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Survey: Connections to terminals and altimeters and "tinning wire"

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SURVEY: How do you make connections to two channel terminals and altimeters? Just getting into "tinning" wire and am wondering how others do things regarding connections to altimeters and two channel terminals. I have terminals where a screw, with a flat bottom, makes the connection inside. (1) Is tinning the wires, which will be inserted into the terminal, good or bad?; (2) Do you stick the wire in straight, or do you make a "j" with it? (3) If you make a "j", do you tin the wires before or after the j is made? (4) Are you answers the same for connecting wires inside altimeters? (5) Suggestions for best quality connections for a 4 inch ebay with dual deploy? Many thanks! I have attempted to post two photos here, to illustrate things. Many thanks!
 

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Reinhard

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1) Usually bad. Tinning stranded wire will result in stress concentration, making the wire more likely to break when it is flexed. The tinned wire will also experience creep, leading to a loose connection in the terminal over time.
The proper way is to use a crimp ferrule. Wire ferrule kits including the tool are nowadays rather afordable. See here for examples:

There are also different terminals that work well with (non-tinned) stranded wire. One example is the Wago 221 series, although I wouldn't use this particular shape in an ebay.

2), 3) doesn't apply. 4) Yes. 5) see 1).

Reinhard
 
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Wayco

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Yes, I tin my wires and install them straight into the altimeter terminal blocks. Then I tighten them down and pull test them.
I bought one of those kits that Reinhard recommends and used it once, only the smallest ferrules work, so you get plenty of parts that you can't use for the terminal blocks on altimeters. Even the smallest ferrules won't fit all altimeters.
I also don't move altimeters around between rockets, and visually inspect and pull test each connection when I open up my avbays. Then I re-tighten all connections.
Occasionally, I will find a wire that has started to fray, and it gets trimmed off and re-tinned.
 

Reinhard

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I bought one of those kits that Reinhard recommends and used it once, only the smallest ferrules work, so you get plenty of parts that you can't use for the terminal blocks on altimeters. Even the smallest ferrules won't fit all altimeters.
Yeah, the selection of ferrules is a bit unfortunate for rocketry. But the sellers basically throw them in for free. On a quick search, I found the tool alone often significantly more expensive than the set.
For rocketry, I'd suggest buying some extra AWG24 ferrules (the sets only go down to AWG22), and if it gets tight, non-isolated ferrules can help too. By the way, it is of always advisable to be aware which wire gauge is in use, because mismatched ferrules wont work reliably.
Something around AWG24 is a good size for e-bays in my opinion. Smaller wire sizes start to get fragile and ferrules are hard to find. Bigger sizes become bulky (especially when the isolation is thick).

Reinhard
 
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1) Usually bad. Tinning stranded wire will result in stress concentration, making the wire more likely to break when it is flexed. The tinned wire will also experience creep, leading to a loose connection in the terminal over time.
The proper way is to use a crimp ferrule. Wire ferrule kits including the tool are nowadays rather afordable. See here for examples:

There are also different terminals that work well with (non-tinned) stranded wire. One example is the Wago 221 series, although I wouldn't use this particular shape in an ebay.

2), 3) doesn't apply. 4) Yes. 5) see 1).

Reinhard
Thank you. I am going the ferrule route. They’ll be here tomorrow
 

watheyak

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I have just recently started using non-insulated ferrules without the little plastic barrel. Works a lot better in the terminal blocks fit-wise.
 
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tOD

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OverTheTop

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As others have said you can use the ferrules to put two wires into the terminal block. That is likely the best solution.

If putting wires into terminal blocks then don't tin them. The solder "creeps" under pressure and the connection can become unreliable over time. If you do tin them then you should check the screw tightness before each flight. As others have said there is also a weakness where the solder stops and the untinned wires exit which is usually the failure point from flexing.

