E-Mag/ P-Mag Wire Breakage

[Jim Ellis]

I have one E-Mag and one P-Mag installed on my engine. I have been extremely pleased with the performance of both for the last three years. Factory support has been outstanding. I say all this because I don?t want the following to be considered in any way as critical of E-Mag or its products.

E-Mag employs a type of pluggable terminal strip that uses captive screws to retain the connecting wires.





While performing an inspection of the engine I found what appeared to be fraying and breakage of the stranded wires at the E-Mag connector.





At the same time the wires going into the P-Mag connector appeared to be fine. There was some wire crushing, but no broken strands. The only difference I could see was there was a much bigger loop of unsupported cable going into the E-Mag than the P-Mag. It is possible that the combination of the crushed wire strands at the connector (I do have a tendency to over tighten fasteners!) and increased vibration movement of the wires led to the broken strands I found.

I started to think about how I could make a more durable connection between the stranded wire and the E-Mag connector block. As luck would have it I explained the situation to a friend in the hanger next door. He is an electrical engineer and had worked many years before as a telephone lineman. He knew exactly what I needed to do and I am passing his advice along.

He told me to purchase a ferrule crimping tool and the right size ferrules for the stranded wire. I went to the local electronics store, explained what I wanted, and was astounded when they handed me just what I needed. What they sold me for less than $15.00 was an Eclipse brand Economy Wire Ferrule Tool with 150 assorted sizes of ferrules in the package. The model number is Eclipse 300-016 and it seems to be available at many sources on-line.





I cut off the frayed wire ends, stripped the wire and crimped a metal ferrule onto each of the wires. The wire ends fit perfectly into the E-Mag connector block openings and will not crush no matter how much you tighten the screw in the connector.



The end result is a nice looking terminal end that appears to be far more robust than the bare stranded wire connection. This whole issue may not be consequential under your particular circumstances, but adding the ferrules to the stranded wires inserted into this type of connector just seems to be the right thing to do.



I hope that this information is useful to others that have E-Mag ignitions.

[N941WR]

Jim,

That is good info. The other thing that I believe has helped me was to put enough shrink tubing on the wires so the clamp could hold them tight.

[SMO]

Thanks Jim. I just recently installed a Pmag - have not had it flying yet - and I also noticed this as a potential problem but didn't have an answer for it. I do now! I will be buying one of these tools tomorrow!

[flickroll]

Would simply soldering the wire ends to make them 'solid' serve the same purpose? Or would the transition from the soldered wire to plain wire be a stress concentrator prone to breakage?

[Mel]

Originally Posted by flickroll

Would simply soldering the wire ends to make them 'solid' serve the same purpose? Or would the transition from the soldered wire to plain wire be a stress concentrator prone to breakage?

Please do NOT solder/tin the ends of the wires. The solder will wick up into the wire leaving a bad stress point.

[Dave Cole]

Soldering could result in stresses focused where the solder ends.

This is an excellent example of how it should be done.

Note in the last photo that heat shrink tubing was applied to the shoulder of the ferrule to stabilize the wire at the exit. This is the finishing touch that adds needed stability to the wire. Follow this example, and properly clamp the wire close to the terminal, and it is unlikely you will ever experience broken wires here.

[Bob Axsom]

The idea presented in the original post is excellent. Solder terminations used to be the standard in connectors until the late 50's or early 60's. The backshells were potted and solderers were trained to use short dwell time with minimum amounts of Sn63 solder with no plastic state between liquid and solid for the task. Formal government/industry studies were conducted to develop standards for high reliability solder joints. Inspectors were trained to look for specific characteristics under magnification and excessive wicking (it cannot be totally eliminated) was one of the problems looked for. When crimp pin connectors were developed the industry problem went away - you don't want to bring it back.

Bob Axsom

[revenson]

Thanks Jim for the great tip....I'm gettin' one.

[az_gila]

Originally Posted by Bob Axsom

The idea presented in the original post is excellent. Solder terminations used to be the standard in connectors until the late 50's or early 60's. The backshells were potted and solderers were trained to use short dwell time with minimum amounts of Sn63 solder with no plastic state between liquid and solid for the task. Formal government/industry studies were conducted to develop standards for high reliability solder joints. Inspectors were trained to look for specific characteristics under magnification and excessive wicking (it cannot be totally eliminated) was one of the problems looked for. When crimp pin connectors were developed the industry problem went away - you don't want to bring it back.

Bob Axsom

The soldered joints are OK as long as the wire is supported by heatshrink, as shown in the first example.

Crimps are good, but the high quality crimping created by the studies mentioned above assume trained operators and calibrated equipment. Where I have worked, the production line operators (and their tools) were calibrated daily.

The crimper shown is not even a ratchet crimper, and a "gorilla" squeeze could actually break the sleeve.

NASA does allow soldering, as long as heat shrink is used - from their workmanship standards -



GENERAL REQUIREMENTS

INSULATION SLEEVING

Sleeving shall completely cover and fit snugly around the terminal and the wire insulation and overlap the wire insulation by a minimum of 5 mm (0.20 in.), or two (2) insulated wire diameters, whichever is larger.

NASA-STD-8739.3 [9.8]

Crimps - done with the correct equipment - are definitely good, but well supported soldered joints are in use in space and USAF avionics with a long history, and are still working....

Connectors with solder cups are included -



SOLDER CUPS
Solder cup terminals are primarily designed for the in-line solder termination of conductors. This style of terminal is principally designed as a precision-machined pin for insertion into connector bodies.

Variations include connectors in which the solder cup pin is captive in the connector body (i.e.: hermetic connectors), or printed wiring board mounted terminals designed for discrete wire terminations.

See Section 6.01 "Through-Hole Soldering, General Requirements", for common accept/reject criteria.

...and, as you say, excess solder should not be used -



ACCEPTABLE

MAXIMUM SOLDER

The solder quantity is the maximum acceptable, but does not spill over (exceed the diameter of the cup), or exhibit a convex profile.

NASA-STD-8739.3 [10.2.3.b]

Soldered in-line splices are allowed, again with heat shrink -



ACCEPTABLE

WESTERN UNION/LINEMAN SPLICE

The termination is fully wetted, smooth and shiny. Tubing is tightly shrunk, with proper strain relief, overlap and no exposed conductive surfaces. Western Union splices are used for solid conductors.

NASA-STD-8739.3 [13.6]

NASA says that even crimp splices should be supported with heat shrink -





Don't knock the lowly soldered joint if it is properly done - support is the key to ALL connections....

Originally Posted by Jim Ellis

I would guess that if one of these wires were to actually break in flight the consequences could be serious.

Not entirely true, at least on the P-mag. With the exception of the ground wire, they could all break off and the thing would keep running just fine. If it could find a good ground through the annodized aluminum case (although the instructions say this is doubtful), it may even keep running with no ground wire.

I really like your idea, but it made me wonder.. Were the connectors specifically designed to grip stranded wire, and does switching to solid ferrules somehow alter the gripping force of the screws? Kind of like when people use wire nuts on stranded wire or crimp-on connectors on solid wire. Sometimes it works, but wire nuts weren't designed for stranded wire and crimp-ons weren't designed for solid wire.

I have no idea whether or not the P-mag connectors were designed for a specific type of wire (stranded or solid) or will work fine with both. Perhaps someone with more knowledge in this area can chime in..