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Author Topic: Securing Wires on Solder Joints  (Read 595 times)
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Yak 52
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« on: January 03, 2019, 03:47:23 PM »

Hi all,

I've been soldering wires on to some N60 brushed motors for E20:
www.ebay.co.uk/itm/N60-DC-6V-7-2V-25500RPM-High-Speed-Mini-12mm-Cylinder-Motor-S-K-FF/153315616553... As you can see the copper terminals are pretty small. I can get a solid solder joint but the terminals wiggle about still and I'm afraid they will eventually fatigue and crack, probably inside the case.

I have some equivalent GWS CN12-RXC motors and they come already wired: www.gwsus.com/english/product/powersystem/edp50.htm
They have some kind of rubbery compound protecting the solder joints but I'm not sure what it is.

Any ideas or suggestions what I can use for this please?

I've considered thick epoxy, plasti-dip, liquid electrical tape, polyurethane adhesive, hot glue etc but I'm not sure what the correct stuff is? I've seen similar on the circuit boards of parkzone bricks also.


Thanks,
Jon
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vtdiy
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« Reply #1 on: January 03, 2019, 04:18:40 PM »

Silicone rubber would give you good vibration damping, solid but flexible support, a good smooth form, and high heat resistance. All of the others mentioned are lacking in one or more of those areas. But as for what Parkzone uses -- dunno.
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Yak 52
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« Reply #2 on: January 03, 2019, 04:36:36 PM »

Thanks vtdiy. I understood that some silicone sealants were acidic and therefore corrosive for electronics?
There's also PU construction adhesive/sealant which might work?

I'm just keen to find out what the best practice would be - the GWS motors arrived that way from the factory.
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Prosper
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« Reply #3 on: January 03, 2019, 04:45:42 PM »

Hi Jon, I think silicone 'potting compound' is the answer too. I used to have some Dow 3145 mil-spec stuff that was very good but it seems to have been supplanted by this, available in the UK: https://www.rapidonline.com/dowsil-dow-corning-rtv-3140-silicone-coating-clear-90ml-87-1222  It's the same stuff as far as I can make out (I keep a tube in the fridge and use it for all sorts - last job repairing gashes in a  rubber pond lining Smiley ). It is single-part, cures normally much quicker than the spec suggests, adheres very well (I've used it as an adhesive) into quite a stiff and very thick surrounding - very shock-absorbing I would think.

Stephen. P.S. last post, these types of silicone are expressly made as electronic 'potting compounds'.
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vtdiy
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« Reply #4 on: January 03, 2019, 05:22:26 PM »

Yak52, you're probably right -- definite acetic acid smell in household silicone rubber. But that potting re. Prosper seems just the stuff.
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Andrew Darby
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« Reply #5 on: January 03, 2019, 06:09:27 PM »

Dow Corning RTV 3140 or 3145 is the stuff to use, it is not corrosive, and sticks like **** to a blanket.  I specify it for covering strain gauges...

Andrew
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Yak 52
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« Reply #6 on: January 03, 2019, 06:28:47 PM »

Ok thanks Stephen and Andrew - that looks like the premium stuff.

You've probably guessed my next question: what's the parsimonious modeller's bodge it option?  Roll Eyes
Would standard epoxy or Plasti-dip work? I presume it doesn't need to be thermally conductive or anything, just a blob to secure the wires. I don't expect I will be doing much of this so it would be ideal if I have it already.

I've had motors break free from the mount and do a decent impression of a broken rubber motor so the wires need the best chance they can get  Roll Eyes

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vtdiy
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« Reply #7 on: January 03, 2019, 06:41:14 PM »

Most everyday epoxies soften at about 200F. Some like JB Weld go quite a bit higher. All form a hard blob, and wire fatigue above that hrd point is the problem -- it just physically moves the break point. And it's hard to remove if it does break and you want to re-solder.

I think something more rubber like and more easily removed would be better than epoxy.
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Don McLellan
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« Reply #8 on: January 03, 2019, 11:47:22 PM »

Hi Jon,

I make similar wire to motor connections all the time in my slot car world and, have to say, they never fail.  Could it be the flux you are using?  I use 'Lucky Bob' liquid flux when making the connections. 

Just wondering.

Cheers,

Don M
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RalphS
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« Reply #9 on: January 04, 2019, 04:58:56 AM »

UHU Por works for me on Spektrum "brick" type receivers.
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Yak 52
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« Reply #10 on: January 04, 2019, 12:43:48 PM »

Thanks guys, I have POR.

Don, I've ordered some liquid flux to see if that helps. It's more the fragility of the thin copper terminals than the solder joint that's worrying me.

Jon
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raggedflyer
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« Reply #11 on: January 04, 2019, 01:39:21 PM »

In the good old days of panel wiring a circular loop would have been included in the wire immediately adjacent to the terminal to provide some give between the weight (or vibration) of the wire and the terminal. Form a loop around a pencil or drill shank before soldering the wire on. The other way would be to lace or nowadays tie wrap or even hot melt glue the wires to the cylindrical end if the motor can, motor mount permitting. Again securing the wires to unstress the terminal.
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fred
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« Reply #12 on: January 04, 2019, 06:09:38 PM »

Frankly I'm not seeing the fixation on the terminals wires fatiguing off. 
Seems unlikely in My experiences with small (no those aren't actually Teeny) wires/terminals.
 IF worried fix the wires solidly a few cms away from the motor so Any flex happens well outboard Wink
And Buy several of those almost free motors as 'insurance'.
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