SG-Electrode
Measuring the SG of battery electrolyte
effectively involves determining the amount of water and sulfuric acid in
the mixture. Water is important because the average concentration of water in the
battery cells is proportional to the degree of charge of the
battery. This is
best understood by considering the overall reaction occurring in a
lead-acid battery, which may be written as:
PbO2(s) + Pb(s) +
2H2SO4(l) <==> 2PbSO4(s) +
2H2O(l)
As the battery
discharges, sulfuric acid (H2SO4) is consumed and
water (H2O) is produced. This process reverses when charging occurs.
The
weight percent water in battery acid may vary from
about 60% (fully charged) to 95% (discharged state) and the measured value
relative to this range can be used as an indication of the fraction of
available energy stored in the battery (i.e. state-of-charge).
Because of the widespread use of hydrometers to determine battery acid
concentration it has become common practice to use specific gravity
as a measure of battery state-of-charge. In recognition of this, the microprocessor
inside the electrode is programmed to convert water
concentration into SG units, standardized to 20oC. In the
case of our multiple sensor network system, each sensor unit contains an RF transceiver
with antenna. The sensors derive power from the cells being
monitored and can be polled in sequence or exclusively in accordance
with user defined settings. Because there are no
wire connections between units they can be shifted from cell-to-cell with ease.
Measured parameters include cell
temperature, voltage and specific gravity. Data is logged and graphically displayed on the Palm
PDA controlling the
network. The system operates at low voltages, is fully battery powered,
intrinsically safe and simple to install.
For a brief schematic
outline download SG_electrode_wireless.PDF
.
For a more detailed
description of the specifications download SGEspecs.PDF.
The
graph in Figure
1 schematically illustrates the influence
of electrolyte agitation on specific gravity measurements during discharge and
charge of a 60 amp hr lead acid battery at a current of 30 amps.
Figure 1.
| Item |
Brief
Description |
Image |
|
SGE-MULTI |
Networked system of
multiple sensors using radio frequency communication at 433 MHz.
Includes 16 sensors, antenna, interface, PDA, software and universal
battery adaptors. Measures SG, voltage and temperature. Data
plotting and logging software included. Suitable for use with strings of
single cells.
|
 |
|
SGE-SINGLE |
Single sensor system with
serial data transmission via wire connection to a monitor with 2x16
character liquid crystal display. Measures SG and temperature.
Serial PC interface and software is available.
Requires no additional hardware.
|
Available soon |
|
