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Sherlock Ohms

Clothespin Pulls Double Duty as Alligator Clip

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warren@fourward.com
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clothes pin clamp
warren@fourward.com   6/26/2013 8:44:59 AM
I sell calibrated clothes pins that can be used for this application for only $19.95 each.  They are ready to go as soon as you have filed them flat and added the copper and connector.  Sounds like a good deal for me, er, you... :-)

I also have a special on calibrated toilet paper centers and individual sheets of paper towels.

Rob Spiegel
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Re: clothes pin clamp
Rob Spiegel   6/26/2013 10:10:14 AM
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Hey, Warren, I'll buy a half dozen. Given their simple and dependable fuctionalality, they're a deal. 

Ann R. Thryft
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Re: clothes pin clamp
Ann R. Thryft   6/27/2013 4:09:19 PM
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What a nifty idea. And kind of obvious, in a 20-20 hindsight way, by the structure.



William K.
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4-wire connecting clothespins
William K.   6/26/2013 10:01:07 AM
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Steve, your idea is brilliant. Over the years I have seen a commercially made clip quite similar, but made just for that purpose. The humble spring clothespin would be a very good basis for the same function, and using the adhesive backed copper foil is a great idea, which beats the dimes glued on with epoxy, although it may have more of a corrosion issue.

mattd
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Re: Clothespin Pulls Double Duty as Alligator Clip
mattd   6/26/2013 10:17:37 AM
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Interesting story, brings back memories of a project many years ago where I designed and built a dedicated 4 wire ohm-meter for testing blasting caps on a production line.  Not only did it have to be 4 wire for the low resistance but it had to have a testing current source guaranteed to stay well below the "firing current" from the very moment of connection, no inrush spikes or anything.  Needless to say, I didn't design the "clips", they were part of an automated machine.

William K.
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Re: Clothespin Pulls Double Duty as Alligator Clip
William K.   6/26/2013 1:25:58 PM
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Interesting about the blasting cap tester. I always wondered about them.

But my guess is that you found a real challenge getting the machine builders to carry the four wires all the way to the test fixture. I have done a few four wire resistance checking machines and the wiring crew always wanted to tie those conductors to each other way back in the electrical panel. It was even a challenge keeping the wire numbers separated. What we arrived at was adding letter extensions to the wire numbers, -A, -B, and so on. But it required constant attention to make sure that no "simplifications" were done. And there were a couple of times when the engineering manager had to back me up.

kenish
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Re: Clothespin Pulls Double Duty as Alligator Clip
kenish   6/26/2013 1:42:38 PM
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A blasting cap tester sounds easy.  Connect it in series with a 110VAC zip cord and a pushbutton switch.  Push the button; if you hear a very loud BANG, the cap *was* good !

mattd
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Re: Clothespin Pulls Double Duty as Alligator Clip
mattd   6/26/2013 2:02:34 PM
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I had a feeling my blasting cap experience would side track the article, but it was interesting.  The wiring was not a problem as the tester was located near the end of the machine and all wiring was direct from the tester to the test fixture.  The system actually tested multiple devices at the same time (as I recall, it was 8 at a time), and no they were not series connected, it actually ran separate current sources for each device.

William K.
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Re: Clothespin Pulls Double Duty as Alligator Clip
William K.   7/21/2013 9:21:46 AM
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It would be possible to use a single current source and a multiplexer to test all 8 devices, with all 8 in series. BUT you would need to use a differential input multiplexer and be very careful about staying within the allowable input voltage offset range.

mattd
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Re: Clothespin Pulls Double Duty as Alligator Clip
mattd   7/23/2013 9:01:22 AM
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Actually you cannot use a single current source...

the actual explosion can cause a static like discharge, if you used a single current source the failure of one device would potentially cause all 8 to fire off.

William K.
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Re: Clothespin Pulls Double Duty as Alligator Clip
William K.   7/23/2013 10:53:40 PM
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MattD, when I stated that one could use a single current source to check all 8 devices, I presumed that all would understand that I meant a regulated constant current source.  So the current would be the same for whatever number of devices were in series, at least up to the compliance voltage limit. And for an application like that I would choose to utilize an intrinsicly safe constant current supply, which would limit any possible static electricity effect. Besides that, the whole system would run with much less power than the recognized as safe power limits.

An explosion does produce plasma, which is a good conductor, but I don't see how an explosion produces static electricity.

mattd
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Re: Clothespin Pulls Double Duty as Alligator Clip
mattd   7/24/2013 9:12:26 AM
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It was a specific application statement from the manufacturer not to use a single current source since it was possible for the actual explosion to generate a voltage at the instant of ignition and that could subsequently cause other devices to trigger...their claim not mine.  I personally never tested anything for this (they wouldn't let me play with the blasting caps ;( or I certainly would have), so I had to accept their claim.

William K.
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Re: Clothespin Pulls Double Duty as Alligator Clip
William K.   7/24/2013 10:41:48 PM
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MattD, very interesting, I had not known that an explosion could produce electrical power.

But for setting things off, the exploding bridgewire is much safer and a lot simpler to test and verify, and it can even provide better timing accuracy. The concept is that a large current with a fast risetime evaporates a chunk of conductor and creates a small cloud of plasma, which is a very good conductor. So the final result is being able to deliver lots of power to a small volume quite rapidly, which "gets things going". And the technology is from the 1950's era.

Cabe Atwell
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Re: Clothespin Pulls Double Duty as Alligator Clip
Cabe Atwell   7/31/2013 7:18:38 PM
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It's fascinating what people will use when other tools are not immediately within reach. 

William K.
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Re: Clothespin Pulls Double Duty as Alligator Clip
William K.   8/1/2013 9:53:25 PM
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Cabe, you are certainly correct about that. Just watch an electrician drive a nail with their pliers. That works quite well, though. And I have a coffee mug that has douled as a hammer to drive tent stakes quite a few times. Of course, it was made to be unbreakable, after several camping trips where less robust mugs did break. This one has lasted at least 20 years.

akron
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Iron
Re: Clothespin Pulls Double Duty as Alligator Clip
akron   8/29/2013 4:28:53 PM
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I was shocked to see this. I've wanted to do this for years, but it never worked quite right until I got a 3D printer.

 There's a link here somewhere for the pictures.

Cadman-LT
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Clothepin
Cadman-LT   7/16/2013 10:52:12 AM
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Neat little trick! It's amazing what you can do on the cheap sometimes!

mattd
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Silver
Re: Clothepin
mattd   7/23/2013 9:05:09 AM
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Speaking of on "on the cheap"...

Ever tried to probe some wires where access to the ends of the wires is impossible or nearly so...try using small sewing needles to pierce the insulation (if it is high voltage, make sure the power is off first), for really high voltage (>1000V) don't do this as it will degrade the speciallized insualtion and may create a leakage point even after the needle is removed.

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