rated current for headers and recepticles

Discussion in 'The Projects Forum' started by kutalinelucas, Nov 7, 2011.

  1. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    Hey guys, just a quick question and I really appriciate the help.

    It may be a silly question, but with rated currents on connectors, does the max current apply to each channel or for the component?

    I'm looking to get a 20-pin header and recepticle to run 5 stepper motors off the same PCB. Each stepper has 0.6A per channel, so 1.2a peak when running. The one I'm looking at has a rated current of 1.5A, will that do the job?

    Cheers.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    The rating should be on a per-pin basis.
    I would de-rate the connectors' current rating by 50%. If you use them at close to their rated current, you will likely have significant power loss, and therefore heating.
     
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    SgtWookie, this is true for almost everything electronic isn't it. Mosfets are especially over rated in there data sheets.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Well, pretty much - more so with current than voltage.

    For example, if you're building a 12v dc supply, you should really use 16v electrolytics rather than 35v or 50v, as the higher voltage rating means a physically larger package, which means longer current paths inside the cap itself, which means more parasitic inductance/resistance, so a higher ESR (equivalent series resistance). You usually want the lowest ESR you can get at a reasonable cost.

    Transistors have a max current rating; you should generally half that. For example, the 2N3904 is rated for 200mA max; but the Vce(sat) curves above 100mA aren't even shown. If you try to push them over 100mA, you're going to run into problems.

    MOSFETs are kind of a special case. The die might actually be able to handle a couple of hundred amps, IF you could keep the die at room temperature - but the legs would melt right off the package long before that. TO-220's max out at around 69A.
     
  5. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    fantastic. Thanks loads
     
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