Application Note 42 - Marine Electric / Electronics
- Many pieces of marine electrical or electronic equipment function perfectly when first installed
and quite often function perfectly when removed for bench-testing.
Unfortunately, they prove to be erratic in their operation when re-installed and returned to use in a marine environment.
This type of failure is quite frustrating both to the owner and to the installer, service technician who has to cope with the type of intermittencies that cannot often be duplicated on the bench.
- What are some of the marine (and other) environmental conditions that cause connector failure?
- Typically, these are those found in coastal or other regions where a combination salt-spray and/or moisture together with high winds and/or vibration combine with large temperature variations to produce an environment which is very hard on electrical connectors.
- What are some of the reasons for connector failure under these conditions?
- There are two types of failure, either of which can render a piece of electrical electronic
equipment so erratic as to be unserviceable. While these can generally b classed as either
physical or electrical failure of the connector and although there are some designs in which
only one or the other failures will occur, normally a combination of the two will take place.
The physical failures generally result from the use of connectors which are not designed for the environmental conditions encountered. Unfortunately, even with a the thousands of designs on the market today, it is often very difficult to find connector which will survive some of the more severe environments. When one is found, the limited market for such a design usually results in a very high cost. The engineer specifying the connector has to face the decision of first cost versus replacement/maintenance costs. It is not unusual for an attractive first cost of the connect coupled with an apparently low replacement costs to account for the choice of connector. Often costs due to such items as: unanticipated corrosion due to galvanism between the connector and the cable, dissimilar metals in a connector an another part of the equipment housing, as well a5 environmental-effects due to increasing pollution levels are underestimated. This is similar to the way in which Ion term maintenance costs due to increased wages are underestimated.
The most common physical failure results from corrosion eating away the parts of the connector holding the male and female components together. The result is that the connector simply disconnects. The cause of the corrosion is usually a lack of resistance of the connector body material and/or finish to the combination of salt/water and/or chemicals in the environment; but the corrosion can be hastened by the use of dissimilar metals. These are materials which are incomparable galvanically.
Quite frequently encountered is an electrical-based erosion caused by the use of the connector shell as both a physical coupling and a current carrying element. This same type of breakdown can occur where a connector no longer is able to carry its rated current without electrical erosion taking place. Eventually so much material is lost from the mating contacts that the actual area of the contact-surface is so reduced that the connector runs hot, or even gets so hot that it destroys itself.
Assuming that the connector cannot be replaced with a type more suitable for the climate, and that the connector is still functioning, the usual solution is to clean all traces of salt/corrosion from the connector and re-assemble it. The final step may be enclosing it in such a way as to prevent the entry of the contaminants. This may consist of "buttering" over the connector body with a high viscosity silicon grease and placing it in some sort of protective sleeve which will prevent the grease from being eroded away although because of the potential for silicone-induced problems the preferable method would be to use a layer of self-fusing tape followed by layers of vinyl tape and vinyl coating as mentioned later.
In spite of the general use of silicone greases, they themselves can introduce a form of connector failure, especially when exposed to salt. Where a silicone is present it can combine with the salt to form a thin, hard film of sodium silicate that is not only non-conductive, but very difficult to remove without damaging the connector. Even where silicon-based water-excluding gaskets are employed in the connector design, migration of the ethyl and methyl-silane based oils that are often added to the silicone rubber as softeners can cause problems. These are usually encountered where a connector is crimped to a cable.
Many physical failures take place because salt water has penetrated into that part of the connector where the wires are crimped or soldered onto the pins. Quite apart from the electrical effects of the corrosion products, these products frequently occupy much more volume than the metal upon which they feed. Occasionally enough pressure can be generated to rupture a shell that has already been weakened by corrosion.
Sometimes it is necessary to use a supplementary means of cable/wire strain relief in order to minimize the effects of wind-induced vibrations in the cable in causing a "grinding' action between the two halves of the connector.
Another Type of failure:
A third type of failure is the exposure of the connector to unusual corrosive liquids or gasses not normally encountered in the environment but which might be generated, from time to time, by other failures in the operating plant. This can also extend to corrosion-inducing chemicals being liberated from connector components subject to overheating due to thermal runaway of contact-wire junctions.
It must also be remembered that there are two elements involved in the electric failure of a connector: the insulation, and the conductor/contacts/connections; in other words, the non-conductive parts and the conductive parts.
Dealing for the moment only with the part of the connector that is meant to disconnect and reconnect (and not with the parts that are attached electrically or other wise, to the cable) any connector may be broken down into a male-female or hermaphroditic component which is designed to mate with an equivalent part, an thereby pass electricity, and the parts needed to hold the former in alignment. The latter are usually insulators. In many connectors carrying Radio Frequency signals it is necessary to have the latter parts dimensioned so that the electrical impedance the connector is the same as that of the wire. Otherwise there will be a discontinue and a reflection will occur in the transmission system. This can reduce the effective radiating power of a transmitter, or cut the signal-strength of a received signal. Insulation leakage can cause loss of signal strength and/or unacceptable modification of the signal caused by line reflections. A good example of the latter is ghosts detail blurring in cable TV.
