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The Perils of Flooded Lead Battery Discharge Below 50% and Partial State of Charge

Depth of Discharge (DoD) is used to describe how deeply a battery has been discharged. Cycle life is the number of times a battery can be cycled to a certain point before the battery will reach the end of its usable life. There is a direct relationship between the DoD and the cycle life of a battery.

Battery Chargers

Any boat that is moored where there is shore power available will benefit by having a battery charger that converts AC power to DC power which can be stored in the batteries.

Battery Charging Rates

Slow and steady wins the race when it comes to battery charging. It is important to bring a flooded lead/acid battery to at least 14.4VDC to get the electrolyte circulating and avoid stratification. However, prolonged charging above 14.4VDC can lead to hydrolysis (cleaving of the water in the electrolyte into hydrogen and oxygen).

Negative Battery Switching Troubles

We recently had to trouble shoot a problem on a boat that had negative battery switching instead of positive. In North America, everything is switched (and fused) on the positive side of the battery. In Europe, some boats have both positive and negative battery switching (i.e. Beneteau) however, we have never seen a negative only battery switching before.

Thermal vs. Magnetic Circuit Breakers

Thermal circuit breakers respond to over-current situations, as their name implies, by the circuit generating an inordinate amount of heat causing the bimetal contacts inside the breaker to disengage due to unequal expansion. A magnetic circuit breaker responds to over-current situations by a loading coil inside the breaker lifting the contacts apart when the current flow through the coil is sufficient to overcome the spring force holding the contacts together.

Engine Starter Circuit

A common calamity for which we often get requests for a service call is the engine failing to start or even “turn over”.


Early electrical pioneers discovered that passing a magnet in close proximity to coiled wire induced an electrical charge, and that a rotating magnet in front of coiled wire created alternating current. This electrical principle is the basis of an alternator. An alternator is a rotating machine designed to produce alternating current that can then be rectified to produce directional current that can be used, or stored for later use in a battery.

Tachometer Signals

Tachometers all look pretty much the same, but there is some variation between the methods that tachometers get their signal information. The function of a tachometer is to display the RPM (revolutions per minute) of the engine. Typical RPMs will be in the 10s of hundreds, so the method for counting the revolutions must be quick and accurate.

Solar Charge Controllers

Solar energy is becoming a very common addition to many boat’s electrical systems as an alternative charging source for their battery bank. Solar energy is harvested by photo-voltaic cells converting the light energy, photons, into direct current that can then be stored in a battery bank; however, like all charging sources it is important that the charge is controlled to prevent battery damage.

Garmin's Product Updates

We recently attended a Garmin training course and thought we would share some of the things we learned. Some we knew and some are new. For 2016, the Garmin GPSMAP 76XX series chartplotters will include the full Western Canada G2 charts. Up until now, only the USA...

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