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Keep an Eye on Those Ring Terminals

Toobuilder

Toobuilder

Well Known Member
Here's a new one on me:

Took off this AM for a quick flight around the neighborhood. Within a few minutes of takeoff I feel a sharp pinch on my bare leg - like a bee sting. A search of the cockpit does not reveal any critters, and my leg looks unscathed. I'm about to write it off as nothing when I catch sight of a pinhead sized metallic object drop out from behind the panel and land right on my leg, with the same painful results as before. I quickly figure out that it's molten solder, leaking out of my instrument panel. OK, time to land and figure this one out. Ammeter shows nothing abnormal, but a careful hand survey of my strobe light switch reveals that the wire is loose and too hot to touch. All lights off and uneventful landing ensued.

Inspection revealed that the screw securing the soldered and crimped ring terminal to the output lug on the switch/breaker was slightly loose, causing enough localized arcing to generate considerable heat. Enough to melt solder. And yes, the breaker is functional.

So the takeaway for me is that you can have a very high localized heat condition that won't show up on the ammeter, pop a breaker, create any radio noise, or show up at all until stuff starts to smoke. I was fortunate in a sense that the builder of my Rocket used soldered connections that gave me an "early warning".

I have a new focus area on my future inspections - just thought I'd share the experience.
 
If a connection is loose, it can arc, creating a lot of heat, and maybe not showing anything abnormal in the ammeter. Snug them up and make that a note for regular interval inspections for a while to look for other possible loose connections.
 
Yes, there is heat shrink on the ferrule of the terminal. But its open on the ring end, allowing the solder to escape.

And, yes, I've known about this in theory, but never experienced it firsthand. I'm reporting it to bring the reality "home".
 
Perhaps this is a good time to ask why solder is being used in a crimped terminal in the first place. A properly crimped connection (using aviation-grade crimp terminals, the correct crimping tools and the proper crimping procedure) will result in a connection that is every bit as strong and electrically-sound as a soldered connection -- and perhaps MORE SO, when you consider that solder can wick up into a wire, causing it to become brittle beyond the crimped portion.
 
In this case, the breaker doesn't pop because you don't have a shorted circuit and the current flow is normal. The poor connection is dissipating the energy at the faulty connection rather than it going to the load (lights). This is another example of why to use aircraft grade tefzel wire. If it was just ordinary commercial PVC insulated wire, you would have had lots of smoke and possibly open flame to go with it.
 
BuckWynd said:
Perhaps this is a good time to ask why solder is being used in a crimped terminal in the first place...
Click to expand...

With all due respect, the soldered connection is irrelevant to cause. I only brought it up to illustrate the fact that this connection got really, really hot.

I suspect that most builders (with the obvious exception of the guy who built my airplane) know the pitfalls of a soldered connection. My airplane will eventually see a total electrical makeover, and the vast majority of the trrminals will be crimped

Again, the focus is that solder or crimp, a relatively benign condition like a loose terminal can make for big problems.
 
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Conventional strobe circuits are notoriously hard on switches. Any kind of resistance will cause thermal runaway. Sounds like you've experienced this. You may have to replace the switch as well.

There was quite a bit of discussion on this about 8 years ago on the Aeroelectric list.

Cheers,
 
Toobuilder said:
I suspect that most builders (with the obvious exception of the guy who built my airplane) know the pitfalls of a soldered connection.
Click to expand...

Actually I think a lot don't. It seems new builders are getting talked into it all the time, so I think it is worthwhile for it to be mentioned.
 
thank you

Bringing up the fact that it was not good practice to have solder on the ring terminal is like saying the Canary was not supposed to be down in the mine shaft. (ASPCA rules or something) I don't think the owner put the solder there in the first place.
The melting solder alerted the alert pilot to the overheat.
The heat came from a loose screw holding the ring terminal. Or not holding it well, as the case may have been.
We should never have loose screws, but I know it can happen.
The posting is a great lesson for ongoing inspections.
Electrical is the least comfortable area of expertise for almost all the builders and owners I have met.
Thanks very much for taking the time to write about your experience.
 
rvbuilder2002 said:
Actually I think a lot don't. It seems new builders are getting talked into it all the time, so I think it is worthwhile for it to be mentioned.
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On the other hand, getting a good crimp on a 6 to 2 gauge wires without a special tool is difficult and prone to errors.

Heck, even Vans shipped starter cables with loose crimp connections at one time -

https://www.vansaircraft.com/pdf/batterycables.pdf

Keep the terminal screws tight and heat shrink the soldered joint and it will be OK...
 
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az_gila said:
On the other hand, getting a good crimp on a 6 to 2 gauge wires without a special tool is difficult and prone to errors.

Heck, even Vans shipped starter cables with loose crimp connections at one time -

https://www.vansaircraft.com/pdf/batterycables.pdf

Keep the terminal screws tight and heat shrink the soldered joint and it will be OK...
Click to expand...

