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'[EE] Potting bare cable connections (low volume)'
2010\07\16@114408 by Chris Smolinski

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Does anyone have suggestions for materials/techniques for potting bare cable connections? Basically, i'm going to have three audio cables (2, 3, and 4 conductors) connected to each other at central location (possibly with a resistor or two between some of the wires). Rather than use a junction box, I was thinking of just potting it. Has anyone done something like this before? I'll need to select a potting material, and figure out something to use for a mold. Any suggestions? Anything else I am overlooking? Does the cable jacket material affect the selection of the potting material?


2010\07\16@120713 by Carl Denk

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I assume that this nneds be weather proof. At the Electrical
contractor's supply house, they should have kits available with a 2 part
material, maybe epoxy, silicone, or urethane. The kit includes a sleeve
that the wires are slid into, and material squeezed in. Available in a
variety of sizes and number of cables. For home use, I have used a shout
piece of plastic tubing or pipe, or better heat shrink, with the splices
in, squeezed some RTV sealant or epoxy to fill, and in the case of the
heat shrink, shrunk it. There is available from places like Mouser,
Digikey, heat shrink with sealant on the inner surfaces. Slide the wires
in and shrink, the sealant squeezes out and hardens to provide a good seal.

On 7/16/2010 11:44 AM, Chris Smolinski wrote:
> Does anyone have suggestions for materials/techniques for potting bare cable connections? Basically, i'm going to have three audio cables (2, 3, and 4 conductors) connected to each other at central location (possibly with a resistor or two between some of the wires). Rather than use a junction box, I was thinking of just potting it. Has anyone done something like this before? I'll need to select a potting material, and figure out something to use for a mold. Any suggestions? Anything else I am overlooking? Does the cable jacket material affect the selection of the potting material?
>
>
>    

2010\07\16@122032 by RussellMc

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Depending on fine detail, "self amalgamating tape" may work well.



    R

2010\07\16@133852 by Steve Smith

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Potting PCB's with standard potting compound (black 2 part stuff) dosent
make the electronics fail so it would be ok for a couple of bare joints....


Steve

{Original Message removed}

2010\07\16@190837 by Dwayne Reid

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At 09:44 AM 7/16/2010, Chris Smolinski wrote:
>Does anyone have suggestions for materials/techniques for potting
>bare cable connections? Basically, i'm going to have three audio
>cables (2, 3, and 4 conductors) connected to each other at central
>location (possibly with a resistor or two between some of the wires).

I've done this in the past, using the kits that the local telephone
company uses for underground splices.  I've used two distinct types:
with a one-part sticky wax-like substance and with a two-part
sealant.  The one-part wax material was the easiest to work with, the
two-part sealant is almost bulletproof.  Both remain flexible and resilient.

Question: have you considered using adhesive-lined heatshrink tubing
and RTV?  I routinely use this to make waterproof splices:

Slide a fairly long piece of adhesive-lined heatshrink tubing on one
side of the splice and slide a short piece of heatshrink on the other
side of the splice.  Do the splice, then goop it up with RTV.  Slide
the short piece of heatshrink over the splice and shrink it.  Clean
up the resulting mess (where the excess RTV squeezed out), then slide
the long piece of adhesive-lined heatshrink over the splice and shrink it.

Done . . .

I've also done the same thing using the wax sealant stolen from some
telco splice kits instead of RTV.

Some of the splices I've done have been in water-filled pipes for 20
to 30 years now and they still work.  The pipes are under
natural-grass sports fields and the ground water contains a LOT of
chemicals (fertilizers and such).  I was surprised at how conductive
the water was when I tested it one time many years ago.

dwayne

--
Dwayne Reid   <spam_OUTdwaynerTakeThisOuTspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
http://www.trinity-electronics.com
Custom Electronics Design and Manufacturing

2010\07\16@203142 by ivp

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> I'll need to select a potting material, and figure out something to
> use for a mold

A local retailer sells "Potting boxes" for this sort of thing. Perhaps
more suitable for embedding circuits/PCBs in epoxy, although no
reason why you couldn't use one to protect a splice. Epoxy isn't
very flexible though, so probably not the best for cables, if you
need a little extra strain relief

http://www.jaycar.co.nz

http://www.jaycar.co.nz/productResults.asp?keywords=potting&keyform=KEYWORD&SUBMIT.x=20&SUBMIT.y=10

For cables I'd go with silicone (neutral cure) or urethane and heat-
shrink, as others have suggested. If this is for outside or underground,
don't forget to check all materials for resistance to corrosion, moisture,
UV etc

Joe

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2010\07\17@032520 by KPL

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Hot glue can be used instead of RTV, It works excellent together with
heatshrink.
I have done this with success, glue melts when shrinking the tube, and
excess is squeezed out.

A bit tricky to get the glue in there, but doable.

On Fri, Jul 16, 2010 at 7:07 PM, Carl Denk <.....cdenkKILLspamspam@spam@windstream.net> wrote:
{Quote hidden}

> -

2010\07\17@032917 by Sean Breheny

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I think that the adhesive inside of the adhesive-lined heatshrink IS a
type of hot-melt glue. I know that it can be reflowed by applying
heat. So, it makes sense that adding additional hot melt would allow
you to make a watertight seal, although I'm not 100% sure that hot
melt glue is completely waterproof and doesn't absorb water
eventually.

Sean


On Sat, Jul 17, 2010 at 3:25 AM, KPL <kpl.listesspamKILLspamgmail.com> wrote:
{Quote hidden}

>> --

2010\07\17@034507 by KPL

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I have several ds1820 temperature sensors sealed this way, hanging
outside for couple of years now, no problems so far. That heatshrink
did not have it's own glue inside.

