FEATURED TOPICHigh Durability Terminal for Hot Plug Charger
Toru SHIMIZU*, Akinori TAKADA and Kazumoto KONDA

Electric vehicles and plug-in hybrid vehicles are now the focus of the world`s attention for their low greenhouse gasemissions. The power chargers for these vehicles are generally used outdoors almost every day. Therefore, thecharging connector has to withstand severe conditions such as dust, sea breezes, rain, and numerous mechanicalcycles. In developing a charging connector, we used our original contact structure to achieve high durability and astable performance.
Keywords: charging connector, mechanical cycles, contact, machine cut

1. Introduction
Greenhouse gas emission reduction measures arebeing promoted in every industry to mitigate global warming. Automobiles are one major source of greenhouse gasemissions. In the automotive industry, both the government and private sector are working on the development
and popularization of electric vehicles (EVs/PHVs)*1, 2.
Electric vehicles use a special charging connector and cable
to receive electricity required for driving from a charge station or wall outlet to charge their batteries. Table 1 shows
the basic specifications for charging connectors and cables
manufactured by Sumitomo Wiring Systems.

Table 1. Sumitomo Wiring Systems charging connector/
cable specifications

a day, reaching 10,000 or more mechanical cycles during
the vehicle’s lifetime. Due to these factors, the charging
connector contacts are subject to a high level of wearing
load while being inserted and withdrawn. Sumitomo
Wiring Systems has designed its charging connector contacts with a proprietary structure to make them highly
durable and able to withstand numerous mechanical cycles.

2. Charging Connector Contacts
The international standard IEC 62196 provides that thecharging connector must have mating compatibility. For
common Type 1 charging connectors, for example, 3.6 mm
dia. round pin contact terminals are specified for installation in the vehicle inlet power supply circuits, and socket
contact terminals that fit the 3.6 mm dia. pins are specified
for use in the charging connector, as shown in Fig. 2.

EV/PHV batteries are mostly charged mostly outdoors.
Charging connectors are exposed to dust, mud, sea breezeand rain. The charging frequency is generally once or twice

Fig. 2. Charging connector contacts

Fig. 1. Charging connector operating environment

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3. Geometrical Features andMechanical Durability
3-1 Mud discharging structure
As described earlier, since the charging process takes
place mostly outdoors, the charging connector is exposed
to dust, sea breeze and rain. Under the above extremely severe conditions, the contact points wear during connector
insertions and withdrawals because of the ingress of contaminants. Sumitomo Wiring Systems has developed its
proprietary socket terminal shape to improve resistance tomechanical wear. Figure 3 compares the structural features
between our proprietary socket terminal and a conventionally shaped one. The conventional socket terminal allows
mud (mixture of dust and rain) in the connector to constantly flow to the area that contacts a mating pin terminal
during connection. In contrast, Sumitomo Wiring Systems’
proprietary socket terminal is constructed so as to discharge most mud sideways before the pin is inserted.

after 10,000 cycles of the mud/salt water dipping andinsertion/withdrawal test based on UL 2251. Contact areasof the conventional terminal were heavily worn, with thesilver-plated surface layer being lost and the base copper
layer being exposed. Sumitomo Wiring Systems’ proprietary terminal shows only minor damage to the contact
areas, maintaining its features as an electrical contact.
3-2 Contact geometry
As shown in Fig. 5, while conventional socket terminal
has an acutely angled contact edge making a circumferential line contact with the pin, our proprietary socket terminal makes a surface contact with the pin.

Fig. 5. Contact shapes

Figure 6 shows photos of the contact area at an advanced stage of mechanical wear. In general, mechanicalwear begins at the portion that first contacts the mating pin
during insertion. The wear progresses gradually rearward.
Since our proprietary socket terminal makes a surface contact over a wide area, it takes a long time for the mechanical wear to spread over the entire contact area, ensuring along useful life.
Fig. 3. Mud discharging design

Figure 4 shows the damage observed by optical microscopy (OM), SEM and elemental mapping*3 of the contact areas of the conventional and our proprietary terminals

Fig. 6. Advanced stage of wear in the contact area

Fig. 4. Worn contact areas (after dipping in mud/salt water and 10,000 mechanical cycles)

44 · High Durability Terminal for Hot Plug Charger

Figure 7 shows the mechanical durability of Sumitomo
Wiring Systems’ charging connector verified by themud/salt water dipping and insertion/withdrawal test basedon UL 2251. The useful life of our charging connector ismore than three times longer than that of the connector
using the conventional socket terminals, with the electricalFig. 7. Life limit verification by mud/salt water dipping andmechanical cycle test
Fig. 9. Socket terminal fabrication processcontact resistance being stable even after 30,000 mechanicalcycles. Such a level of durability is highly significant because
damaged contact surfaces can lead to serious accidents suchas overheating during charging, resulting in fusion and fire.

