SPIKES are high frequency oscillatory variations from a steady state level generated when reactive loads are switched. In a properly operating electrical systems, spikes can be expected to reach +/- 250 volts for durations up to 70 us decaying slowly to a steady state voltage.
These are faults which cause the voltage of the power supply to go outside normal limits for a period of time. Many transients are capable of causing immediate equipment failures. But, most of the time they cause minor damage to semiconductors, degrading their performance. This damage is cumulative and eventually reaches a point where sudden and complete failure of the component results.
OVERVOLTAGE is a sustained voltage that exceed normal steady state limits. In a 12 volt system, this is defined as any voltage that exceeds 15 volts. In a 24/28 volt systems, the limit is 30 volts. Overvoltage is caused by malfunctioning alternators, voltage regulators, poorly adjusted 'fast charge' controllers, battery chargers and solar panels. Another source, often overlooked, is the jump starting of vehicles during cold weather. This is usually done using a 24 volt battery to jump start a 12 volt system.
A sudden dip in voltage caused by engine starting or other heavy loads. This is one of the primary causes of memory loss in GPS navigation systems and crashes in mobile computer systems. Cranking voltage with a fully charged battery can drop to 6 volts during the initial engagement of the starter motor. With the engine OFF, battery voltages can be expected to drop to 10 Volts in a 12V system, or 20 Volts in a 24/28 volt system under normal use. Frequent events, like a fuse blowing on a lighting system, will drop system voltages below this for a few seconds before the fuse or circuit breaker opens.
SURGE DC and AC
Technically, a 'surge' is a variation from the controlled steady state level. When applied to a DC system like those in mobile and marine applications, it results in a temporary increase in DC voltage. But, we also need to consider surges on AC power lines, since at one time or other most DC systems will be connected to battery chargers.
ELECTRO MAGNETIC INTERFACE
E.M.I. is noise and interference from electrical appliances and nearby transmitters. EMI from VHF/UHF radios, Cellular phones, SSB marine or ham radio transmitters effect mobile equipment and degrade performance. The RF voltage levels present at equipment terminals varies over a wide range depending upon frequency, proximity and power output of the interfering device. Installations cause even more variability. The length of power supply wires and cables often determines whether the fault is a 'minor annoyance' or a major cause for failure within the equipment. If the wire becomes 'resonant' at the operating frequency it can absorb significant amounts of power from the transmitter and present very high voltages at the equipment power terminals.
INDUCED ELECTROMAGNETIC FORCE
INDUCED EMF are excessive voltages are induced into electrical wiring (which acts like an antenna) by nearby lightning strikes. Particular care should be exercised when using solar panels since their large conductive surface area acts like an antenna that couples lightning induced emf directly into your electrical system.
Reverse Polarity faults typically occur while jump starting vehicles or installing new batteries. While these are the result of 'accidents', their damaging effect can be devastating. Because of poor design techniques, much of the electronic gear brought into the marketplace over the past several years can be severely damaged by reverse polarity.
RIPPLE is defined as the regular or irregular variations of a voltage about a fixed DC voltage level during steady state conditions.