EL1002
The EL1002 single-quadrant potentiostat was designed as an extension for the IM7 series to perform measurements on high-power electrochemical systems such as PEM or solid oxide fuel cells. This highly dynamic electronic load was optimized for EIS measurements on frequencies on the order of 10 µHz to 100 kHz at high current densities.
The EL1002 is suited for power dissipation up to 1 kW at voltages up to 100 V. It can modulate and control currents of up to 200 A. Due to the innovative connection concept of the EL1002, additional power supplies or electronic loads can extend the current range up to 680 A. The EXT-concept allows for outstanding EIS quality at high currents and conserves a good value-to-price ratio.
The versatile interconnection capabilities of the EL1002 give access to measurements at high currents on large-scale batteries, electrolyzers or fuel cells.
Power extension of IM7 potentiostat for battery, fuel cells, or electrolyzer stack measurements up 68 kW
Dynamic EIS measurements at high power from 10 µHz bis 100 kHz
High bandwitdh and outstanding EIS data quality
Packing List
Zahner products are carefully manufactured, calibrated and tested to ensure our high-quality standard. Packing of the electronic load EL1002 and accessories is done with great care to avoid damage during transport. Upon receipt of the Zahner shipment, please check the device and accessories to make sure they are intact. If a product is damaged during shipment, please immediately contact your Zahner’s service partner.
EL1002
EPC42 cable
Sense cable (Lemosa plug to blue & green twisted cables)
USB cable
Power cord
Ring binder
Calibration report EL1002
Risk assessment document
Zahner Analysis license keys
Product manual description
Caution
Caution
Please read the risk assessment document before operating the potentiostat.
Prevent the inputs of the potentiostat from electrostatic discharge (ESD)! ESD may damage the potentiostat. ESD-related damages are not covered by the warranty of the potentiostat. The user must make sure to discharge themselves from any electrical charge before touching the potentiostat (TIP: use grounded ESD-matts).
Zahner’s potentiostats require a warm-up time of 30 minutes for optimum performance.
Do not leave the active objects such as batteries or fuel cells connected to the power outputs of the potentiostat when the potentiostat is switched off! This may damage the potentiostat.
To drive high currents with an EL1002, the customer must use a cable set recommended for high current applications and fasten it to the terminals with suitable cable lugs.
Pay attention to the cable connection schemes and strictly follow the guidelines of this manual. A connection scheme with reversed polarity may damage your device.
During operation, the potential directly on the positive (+) terminal of the EL1002 should be at least 1 V higher than the negative (-) terminal.
Always turn ON the EL1002 after turning on the external load or the external power supply (if any is connected).
No current should flow through the EL1002 immediately after turning on the EL1002.
No current should flow through the EL1002 at dc calibration.
Always turn OFF the EL1002 prior to turning OFF the external load or the external power supply (if any is connected).
Properly fasten the EPC42 cable with the EL1002 using screws. Accidental unplugging of the EPC42 cable during operation may damage your device.
When working with high currents, remove all metallic jewelry/watches which can possibly create short circuits.
Don’t touch the electrical connections during operation.
Never expose potentials higher than 100 V to the EL1002.
The maximum current through the positive (+) terminal of EL1002 must never exceed 200 A.
The maximum current through the shunt/current measurement unit of the EL1002 must never exceed 680 A.
The current cables from EL1002 to the test object must be as short and thick as possible.
During EL1002 start up and calibration, do not sink external DC current.
Introduction
Zahner’s electronic load EL1002 can be used as an extension to the IM7 series potentiostat or in a stand-alone configuration. In the following sections, both scenarios are discussed.
Modular concept - extension to IM7 series potentiostat
Dynamic measurements (e.g. impedance spectroscopy) on electrochemical objects is a topic of high interest in the field of electrochemistry. Modern EIS instruments cover a broad frequency range from µHz to MHz and can handle impedances ranging from µΩ to GΩ. However, the maximum applied current is mostly limited to a few amperes. For many applications in the field of batteries and fuel cells, measurements at high currents are desired. For the IM7 series potentiostats, the current range can be significantly extended using Zahner’s electronic load EL1002.