The result can be a radio, communication system, a GPS or Loran, or even a radio system that is unserviceable!
Where the RF impedance is not a consideration we still have to deal with losses in on the electrical insulation. Excessive leakage across the insulation will result in heating in high-power applications, insulation breakdown in high-voltage applications, signal leakage in multiple-pin control circuits. None of these are acceptable, and the consequences could be destruction of the connector and a fire hazard to consequential damages due to failure of a process-control, alarm, or communications system.
The introduction of corrosion products into the gap between the connecting pair connecting means can also result in problems ranging from rectification effects (most corrosion products can act like crude semiconductors) which can produce strange modulation distortion of the signals or even introduce spurious signals derived from the rectification of whatever RF (conventional RF of even fast rise time) signals may be present in the environment. Generally this is characterized as excessive sensitivity to "electronic smog".
As noted earlier, corrosion products can completely break the contact means through its increased volume, lock-up the connector so that it cannot be disconnected.
- How can I achieve electrical contact improvement?
- If a mated contact were potted in a clear material, sawn along at right-angles to, the connection
plane polished, and examined under a microscope, it would be seen that what we think of as smooth
contact surfaces are really almost mountainous. As consequence, the contact area is far from
continuous. One of the benefits of gold plating in the days when gold was much less expensive was
derived from the fact that gold is soft and malleable. Under the action of making the connection,
the gold deformed, producing a much larger total contact area. The plating, being thicker was much
less likely to be porous, and so corrosion was also prevented. In addition the closely mated surface
prevented the intrusion of oxygen and other contaminants.
At the present cost of gold, where gold is used, it is applied in as thin a "flash" a possible consistent with low porosity. Even so, special processes must be used to minimize this porosity as will be evident upon reading almost any connector manufacturer's brochures.
Where gold is not used on both surfaces, the question becomes one of the compatibility of the connecting surfaces both with one another and with the intrusion environment. Often when less noble metals than gold are used in a contact pair and combined with sufficiently high contact pressure, they perform with greater reliability than gold to gold, or gold to ? at lower pressure. The key here is to have enough pressure to exclude oxygen and other contaminants.
Stabilant 22 (or either of its diluted form, Stabilant 22A - isopropanol or Stabilant 22E - ethanol) when used on a contact need only be present in a film thick enough to fill the interstices (or gaps) between the contact surfaces. Because of its switching ability, it will become conductive across these minute gaps without becoming conductive between adjacent pains or causing leakage across insulating surfaces.
The conductivity of a new connector will not be substantially improved by the Stabilant for the reason that there will probably be a sufficient contact-area already. Thus any added contact- area (aided by a material which has a higher volume resistance than the contacting metal) will be of minor consequence. However the Stabilant's presence will help to exclude oxygen and corrosive materials from the contacts, and its surfactant action will keep existing contaminants in suspension.
The action of Stabilant on an ageing or older contact is somewhat different. Here the contact will not be as good; thus the conductivity of the Stabilant (once switched on) will appreciably lower any contact resistance.
On high current applications, the lowered resistance well may be enough to stop thermal runaway of the contact means, a situation where the heating of a joint causes expansion which by stretching the clamping means beyond their elastic limit results in a reduced contact pressure, increasing the resistance of the contact area, and further increasing the heating. In extreme cases this can literally cause a high current connector to explode.
Because of the "switching threshold effect", Stabilant will not "switch" to a conductive state between adjacent contacts and its "off" resistivity is high enough to prevent signal leakage.
Another potential problem in connectors is the area where the wire and or cable is connected to the contact means. Frequently the wire may be of solder or tin plated copper, while the rear of the contact body could be anything from gold-plate, through silver or tin plate, to an as-machined alloy. The introduction of solder itself on a bare copper wire can provide a potential problem of galvanic corrosion while some of the fluxes themselves can cause problems if they wick up into stranded wires. Then too there is the possibility that breakdown products from the cable jacket can cause corrosion of the copper.
Multiple point crimps, (made with properly designed tools) which insure that there is sufficient pressure on the conductors to absolutely exclude the entry of oxygen (and any contaminants as well) are often much more reliable than soldered joints besides having greater consistency, The Stabilants can be used to enhance the operation of such joints.
- What procedures can be followed on completed connectors?
- Once a connector is assembled, it may be necessary to protect it against the environment by
somewhat (in the eyes of the connector manufacturer) less orthodox mean One of the simplest of
these is the use of a heat-shrinkable polyolefin tubing with a internal low-molecular weight
polyolefin (or equivalent) material that literally melted when the outer tube layer is being
shrunk. This provides a much more intimate sea especially when the length is long enough to
stretch from the wire jacket over the connector and over the connecting wire jacket. A problem
with this material is that it looses its elasticity and gets stiff at low temperatures.
Because the polyolefin material looses its resiliency at low temperatures, leaks may occur when it's cold. We have seen this material used with rubber splicing compound (as used on high voltage connections) where a single layer of stretched splicing co pound is wrapped around the wire-connector-wire area before the heat shrink tubing is used. The elasticity of the splicing compound under compression is certainly better than that of any of the heat shrinkable materials and the resultant "booted joint" much less messy to open up.
