What is Overvoltage?
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.
Overvoltages are continuously applied to the DC power system. The total energy produced is extremely high and very destructive. Ordinary 'surge suppressors' available from many manufacturers are only able to handle a few joules (watt-seconds) of energy for periods of 100 to 500 milliseconds or less. When an overvoltage is applied to these devices, they quickly heat and are destroyed often bursting into flame in the process!
So what started out as an overvoltage fault can quickly escalate into the loss, or severe damage, of the entire vehicle or vessel - not to mention the potential for loss of life.
Operator-Induced OVERVOLTAGE Problems
In the marine world, 3 and 4 stage battery charging systems have become common. One of the selling features of these systems is their ability to 'fast charge' batteries at high current rates. In theory, this sounds quite reasonable - charge the battery bank with a minimum of engine running time. In reality, ohmic losses in battery cables, and poor battery maintenance mean that the system never quite achieves a 'full charge' rate when properly installed.
Customers who were oversold on the benefits of the system by the local sales clerk want to see their ammeters register all '100 amps' from their 100 amp alternator flowing into the batteries! So the hapless tech who installed the system, or a 'knowledgeable' boater, adjusts the output voltage level to 18 volts or more to achieve 'proper' charge levels. Battery heat up to near meltdown conditions, electrolyte is rapidly boiled away, battery plates buckle, and system voltages skyrocket to dangerous overvoltage levels.
As a result, the batteries are cooked and must be replaced every 6 months while the electronic gear suffers from endless failures. But, for some odd reason, the owners of such systems refuse to acknowledge the electronic failures are due to stupidity!
So, if you're an equipment dealer and find yourself in this type of no-win situation, get your customer to install a STO-P UPS system. Then the overvoltage condition won't get to the electronic gear and the boat owner can continue to cook his batteries without costing you waranty repair time and money!