On Sat, Jul 17, 2010 at 10:29 AM, Sean Breheny <EraseMEshb7spam_OUTspamTakeThisOuTcornell.edu> wrote:
{Quote hidden}

--
KPL

2010\07\17@081847 by Carl Denk

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I like that, the hot glue, other than waiting for the gun to warm up
(plan ahead), quick. But might heat sensitivity of a component be an
issue? I can see where the hot gun tip and extruded glue would shrink
the tubing.

On 7/17/2010 3:25 AM, KPL wrote:
> Hot glue can be used instead of RTV, It works excellent together with
> heatshrink.
> I have done this with success, glue melts when shrinking the tube, and
> excess is squeezed out.
>
> A bit tricky to get the glue in there, but doable.
>    
>

2010\07\17@091108 by Chris Smolinski

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Thanks to everyone for the suggestions. I need something that isn't too "ugly" for customers to want to buy it, so I'll need to try a few of these suggestions out, and see how they look.


2010\07\17@095530 by ivp

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One thing I've noticed about silicone is that after a time its adhesion
to some surfaces isn't so good. It's OK for glass tanks but the joints
and seals on the plastic materials (PVC and acrylic) on my outdoor
fish pond weren't as permanent as I'd hoped. Within a few months
the silicone started to peel at the edges, and I could see water starting
to creep in. So I switched to this

http://www.selleys.com.au/Selleys-All-Clear/default.aspx

with much better results. They say it's not meant for water immersion
but I've not noticed any deterioration after nearly 3 years. And the
sealing part of the joint is not in direct water contact. It's solvent
based so I had to wait for it to set fully and then flush the system to
avoid exposing the fish to any nasties. It really sticks and is much
harder than silicone to remove, yet is just as flexible

Joe

*
*
**********
Quality PIC programmers
http://www.embedinc.com/products/index.htm

2010\07\17@100530 by Jean-Paul Louis

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Chris,

Have you considered using heat shrink tubing and potting compound? You shrink one end of the tube, then add some potting compound, then shrink the remaining part of the tubing.
That would be weather proof

Just my $0.02

Jean-Paul


Forwarded Message: [EE] Potting bare cable
connections (low volume)Friday, July 16,
2010 11:44 AM
               
           
           
           From:
           "Chris
Smolinski" <@spam@csmolinskiKILLspamspamblackcatsystems.com>
                   
                   
                   
               To:
               "Microcontroller discussion list -
Public." <KILLspampiclistKILLspamspammit.edu>Does anyone have suggestions for
materials/techniques for potting bare cable connections? Basically, i'm
going to have three audio cables (2, 3, and 4 conductors) connected to
each other at central location (possibly with a resistor or two between
some of the wires). Rather than use a junction box, I was thinking of
just potting it. Has anyone done something like this before? I'll need
to select a potting material, and figure out something to use for a
mold. Any suggestions? Anything else I am overlooking? Does the cable
jacket material affect the selection of the potting material?

\



     

2010\07\17@104451 by Carl Denk

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Might try urethane sealants, they come both no mix and 2 part varieties.
>From contractor sealant supply houses, check Sika, Tremco, Vulkem as a
few of the manufacturers. At home depot, it might be sold as a concrete
caulking, but will be clearly labeled. Cleaning the surfaces is very
important, generally use a solvent like lacquer thinner. I see that the
Selley's is not for water immersion. A concern if any of these materials
are safe for humans and others including fish contact or consumption.
There are products that are safe for these uses, but needs checking

On 7/17/2010 9:55 AM, ivp wrote:
{Quote hidden}

2010\07\17@114344 by RussellMc

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>> ... RTV, ...

Note that RTV MUST be neutral cure, as Joe noted.

"Standard" RTVs release Acetic Acid during curing and corrosion is probable.

There are two commomn "neutral cure" RTV families, with variations in
characteristics within each family.

Dow Corning offerings here

    http://www.dowcorning.com/contentcomponents/multimedia/Sealants_Flash_Final.swf

Dearest is Alkoxy cure with variants releasing pure Ethanol in some
cases and Ethanol/Methanol mix in others.
(Dow 738, 739, 748, 832) (Se re HM25xx below)

Cheaper and more common in domestic use are the Oxime cure versions
which also release oximes (probably mainly ketoxime) which looks a
little scary on first look at the MSDS but is not too bad on
consideration compared to other typical materials in common use.
http://en.wikipedia.org/wiki/Oxime
(DOW 735, 737, 236)

Any neutral; cure in retail sale which does not specify cure method is
99%+ liable to be oxime cure.

_____________

The Dow Corning HM-2500 and HN2110 are very special and worth noting.
They cost about twice as much as other Alkoxy versions BUT they are
applies as a hot melt glue and then cure to an RTV. This gives you the
very valuable fast set times of hotmelt and equally valuable long
lifetime characteristsics of silicones.

I haven't tried these yet but intend to as they offer superb
advantages in some manufacturing situations. Not available in New
Zealand but can be imported from next-door plus an ocean (in the more
enlightened) Australia.

___________

An important point to note. The long life outdoor performance of RTVs
aka "silicone rubber" is due to the high energy Si-Si bonds which are
essentially UV impervious. A properly formulated TTV wioll last 20+
years in extremely adverse outdoor conditions. The shorter lifetime of
epoxy products is due to the lower energy C-C bonds which are UV
attacked. I do not goes into Joe's recommended co-polymer sealants,
but if long term performance similar to that of silicones is desired
it would be worth seeing what their chemical makeup is and whether
there are liable to be any lifetime issues.

______

Joe mentioned loss of adhesion of RTVs to some materials with time.
Manufacturers (DC and others) supply comprehensive tables of
compatible materials, and surface primers are often available to
improve adhesion.



    Russell McMahon

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