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©2010 Enerdrive Pty Ltd
Introduction
Why should I use the MagnaSine Battery Monitor? To ensure your batteries
perform satisfactory and have a long life, they need to be properly maintained and
charged. There are several devices that help to determine if the batteries are be-
ing fully charged, they are:
• DC Voltmeter: An accurate DC voltmeter can be used to measure the Open
Circuit Voltage (OCV) across the battery terminals and compare the readings
with the OCV values from the battery manufacturer. A DC voltmeter is the least
costly, but is also the least accurate and requires the batteries to be at “rest”.
This “rest” requirement means the voltage measurement should only be done
when there is no current moving through the battery for a long period of time
(most experts say a minimum of 1 hour). Using a DC voltmeter when the
batteries are at “rest” is usually impractical, because the batteries are usually
always powering loads or being charged.
• Hydrometer: A good hydrometer can be used to measure the concentra-
tion of battery electrolyte in each individual cell and compare these readings
with the specific gravity values from the battery manufacturer. A hydrometer
is very accurate, but can be time-consuming and becomes unpleasant when
working with sulfuric acid. A hydrometer will not work with sealed batteries.
• Amp-hour Meter: An amp-hour meter is an electronic measuring device
that uses a precision shunt to calculate the amp-hours going in (charging) and
coming out (discharging) a battery. This meter tracks the amp-hour usage
and compares it against the amp-hour capacity of the battery to determine
its charge condition. Calculating Amp-Hours in vs. Amp-Hours out is fairly
accurate, is easily displayed, but doesn’t provide an accurate State Of Charge
under all charge and discharge conditions.
Theses devices have advantages and disadvantages based on accuracy and ease
of use. The MagnaSine Battery Monitor combines the advantages of these devices
with additional information such as monitoring battery temperature and calculating
battery efficiencies to provide an easy and accurate means to determine the bat-
tery’s State of Charge (SOC) condition. Therefore, if the battery’s State of Charge
is easily determined and accurate, the more likely you will attempt to keep the
batteries charged and enjoy your battery system performance.
What is the difference between Amps and Amp-Hrs? Amps indicate the flow
of current going in or out of the battery. Amp-hours indicate the amount of cur-
rent returned to or removed from the battery. Amp-hrs are a common rating used
to calculate the battery’s available capacity. For example, if a constant 3 amperes
where removed from a 100 AH battery each hour, the battery bank’s capacity would
be 94 AH after 2 hours (6 amp-hours less).
To help understand the difference, imagine the battery bank is equivalent to a
water tank. When viewing the amps display, it would be similar to watching a
water gauge. You can see that the water is flowing a little or a lot, but this doesn’t
indicate how much water is left. When viewing the State Of Charge (SOC) display,
it would be similar to viewing the water tank’s level indicator, which tells you how
much water is left in the tank.
For example: If you have a 100 litre water tank and you remove water from the
tank with a 10 litre bucket. The water level indicator would show the available
water has decreased by 10%; leaving 90% of the water still available. If this was
a battery bank, then you would know that 10 percent of the battery’s capacity has
been used and its State of Charge (SOC) is now 90%.