The EL1002 is a single quadrant potentiostat (it can sink but cannot source current) and is designed to be used as an extension of the IM7 potentiostat to investigate high power electrochemical systems. The highly dynamic EL1002 load is optimized for galvanostatic EIS measurements up to 100 kHz on energy storage and conversion devices such as proton-exchange membrane (PEM) and solid oxide (SO) fuel cells.
The EL1002 allows for power dissipation of up to 1 kW in terms of voltages up to 100 V and currents up to 200 A. In combination with a third-party instrument (electronic loads or sources), measurements at higher currents (up to 680 A) can be carried out. Moreover, the EL1002 setup can be combined in different ways with power supplies to allow for measurements on electrolyzers and large format batteries.
Equipping our IM7 potentiostat with our parallel measurement channel cards (PAD4 zahner website, PAD4 documentation), the EL1002 and an optional power supply upgrades the whole system as an optimal system for all kinds of stack measurements on batteries, fuel cells and electrolyzers. For the connection of the EL1002 with the IM7 potentiostat, an EPC42 interface card is also used.
Caution
External power potentiostats connected to the IM7 series can only be operated sequentially. Simultaneous control of multiple power potentiostats is not supported.
Never connect or disconnect the D-SUB connector on the rear of the power potentiostat while either of the two devices is switched on. Failure to observe this precaution may result in damage to both the device and the test object.
Secure the D-SUB connector with the provided screws to prevent accidental disconnection.
When switching between devices, the non-selected external potentiostat will maintain its DC conditions, including DC potential or current and on/off status.
Voltage and current outputs of non-selected external potentiostats are neither measured nor monitored for compliance with defined voltage/current limits.
Only the currently selected external potentiostat is internally connected to the FRA (Frequency Response Analyzer) of the IM7 series potentiostat. Consequently, only the active external potentiostat can generate AC signals.
Stand-alone mode
Zahner’s power potentiostats or electronic loads (PP2X2, XPOT2, EL1002) can also be operated in stand-alone mode, for which a Windows 10/11 or Linux computer is necessary. For software updates, Windows 10/11 is required and the use of a virtual machine is not permitted. The application of a USB hub for connecting the device is not recommended.
The PP2X2/XPOT2/EL1002 potentiostat can also be controlled with other third-party software (e.g., Python). This allows for the integration in already established experimental setups. The potentiostats provide serial interfaces via the USB serial port which can be used to communicate with the potentiostat via the SCPI protocol. In the future, it is planned that the ethernet interface will be activated via a free software update.
Zahner has prepared a GitHub library for controlling the PP2X2/XPOT2/EL1002 potentiostats with Python via SCPI:
https://github.com/Zahner-elektrik/zahner_potentiostat
And a GitHub repository with examples using the library:
https://github.com/Zahner-elektrik/Zahner-Remote-Python
The API documentation can be found at:
https://doc.zahner.de/zahner_potentiostat
Only DC measurements can be carried out in the stand-alone mode.
Operation basics
The EL1002 electronic load is a one quadrant potentiostat. This means that it can sink (but cannot source) current in a fixed, given polarity. Hence, when the EL1002 is connected to a battery, it can only discharge the battery, while charging is not possible without a third-party source.
Typical applications of the EL1002 are discharging experiments at (rechargeable) batteries and fuel cells. The EL1002 can be operated in both potentiostatic and galvanostatic modes, controlled by the software. For low impedance objects such as batteries and fuel cells, the galvanostatic mode is highly recommended. The EL1002 is optimized for galvanostatic impedance measurements.
Signals & connections
Fig. 17 EL1002 front panel
Fig. 18 EL1002 back panel
Conductor rails
The EL1002 copper rails feature M10 screw threads for proper mounting of the cables. The screws should be tightened with a maximum torque of 47 Nm, corresponding to the torque of screws with a strength class of 8.8. The screws must be driven through the entire copper rail (15 mm thread depth in the copper). It is recommended to use screws with a strength class of 8.8 and a length exceeding 15 mm, depending on the thickness of the cable lug.