Gil, what exactly is your point?

I doubt that the wire on the terminal that started this thread is 6-2 gauge.

That fact that a mistake can be made by a human when crimping only?

The point is a properly done crimp is totally sufficient. Improperly using solder (proper soldering takes a lot more knowledge and skill than crimping) can cause a lot more problems than it solves. I have seen it first hand. Even on heavy gauge cables.
 
rvbuilder2002 said:
Gil, what exactly is your point?

I doubt that the wire on the terminal that started this thread is 6-2 gauge.

That fact that a mistake can be made by a human when crimping only?

The point is a properly done crimp is totally sufficient. Improperly using solder (proper soldering takes a lot more knowledge and skill than crimping) can cause a lot more problems than it solves. I have seen it first hand. Even on heavy gauge cables.
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My point is that solder applied correctly is acceptable, and crimps are not as infallible when made in a garage environment, especially for the large wire sizes.

I did assume it was a heavy gauge wire from the amount of heat generated and with no breaker trip. How many solder blobs/drops can a small gauge soldered wire terminal create?

Quite a few amps must have been involved and the wire itself did not fail.

We also don't know if the failed terminal was on the protected side or the bus side of the switch and/or breaker.
 
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Toobuilder said:
In this case, it was the protected (load) side. 14 AWG.
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Thanks, at 14 g all of the solder must have drained onto your leg...:)


The other interesting question about the use of switch screw terminals is the use of lock washers.

Some switches come with them and other seem to not use them. Since the lock washers are usually steel, I presume that they don't fully deform against the copper terminals and can actually be re-used, but haven't found any literature confirming this.

Did your terminals have lock washers?
 
rvbuilder2002 said:
Gil, what exactly is your point?

I doubt that the wire on the terminal that started this thread is 6-2 gauge.

That fact that a mistake can be made by a human when crimping only?

The point is a properly done crimp is totally sufficient. Improperly using solder (proper soldering takes a lot more knowledge and skill than crimping) can cause a lot more problems than it solves. I have seen it first hand. Even on heavy gauge cables.
Click to expand...

What are the downside to solder after crimp if it is done right?
 
You wick solder into the wire, making it stiff. Where the stiffness ends, and the flexible wire begins, you end up with a spot where the wire flexes with vibration, and can eventually fail. This really isn't an issue with solder joints in the middle of wires, but can create broken wires at terminals, where one end of the wire is constrainted, and the unconstrained wire can move.

Soldering can be done right, and is used throughout aerospace - but crimps are designed to last forever without soldering.

This is a case where adding suspenders to your belt can actually hurt you.

BTW Mike, when you said solder was dripping out from under the panel, I figured it was just another typically warm day in the Mojave.... ;)
 
Bavafa said:
What are the downside to solder after crimp if it is done right?
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I don't like crimps. I also don't like eyes and screws.... I like push-ons. They do give a superior electrical bond pressure at contact point.

So I do crimp.... but as I do it, I push a small tail through the crimp tube to extend 1/16th or so on to the flat. I heat the flat with a solder iron from under side and touch a SMALL amount of solder to the tail. It never wicks even to the center of the crimp tube.

I heat shrink all connections.... The original plastic collar was removed at the start.

The next time you go to solder a connection, see how much solder you need to apply for it to drip in a 1G situation. I expect it to be over 10 times the amount needed for a proper connection.

It was not the solder, It was the application. Like all the other skills needed to build your A/C, take a little time to learn how to do it right..... But wait, did I do it right?......;)
 
vlittle said:
Conventional strobe circuits are notoriously hard on switches. Any kind of resistance will cause thermal runaway. Sounds like you've experienced this. You may have to replace the switch as well.

There was quite a bit of discussion on this about 8 years ago on the Aeroelectric list.

Cheers,
Click to expand...

Update: Thermal runaway is caused when there is a negative correlation between circuit voltage and load current. Most switching power supplies, including strobe power supplies, exhibit this effect.

For example, at 12 volts, the circuit may only draw 3 amps;
At 6 volts, the circuit would draw twice the current, 6 amps to deliver the same power.

Now put a resistive bad connection or cheap switch in series and the power dissipation of the bad connection quadruples (proportional to load current squared). The heat generation further degrades the connection, increasing the current and so on.

The terminal is toasted and the switch is toasted.
Terminal: http://www.vx-aviation.com/rv-9a/photos/Electrical/IMG_0935_2.JPG
Switch guts:http://www.vx-aviation.com/rv-9a/photos/Electrical/IMG_0956_2.JPG
 
gasman said:
I don't like crimps. I also don't like eyes and screws.... I like push-ons. They do give a superior electrical bond pressure at contact point.)
Click to expand...

Do you have data to substantiate that push-on connectors provide superior electrical "bond pressure"......Or what ever that means?
 