4. Engineering Features andDimensional Stability
The sectional front view of the contact part of a socket
terminal is noncircular before connection but circular afterconnection to match the diameter of the mating pin asshown in Fig. 8.
Fig. 10. Dimensional stability of contact partthe contact part between conventional and our proprietaryterminals. The variation of our proprietary terminals is lessthan one-third that of conventional terminals. The dimensional accuracy of the contact part is extremely importantfor stable contact performance of charging connectors.
Our proprietary terminals achieve a favorable contact condition both in radial and axial directions, as shown by thephotos in Fig. 11.

Fig. 8. Front view of contact part

Figure 9 shows the manufacturing process of socket
terminals. The conventional socket terminal is manufactured by machining processes of turning, boring and slotting, followed by a drawing process to form the contact part(shape shown in Fig. 8). In contrast, our proprietary socket
terminal is fabricated and completed by using our proprietary integrated machining process and proprietary special
tools without using a drawing process.
Since the contact parts of our proprietary socket terminals are formed not by drawing but by machining, theirdimensional stability is excellent, free of the effects of residual stresses resulting from bending. Figure 10 compares
histograms of variations in the inscribed circle diameter ofFig. 11. Contact condition of our proprietary socket terminal

5. Surface Treatment
As explained earlier, the charging process, which takes
place mostly outdoors, is naturally subject to exposure to a
corrosive environment, such as rain and sea breeze. Figure 12

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and complete contact parts with high dimensional stability
and high quality. Sumitomo Wiring Systems commenced
mass production of the charging connector in 2012,achieved regional safety certifications (US UL, European
CE Marking, etc.) and has been shipping it to various countries. Our charging connector is expected to come intowider use as ecological EVs and PHVs become popular in
the future.

Technical Terms*1 Electric Vehicle (EV): A vehicle driven by an electric
Fig. 12. Surface treatment and electrical contact resistanceshows an evaluation of the stability of connector terminals
in the electrical connection, tested through a repeatedprocess of immersion in high-concentration salt water andexposure to the air. The electrical contact resistance of
Nickel-plated contact surfaces, commonly seen on home
appliance plugs, or of bare contact surfaces increases possibly due to the formation of an insulating oxide film. Silver
plating is virtually immune to that effect. For charging connectors intended for outdoor use, stability in the electricalcontact resistance of silver plating is highly assuring. Sumitomo Wiring Systems’ connector terminals also employ silver plating.

motor. In contrast to this, gasoline-fueled vehicles burnthe fuel to drive. In recent years, EVs have come into
focus against a backdrop of natural resource constraints
and environmental problems.
2* Plug-in Hybrid Vehicle (PHV): A hybrid electric vehicle
that uses external power sources to charge. PHVs offer
the advantages of an electric vehicle that emits no CO2
or other exhaust gases during driving and of a hybrid
electric vehicle that uses both a gasoline engine andelectric motor to enable long-distance driving.
*3 Elemental Mapping: An elemental analysis method thatuses characteristic X-rays. Elemental mapping scans anelectron probe and images differences in X-ray emissions from different points, using the counting rate of
X-rays at a specific energy as the signal.

References

6. Conclusion
To develop a charging connector for electric vehicles(EVs/PHVs), Sumitomo Wiring Systems provided socket
contact terminals with a proprietary design. The proprietary socket terminals exhibit high mechanical durability
in the assumed outdoor environment and have nearly threetimes longer useful life than that of conventionally shaped
socket terminals. Moreover, our original engineering method
has enabled an integrated machining process to manufacture

(1)
(2)
(3)

IEC62196-1, -2
UL2251SAE J1772

Contributors (The lead author is indicated by an asterisk (*).)

T. SHIMIZU*• Program Manager, SUMI REMA EV Solutions GmbH

A. TAKADA• General Project Manager, Speciality Harness Group Division 2, Sumitomo Wiring
Systems, Ltd.

K. KONDA• General Project Manager, Speciality Harness Group Division 2, Sumitomo Wiring
Systems, Ltd.
Photo 1. German user Sumitomo Wiring Systems’ charging connector

46 · High Durability Terminal for Hot Plug Charger