EL1002 has three terminals at the backside of the device labeled as positive (+), negative (-) and external positive (EXT+) terminals (Fig. 19). The EL1002 only allows current (I) flow into one direction from the + to the - terminal. This means that a device under test (DUT) e.g., a battery may only be connected to the EL1002 in one polarity. Always connect the negative (-) pole i.e., anode of a battery with the - terminal of the EL1002 and the positive (+) pole i.e., cathode of a battery with the + terminal. If the DUT is connected to the EL1002 using wrong polarity, the polarity error LED will light up. However, when the EL1002 is combined with an external power supply via the EXT+ terminal (see General notes for applications with external supply or load), then the current (i) may flow into both directions between the EXT+ and - terminals.
Fig. 19 EL1002 connection scheme
For simplification, we will distinguish the current between the + and - terminals of EL1002 with I and current between EXT+ and - terminals of EL1002 with i.
Warning
The current I is limited to +200 A (unidirectional, single quadrant, sink).
The current i is limited to ±680 A (bidirectional).
Safety interlock
The output stage of the EL1002 can be switched off by a potential-free relay contact by opening the interlock contact. The cable should be as short as possible and twisted to avoid interferences. The connection from the copper rails EXT+ to - is not interrupted when the interlock is opened. The EL1002 and the software do not recognize whether the interlock is open or closed.
Warning
The interlock only interrupts the gate voltage (control voltage) of the power transistors of the current controller. No relay or anything comparable is opened. If the power transistors are faulty and short-circuited, they cannot be interrupted.
Carefully read the risk assessment document for the operation of the EL1002.
Signal LEDs & buzzer
The EL1002 is equipped with various signal and warning LEDs on the front panel as well as a buzzer.
The status LED lights up green when the CPU of the EL1002 is running and the device is ready for use. When the CPU is busy with a task or command, the status LED lights up orange. The active LED lights up green when the power supply of the device is switched on. When the output stage (current controller) of the EL1002 is switched on, the LED lights up orange.
The polarity error indicating wrong connection between EL1002 and an active object is only shown by a LED as warning signal. All other errors such as over-current or over-voltage, power or temperature limits are displayed by LEDs lighting up above certain threshold values and additional buzzers beeping above a second set of threshold values.
The warning threshold at which the LEDs start to light up is set at about 95% of the maximum allowed limits, whereas the buzzer sets in when the limit is exceeded.
Operation steps
Turn ON external power supply/load (if it is planned to be used).
Turn ON the IM7 device as well as the EL1002 and allow for 30 minutes of warm-up time.
Start the Zahner Lab software.
Run DC Calibration tool. This will initiate a calibration procedure of the IM7 and all connected devices (including the EL1002). At this time, no current should flow between EXT+ and - terminals under any circumstances.
Open the hardware configuration and select the EL1002 device as the default potentiostat. Here you can also select the desired potential range.
Connect the sense cables to the DUT with correct polarity - connect the blue sense cable to the negative terminal and the green sense cable to the positive terminal of the DUT.
The displayed potentials in the Test Sampling Window must be negative.
The potential difference between the positive and negative terminal of EL1002 must not exceed the selected voltage range of 4 V or 100 V, respectively (absolute limit: 100 V)
Connect the power cables to the DUT (as well as to an external power supply or load/sink, if necessary) according to the preferred configuration.
Connect the PAD4 sensing cables (if required) and activate the data acquisition from PAD4 cards in the Zahner Lab software.
Select the potentiostatic or galvanostatic mode and turn ON (for low Ohmic DUT the galvanostatic mode is recommended).
Perform the experiment.
Turn OFF the potentiostat/galvanostat.
Shut down the Zahner Lab software.
Turn OFF the EL1002 and IM7.
Turn OFF the external power supply/load.
Remove all the cables (sense and power cables).
