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Power Connector Features That
Affect Performance – What
Matters?
By
John Dodds, Global Product
Marketing Manager – Power
Products,
FCI
System power engineers have many
choices in today’s power
connector market, and the list
of options is growing as the
industry diversifies to offer
more specialized products. Here
are some commonly asked
questions: “I have a power
application that requires a
certain amount of current at a
certain voltage with a certain
amount of available space. What
power connector should I use?”
Or, “I have a power application
that requires a significant leap
in efficiency. What power
connector should I use?”
These questions have always been
important with respect to power
connectors. However, the
frequency of such questions in
today’s business and social
environment is significantly
increasing. Individuals,
businesses, investors,
governments, and consumers are
demanding more efficient systems
that cost less to operate (i.e.,
consume less power) without
sacrificing performance. From a
power connector standpoint, this
means increasing power density
(linear current density) and
decreasing contact resistance.
Decreased contact resistance
results in reduced power loss
through the connector, thus
contributing to a more efficient
power system.
System designers are being asked
to increase overall power
efficiency while maintaining or
even increasing system
functionality. Increased rack
density and higher wattage power
supplies are requiring more
effective thermal management.
These increased performance
demands apply across all market
segments — data, telecom, datcom/networking,
medical, alternative/renewable
energy (solar, wind, etc.),
battery technology, and
instrumentation to name a few —
and are driving component
manufacturers toward significant
advances in product technology.
Power connector technology is
evolving to meet these trends in
a variety of ways.
At this point, it’s beneficial
to consider the power connector
features that have a material
effect on system/connector
performance (with performance
being primarily defined as
current carrying capability and
contact resistance). The
following list is not
exhaustive, but it attempts to
capture the most significant
features:
-
Power contact design for low
contact resistance and
increased linear current
density
-
Vented housing design for
enhanced heat dissipation
-
Power contact pitch options
for linear current density
and voltage flexibility (AC
& DC)
-
Lower connector profile
heights that block less
airflow
-
Number of adjacent power
contacts energized
simultaneously and their
relationship to linear
current density
-
System airflow availability
(airflow helps power
connector performance)
-
Second source availability
and joint qualification
testing/documentation for
guaranteed performance
-
Temperature rise
requirements/system ambient
conditions and their
relationship to current
rating performance
Power contact design includes
material selection and
thickness, beam design, and the
number of tails that terminate
into the PCB. Optimization of
these characteristics results in
reduced overall contact
resistance and increased linear
current density. For example,
the new FCI HCI®
power connector system (shown
below) features ultra-low
contact resistance (< 0.5 mΩ
after environmental exposure),
very high linear current density
(> 339 A/linear inch with <
30°C temperature rise, zero
airflow, and 10 adjacent
contacts energized
simultaneously). This power
connector achieves superior
performance by using a high
conductivity copper alloy, an
optimized beam design with
multiple points of contact, and
18 tails per contact to route
current into the PCB.
Contact resistance is an
important feature since it
directly relates to power loss
through the connector. Reducing
contact resistance from 2.0 mΩ
to 0.5 mΩ reduces power loss
through the connector by a
factor of 4. As a result,
systems with high-performance
power connectors can achieve
improved power efficiency,
particularly in high-wattage
systems.
Vent windows in the connector
housing enhances the structure’s
heat dissipation capabilities.
Strategically located vent
windows and coring have been
shown to reduce temperature rise
by as much as 13% at rated
current (neglecting airflow
effects). This significantly
increases the power connector’s
ability to carry more current at
a given temperature rise by
allowing heat to escape the
working parts of the power
contact/housing system.
Power contact pitch plays an
important role in linear current
density and voltage rating. For
a given contact design, current
rating increases by as much as
10% to 20% when the power
contact pitch increases from
6.35mm to 7.62mm. Also, voltage
rating increases by 50% due to
larger creepage and clearance
distances. As such, the larger
pitch is generally reserved for
higher voltage requirements
(6.35mm for DC power and 7.62mm
for AC power). Varying power
contact pitches often fall
within the capabilities of
today’s modularly tooled power
connectors.
Connector profile height is also
a key design criterion in many
1U and 2U chassis-based systems.
Taller profile heights block
more airflow in these
height-constrained systems. This
blocked airflow could be
otherwise used for system
cooling. For example, the new
FCI HPCE™ straddle-mount
configuration (shown below)
features an ultra-low 2.8mm
profile height. This
configuration is highly popular
in 1U and 2U power supplies
because of its ultra-low profile
height as well as its ultra-low
contact resistance (≤ 0.6 mΩ
after environmental exposure)
and very high linear current
density (>180 A/linear inch with
≤ 30° C temperature rise, zero
airflow, and multiple adjacent
contacts energized
simultaneously).
The number of power contacts
energized simultaneously has a
significant impact on current
rating. The chart below shows a
28% difference in current rating
performance between energizing
one and six adjacent power
contacts. The effect is less
noticeable between six and 10
adjacent power contacts. One
practical application of this is
locating power and ground
contacts separately on either
side of a signal field to
increase the per power contact
current rating.
While system airflow is external
to the connector, it has a
significant impact on power
connector performance. For
example, the previously
mentioned HCI power connector’s
temperature rise decreases by
57% when using 400 LFM of
airflow, versus still air (90
amps per contact with 10
adjacent power contacts
energized simultaneously). Even
with only 100 LFM of airflow,
the resulting temperature rise
decreases by 34% (same test
conditions as noted above).
Second source availability and
joint qualification testing also
have an impact on power
connector selection. Most
customers require that power
connector solutions be available
from at least two sources. Dual
sourcing ensures continuity of
supply, shorter lead times,
competitive pricing, and
superior customer support. As
important as these items are,
second source partners should
also be engaged on an additional
level. Joint intermateability
testing and joint control
documentation between licensed
products should be maintained to
ensure full electrical and
mechanical inter-operability
over the product life. This
level of control is a safeguard
against the malfunction of
non-licensed product. Many
non-licensed products do not
undergo rigorous product
qualification testing and do not
have safety agency approval (UL,
CSA, TUV, etc.).
Temperature rise requirements
and system ambient conditions
also affect power connector
performance. For example, a 30°C
temperature rise is an industry
benchmark for rating power
connectors. However, most power
connectors are rated to at least
a 105°C maximum operating
temperature. As long as the
system ambient temperature plus
the associated temperature rise
for a given current do not
exceed 105°C, the power
connector can be safely used at
something greater than a 30°C
temperature rise. As an example,
HCI can accommodate
approximately 100 amps per power
contact at a 40°C temperature
rise (10
adjacent power contacts
energized simultaneously).
If the system ambient
temperature is 55°C, the
resulting 95°C temperature is
well within the 105°C maximum
operating temperature.
System power engineers have many
choices when specifying power
products. They can choose from
power connectors with innovative
features, ultra-low contact
resistance, vented housing
designs, high linear current
density, modular tooling and
second source agreements with
joint qualification testing, and
design control. The end result
is tighter, more efficient, and
more successful systems.
Visit
FCI online.
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