Often during the excitement of designing a challenging new system, some of the more mundane engineering aspects get overlooked. This is especially true of connections between the power supply and the load. The extent to which connector resistance causes voltage drops and even connector damage is not widely understood. Without a good connection, even the best switching power supply cannot provide the various output voltages essential for proper system operation. This blog will outline the principles with which we can analyze the Connector and Cable resistance problems.
CONTACT RESISTANCE
Resistance in connectors
This causes major problems by creating voltage drops and generating heat. The majority of resistance in an entire power supply cable occurs at the contacts of the connectors. This is referred to as contact resistance. A 7 amp quick disconnect connector, which will be discussed in more detail later, has a typical contact resistance of 20 milliohms. This is quite high compared to the 6.4 milliohms in one foot of 18 AWG wire. A very poor connection with this type of connector can have a contact resistance of as high as 100 milliohms.
Voltage drops
Voltage Drops due to contact resistance also degrade the regulation of a power supply. A good supply with 0.1% load regulation on the 5 volt output would have a 5mV drop during a change from a no load to a 5 amp load condition. However, there would be a 500mV drop if there were an additional 100 milliohms of contact resistance at the connector. The 5 volt output would drop to 4.5 volts, degrading the regulation to 10%.
Heat generated
Heat generated from current passing through contact resistance in a connector will increase if the resistance increases. Heat, along with oxidation, will deteriorate the mating surfaces of contacts by accelerating the buildup of tarnish. Tarnish contributes to additional contact resistance. Heat will also diminish then force with which spring loaded contact terminals interface with mating pins. Thus, heat and resistance can escalate until a connector is degraded to a point where the proper output can no longer be delivered from a power supply to the system load. In extreme cases, the plastic connector parts and even the PCB of the power supply can discolor.
The Resistance in a Connector is determined by the following factors:
1. The total amount of surface area between the two mating connectors.
2. The quality of the finish of the conductor surface between the two mating
3. The amount of force pressing the two conductor surfaces of the mating connectors together.
Thank you for reading the blog,
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http://tenettech.com/category/260/terminals-connectors
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