If the external power supply is required to supply the DUT, skip the last two steps.
Danger
Do not sink external DC current during EL1002 start up and calibration. No current is allowed to flow through the current measuring device, otherwise it will be calibrated as an offset or the DC calibration will fail.
Cell Connection Scheme
All Zahner potentiostats and power potentiostats follow the same cell connection scheme (4-electrodes connection scheme). The 4-electrode connection scheme includes connections for working electrode (WE), working electrode sense (WEs), reference electrode (RE), and counter electrode (CE). These connections are specified by their color code, WE: black, WES: blue, RE: green, and CE: red. To minimize interference, stray- and mutual inductance, the red and black power cables (current carrying cables) must be twisted together, and the green and blue sense cables must be twisted together before the measurement. Twisting is not shown in the schematic below.
Fig. 20 4-electrode connection scheme. The current is carried through the black (WE) and red (CE) wires. The voltage is measured between the green (RE) and blue (WEs) wires.
For large current flow the object must be connected with a four-electrode connection scheme in order to minimize the error margin in the measurement.
Contact Resistance
This figure shows a typical electrical wire used to connect the potentiostat with the test object. The resistance of the wire can be divided in to two parts (wire resistance and contact resistance).
Fig. 21 Typical electrical wire used to contact potentiostat with the test object. Resistance of the electrical wire is divided in to two different parts. 1) contact resistance and 2) wire resistance.
Two Electrode Cell Connection Scheme
Here a 2-electrode cell connection scheme is used for measurements on a cell. The WE and WEs cables are joined together to make one electrode connection and RE and CE cables are joined together to make the second electrode connection.
Fig. 22 The measured impedance (between RE and WEs electrodes) is the sum of the cell impedance and both contact impedances.
This means that the measured voltage is the sum of the object voltage and the two voltage drops across the contact resistances.
Four Electrode Cell Connection Scheme
The advantage of a 4-electrode connection scheme is illustrated here. With the WEs and RE being directly connected to the cell, the contact resistance for the WE and CE can be ignored as they don’t affect the voltage value (not possible with 2-electrode connection scheme).
Fig. 23 Four-electrode connection scheme and equivalent circuit diagram for a 2-electrode pouch cell.
For optimum measurement results, the WE and CE as well as the RE and WEs cables must be twisted together (not shown in the image).
Due to the high input impedance of the potentiostat the input current to the sense inputs is negligible. This means that there are no voltage drops across the contact resistances of the Sense connections. With the 4-electrode connection scheme, the contact resistances are in most cases not significant in the measured cell impedance. This is only true if the cell resistance of the test object is much smaller than the input resistance of the potentiostat. The input impedance of the potentiostat is provided in the specifications.
Parasitic Inductances
For low impedance objects and applications with high current amplitudes in the >1 A current range, particular attention must be paid to the measurement setup and wiring, since the parasitic resistances and inductances of the cabling can become as large as the impedance of the object under test.
As an example, a commercially available 70 mm² copper wire with 1 m length and cable lugs for the connections is examined, which could be used to connect the EL1002 to the object. Two of these wires are attached to each other by cable ties to minimize the mutual inductance. Theoretically, twisting the cables around each other is the most preferable configuration as the magnetic fields are mutually compensated (canceled out), most effectively. However, it is difficult to twist the wires with a wire cross section of 70 mm².
Fig. 24 Pair of wires which are analyzed.
These cables are screwed together with a cable lug at one end to determine the inductance and resistance of the cable without a connected DUT. Afterwards, an impedance spectrum is measured which is fitted by a resistance and an inductance. The next figure shows two impedance spectra in the bode representation. The phase is plotted in red and the magnitude of the impedance in blue. The solid lines shows the measurement result of the 70 mm² and 1 m long wire pair described above. The dashed lines are the measurement result of a similar wire pair with 2 m length.
Fig. 25 Impedance spectra of 1 m (solid lines) and 2 m (dashed lines) connected wire pairs (70 mm²) in Bode representation.
