Forums

non-destructively finding a break in an insulated DC wire

Started by Adam Funk June 4, 2014
I have a wall-wart charger that put out 4.2 V DC on a figure-8 cable
just over 1 metre long.  There seems to be a weak spot or intermittent
break in one of the wires --- sometimes it doesn't work but jiggling
the cable makes it work.

Is there any non-destructive way to find the position of the break?
(I know I could cut it in half, test both halves, repeat as necessary,
...  solder all the good bits back together; but I'd rather not make a
big mess.


-- 
A lot of people never use their intiative because no-one
told them to.                                 --- Banksy
On 2014-06-04, Adam Funk <a24061@ducksburg.com> wrote:
> I have a wall-wart charger that put out 4.2 V DC on a figure-8 cable > just over 1 metre long. There seems to be a weak spot or intermittent > break in one of the wires --- sometimes it doesn't work but jiggling > the cable makes it work. > > Is there any non-destructive way to find the position of the break?
A> with the break broken measure capacitance from both ends. or B> put a noisemaker on it such that a working wire makes noise and manipulate it until you have located the break. or C> in my experience 80% peobability it's near tip 18% near rhe box 2% elsewhere. -- umop apisdn --- news://freenews.netfront.net/ - complaints: news@netfront.net ---
On Wed, 04 Jun 2014 12:47:30 +0100, Adam Funk <a24061@ducksburg.com> wrote:
> I have a wall-wart charger that put out 4.2 V DC on a figure-8 cable > just over 1 metre long. There seems to be a weak spot or intermittent > break in one of the wires --- sometimes it doesn't work but jiggling > the cable makes it work. > > Is there any non-destructive way to find the position of the break? > (I know I could cut it in half, test both halves, repeat as necessary, > ... solder all the good bits back together; but I'd rather not make a > big mess.
And, besides, the tortoise might win. <grin!> (*) More seriously, I'd think that the simplest approach, based on the information provided, would be to replace the cable and see if the problem goes away. If there are no further "hiccups" you can assume the cable was at fault and pitch the old cable as scrap. If the problem recurs, it probably wasn't the cable, and you can concentrate on other possible causes. Frank McKenney McKenney Associates (*) http://en.wikipedia.org/wiki/Zeno%27s_paradoxes#Achilles_and_the_tortoise -- ...I am convinced that scientists have an obligation to communicate with the public, people who do not know the difference between an anaysis of variance and a factor analysis but who are eager to read about current research findings and the hot controversies in our field. The trick is to inform readers about the latest results in a way that is interesting, but at the same time respect the complexity of the issues and be honest about what we know and what we don't. -- Hal Herzog / Some We Love, Some We Hate, Some We Eat -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney aatt mindspring ddoott com
On Wed, 04 Jun 2014 12:47:30 +0100, Adam Funk <a24061@ducksburg.com>
wrote:

>I have a wall-wart charger that put out 4.2 V DC on a figure-8 cable >just over 1 metre long. There seems to be a weak spot or intermittent >break in one of the wires --- sometimes it doesn't work but jiggling >the cable makes it work. > >Is there any non-destructive way to find the position of the break? >(I know I could cut it in half, test both halves, repeat as necessary, >... solder all the good bits back together; but I'd rather not make a >big mess.
A thermal imaging camera? Might work if the intermittent connection is generating enough additional heat to be visible. A TDR? Depending on what you have around the shop, you might be able to throw one together. A one meter cable is kind of tight for a "what's in the junk drawer" project, though. As Jason mentioned, a "fox and hounds" cable tracer might do the trick.
On Wed, 04 Jun 2014 12:47:30 +0100, Adam Funk <a24061@ducksburg.com>
wrote:

>I have a wall-wart charger that put out 4.2 V DC on a figure-8 cable >just over 1 metre long. There seems to be a weak spot or intermittent >break in one of the wires --- sometimes it doesn't work but jiggling >the cable makes it work. > >Is there any non-destructive way to find the position of the break? >(I know I could cut it in half, test both halves, repeat as necessary, >... solder all the good bits back together; but I'd rather not make a >big mess.
Take a fine sewing needle and poke it through the insulation. This is non-destructive because that small hole does not matter. The plastic insulation is flexible enough to close the hole completely again. w.
On Wed, 4 Jun 2014, Adam Funk wrote:

