Do Wiggle Stick Meters Wear Out?

I had to repair a taut band suspension because I had acceidentally trashed its mounting (don't ask). Fortunately, the band itself was intact and could be unsoldered from the remaining debris. It's not fun but is possible, more so I'd say than for a typical jeweled movement simply because there is not hairspring to cause problems.

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Reply to
Sam Goldwasser
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When in doubt, use a keeper. I've seen servo and stepper motor PM magnets die if the rotor is just pulled out.

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Reply to
Sam Goldwasser

Yes, but it also won't put much in the way of current into the coil. You might as well use a straight DC supply, and just press the button for an instant.

I big honking diode would work better. Charge your capacitor up to

400V or so, and dump it into a coil that has a diode in series. The current will quickly ramp up to some maximum value. There will be a nasty back emf spike, but such is life.

-Chuck

Reply to
Chuck Harris

Everything wears out. The Rockies and the Sierra are dwindling down at about an inch every 1000 years. If you mean in your lifetime, probably not unless you start to bang the needle off the peg every so often.

Jim

Reply to
Jim Weir

On 31 Dec 2003 19:12:30 -0500, Sam Goldwasser Gave us:

I'm having a tough time with this one.

Reply to
DarkMatter

In what way? :)

I think one example was a "Slo-Syn" motor. I removed the rotor out of curiosity. When it was put back in, the motor had lost 75 percent of its torque. Definietly a weak magnet. I probably still have it and an identical good unit.

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Reply to
Sam Goldwasser

On 31 Dec 2003 20:43:57 -0500, Sam Goldwasser Gave us:

die

It was the sliding action, perhaps. I'm still finding it hard to believe that it just didn't get overheated, and went above it's curie point temperature, causing loss, and you didn't catch the torque loss.

Are you saying that you made a before and after measurement with it, when you did it? Or was it "in for repair" already?

Reply to
DarkMatter

I read in alt.binaries.schematics.electronic that Chuck Harris wrote (in ) about 'Do Wiggle Stick Meters Wear Out?', on Wed, 31 Dec 2003:

It put enough.

Oh, yes A 4 A DC supply is much easier that a 34 mA one.

This capacitor has infinite capacitance?

I don't really think you understand what happens.

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Reply to
John Woodgate

die

Yes, at least by hand. I didn't actually use instruments. They were identical before, very different after. Neither was subjected to any abuse.

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Reply to
Sam Goldwasser

And who said it did?

You think there won't be a back emf spike when the diode stops conducting? Hmmm?

-Chuck Harris

Reply to
Chuck Harris

On 01 Jan 2004 10:07:05 -0500, Sam Goldwasser Gave us:

magnets die

I'd bet that a check on the "magnetized state" of the rotor would show that it had become magnetized thereby offsetting what work gets done upon re-assembled.

If you demag the rotor, then return it, the torque should return.

Just one possibility that immediately came to mind. I'm not saying that is what happened, just throwing it out to see who salutes it.

Reply to
DarkMatter

On Thu, 01 Jan 2004 11:01:25 -0500, Chuck Harris Gave us:

When one dumps a cap into a coil, there is a current inrush. When one attaches a constant voltage DC source to a coil, there is a current inrush, and then a standing magnetic field is exhibited until the source is removed.

The collapse of the flux will be slower from the cap than if a DC source is applied, a standing field is exhibited, and then said source is immediately released. That second method will exhibit a MUCH higher slew rate on the collapsing flux, and a much higher potential will be "seen" at the coil terminals.

A cap makes for a slow collapse, and the back emf is nowhere near as high. As the cap discharges, the voltage decreases to zero. The coil does not recharge the cap, even without the diode. At least not enough to make a difference. Ther are a few perturbations, but it looks similar to a slightly under damped feedback loop, with each reverb being vastly smaller than the previous...then to zero.

Reply to
DarkMatter

I don't claim to fully understand the cause, but I do know that it can certainly happen with certain kinds of magnets.

Sturmey-Archer, the maker of the 3-speed bicycle hubs that you're probably familiar with, also made a hub with a generator built into it. If you pull the armature out of the multipole circular magnet it will lose most of its field. I've never done this, but I have the factory manuals that explain to only slip the armature out as you slip the keeper in.

I also have a NOS magnet, shipped from the factory with a keeper in place.

-

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

-----------------------------------------------

Reply to
Jim Adney

Damn! I wasted all that money going to engineering school!

Inductors resist a change in current. When you apply a voltage to an inductor, the current is initially *zero* and it rises linearily until it reaches V/Rcoil, or the saturation of the core if you have one.

When you clamp a charged capacitor to an inductor, you create a tank circuit. The capacitor and the inductor pass energy back and forth. They would do so forever, but for radiation losses, and losses in the coil and inductor.

Either I am not understanding what you meant to say, or you need to study the basic circuit elements, and resonant circuits some more Mr. DarkMatter.

-Chuck Harris

DarkMatter wrote:

Reply to
Chuck Harris

On Wed, 31 Dec 2003 12:38:03 -0500, "BFoelsch" Gave us:

Take a look at the link I posted earlier in this thread, and you'll see (read and see) how important it is.

Of course it is still valid. Valid for all magnetic media.

Why else would we actually develop different magnetic alloys unless properties, and characterizations of any and all known and attainable principles were not the goal?

Reply to
DarkMatter

On Thu, 01 Jan 2004 13:21:37 -0500, Chuck Harris Gave us:

Losses, losses, losses. I think I said that.

Reply to
DarkMatter

On Thu, 01 Jan 2004 13:21:37 -0500, Chuck Harris Gave us:

It will cycle a few times, but will essentially stabilize at a DC voltage, with a standing field on the coil, and slowly leak down from there on high turn count, high DC resistance coils, and on low turn coils, even faster. Continuous self oscillation requires a pump.

Resonate that.

Reply to
DarkMatter

In article , jim@rst- engr.com mentioned...

Yeah, I'd guess as much, now that I've read the other followup about a jeweled watch escapement moving back and forthe five times a second for decades.

About the mountains.. I was watching some program on PBS this morning that went along with a guy who survived Mt. St. Helens "eruption", if you can call seven tenths of a cubic mile of a mountain blowing away an eruption. ;-)

They took a hike back around (what's left of) the mountain. After almost 24 years, the landscape still looks as bleak as the moon in some places.

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Reply to
Watson A.Name - "Watt Sun, Dar

On Thu, 1 Jan 2004 13:30:40 -0800, Watson A.Name - "Watt Sun, Dark Remover" Gave us:

an

Yet another man was the last to be heard from at the time of the eruption.

He was on the radio phone with:

"Yes, there it goes... Yes, it's very big... Yes, it's going to get me too..."

Poor guy. Fertilizer for thinking he was far enough away at five miles.

Trees combed over like a giant hair brush came through for miles.

Atomic blast force levels many times that of hiroshima, or even our biggest Cobalt Hydrogen devices ever got... many times over.

Reply to
DarkMatter

Apparently so. Read the last part of this sentence very carefully:

When the core reaches saturation, L decreases dramatically, and so dI/dT has to increase, which is the opposite of what you've said. ;-)

So it'll just reach V/Rcoil sooner than if it hadn't saturated.

I haven't got to the rest of your post yet, impulsive nitpicker that I am. :-)

Cheers! Rich

Reply to
Rich Grise

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