The fitting results for the 1 m wire pair read as 828 µΩ resistance and 529 nH inductance. The real impedance is even higher than the result of the fit, because the parasitic wire inductance is not an ideal inductance due to the skin effect and the proximity effect. The fitting results for the 2 m cable pair amount to 1.65 mΩ and 1.03 µH, which is about twice the resistance and inductance compared to the 1 m cable. This measurement was performed to demonstrate that the parasitic elements are directly proportional to the cable length. Therefore, the 2 m wire pair will not be considered further in the following.
The 1 m wire pair can be treated as a series connection of 828 µΩ and 529 nH. This must be carefully considered especially in impedance measurements due to the voltage drop at the cable impedance. The latter splits up between the two wires when the test object is connected between both cables. This setup is shown below.
Fig. 26 4-electrode connection scheme considering the parasitic elements resistance and inductance within the current-carrying wires.
The following table shows the theoretical cable impedance and the peak voltage amplitude that would drop across the cable at 10 AAC peak current amplitude for different frequencies, using the 1 m cable pair:
Frequency |
Impedance |
Voltage Drop Amplitude @ 10 A Curret Amplitude |
100 Hz |
892 µΩ |
8.92 mV |
1 kHz |
3.43 mΩ |
34.3 mV |
10 kHz |
33.2 mΩ |
332 mV |
50 kHz |
166 mΩ |
1.66 V |
100 kHz |
332 mΩ |
3.32 V |
Consider a battery with a typical voltage of about 3 V, it can easily be seen that measurements above 100 kHz become very difficult as the compliance voltage necessary for a sufficient amplitude becomes too low. The EL1002 also requires a voltage drop of 1 V between its + and - terminals for proper functioning. This means that the maximum affordable voltage drop in this case is 2 V. This further restricts the upper frequency limit for impedance measurement on the 3 V battery to somewhat between 50 kHz and 100 kHz. At higher frequencies, the voltage drop in the cables will consume most of the compliance voltage, leaving less than 1 V between the EL1002 + and - terminals. If the voltage falls below 1 V, the control loop of the EL1002 will not work properly, causing collapsed amplitude and/or distorted excitation signal (current or voltage). In such cases, an external power supply is required which can compensate for the voltage drop.
The voltage drop problem also exists when using four-quadrant potentiostats like IM7 series potentiostat or PP2X2, however, these have a high output (compliance) voltage range, such as the 28 V of the IM7 potentiostat. This makes the object voltage less relevant as the voltage drop across the wire can be compensated. Electronic loads or one-quadrant potentiostats such as the EL1002 do not have a voltage output that could compensate for voltage drops.
In summary it should be noted that the cabling is essential for high current applications. The cable should be as short as possible with a high cross section. The inductance of the setup should be kept as small as possible by using cables that are brought together as close as possible, in the best-case coaxial cables or densely twisted cable pairs.
Connection configurations
The following chapter describes the different connection schemes of the EL1002 for measurement setups with and without external source or load.
Warning
The EL1002 must only be connected to or disconnected from the IM7 system if both the IM7 and the EL1002 are switched off.
It is important to know that EL potentiostats SINK current from the DUT and therefore the cell cables must be as short and thick as possible to minimize the resistive losses. In the case of very long cables, the measurements may be faulty and it may even look as if the EL1002 is defective.
It is also important to connect the DUT to the EL1002 with the correct polarity. For the case of wrong connections, the EL1002 has a protection circuit which will indicate a polarity error. To avoid polarity error issue, we recommend connecting the sense cables before connecting the power cables as described in Operation basics.
Note
For the sake of convenience and simplicity, we will distinguish the current between the + and - terminals of the EL1002 denoted as I from the current between the EXT+ and - terminals of the EL1002 denoted as i.
