beads and zero ohm resistors

Excuse my ignorance, but aren't these basically just jumpers - and used as such?

Larkin isn't getting enough podium time... thus the stupid question

...Jim Thompson

The spec sheets I've seen say around 20 milliOhms for the 0805 or 0603 zero Ohm resistors.

I have tended to shy away from using "zero" Ohm resistors as option jumpers in PCBs because I find that they open up too often.

Need lower resistance than zero Ohms I guess.

boB

I grabbed one of the generic 0r 0805 parts from our stock. I had to run an amp through it to get enough resolution; it measures 5.75 milliohms.

A *very* rough temp test, with freeze spray, came up +3000 PPM/K, which is consistant with most pure metals, which run around 4000.

This is an electronics discussion group. It will die if we don't discuss electronics. Like, if all people like you post is home woodworking problems and redneck political links.

And neither of my questions are stupid. Both could matter; right now, to me, both do matter.

The resistors are just the usual lowish-tempco metal-filled enamel, slathered on thick without laser trimming.

Multilayer beads/coils are probably something like Cu/Ag/Pd, applied as a ceramic glaze formulation that bakes into mostly-solid metal on heating. Noble metal content is needed, otherwise the ferric iron (a required part of a _ferri_te) oxidizes it, destroying the contact. Not to mention making the ferrite terrible (too much Fe(II) would probably crystallize as magnetite, which sucks).

Caps have the same construction, but they get away with semiprecious metals more effectively as they only have to carry displacement current. The metal layers can be very thin indeed.

Tim

I measured a bunch some years ago. I couldn't find my notes, so I re-measured a few:

#1 0805 0.020 ohms #2 0603 0.0085 #3 0808 0.0085 #4 0603 0.0165

I was considering using them as non-critical current-sense resistors.

Cheers, James Arthur

How much current does it take to make them blow?

I'm still hoping you'll take a grinder to one and see what's inside. (The FB's) Well and post pictures too.

I'm using some of these..

George H.

Ooops, s/#3 0808/#3 0805/

These are from separate reels, BTW.

Cheers, James Arthur

If you whack an SMD F.B. with a hammer, I've only ever found an alloy strap inside.

Cheers, James Arthur

Nice, thanks John

George h.

That is nice, thanks. I guess I need to whack them more often--the last one was a decade or two ago.

Cheers, James Arthur

Perhaps the higher current / lower Z types would tend towards your alloy strap model.

These are the sorts I was thinking of:

I'd forgotten all about the newer "chip" styles.

Cheers, James

The end of this unit's left terminal looks like a plated copper strap:

But it looks almost like that guy's strap was inserted into a completed ferrite bead, then bent; the ferrite units in my stock look like the ferrite was formed in place around the strap. No seams.

Cheers, James Arthur

I can't remember but it should be easy to test for. I think our main problem was in the coil lead of a relay. I've seen them open up in other applications so I try not to use them. Typically I only use them for "options" on a PCB anyway.

Another thing regarding small-ish parts like these is that, for all resistors, say less than a hundred Ohms, should be "pulse rated"... meaning, they shiould at least publish the overload specs for the resistors unless there is just very very low current through them. It's a rule my company has adopted though.

It may be that the zero ohm resistors we have used were not made by Vishay or Stackpole or one of those companies that specify a decent maximum repetitive pulse power.

This is especially important for gate drive resistors where a capacitor is charged and discharged rapidly.

boB K7IQ