Another engineer posted that 100mA was my current capacity for 5 volts over IDC connectors through 7 stranded 36AWG wire (listed as 28AWG) ribbon cable. But I don't know where that information comes from. I'm going through about 12" of ribbon cable. Other tables I look up suggest that I could theoretically expect to pass between 200 and 250mA.
I'm pinning out IDC connectors that will carry between 100mA and 300mA of 5 volts and need to minimize the number of pins dedicated to the power. If I'm out of pins, could I get away with 2 pins for 300mA?
Thank you for any replies.
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\$\begingroup\$ Welcome to EE.SE! How much voltage drop can you tolerate? \$\endgroup\$– winnyCommented Jul 6, 2020 at 20:57
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\$\begingroup\$ 5V over 2 feet round trip on 28 AWG is only .1 V drop. That's negligible. \$\endgroup\$– PasserbyCommented Jul 6, 2020 at 21:21
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\$\begingroup\$ Please check the specifications for the connector also. Usually connectors also have a current limit which could be less than the current limit for the wire itself. Connector current limits are based on temperature rise above ambient. \$\endgroup\$– user57037Commented Jul 6, 2020 at 23:56
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2 Answers
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Based on this page which is super nicely detailed: http://www.mosaic-industries.com/embedded-systems/electronic-instrument-design-new-product-development/cables/ribbon-cable-current-rating
Ribbon cable is closer to chassis wiring (Free to air wires) than it is power transmission wiring (Closely bundled wires, some not exposed to outside air). A single 28 AWG (or in your case 36/7 stranded) wire can conservatively handle 1.4A by itself. 500 mA is much lower. 3M also finds 1.5 Amps as a max for their ribbon cable, as a derated to 30 Degree over ambient temperature rise. The absolute max is closer to 2.5 Amps!
If you dedicate 2 wires, (4 if you include ground), the temperature rise over each and the voltage drop over both will decrease, making it a better solution. But you can use a single wire if you wanted to.
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Short bare wires soldered to PCB areas that can pull heat from the wires, will carry the most current.
Long insulated wires, in large bundles, with no air flow, will get the hottest in the middle.
So length is the biggest variable, which you may not have control over.
answered Jul 6, 2020 at 22:20