Applications for the EL1002 without external devices
Full cell configuration (standard Kelvin scheme)
This configuration is used with DUTs like (rechargeable) batteries and fuel cells if a complete cell is to be investigated. First, the sense cables are attached to the DUT with the correct polarity and then the power cables are connected. Since EL1002 is a one-quadrant potentiostat, it cannot work as a source but only as an electronic load. Hence, it is recommended to use as short and thick cables as possible to minimize the resistive losses during operation.
Fig. 27 One-quadrant representation showing a battery or fuel cell connected to the EL1002.
Fig. 28 One-quadrant representation showing a battery or fuel cell connected to the EL1002 potentials.
The graph in the previous figure shows the one-quadrant representation of the EL1002 connection with a DUT (i.e., 3 V battery or fuel cell stack). In this graph, the X-axis represents the - terminal of the EL1002 and Y-axis represents the voltage difference between the - and + terminals of EL1002 (with a maximum potential limit of 100 V). In part a), the anode (negative electrode) of the DUT is connected to the - terminal (X-axis) of EL1002, while the cathode (positive electrode) is connected to the + terminal of EL1002 (connected to the Y-axis via the blue dashed line). In this configuration, the potential is positive but will be displayed as a negative value in the IM7 software.
In this representation, the current flows counter-clockwise (i.e., current > 0). The EL1002 measures the potential with the sense cables and will always display the correct voltage of the DUT, here -3 V. However, the potential between the terminals of the EL1002 will be less than 3 V. This decrease (Fig. 14, b) is caused by the voltage drop (Udrop = R*I) within the system, which depends on the current flowing through the system. If the current is high then the voltage drop will also be high. When sinking high currents from low potential cells (such as for large area fuelcell), the potential at the + terminal of EL1002 may become less than 1 V. In such conditions, the EL1002 will not work properly. Hence, when controlling current keep in mind that high currents will increase the voltage drop and pay attention to the voltage drop between the - and + terminals of EL1002.
A PAD4 card provides 4 additional channels for parallel impedance measurements on a stack. These channels allow for a simultaneous investigation of several different parts of the DUT. With a IM7x, up to 4 PAD4 cards can be installed which allows for up to 17 parallel impedance measurements on a stack. A possible application of such a setup is the simultaneous investigation of 17 cells in a battery or a fuel cell stack as shown in the next figure. The sensor cables (green and blue) of the PAD4 card must be twisted around each other in analogy to the main channel to minimize artifacts.
Fig. 29 EL1002 with PAD4
Danger
The voltage used to calculate the power dissipation is the one that drops across the current controller in chapter Operation basics, i.e., the voltage between the + terminal and EXT+ or - terminal, respectively.
If we assume, no voltage drop in the cables then the voltage of test object will be the same as the voltage drop across the current controller. In case of voltage drop in the cables, the actual power dissipation will be lower than what will be calculated using the test object voltage.
Since voltage drop in cable varies from setup to setup hence, for simplicity, we will calculate the power dissipation using the voltage of test object.
The current used to calculate power dissipation is the current that flows through the current controller, which does not necessarily have to be the same current that flows through the current measuring unit if external sources or sinks are used.
Half-cell configuration - Cathode
This configuration is used with DUTs such as (rechargeable) batteries and fuel cells if only the cathodic part of the cell is to be investigated.
Fig. 30 EL1002 full cell cathode configuration
In this case, the sense cables are only connected to the cathode and not to the complete cell.
Half-cell configuration - Anode
This configuration is used with DUTs such as (rechargeable) batteries and fuel cells if only the anodic part of the cell is to be investigated.
Fig. 31 EL1002 full cell anode configuration
In this case, the sense cables are only connected to the anode and not to the complete cell.
Partial cell configuration
This configuration can be used if a certain part of a battery or fuel cell stack is to be investigated.
Fig. 32 EL1002 partial cell configuration
General notes for applications with external supply or load
Danger
During the startup and calibration of the EL1002, do not sink external DC current. No current is allowed to flow through the EL1002 otherwise, it will be calibrated as an offset.
The total current must NOT EXCEED 680 A (thereby, max. 200 A through the EL1002 current regulator).