I would like to see some scientific testing of that, too. I do know that "AeroElectric Bob" did a write-up that suggests Fast-Ons are certainly very suitable for aircraft use, despite some long-held wives'-tales by certain folks. He also tested Fast-On tabs and found that it would take something like 200 Gs to pull them off.

You can read the whole article here:
Fast-On Tabs vs. Ring Terminals -- What's the Difference?


Edit: Gasman beat me to it! :).
 
gasman said:
Here...... http://www.aeroelectric.com/articles/faston3.pdf

If you are wiring your aircraft, you might want to purchase his book....https://matronics.com/aeroelectric/Catalog/pub/pub.html
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I have read the article you referenced a few times and I have to raise the BS flag. Bob talks in circles and gives you plenty of opinionated "reasons" why spade terminals are "better" such as "The FAA will not allow them because they are years behind and backwards" "you can install them with one hand" "half the parts means twice the reliability" etcetera.

There is no mention in this article of current ratings for spade vs ring terminals, typical failure modes for each type of connector or any other real data for that matter. I have 25 years of experiance chasing electrical problems due to spade connectors on boats, cars and aircraft.
 
The fact that you can't buy a decent switch or breaker with a "fast-on" terminal pretty much limits them to ANL fuse blocks for me, which I do use for non-critical circuits.
The only wires I solder are small signal wires such as data bus or audio, everything else I do is crimped only using the right tools and materials.
 
Beware switch-breakers

I am not a fan of switch-breakers. Over the years I have seen a half-dozen fail, putting smoke in the cockpit, burning through the switch-breaker housing and scaring the heck out of the pilot. The problem is that a switch is designed to open and close a set of contacts many many times and so the contact spring and points are designed to repeatedly flex without a major change in properties. On the other hand a breaker is intended to have its spring change shape with heat causing excessive heat to open the contacts. These tasks are exclusive and not long term compatible. With time a switch breakers spring can work harden, requiring greater amperage to trip. If you are unlucky and this wear combines with a gradual burning of the contacts and associated increase in resistance the unit functions but is slowly getting hotter and hotter as the days pass ........ fortunately this is less common than the unit just quitting and simply being unable to turn on which ever device is connected to it. My preference is for dedicated, separate switches and circuit breakers. My .002 Russ
 
Walt said:
The fact that you can't buy a decent switch or breaker with a "fast-on" terminal pretty much limits them to ANL fuse blocks for me, which I do use for non-critical circuits.
......
Click to expand...

Not quite....

On the Carling Military selection page -

Breaker - https://www.carlingtech.com/hm-cb-ms-series - see terminal options

Honeywell switches from the TL military line - http://sensing.honeywell.com/product-page?pr_id=34488


Good switches certainly are available with Quick Connect terminals.
 
az_gila said:
Not quite....

On the Carling Military selection page -

Breaker - https://www.carlingtech.com/hm-cb-ms-series - see terminal options

Honeywell switches from the TL military line - http://sensing.honeywell.com/product-page?pr_id=34488


Good switches certainly are available with Quick Connect terminals.
Click to expand...

I stand corrected! Guess cause I've never seen one used I figured they didn't exist. At least on the TL switch it looks like they just added an adapter to the standard screw terminal switch.
 
az_gila said:
On the other hand, getting a good crimp on a 6 to 2 gauge wires without a special tool is difficult and prone to errors.

Heck, even Vans shipped starter cables with loose crimp connections at one time -

https://www.vansaircraft.com/pdf/batterycables.pdf

Keep the terminal screws tight and heat shrink the soldered joint and it will be OK...
Click to expand...

And yet, four years later, they were still shipping bad cables.

https://www.youtube.com/watch?v=cXdqzAdJCRk

Bottom line: Trust no one.
 
Switches With Fast-On Terminals

az_gila said:
Not quite....

On the Carling Military selection page -

Breaker - https://www.carlingtech.com/hm-cb-ms-series - see terminal options

Honeywell switches from the TL military line - http://sensing.honeywell.com/product-page?pr_id=34488


Good switches certainly are available with Quick Connect terminals.
Click to expand...

I used all APEM 600H series switches in my RV-8.

APEM 600H Catalog

This is the same switch that Van's supplies (or at least used to supply) for the flap switch. These have been absolutely rock solid for me in 500 hours. The switches have clamping screw terminals that are 1/4" fast-on terminal with a screw and clamp nut. I used them without the screw and nuts. These are offered in a very wide variety of configurations including 2 and 3 position locking toggles.

Skylor
RV-8
 
Aveo Rockracks (basically, Carling switches with custom tops) here...they used a type of Fast-on (but without the insulation so as to allow them to slide into a block of connectors which then goes on the back of the switch...and is harder than **** to get off, by the way, because of the clamping force of each connector times n connectors).

350 hours, no issues (fingers crossed).
 
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