Another
 
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1) Usually bad. Tinning stranded wire will result in stress concentration, making the wire more likely to break when it is flexed. The tinned wire will also experience creep, leading to a loose connection in the terminal over time.
The proper way is to use a crimp ferrule. Wire ferrule kits including the tool are nowadays rather afordable. See here for examples:

There are also different terminals that work well with (non-tinned) stranded wire. One example is the Wago 221 series, although I wouldn't use this particular shape in an ebay.

2), 3) doesn't apply. 4) Yes. 5) see 1).

Reinhard
This is super helpful and I thank you! I have decided to really make ferrules work. I have ordered a crimper and will look at different types of ferrules. It seems so much cleaner and more efficient. The crimper comes tomorrow. Hopefully some of those ferrules will work
 
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Yes, I tin my wires and install them straight into the altimeter terminal blocks. Then I tighten them down and pull test them.
I bought one of those kits that Reinhard recommends and used it once, only the smallest ferrules work, so you get plenty of parts that you can't use for the terminal blocks on altimeters. Even the smallest ferrules won't fit all altimeters.
I also don't move altimeters around between rockets, and visually inspect and pull test each connection when I open up my avbays. Then I re-tighten all connections.
Occasionally, I will find a wire that has started to fray, and it gets trimmed off and re-tinned.
Thanks. I am going to give ferrules a chance. I have ordered the crimper and hope, hope hope that some of those small ferrules work. It's hard to know what you will like until you try it. If the ferrules don't do it your method will be what I will try. What annoys me more than anything is trying to get that stranded wire in the little slot. Do you trim the tinned end of the braided wire with a wire cutter to get a good clean end? Thanks for taking the time to help. GLP
 
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Yeah, the selection of ferrules is a bit unfortunate for rocketry. But the sellers basically throw them in for free. On a quick search, I found the tool alone often significantly more expensive than the set.
For rocketry, I'd suggest buying some extra AWG24 ferrules (the sets only go down to AWG22), and if it gets tight, non-isolated ferrules can help too. By the way, it is of always advisable to be aware which wire gauge is in use, because mismatched ferrules wont work reliably.
Something around AWG24 is a good size for e-bays in my opinion. Smaller wire sizes start to get fragile and ferrules are hard to find. Bigger sizes become bulky (especially when the isolation is thick).

Reinhard
I will be getting some ferrules tomorrow. I may need to make a separate order for the AWG24 ferrules. I have also ordered 22awg wire, so I suppose that means I need to stick with AWG22?
 
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Doghouse Rocketry has color coded ferrules 10/$1.00, 22AWG. I just got some but need to get on Amazon and get a crimp tool. This one was suggested
I suppose there are others that would do the job.
I will order those from Dog House Rocketry if the ferrules in the crimper set don't fit. Thanks for this.
 
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As others have said you can use the ferrules to put two wires into the terminal block. That is likely the best solution.

If putting wires into terminal blocks then don't tin them. The solder "creeps" under pressure and the connection can become unreliable over time. If you do tin them then you should check the screw tightness before each flight. As others have said there is also a weakness where the solder stops and the untinned wires exit which is usually the failure point from flexing.

Another
Thanks. A lot of people advise tinning but a lot of people say don't do it. I think one expert indicated it was against an electrical code, for this reason you suggest. It makes sense that that weak spot would be where it is. I hope the ferrule solution works. Thanks again!
 

Reinhard

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I will be getting some ferrules tomorrow. I may need to make a separate order for the AWG24 ferrules. I have also ordered 22awg wire, so I suppose that means I need to stick with AWG22?
Both will work very well for e-bays. I'd suggest you pick one that you prefer and stay mindful which one it is. As you already ordered AWG22 wire and the ferrules are a bit more widespread, this seems like the right fit for you.

Reinhard
 

FredA

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Do NOT tin your wires.
As stated above - solder creeps under pressure and the connection will loosen over time.
Also - the line where the tinning stops becomes a stress point.

If you want to do it RIGHT.
Remove the terminal blocks and solder the wires to the flight computer.
 

Reinhard

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If you want to do it RIGHT.
Remove the terminal blocks and solder the wires to the flight computer.
This requires some potting or other measures to eliminate any flexing of the wire near the solder joint, because the stress point that still exists then.