There are two current loops and both currents flow through the EL1002 current measurement unit:
From EL1002 to DUT (I Operation basics)
From EL1002 EXT+ to third-party load to DUT (i Operation basics)
Make sure to switch ON the external device before switching ON the EL1002.
Make sure to switch OFF the EL1002 before switching OFF the external device.
The maximum power dissipation of the EL1002 must not exceed 1000 W.
It is recommended to test different DC currents of the EL1002, because depending on the setup the ratio of DC to AC current may affect the bandwidth of the EIS measurement or may cause interference with harmonics. A good starting value for the DC current of the external source is I DC EL1002 = 3*I AC EL1002 for measurements at the open circuit voltage/potential (OCV) of a DUT.
Note the operation steps for the devices in Operation basics
To give a brief note on nomenclature, a source or supply outputs constant current or constant voltage. A sink or load consumes constant voltage or constant current. To optimize the setup and to avoid artifacts in the measurement, it is important to consider whether constant current or constant voltage is given out of the external device.
In constant voltage operation of the external device, a low-inductive connection of the external device close to the ideal 0 zero-Ohm internal resistance is important. On the other hand, ideal constant current sources or sinks have an infinitely large internal impedance. However, this is not achievable in reality due to the control loops and the electrical construction, among other things. A high connection inductance of the device setting the DC operating point at constant current therefore has a positive effect, because the connection inductance increases the impedance of the source in the high-frequency range. This brings the real behavior closer to the ideal behavior.
To avoid errors with this more advanced setup involving an external source or sink, it is a good idea to automate the measurement process. To control the EL1002 and a power supply with Python, we provide an example on PAD4 zahner website GitHub.
Applications with an additional DC load
Danger
The measured current (sum of both currents sunk by the EL1002 as well as the external load) must be positive I ≥ 0.
The external load must operate in constant current mode.
The current flow cannot be switched off by the EL1002 in this configuration, as it is also dependent on the external device, which is controlled separately.
DUT connected to the EL1002 with an additional DC load through EXT+
Fig. 33 EL1002 with additional DC load using EXT terminal schematic
Fig. 34 EL1002 with additional DC load using EXT terminal currents
The first figure shows the correct cable connection scheme whereas the schematic on right emphasis on different current loops for a better understanding.
Power dissipation:
DUT: Battery of 9 V potential at 220 ADC and additional EIS with 5 AAC amplitude EL1002 part of the DC current: 20 A EL1002 AC amplitude: 5 A EL1002 power dissipation: 9 V * 25 A = 225 W (<1000 W) External load part of the DC current: 220 A - 20 A = 200 A
The power dissipation in EL1002 is limited to 1000 W.
EIS settings in the control potentiostat menu: Galvanostatic mode, DC CURRENT 220 A, Amplitude 5 A. 200 A of the external load must be adjusted separately and directly at the external load. With these parameters, the EL1002 automatically adjusts the current flow through its + terminal so that a total of 220 A of current flows. The total current can only be greater than the current through the sink.
Note
It is recommended to test different DC currents with the EL1002 because the ratio of DC to AC current may affect the bandwidth of the EIS measurement or cause interference with harmonics, depending on the setup. A good starting value for the DC current of the external source is I:sub:DC EL1002 = 3*I:sub:AC EL1002 for measurements at the open circuit voltage/potential of a DUT.
Here, PAD4 cards can also be used to investigate the individual cells of a battery or a fuel cell stack. The potential range of PAD4 cards is fixed at ±4 V with a compliance voltage of ±100 V. Higher input voltage ranges can be achieved by special sense cables (±5 V, ±10 V, ±12 V, ±20 V, ±24 V). However, the resolution of the impedance spectra measured by PAD4 channels will decrease with increasing potential range.
Fig. 35 EL1002 with EXT connection and PAD4
DUT connected to the EL1002 with a parallel DC load
To sink more current from the DUT than possible through the EXT+ extension of the EL1002 (current > 680 A), an external load can be connected in parallel to the DUT and EL1002 as shown below. This allows independent control of the EL1002 and the external load connected to the DUT.
