Magnum Energy Battery Monitor Kit ME-BMK - Manual (Page 6)

© 2010 Magnum Energy, Inc. 2
Introduction
Why should I use the Magnum Battery Monitor? To ensure your batteries
perform satisfactorily 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 being fully charged:
• 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 pe-
riod of time (most experts say a minimum of 1 hour). Using a DC voltmeter
when the batteries are at rest is generally 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 specifi c 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 won’t 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 into (charging)
and coming out of (discharging) a battery. This meter tracks the amp-hour
usage and compares it against the amp-hour capacity of the battery to de-
termine its charge condition. Calculating amp-hours in vs. amp-hours out is
fairly accurate and easily displayed, but doesn’t provide an accurate State
Of Charge (SOC) under all charge and discharge conditions.
These devices have both advantages and disadvantages based on accuracy and
ease of use. The Magnum Energy battery monitor combines the advantages of
these devices with additional functionality (such as monitoring battery tempera-
ture and calculating battery effi ciencies) to provide an easy and more accurate
means to determine the battery’s SOC condition. Therefore, you are more likely
to keep the batteries properly charged, and in turn be satisfi ed with your battery
system performance.
What is the difference between Amps and Amp-Hrs? “Amps” indicate
the fl ow of current going in or out of the battery. “Amp-hours” indicate the
amount of current 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 were 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. Viewing the amps display would be similar to watching a water
gauge. You can see that the water is fl owing a little or a lot, but this doesn’t
indicate how much water is left. When viewing the 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: You have a 10 gallon water tank, and you remove water from
the tank with a one gallon bucket. The water level indicator would show the
available water has decreased by 10% – leaving 90% of the water still avail-
able. If this was a battery bank, then you would know that 10 percent of the
battery’s capacity has been used and its SOC is now 90%.