> I have a wall-wart charger that put out 4.2 V DC on a figure-8 cable > just over 1 metre long. There seems to be a weak spot or intermittent > break in one of the wires --- sometimes it doesn't work but jiggling > the cable makes it work. > > Is there any non-destructive way to find the position of the break? > (I know I could cut it in half, test both halves, repeat as necessary, > ... solder all the good bits back together; but I'd rather not make a > big mess. > >
Way before anywhere else, the problem is at the connector end, or where the cable comes out of the AC adapter. Those are the two stress points, and anywhere else will be way down in terms of chances of a problem. Cut off the connector, and cut a bit of the cable off, and resolder. Chances are good you've fixed the problem, unless it was at the other end. Someone suggested just changing the cable, that's not only cleaner (except for having to open up the AC adapter) but put things in a clean slate to begin with. Michael
On 6/4/2014 7:38 AM, Jasen Betts wrote:
> On 2014-06-04, Adam Funk <a24061@ducksburg.com> wrote: >> I have a wall-wart charger that put out 4.2 V DC on a figure-8 cable >> just over 1 metre long. There seems to be a weak spot or intermittent >> break in one of the wires --- sometimes it doesn't work but jiggling >> the cable makes it work. >> >> Is there any non-destructive way to find the position of the break? > > A> with the break broken measure capacitance from both ends. > > or > > B> put a noisemaker on it such that a working wire makes noise > and manipulate it until you have located the break. > > or > > C> in my experience > 80% probability it's near tip > 18% near rhe box > 2% elsewhere.
Yes, those are exactly the numbers I have. Push pins* into the wire 3" and 4" from the tip, and measure your 4.2 volts, now see is you can wiggle the wire and lose your 4.2v. If you don't lose it, the problem is at tip. *just enough to make the connection, somewhat angled lengthwise to the wire. Clipleads from the pins to the meter. Mikek --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com

"Adam Funk" <a24061@ducksburg.com> wrote in message 
news:ijd36bxmkp.ln2@news.ducksburg.com...
> I have a wall-wart charger that put out 4.2 V DC on a figure-8 cable > just over 1 metre long. There seems to be a weak spot or intermittent > break in one of the wires --- sometimes it doesn't work but jiggling > the cable makes it work. > > Is there any non-destructive way to find the position of the break? > (I know I could cut it in half, test both halves, repeat as necessary, > ... solder all the good bits back together; but I'd rather not make a > big mess.
If it was a high value cable, you could use time domain reflectometry to pinpoint the break. Usually, passing the current for a car headlamp bulb through the cable will finish off any of the broken strands that are making intermittent contact - if you're lucky the heat will deform the plastic covering and reveal the break. IME - most wall warts have cheap wire leads, often the copper wire wasn't annealed properly and is brittle - if you fix one break another will be along soon. On some, you may be able to exorcise the old wire from the strain relief gland and glue a new one in. You can probably get the replacement leads with a molded power jack on the end - but they're probably same quality as the original!
On Wed, 4 Jun 2014 12:18:20 -0400, Michael Black <et472@ncf.ca> wrote:

>On Wed, 4 Jun 2014, Adam Funk wrote: > >> I have a wall-wart charger that put out 4.2 V DC on a figure-8 cable >> just over 1 metre long. There seems to be a weak spot or intermittent >> break in one of the wires --- sometimes it doesn't work but jiggling >> the cable makes it work. >> >> Is there any non-destructive way to find the position of the break? >> (I know I could cut it in half, test both halves, repeat as necessary, >> ... solder all the good bits back together; but I'd rather not make a >> big mess. >> >> >Way before anywhere else, the problem is at the connector end, or where >the cable comes out of the AC adapter. Those are the two stress points, >and anywhere else will be way down in terms of chances of a problem.
...unless there is some physical damage along the cable - was the cable squeezed in a door jamb or drawer? Feel along the cable to see if there are any kinks or unevenness that may be the source of the problem. -- Peter Bennett, VE7CEI Vancouver BC peterbb (at) telus.net Vancouver Power Squadron: http://vancouver.powersquadron.ca
On Wed, 4 Jun 2014, Peter Bennett wrote:

> On Wed, 4 Jun 2014 12:18:20 -0400, Michael Black <et472@ncf.ca> wrote: > >> On Wed, 4 Jun 2014, Adam Funk wrote: >> >>> I have a wall-wart charger that put out 4.2 V DC on a figure-8 cable >>> just over 1 metre long. There seems to be a weak spot or intermittent >>> break in one of the wires --- sometimes it doesn't work but jiggling >>> the cable makes it work. >>> >>> Is there any non-destructive way to find the position of the break? >>> (I know I could cut it in half, test both halves, repeat as necessary, >>> ... solder all the good bits back together; but I'd rather not make a >>> big mess. >>> >>> >> Way before anywhere else, the problem is at the connector end, or where >> the cable comes out of the AC adapter. Those are the two stress points, >> and anywhere else will be way down in terms of chances of a problem. > > ...unless there is some physical damage along the cable - was the > cable squeezed in a door jamb or drawer? > > Feel along the cable to see if there are any kinks or unevenness that > may be the source of the problem. >
That's a point. But it isn't likely to happen except under certain circumstances, so it likely still comes third. Michael