Comments on: Current-Sense Resistors: Mind the Power

By: Ed

Ed — Thu, 13 Sep 2012 15:48:24 +0000

I have another resistor in the heap, but … yeah, a pair of power diodes looks like a really good idea!

The 3 ADC “fault current” would require something bigger than 1N4001s. With a bit of luck, there’ll be room inside the box for a pair of junkbox stud diodes.

By: hexley ball

hexley ball — Thu, 13 Sep 2012 15:38:25 +0000

A couple of shunt diodes in parallel with the sense resistor might keep the new resistor from going all crispy critter, no?

By: Ed

Ed — Thu, 13 Sep 2012 13:35:56 +0000

the appropriate gauge copper wire as a sense resistor

Copper’s thermal coefficient (something like 0.4%/C) pretty much kills any hope of accuracy for a precision meter, but for typical currents in fat wires under shirt-sleeve conditions it works surprisingly well.

I’ve seen cheap meters using a 10 AWG copper wire resistor calibrated with a diagonal cutter: squeeze until the meter reads the right current! Of course, that puts all the resistance in the notch, but …

many strange things were done to the supplies

Improvements, all of them, I’m sure of it! [grin]

By: ewf

ewf — Thu, 13 Sep 2012 12:31:38 +0000

I did a tour of duty at Circuit Power Inc. (now defunct) and they used the appropriate gauge copper wire as a sense resistor, in their larger (>30 Amperes) supplies. It was mounted on the bottom of the printed circuit board, in staked-in turret posts that were open at the top (in this case, the bottom). They were soldered into the post with eutectic solder, which allowed gravity to open the circuit, as a fail safe, if the fold-back current electronics were not working (mostly tampering). Their primary customers were universities and many strange things were done to the supplies. Testing this feature usually drew an audience.