Relay for DC Charging Station: 48VDC 150A Latching Relay Guide for EV Chargers

Why the relay is the safety gate of a DC fast charger

When an EV is plugged into a DC fast charger, the first switching decision is made by a latching relay inside the power distribution unit (PDU). The relay closes to connect the charging current, and it must open just as decisively when the session ends or when a fault is detected. In DC fast charging, the relay is not an accessory: it is a safety and performance component that must carry high current continuously and interrupt DC load current reliably.

DC fast charging follows the Mode 4 principle defined in IEC 61851. The station converts a three-phase AC supply into controlled DC and feeds the vehicle battery directly, bypassing the onboard charger. Because a DC waveform has no natural zero crossing, the arc created when the relay opens at load current does not extinguish by itself. The contact gap, the arc chamber and the contact materials have to break that arc on every operation. Selecting a relay for DC charging station applications therefore starts with DC interruption behaviour, not with the continuous rating alone.

The safety implications extend across the whole charging system. The safety benefits of a charging station depend on every switching element performing under load; a relay that welds its contacts during a fault can leave the battery connected, which is the worst single failure mode for a charging pile.

Key selection criteria for a relay for DC charging station

Engineers selecting a relay for a new DC charging pile usually settle on four parameters. The table below summarises what to compare and why.

DC interruption is the first thing to verify

At 150 A on a DC bus, opening the contacts at full current is a harsher event than switching the same current on AC. Line-frequency AC gives the relay many natural zero crossings per second to cool and clear the arc. A DC relay must stretch the arc, cool it and establish a contact gap before the voltage can restrike. For that reason, a DC-rated relay is rarely a drop-in replacement for an AC relay of the same nominal current, even if the continuous rating looks identical.

Latching relays cut standby power and heat

A magnetic latching relay changes state with a short coil pulse and remains in that state with zero coil power. A charging pile can spend many hours per day in standby, so eliminating continuous coil dissipation reduces the temperature inside the PDU. A cooler enclosure improves the derating margin of the surrounding electronics, which is an indirect but measurable benefit in DC power designs.

Coil drive: 48 VDC pulse behaviour

Most charging-pile control boards in our engineering practice operate with a 48 VDC auxiliary rail, and the relay coil is driven from that rail through a capacitor-discharge circuit. Two parameters matter. The first is pulse width: it must be long enough to guarantee a state change at low ambient temperature. The second is the suppression circuit: a poorly designed freewheeling path can cause the latching relay to bounce back into its previous state. Verifying both on the actual control board is part of any serious relay qualification.

AC versus DC charging station relays

Because AC and DC piles are sold into the same infrastructure market, buyers often ask whether one relay can cover both applications. The underlying relay platform is similar, but the ratings and the verification focus are not.

• An AC charging station PDU typically switches 250 VAC at continuous currents in the 120 A class. The AC waveform clears the arc at current zero, so the relay design centres on long life and low contact resistance.
• A DC charging station demands DC interruption performance at high current. The coil interface usually matches the 48 VDC control rail, while the contact system must demonstrate real DC breaking capability.

Our AC charging range includes a 120 A 250 VAC latching relay for PDU applications, sized for the AC load profile and the PDU board layout. On the DC side, the 150 A 48 VDC latching relay for DC charging pairs a 48 V DC coil interface with a 150 A contact system designed for DC switching duty. Choosing the relay that matches the station type avoids both the cost of over-specification and the risk of under-rated field failure.

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Wholesale HJE11F-120A-250VAC Latching Relay for PDU Suppliers, OEM/ODM CompanyHuajin Technology Jiaxing Co., Ltd. is China wholesale HJE11F-120A-250VAC Latching Relay for PDU suppliers and OEM/ODM company, Product O...View Product →

Reliability, endurance and certification

Endurance and contact wear

Charging piles switch far less often than electricity meters, but each operation is electrically severe. The dominant wear mechanism is contact erosion caused by DC arcs at high current. When comparing relays, look for electrical endurance values measured at rated load and at a realistic ambient temperature. Mechanical endurance figures alone can be misleading, because a latching mechanism can outlive its contacts by a wide margin.

The same engineering discipline shows up in the metering industry, where high-reliability control for smart meters depends on contact material and coil stability across millions of pulses. The philosophy transfers directly to charging piles: verify the contact material, the insulation system and the production tolerances on real samples, not only on the datasheet.

Certification evidence buyers check

Charging-station OEMs, in our experience, ask three questions before sampling: Is the relay TUV-certified? Does it carry CCC marking? Is the factory ISO9001-certified? For programs tied to utility or grid infrastructure, evidence related to State Grid requirements is also part of the supplier audit. These checks exist because the relay becomes part of a product used in public infrastructure, exposed to weather, vibration and non-expert users.

At the bench stage, we recommend running three tests on the first batch: dielectric strength between coil and contacts, insulation resistance, and temperature rise at rated current. Performing these tests on production samples rather than engineering samples gives a realistic view of the relay that will actually be shipped.

What to specify in a DC charging project

The selection of a relay for DC charging station hardware can be condensed into five practical points.

1. Specify the worst-case continuous current of the pile, not the average charging current.
2. Verify DC breaking capability at the actual bus voltage and at low ambient temperature.
3. Match the coil drive to the control board: 48 VDC pulse architecture, pulse width and suppression circuit.
4. Compare electrical endurance at rated load, and review certification documents such as TUV, CCC and ISO9001 before approving samples.
5. Evaluate the manufacturer's production capacity and quality controls so that the first batch matches the performance of the samples.

Huajin Technology's background illustrates the supply-side question that OEMs should ask. The history of Huajin Technology Jiaxing shows a relay manufacturer that grew from metering relays into charging-station products, with an annual production capacity of more than ten million latching relays and export sales of about 30 percent. A facility of that scale can support standard product supply as well as custom coil and terminal variants for a specific charging-pile programme.

Get the contact system and the coil interface right, and the rest of the PDU design has a simpler job. That is why the relay should be locked down early in a DC charging station project.