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Impact of lightning or electrostatic charge

Whether it be a direct hit or near strike, the likelihood is that all electronics on board a vessel will have some measure of damage caused by a direct lightning strike or close proximity to a significant Electrostatic discharge.

Given the nature of an integrated system onboard of electrics and electronics it is impossible to predict what route the static discharge will take as is goes to ground and it also depends whether the boat or boatbuilder or installer made any precautions to try to protect against such an event.  

The damage to equipment, cabling and ancillaries can be immediate and components are blown up instantly or damage can be partial and the components will fail at an indeterminate period thereafter.  It is also likely the majority of other electrical equipment onboard will either be damaged or partially affected and will prematurely fail at some future point in time.

The Electrostatic discharge will cause random damage to PCBs and especially will destroy ICs and flat pack devices, as well as arc across copper tracks completely or partially severing them.

There is limited protection which can be provided to electronics to protect against static damage, simply due to the massive energy levels involved, however, installations can be given limited protection, simply by bonding all rigging to deck fittings and to an independent grounding plate using appropriate sizes of copper strapping will offer a reasonable level of protection.

The provision of lightning protection should be considered if the craft is intended for use in an area where there is likely to be a high incidence of electrical storms, for example inland lakes, Caribbean, North East Asia are all areas of significant Electrostatic activity.

There is a standard ISO 10134 : 1993 for lightning protection on small craft.

GENERAL PRINCIPLES

Lightning protection is the provision of a direct low resistance path from the masthead to a ground plate on the craft. It should be noted that lightning tends to take the shortest path. The connection from each mast or air terminal should be in a straight direct path vertically down to low level then horizontally direct to the ground plate on the hull or to a metal keel.

Usually the mast, rigging, stanchions and toe rail are all bonded together and are grounded to the sea through a grounding plate, this offers a good degree of protection, but again, depending on the size of discharge may still not offer a complete solution

ZONE PROTECTION

The zone of protection is equivalent to a cone, its point coincident with the top of the mast and the cone having a radius round the craft equal to the height of the mast and centred on the mast base – for example this can be formed by the effective bonding together of mast, shrouds and other standing rigging.

GROUNDING CONDUCTOR/WIRE CONDUCTOR

To provide an adequate lightning grounding conductor the entire circuit from the top of the mast or air terminal shall have a mechanical strength and conductivity not less than that of an 8 mm2 copper wire conductor., this can also be in the form of flat copper tape or strip of a similar cross section area.

LIGHTNING GROUND CONNECTION/PLATE

Any metal surface which is submerged in the water in any condition of heel or trim and the wetted surface area of which has an area of least 0.1m2.

Metallic radio ground plates or dynaplates may be used for the lightning ground connection.

NOTES:

i) Complete protection from equipment damage or personal injury may not be achieved and is not implied.

ii) Craft with metal hulls, if there is electrical continuity between the hull and the mast or other metallic superstructure of adequate height, no further protection against lightning is necessary.

iii) If a craft has been stuck by lightning, the compass, electronic and electrical gear should be checked for damage or change in calibration.

It is the customer’s/ boat builder’s responsibility to ensure the equipment onboard is correctly and effectively bonded and grounded and adequate lightning protection is provided

Our recommendation to customers is to completely replace all electronics that are in the affected circuit – replace cabling and switch gear since they may also have been damaged or burned as well as replacing any associated ancillary equipment which may also have been affected.

 

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RFi Interference from LED lighting

Radio Frequency Interference RFi takes many forms and is a term generally used to cover the impact of uncontrolled Radio frequency emissions from one piece of equipment adversely affecting the performance of another piece of equipment.

The increasing use of LED lighting onboard vessels has coincided with an increase in interference affecting the performance of onboard VHFs, AIS, GMDSS and GPS systems.  There are various published articles referring to one of the causes of the interference being attributed to the LED lighting systems themselves, whether the power supply, the transformers or even the lighting drivers themselves.

Examples range from situations where a maritime rescue coordination center in one port was unable to contact a ship that was involved in a traffic separation scheme incident by VHF radio. The ship involved was experiencing very poor AIS reception. AIS is dependent of using the VHF frequencies on the VHF radios for their communication links and are often integrated into the VHF transceivers. Other ships have experienced degradation of the VHF receivers, including AIS, caused by their LED navigation lights. The problem can be particularly severe when the LED lighting is installed near to the VHF antenna which has been shown to compound the reception problems which could account for the focus on navigation light sources of LEDs.

In a second example a customer installed two new LED spreader lights and both his VHF radios cut out when the lights are turned on. The power bar screen looked like he was transmitting on one of the radios and the other one just appeared dead even with local weather on. He never had any problems the previous year using halogen lights with the same wiring set-up.

A Final example was another customer just installed an LED tri-colour and an LED anchor light simply by changing a lightbulb. However, whenever the light is turned on (either one) he can only hear static on all stations on his VHF, no matter where the squelch is set.

LEDs don’t produce RF noise, however the LED drivers do.  Although LEDs are efficient, the brighter ones do create heat which must be dissipated. As with any diode, a constant forward voltage applied sufficient to heat the device will cause current to increase, and if not limited will cause thermal runaway, causing it to fail. To avoid this problem, electronic LED drivers are necessary to regulate the current and maintain specified luminosity as input voltages vary and the LED heats up.

Low power LEDs that dim when voltage is reduced do not have regulators and will not cause RF interference. When regulators are used, LED drivers are normally part of the LED package itself.

The most efficient LED drivers operate with high switching frequencies which are necessary to reduce heat generated by the drivers as well as to minimize current consumption. The downside to this energy efficient LED driver switching circuitry is the generation of radio interference at higher frequencies. Switching circuitry has long been a source of HF interference.

Isolating the cause

It may be possible to test for the presence of LED interference by using the following procedures:

  1. Turn off all equipment onboard to create a full ‘quiet ship’ condition, this includes electronic navigation equipment, onboard domestic equipment, heaters, refrigeration, lighting systems, power generation equipment, pumps, fans and any other electric motors as well as engines. Disconnect any external power sources to effectively shut the vessel down.
  2. Turn the vhf radoio on, if possible only use a hand held vhf to eliminate any possible power supply induced interference
  3. Tune the vhf to a ‘quiet’ channel for example channel 13
  4. Adjust the VHF radio’s squelch control until the radio just outputs audio noise.
  5. Re-adjust the VHF radio’s squelch control until the audio noise is quiet, only slightly above the noise threshold.
  6. Turn on the LED light(s).
  7. If the radio now outputs audio noise, then the LED lights are causing interference and depending on the level of this interference it could prove difficult to receive valid signals on that channel. If the radio does not output audio noise, then the LED lights are not causing a problem.

If the interference noise is found to have been raised, then it is likely that both shipboard VHF marine radio and AIS reception are being degraded by LED lighting.

Currently there is no EMC standard widely recognized by manufacturers of shipboard LED navigation and deck lighting.

Until a standard for shipboard LED lighting installed within three meters of VHF antennas is recognized, the best solution may simply be to ensure that any LED light purchased is warranted and then to perform EMC tests once installation is completed.

In short, those who may be considering use of LED vs incandescent lighting onboard their boats or have boats which have been manufactured with LED or CCFL lighting, please note that LED and CCFL lighting may interfere with receivers within marine electronics (ex. GPS receiver circuitry), communications equipment (VHF radio receivers, AIS receivers), and AM/FM receivers within entertainment systems. If experiencing such issues, the customer should test their systems under quiet ship conditions (to now include switching off all LED and CCFL lighting.  Should the problem persist, then the customer may need to revert to incandescent lighting onboard the vessel.