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Suggestions for Cell Connection – Avoid Short Circuits in Cell Connections
Chapter 5: Suggestions for Cell Connection
This chapter contains suggestions for making connections to an electrochemical cell. We assume a Reference
3000/Reference 30k Booster system using the standard cables unless otherwise noted.
Avoid Short Circuits in Cell Connections
When you are testing a battery or other energy-storage device, you must avoid short circuits across the cell
terminals. Short circuits are likely to destroy the device under test and can create dangerous conditions.
Warning:
including fire, explosion, and chemical discharge.
Always be very careful when designing your experiment: make sure you cannot short-circuit the cell under all
conditions. Don't forget the possibility of short-circuits when you are connecting or disconnecting the device.
Voltage Errors Caused by Wire and Contact Resistance
In electronics, the resistance of a wire is often assumed to be zero. This is usually okay, because voltage error
(iR-drop) caused by current flow through the wire resistance is small compared to the voltages in the system.
For example, 1 mA of current flow through 1 meter of 20 AWG (0.8 mm diameter) solid copper wire creates
an iR voltage drop of: 1 mA × 33 mΩ/m = 33 µV. This voltage can safely be ignored in most electrochemical
tests.
But if the current is much higher, for example 5 A, the voltage drop through 1 meter of 20 AWG wire is
165 mV. This is a significant error in any electrochemical test.
This problem becomes very significant in EIS testing of energy-storage and -conversion devices. Large high-rate
batteries often have cell impedance less than 1 mΩ. Test set-ups for these devices require contact and lead
resistances less than 10 µΩ. Fortunately, you can often employ a technique called 4-terminal measurements to
minimize errors due to contact resistance.
4-Terminal Cell Connections
Accurate measurements of the current-voltage characteristics of high current electrochemical cells require 4-
terminal (also known as Kelvin-type) connections. In a 4-terminal connection, the four leads that connect to the
cell under test are grouped into two pairs.
•
One pair of leads conducts the current between the cell and Reference 30k Booster. These leads are
the "current-carrying leads".
•
A second pair of leads measures the voltage across two points in the cell. These leads will be called the
"sense leads".
In all Reference 3000 or Reference 30k Boosted systems, the Counter (Red) and Working (Green) high-current
cell connections are the current-carrying leads.
In low-voltage systems, the sense leads are the Reference (White) and Working Sense (Blue) leads. The voltage
sensed by these leads is generally assumed to be a cell voltage, although other voltages (such as a half-cell or
multiple-cell voltage) can also be sensed. The maximum voltage on either lead is limited to 10 volts. All
standard Gamry application scripts, except those in the Electrochemical Energy software, assume low-voltage
potential sensing.
In the Gamry Electrochemical Energy software, the Counter Sense (Orange) and Working Sense (Blue) leads
can act as high-voltage sensing leads.
Short circuits across an electrochemical cell can create hazardous conditions,
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