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CTIS # 29954

Prepared By John Yurtin

Updated 2-3-2005

Connection Systems Training

Electrical Performance & De-Rating

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Having a good technical understanding of the expectations and performance of connections can help you properly apply them within the vehicle. Electrical performance should be clearly understood since it is the basic function of our products.

This training help you understand electrical performance and how it applies to specific applications.

Excellence

Performance Goal: Do it right the first time, every time

Method: Innovation and continuous improvement

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Contents

Understanding De-Rating

Crimp-To-Crimp Resistance

Example

Various Specifications

It’s Not That Simple!

Cable Examples

Actual Failure Analysis

What Do I Need To Know?

Resources

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Understanding De-Rating

De-Rating limits the circuits current to assure that heat generated does not exceed the limits of the connection materials.

The temperature rise generated by the current + the ambient temperature must not exceed the material limits

Temp Rise + Ambient < Lowest Material Limit

Example: If cable insulation is limited to 1350C and ambient is 1250C then there cannot be more than 100 of temp rise.

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A mating set of terminals is simply a resistance– We call this “Crimp-to-Crimp resistance

– It is measured before and after testing

– It unfortunately can vary over the life of the product

The mated terminals replace the resistance of an equal length of wire .

35 mm length

35mm of 16 ga cable is .53 m/ohm

Crimp-To Crimp Resistance

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Crimp-to-Crimp Resistance•Interface resistance•Bulk resistances•Two Crimp Resistances

Crimp-to-Crimp resistance at the end of testing is usually only several milliohms and varies with design, size and materials

– Example - 280 Metri-Pack 1.1 m/ohms

But, many specifications allow resistance to be up to 10 m/ohms or more

As Current flows through the terminals, they heat up (I2R=P)

Heat is dissipated through:

– Conduction down the core of the wire (approx 80%)

– Radiation to other bodies

– Convection through air

=

Crimp-To Crimp Resistance

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Example

In a connection system, there is some weakest link with regard to temperature, e.g. maybe the cable insulation

If the ambient temp is 1250C and we start passing current, the terminal is going to heat up based on I2R effect

Once the ambient plus the rise due to current reaches the insulation limit,then we have a max operating current.

Limitations (example):Cable Insulation: 1350CTerminal Plating: 1750CConn Body Material: 1500CCopper Core: 2000CSilicone Seals:

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Cross Link Cable is good for 1350C, so in a 1250C ambient we can only allow a 100 rise.

If we rate terminals for maximum cable current then:For 16 ga cable, the max current is (for example):

15 amps per SAE J 2030 (*29.20 Temp Rise)13 amps per Deutsch Spec (22.20 Temp Rise)

Because you can’t exceed the max rating of the cable insulation, you need to limit the current …

…again, this is called De-Rating.

* Calculated Values

Example

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Average Crimp to Crimp Resistance Values

" Micro 64“ “gold plated“ 5.5 mΩ

“ Metri-Pack 150“ "unplated“ 8.5 mΩ " Metri-Pack 150“ “tin plated“ 2.7 mΩ " GT 150“ “tin plated“ 4.0 mΩ " Metri-Pack 280“ " unplated“ 1.8 mΩ " Metri-Pack 280“ “tin plated“ 1.1 mΩ " GT 280“ “tin plated“ 3.0 mΩ " Metri-Pack 480“ " unplated“ 2.5 mΩ " Metri-Pack 480“ “tin plated“ .65 mΩ " Metri-Pack 630“ “tin plated“ .45 mΩ " Metri-Pack 630“ " unplated“ .50 mΩ " Metri-Pack 800“ “tin plated“ .40 mΩ

It is important to understand that there is no one resistance for any set of terminals, The resistances vary depending on the test and test sequence.

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SAE/USCAR Specification

Temperature Rise Test

Test at 230C in open air, not in connectors

Increase the current in increments until:

a) The temperature of any terminal interface exceeds a 55 o C rise, or the maximum temperature recommended by the terminal manufacturer, whichever is lower.

b) The Total Connection Resistance of any terminal interface exceeds... (10 mΩ for 1.5mm Terminals)

Plot the temp rise curves for each wire size. “These graphs are NOT to be used for actual terminal application in a vehicle.”

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ISO 8092 Specification

Really has no requirement for specifying max current capability!

Temperature Rise Test

Test in connectors at 230C (room temp)

Test currents for each cable size are found in the specification.

(13.5 A for 1mm2 cable)

A current reduction coefficient is applied for multiple connectors.

The temperature shall not exceed 400C rise

Note: The temperature rise shall not be used as a guide to the capability of the connector to operate at elevated ambient temperatures.

Current Cycling

Apply 500 cycles, each 45 min current on, 15 min current off

Current is specified by the manufacturer

Resistance not to exceed 30 mΩ or 200% of initial value, whichever selected by supplier and user. (1.5mm terminals)

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If several circuits within a connector are powered simultaneously, their heat can add requiring additional de-rating.

Most circuits are not continuously powered, but rather have cyclic currents (on/off cycles).

In multi-way connections, and in wire bundles, simultaneous powered circuits can add up heat, or, in the same way, harness bundles can act as heat sinks.

In device connections, the device can be a heat sink or a heat source complicating the de-rating

And It’s Not That Simple!

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Cable Example 13 A

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Cable Example 15A

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Temperature Rise Curve

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Typical Transient Curve

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Terminal Temperature Tool (Intra-Net)

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Contact resistance increases (next slide)

Excessive heat is generated weakening the contact

Low contact force results in even greater resistance and heat

Temperature reaches limits of the plastic

Eventual total circuit failure

Actual Resistive Failure Example

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Wrong application of the connection Wrong terminals Wires too small Unexpected duty cycle

Poor Crimps

Improper fusing or circuit protection

Environmental corrosion of the terminal interface As a “rule of thumb”, oxidation and stress relaxation rates double

with every 10OC rise in terminal temperature.

High resistance from worn out motor

What Causes Resistance Failure?

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So What Do I Need To Know?

Understand the complete circuit in which the connection performs

– Know for sure what the expected worst case current will be.

– Is the current steady state or intermittent?

– Fusing and circuit protection

Should the system be sealed?

Understand the real limits of the connection.

Use the prediction tools

Look at the actual validation test results

Perform testing if necessary

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Resources

Product Data Sheets

Connection Systems E-Catalog

Product Handbook

Electrical Performance Programs On-Line

Actual Validation Test Reports

So What Article

George Drew – Contact Physics Expert

Product Line Managers