1612452146421.png

Image credit: Windell Oskay, CC-BY


Reinhard
 

FredA

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This requires some potting or other measures to eliminate any flexing of the wire near the solder joint, because the stress point that still exists then.
Holding onto the end of something wiggling is always going to create a stress point. Yes, you need to deal with it.
 

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The definitive NASA standard for workmanship on interconnects, wiring, harnesses and crimping is here: https://nepp.nasa.gov/files/27631/NSTD87394A.pdf

It's rather boring overall but does have some relevant info:
  • Crimp connectors are only allowed on stranded wire. Crimping explicitly prohibited on solid wire, whether tinned or not.
  • Minimum wire size 24 AWG
  • No mention whatsoever of terminal blocks or ferrule systems, except for an annotation on a diagram saying terminal points are "typically for ground systems only". This strongly implies they are not allowed on flight articles.
  • Stress relief is mandatory on all wires, harnesses, connector entry points, etc., without exception. Methods mentioned are backshells, encapsulation (potting), and stress relief boots.
To answer the survey, I usually solder leads (22 AWG with silicone insulation) to the board, put a JST connector (hand assembled from genuine Digi-Key parts) on the end, pot the wires at the board with epoxy, and tie the wires down to the sled with at least one zip-tie so there is zero stress on the soldered connection. The main thing I don't do is use the $500 ratcheting crimper, because $500. No failures to date.
 

OverTheTop

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This requires some potting or other measures to eliminate any flexing of the wire near the solder joint, because the stress point that still exists then.

View attachment 449271
Image credit: Windell Oskay, CC-BY


Reinhard
I used that method back in the 80's for some equipment that went onto our buses and trams, although slightly modified with an extra hole so the wires exit the top of the board. We never had any problems with all those modules. No extra strain relief was added at the solder joint in that case.

Crimp connectors are only allowed on stranded wire. Crimping explicitly prohibited on solid wire,
That is because the nick or indentation that can be caused by the crimping process becomes a stress raiser and creates a crack that propagates through the metal.
 

FredA

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Crimping explicitly prohibited on solid wire
Yet our houses are full of crap crimp connectors on Romex wire which is also not in-wall rated.
Yes, only slightly on-topic....
 

JohnCoker

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I solder the ends of stranded wire and insert them straight. For me, it's about keeping things neat and easy for use in the field and I don't want to have to worry about a stray strand remaining outside the terminal block and risking a short.
 

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Ematch wire is 22 ga and solid. I run the ematch wires directly to the altimeter and connect to the terminal blocks. I tie a knot in the wire just inside the bulk plate for strain relief. All wires are replaced each flight so every flight has new wires and you don't have to worry about metal fatigue.
 

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Summarizing this thread:
1. If you must use a terminal block, use a solid conductor with elasticity. Required to keep compression on the joint.
2. If you must use stranded wire then convert the end to act like a solid wire with elasticity. Tinned wire does not meet this requirement.
 

Wayco

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I'm with John Coker on this. It's nice to know what NASA recommends, and some of the comments in this thread are interesting, but I have 44 rockets with redundant dual deploy, I'm not changing a method that's been working for me since I started building dual deploy rockets back in 2015. That's several thousand flights.
I will say that stress relief is as simple as a hot glue gun, and visual inspection, including a pull test on all altimeter connections to terminal blocks is included when I prep a rocket for flight.
As long as you are inspecting your connections, any method you use will work, and if it doesn't, you will figure it out before it's an issue in flight.
 

FredA

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Nice to talk about best practices instead of "I saw it done like this and it didn't fail so must be good"
 

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In my experience, there are two situations; static - unmoving and without vibration, and moving or experiencing vibration. In a recent research project, I wired a control panel with stranded wire and soldered the pins to molex connectors. Once in place, the wiring experienced no loads or stresses, nothing to cause the connections to weaken or break. However, for automobile, boat, lawn mower, etc. use, I would crimp the connectors only, and use whatever strain relief was available (or could be fabricated).
 
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