rated current for headers and recepticles

Thread Starter

kutalinelucas

Joined Nov 20, 2007
98
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.
 

SgtWookie

Joined Jul 17, 2007
22,210
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.
 

shortbus

Joined Sep 30, 2009
7,613
SgtWookie, this is true for almost everything electronic isn't it. Mosfets are especially over rated in there data sheets.
 

SgtWookie

Joined Jul 17, 2007
22,210
SgtWookie, this is true for almost everything electronic isn't it. Mosfets are especially over rated in there data sheets.
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.
 
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