” by an intermediary, the label and packaging match your brand, and the unit cost drops as your order size grows. With MOQ 10 pcs and 15-25 day lead time, you can stock a full range of common ratings without tying up too much capital.
Control transformer vs power transformer
People sometimes confuse control transformers with general-purpose power transformers. A control transformer is optimised for the short, high-inrush loads of relay and contactor circuits, and is sized for the control circuit only. A power transformer feeds the main machine load. Using the wrong type means either an undersized unit that sags under inrush, or an oversized unit that wastes money and panel space. When you order, tell us it is for a control circuit and we will supply the right class of unit.
Thermal protection is another differentiator. Control transformers for export are often specified with built-in thermal fuses or temperature protection so a stalled contactor or shorted control circuit does not turn the transformer into a fire risk. Ask about protection options when you place your order — it is a small extra that matters for insurance and safety audits in many markets.
Documentation for export
Each order ships with a commercial invoice, packing list and the relevant CE / RoHS certificates. Batch test reports can be attached for customers who need them for market registration. If your machine builder or panel customer requires a declaration of conformity, we can prepare that as part of the order documentation.
We also mark every carton clearly with the model, rating and quantity, which speeds up your receiving and keeps your stockroom accurate. For large panel-builder programs we can print your internal part numbers on the units so the installation team recognises the parts at a glance.
Delivery is from Ningbo or Shanghai seaport with FOB or EXW terms, and for urgent machine-down situations we can arrange air freight for small quantities. Most of our control transformer customers hold a small stock of the common 150VA and 300VA units so they can respond to field service calls the same day.
Frequently asked questions
The Inrush Problem: Why Coil-Heavy Panels Fail
The most common reason a control transformer fails on site is not the transformer itself, it is inrush current from the coils it feeds. When a contactor or relay coil energizes, it draws several times its holding VA for the first few cycles, and if the transformer is sized on the steady-state total, the voltage sags and the contactor chatters or fails to latch. The fix is to size with 20 to 30 percent margin and to use the inrush figure for coil-heavy panels, not just the running VA. For a panel with a PLC, six relays, and four contactors, a 150VA transformer is usually safer than a 100VA unit even if the steady-state total looks like it fits. We print the inrush guidance on our datasheets, and our team will walk through your load list with you. Sizing for inrush the first time saves you the cost and downtime of a field failure.
Insulation Class: Matching the Transformer to Your Environment
The insulation class on a control transformer label tells you the maximum operating temperature before the winding insulation degrades. Class B is rated for 130°C total, class F for 155°C, and class H for 180°C. For a panel in a normal workshop, class B is standard and fine. For panels near ovens, furnaces, or in hot climates, move up to class F or H, because every 10°C above the rated temperature rise roughly halves insulation life. We use class F insulation on our larger control transformers as standard, and we can wind class H on request. The label states the class, and the batch test report confirms the temperature rise measured during testing. If your environment runs hot, choosing the right insulation class is cheaper than replacing a failed transformer in a production line, and it is one of the first questions we ask when you send us your application.
Export Documentation for Control Transformers
Importing control transformers into most countries needs the same core documents: commercial invoice, packing list, bill of lading, and often a certificate of origin and a test certificate. We provide all of these with every order, and the batch test certificate doubles as the quality document your customs broker may ask for. For markets with specific requirements, such as CE marking for Europe or certification for certain industrial markets, we can advise on what your destination expects and provide the paperwork we can. We ship control transformers to panel builders and distributors across Southeast Asia, the Middle East, Africa, and Latin America, so the documentation questions are familiar to us. If your buyer or your customs broker asks for a document we do not normally provide, tell us early, because some certificates take time to arrange and it is easier to plan them into the order than to chase them at the port.
Why Panel Builders Buy Control Transformers from Us Direct
Panel builders and OEMs buy control transformers from us direct for three reasons. First, consistency: our batch test reports and quality control mean the transformer you get on order ten matches the one you got on order one, which matters when you are building repeat machines. Second, customization: we can wind to your voltage combination, fit DIN-rail mounting, match a specific footprint, and print your brand on the label, so the transformer fits your panel design instead of forcing your design around a stock part. Third, support: we answer sizing questions and work through your load list with you before you order, not after you have a problem. For a panel builder, a failed transformer means a stopped production line at your customer’s site, and the supplier who prevents that failure is worth more than the one with the lowest unit price. Send us your panel load list and we will confirm the right model.
How do I size a control transformer for a PLC panel?
Add the VA of all loads on the control circuit and multiply by 1.2-1.3 to cover inrush from contactors and relays. A 150VA unit suits most small panels.
Can you build a 380V to 220V control transformer?
Yes, we build 380V to 220V control transformers for machines with three-phase supplies, in the same JBK3 range.
Do you supply CE certificates for control transformers?
Yes, CE and RoHS documentation is available for the JBK3 series. Test reports can be provided per batch.
What is the MOQ for control transformers?
Our MOQ is 10 pcs per model. Different ratings can be combined in one order.
How long does a custom control transformer take?
Standard models ship in 15-25 days. Custom voltages take the same time once the specification is confirmed.
Related reading
Get a factory-direct quote
Send your panel schematic or load list to sales@wilmall.com or WhatsApp +86 197 3022 6757 for a recommendation and price within 24 hours.
