MDE300-100S24: Powering the 24V Control Circuits of an Entire Train or Substation From the 110V Bus

On a metro train, or inside a 220kV substation, one DC bus runs through everything: 110V. Fed by a battery bank, it's the system's last line of defense — if external power fails, the battery keeps breaker trip circuits, signaling, and emergency lighting alive.

But the actual secondary devices on that 110V bus — relay coils, indicator lights, control circuits, emergency lighting, ventilation fans — almost all run on 24V. 110V is the "primary supply"; 24V is the "control supply." Between them sits an isolated DC-DC converter. The MDE300-100S24 is that converter.

66-154V wide input covers every battery state

Rated at 110VDC, it actually works from 66 to 154VDC. That range maps directly to a 110V battery's real duty cycle: sagging to ~66V near depletion, floating around 110V, charging up past 140V. Whatever the battery does, the module holds a steady 24V output — control circuits never misoperate because of battery voltage drift.

24V at 12.5A — enough for a whole train's control loads

24V at up to 12.5A, 300W continuous. The control relays, signal lamps, emergency lighting and ventilation fans on a metro train — or the protection relays, signaling circuits and automation devices in a substation — can be consolidated onto this one module. For higher capacity, units can be paralleled.

Set-point accuracy ±2%, line/load regulation ±0.5%, ripple 200mV P-P. More than enough for relay coils and indicator lamps; isolation handles the protection-grade loads.

Why the control supply must be isolated

The 110V bus is not a quiet signal rail. When a train traction system switches or a substation breaker operates, spikes and ground-potential differences are severe. This module isolates input-to-output at >1500VDC, input-to-case >1050VDC, output-to-case >500VDC. The small 24V signals in the control circuits survive primary-side transients intact — that's a safety baseline in the rail and power industries.

Efficiency is 89%; at 300W full load self-loss is around 37W, handled by the metal case's natural convection — no extra ducting inside the cabinet.

In unmanned sites, reliability beats specs

Substations and trains aren't places you pop open for service. Five protections are built in: input undervoltage, input overvoltage, over-temperature, output over-current (120% limit), output short-circuit. Under a fault the module current-limits rather than destroying itself, and recovers automatically once the fault clears.

Industrial case temperature -25°C to +85°C, with Military I (-40°C) and II (-55°C) options. Outdoor substations in the frozen north, locomotive cabs in the desert summer — all within design range.

Where it belongs

• Metro, locomotive and light-rail vehicles: taking 24V for control circuits, lighting and ventilation from the 110V battery bus

• Substations: powering protection relays, signaling and automation from the DC110V operating supply

• Power plants and distribution DC switchboards needing a 24V control branch

• Industrial 110V DC systems feeding 24V secondary circuits

• Anywhere there's 110V DC up front and a 24V control supply required downstream

In the MDE 100-300W lineup, the MDE300-100S24 is the 110V-input, 24V-output workhorse. Need 12V output? That's the MDE240-110S12. Custom designs available.

Samples and datasheets: Guangdong Mingzinc, +86 400-019-3997, shturl.cc/RhOH.

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