Charged EVs | Excessive-potential testing for EVs: why reed relays increase confidence in insulation and security

EV platforms stay on the intersection of excessive voltage, excessive energy and strict security necessities. From battery packs and traction inverters to DC quick chargers and cable harnesses, engineers should show that insulation is sound throughout growth and at end-of-line. That’s the function of high-potential testing. In a face up to check the product is pressured above regular working voltage and leakage is measured. In a breakdown check the voltage is elevated till insulation fails in order that secure design margins will be set. Each require exact management of kilovolt sources, very low leakage measurement and secure discharge paths.

This text reveals the best way to construct dependable hipot levels for EV testing and why high-voltage reed relays are a robust match for the switching and security capabilities inside these levels.

The place hipot matches within the EV lifecycle

Battery modules and packs
Confirm isolation from chassis, examine coolant ingress threat, validate contactor assemblies and pre-charge networks. Finish-of-line stations sometimes carry out DC face up to exams and retailer leakage outcomes as a baseline for subject service.

Traction inverters and DC-link assemblies
Validate the isolation barrier between the high-energy DC bus and management electronics, then repeat after thermal biking or vibration stress.

Onboard chargers and DC quick chargers
Verify isolation from the AC grid and between energy levels. For megawatt-class techniques, secure discharge after a check step is crucial earlier than operators can join the subsequent unit below check.

Excessive-voltage wiring harnesses and connectors
Cable hipot checks for pin-to-pin shorts and pin-to-shield leakage, usually throughout a whole bunch of nets via a switching matrix.

These use instances push the identical core necessities on the hipot station: apply and measure at kilovolt ranges, restrict fault vitality, sequence exams safely, minimise check time, and preserve leakage measurement reliable.

Why the change expertise issues

Inside most hipot rigs you’ll find a programmable HV supply, measurement and safety {hardware}, and a financial institution of switches that route the supply and meter to the unit below check or to a discharge load. The switches shoulder a number of jobs directly. They have to:

• face up to excessive open-circuit voltage with out breaking down
• change the specified voltage and vitality when required
• contribute little leakage or parasitic capacitance
• isolate management electronics from the HV area
• function shortly and repeatably over lengthy responsibility cycles

Electromechanical relays are reasonably priced however their open-air contacts restrict sensible switching voltage and standoff. Stable-state relays are quick and compact, but introduce non-linear leakage and better off-state capacitance that may masks actual leakage within the gadget below check. Excessive-voltage reed relays remedy a special set of issues. The contacts are sealed in an inert vacuum, in order that they tolerate increased electrical fields in a small package deal and ship extraordinarily low off-state leakage with very low parasitics. The coil is galvanically remoted from the sign path, which protects management electronics. Function occasions are quick, sometimes below a millisecond, which helps preserve cycle time down.

In brief, the change behaves extra like a near-ideal open or closed conductor, which is strictly what you need when measuring microamp or nanoamp leakage.

This graph reveals a comparative plot of leakage present versus isolation voltage for a number of change lessons. Conventional EMRs rise early and are restricted by their decrease standoff. Typical high-voltage SSRs maintain longer however nonetheless leak within the microamp area as voltage climbs. Instrument-grade reed relays preserve a lot decrease leakage at increased voltages as a result of insulation resistance is orders of magnitude increased, into the 10¹² to 10¹³ ohm vary for traditional units and as much as 10¹? ohm in customized builds. For battery, inverter and charger hipot, that distinction is the hole between a clear cross and a false failure.

Architecting a hipot stage with reed relays

A sensible EV hipot station will embrace a number of relay-controlled paths:

1. Supply routing. Choose the specified voltage area, for instance pack constructive to chassis, pack damaging to chassis, or pin-to-pin on a harness. Reed relays with excessive standoff scores function the isolation components right here.
2. Measure path. Change the meter throughout the gadget below check or to a reference load for self-check. Low leakage and low capacitance within the relay assist protect measurement constancy.
3. Discharge and bleed. After a check step, route a resistor throughout the output so saved vitality is eliminated earlier than the operator proceeds. Utilizing a devoted reed relay for this operate creates a predictable, secure discharge path each time.
4. Safety and interlock. Separate relays can implement permissives, for instance open the supply path immediately if restrict present is exceeded and latch the system till the discharge completes.

As a result of reed relays are compact and magnetically screened, many channels will be packed on a single board to construct scalable harness or pack fixtures. In the event you want Kelvin measurements elsewhere within the station, two-pole units cut back the channel depend for four-wire connections.

