© 2016 Sensata Technologies
2
Introduction
1.3
Advantages of using a Battery Monitor
Why use a 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—you can then 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 period of time (one
hour minimum). 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
concentration of battery electrolyte in each individual cell—you
can then compare these readings with the speci
fi
c gravity values
from the battery manufacturer. A hydrometer is very accurate
but can be time consuming, and working with sulfuric acid may
be unpleasant. A hydrometer won’t work with sealed batteries.
• Amp-Hour (AH) 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 AH usage and compares it
against the AH capacity of the battery to determine its charge
condition. Calculating
AH In
versus
AH Out
is fairly accurate and
is easily displayed, but it doesn’t provide an accurate State Of
Charge (SOC) under all discharge and charge conditions.
These devices have both advantages and disadvantages based
on accuracy and ease of use. Magnum’s ME-BMK battery monitor
combines the advantages of these devices with additional
functionality (i.e., monitoring battery temperature and calculating
battery ef
fi
ciencies) to provide an easy and more accurate means to
determine the battery’s SOC condition. This helps keep the batteries
properly charged.
What is the difference between Amps and Amp-Hrs?
“Amps”
indicate the
fl
ow
of current going in or out of the battery. “Amp-Hrs”
(AH) 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. To understand the difference, imagine
the battery bank is equivalent to a water tank. Viewing the amps
display is like watching a water gauge. You can see the rate of
water
fl
ow, but you do not know how much water is left in the tank.
Counting ‘amp/hrs in/out’ (i.e., SOC) is like viewing the water tank’s
level indicator—which tells you how much water is left in the tank.