A better method for environmental sealing to protect against the weather (as practiced by the U.S. Navy) is as follows:
- A layer of Scotch™ 3M type 79 self-fusing tape wound with a 50% overlap and stretched while being applied.
- A Layer of Scotch™ 3M type 33+ Vinyl tape wound with a 50% overlap and stretched while being applied, followed by a similar layer wound in the opposite direction. (also stretched with a 50% overlap).
- A sealant layer of Scotchkote™ Liquid Vinyl is applied overlap the layer of 33 tape. Scotchkote™ has a MEK solvent which melts into the surface of the 33+ tape to form a continuous layer of vinyl material.
This type of sealant procedure can be applied over any type of connector including heat-shrink boots to protect the polyolefin material against UV rays), although in this latter case only the 33+ and Scotchkote is needed to provide a protective an flexible layer.
This and other solutions are, of course, designed to exclude the salt and moisture from the connector and a choice of which treatment to use will be based on the location of the connectors, the ease of application of the treatment, and the life the materials used. Consideration must also be given to possible degradation of he shrink materials themselves by ultraviolet, ozone, or chemical contaminants.
- What other uses are there for Stabilant materials in the marine/maritime field?
- Mechanical switches in radios - digital, audio, RF, or high-voltage usage:
- Typically a Radio consists of a transmitter/exciter, a RF power-amplifier, and a receiver
(possibly mounted separately), as well as high and low-voltage power-supplies all which may be
connected with multiple-pin plug and socket connectors. These usually are often modular for ease
of service and the modules/cards may be, in turn, into connected with a combination of card-edge,
discreet card-connectors, as well as connectors which allow cards to be stacked, wiring-harness-
mounted connectors, coaxial RF connectors (either discreet or modular) and header connectors just
to mention few. The units may also have manual or motor-driven rotary selector switches that carry
DC, AC or RF energy at many different levels. An area of significant failure within HF, VHF, and
UHF transmitters is the final amplifier switching circuits. These often use relays and/or rotary
switches. Failures are usually caused by heating and conductivity erosion. The application of
Stabilants to all of these areas would improve the service life of the equipment and reduce
"resistance erosion" with the concomitant increase in operational reliability.
One caveat; Where connectors operate under high-voltage conditions (such as on some power amplifier tubes) it is advisable to confine the Stabilant coated areas to the actual contact surfaces.
- RF connections - Interior and Exterior:
- Radio-Frequency Coaxial and Waveguide connections operate in both dry-air pressurized and unpressurized (ambient-air) conditions. Stabilants would provide the appropriate protection for these connections.
- RF wipers and Matrix RF power switches:
- These applications provide switching for HF transmitter to Antenna coupling connections. In some of these applications the control signals are digitally multiplexed on the Coaxial cable center-conductor and the matrix connection conductivity is critical, an obvious application for Stabilants.
- Transmitter/Receiver switchboards on Military Ships:
- Transmitter and receiver switchboards consist of rotary wafer-type switches with typically 5 receiver or 20 transmitter positions and 2 receiver to 12 transmitter poles of switches for each equipment position. Each patch panel consists of 10 of these switch elements. In a typical large ship installation, there may be over 4,000 individual switch wafers in the transmitter patch panel alone. These are a common source of intermittent operational problems. An obvious Stabilant application.
- Instrument connections:
- These include everything from navigational equipment to pilot lights and comprise every imaginable sort of connection from microprocessors to remote-compass readouts (not to forget engine instrumentation). Stabilants can reduce or eliminate problems here.
- Miscellaneous Applications in the Marine Field:
- These can cover everything from outboard-motor connections, flashlight batteries, to emergency equipment and cameras. One often overlooked use is the application of a minute amount of Stabilant to the micro-power battery of a wristwatch or camera.
Quite literally, every electromechanical connection can benefit from the use of the Stabilant family of materials.
- In what forms is Stabilant available?
- The Stabilants come in several common forms. The basic material or concentrate is called
Stabilant 22, while the isopropanol-diluted form is designated Stabilant 22A. This is a 4:l
dilution (by volume) and is much easier to apply. (A third type is used for some military
applications where isopropyl alcohol cannot be used, This is Stabilant 22E, which has an
ethanol diluent. It is available on special order.) When used at normal room temperatures
or higher, the diluent will evaporate after the application, leaving a thin film of the
concentrate in place. In some applications such as socketed IC's it is not even necessary
to unplug the IC to treat the connection.
The dilute form should be used for treating existing crimp type joints between multiple stranded wire and the contact.
- What are the names of some of the materials that can be used to exclude water?
- Heat Shrinkable tubing is manufactured by such companies as Alpha. The surface irradiated type with the soft inner core is their type FIT-300 and FIT 321. The standard shrinkable polyolefin tubing is type FIT-221 and the 6:1 High-ratio is FIT 621
Stabilants™ are a product of Dayton Wright research & development and are made in Canada
NATO Supply Code 38948
15 ml of S22A has NATO Part # 5999-21-900-6937