Choosing the right gadget: what to search for

If you select relays for hipot switching, match the specification to the job:

• Minimal standoff voltage. That is your open-contact survival quantity. For EV and charger work, units with 5 kV, 10 kV or 20 kV scores give snug headroom.
• Most switching voltage and energy. For breakdown exams and for managed discharge, make sure the relay can change the supposed voltage and vitality with out contact erosion.
• Change-to-coil isolation. Protects your controller if the HV path faults. Pickering’s customizable Sequence 600 will be configured for as much as 25 kV switch-to-coil isolation.
• Insulation resistance. Increased is best for leakage constancy. Normal Pickering HV relays are examined to larger than 10¹² ohm, and customized components can attain larger than 10¹? ohm.
• Function and launch occasions. Sooner function reduces dwell, sooner launch shortens the discharge-to-ready interval.
• Bodily format and shielding. Inner mu-metal shields enable side-by-side packing with minimal magnetic interplay, which issues if you scale to giant matrices.

Product choices that map cleanly to EV hipot

You may construct most EV hipot matrices from a small set of households:

• Sequence 63 and the customizable Sequence 600, for the best isolation calls for. As much as 20 kV standoff with switching as much as 12.5 kV, 200 W max. Sequence 600 provides modular choices for voltage, coil, shielding and mounting, and will be configured for as much as 25 kV switch-to-coil isolation. Each collection additionally embrace changeover choices as much as 2.5kV switching and 5kV standoff. Good matches embrace pack and charger isolation exams, inverter barrier validation and long-duration burn-in the place standoff margin helps.
• Sequence 60 and 65, for high-voltage routing the place area is tight. As much as 12.5 kV switching and as much as 15 kV standoff, with change currents as much as 3 A at 50 W and carry currents as much as 3.5 A. Usually utilized in cable and harness hipot fixtures.
• Sequence 104, compact units with 5 kV standoff and 1.5 kV switching. Helpful as measurement selectors, discharge path management, or security interlocks contained in the rig.
• Sequence 67 and 68, high-power choices that carry 200 W switching right into a dense package deal with as much as 10 kV standoff and seven.5 kV switching. Useful the place you want increased present discharge networks or stress steps. Additionally they have a singular design to allow increased density packing, while nonetheless sustaining applicable distances between pins. Changeover choices are additionally obtainable as much as 2.5kV switching and 5kV standoff.
• Sequence 119 and surface-mount Sequence 219, for compact boards that also want as much as 3 kV standoff and 1 kV switching. These allow dense multi-channel fixtures that slide into modular testers.

In case your topology requires two-pole components, Pickering additionally provide a variety of 2-pole configurations to assist Kelvin connections and cut back channel depend.

Design ideas that save time on the bench

• Assume in vitality, not solely voltage. A 5 kV breakdown step right into a capacitive load shops vitality that should be discharged safely. Fee the discharge relay and resistor for each voltage and pulse vitality.
• Guard your measurements. Use guarded layouts and high-resistance supplies across the relay pins so leakage paths don’t bypass your meter. Inner shields keep away from the exterior clearances that may restrict open-contact voltage in some designs.
• Sequence for operator security. Interlock the supply path with the discharge path and door switches. Use the relay’s quick function and launch occasions to shorten the safe-to-touch interval between DUTs.
• Validate at temperature. Leakage and standoff are temperature delicate in lots of techniques. Run a brief design validation that sweeps temperature along with your chosen relay set earlier than freezing the BOM.

Closing the loop with manufacturing wants

EV applications stay on throughput. Cycle time and uptime matter as a lot as headline voltage. Reed relays assistance on each fronts. Function occasions will be sub-millisecond, so routing steps don’t dominate the check. Mechanical life extends to hundreds of thousands and even billions of operations when used inside score, which retains fixtures in service and reduces upkeep. Low coil energy additionally helps thermal design in dense racks.

For engineers who must standardize throughout platforms, the identical relay households present up in pack hipot, charger isolation, inverter barrier checks and cable harness testers. That simplifies spares and documentation and allows you to reuse known-good layouts.

The place to begin

If you’re constructing or refreshing an EV hipot station, a sensible choice is among the Sequence 63 or Sequence 600 units for the primary isolation paths, Sequence 104 for measurement and interlocks, and Sequence 67 or 68 for discharge management when increased energy is required. For compact harness fixtures, have a look at Sequence 119 or 219 to maintain density excessive. If in case you have a constraint {that a} catalog gadget doesn’t meet, Pickering’s engineering staff can tune coil voltage, shielding, pinout and isolation to match your design guidelines.

Have questions or need to assessment a schematic? Pickering’s knowledgeable reed relay engineers are glad to assist choose components, talk about creepage and clearance in your board, and advise on discharge sizing and security interlocks in your voltage and vitality ranges.

Contact: techsales@pickeringrelay.com