Fig. 36 EL1002 and an external electric load connected in parallel to a test object
Power dissipation:
DUT: Battery of 9 V potential EL1002 part of the DC current: 20 A EL1002 AC amplitude: 5 A EL1002 power dissipation: 9 V * 25 A = 225 W (<1000 W)
The power dissipation in EL1002 is limited to 1000 W.
Fig. 37 One-quadrant representation of a battery or fuel cell connected to the EL1002 and a parallel external load
Fig. 37 illustrates the two independent current loops for the parallel connection of the EL1002 and an external load with the DUT in the one-quadrant representation. Here, the current flowing through and controlled by the external load (I:sub:2) does not flow through the EL1002 and the current limitations valid for the EL1002 do not apply to I:sub:2. In this configuration, the EXT + terminal of the EL1002 is not in use. The resistance (R) represents the voltage drop in the EL1002 current loop during operation.
Warning
Zahner Lab only measures and displays the current through the EL1002. In impedance measurements, the external load is also seen as a parallel object to the DUT. This makes the impedance spectrum recorded in this configuration, prone to artifacts.
In this setup, the parallel connection between the DUT and the external load is measured. However, since the DUT usually has a much lower impedance than the load, the load only has a minimal effect on the measurement. With increasing connection inductance of the load, the total impedance of the load becomes even higher, leading to a further decreased influence of the load on the high-frequency measurements.
Applications with an additional power supply in series
This configuration may be used if the voltage drop on the cabling is too high to reach the high-current test conditions. In addition, it allows experiments on passive objects, batteries under charging conditions & electrolysis cells etc.
Danger
The external power supply must operate in constant voltage mode.
In this application, the voltage source must be connected as low inductively as possible to avoid artifacts.
Electrolysis / charging batteries
For charging batteries or electrolysis, an EL1002 is connected in series with a DUT (i.e., an inversed battery) and an external power supply.
Charging batteries
This configuration is used for experiments on batteries under charging conditions.
Fig. 38 Cable connection scheme for serial connection scheme and one-quadrant representation of an EL1002 in series with a battery and an external power supply
Fig. 39 EL1002 with external supply in series charging potentials
The graph in Fig. 38 follows the same scheme as described in Fig. 27. The EL1002 allows current flow in one direction (counter-clockwise, Fig. 38 a), which is represented as I+. When the EL1002 as load is connected to a battery, the battery is discharged. For charging the battery, a reversed current (I-) must flow through the battery which is not possible with only the EL1002. Hence, to charge a battery using an EL1002, an external source is required as shown in Fig. 38 b. This external source applies a potential against the battery and forces a change in the current direction in the battery which leads to charging. It should be noted that the potential of the external source should be higher than the battery’s internal potential. Fig. 38 c indicates the same situation as described in Fig. 38 b, but under consideration of the voltage drop in the system. The blue line at the y-intercept shows the potential output between the + and - terminals of EL1002. Here the potential difference between the + and - terminals of the EL1002 is lower than 1 V. A simple schematic in Fig. 38 c is also shown below to clearly indicate the connection scheme of the (reversed) battery to the EL1002 and the external source.
Fig. 40 EL1002 in series connection with a battery and an external power supply in reversed connections
Usually, a cathode (positive terminal) of a battery is connected to the + terminal of the EL1002 during discharge. However, during charging, the anode (negative terminal) of the battery is connected to the + terminal of the EL1002. Therefore, this is also referred to as the reversed connection of a battery to the EL1002.
In the previous image the EL1002 will read a potential of less than 1 V between its + and - terminals. The potential applied by the external power source should be increased up to a certain extent so that the total potential across the + and - terminals of EL1002 becomes higher than 1 V after compensating for both the opposing battery potential as well as the voltage drop (R).
Note
The potential will be indicated as positive in the EL1002, because the battery connection is now reversed with regard to the sense cables.
The measured current must be positive (I ≥ 0).
Electrolysis
This configuration is used to allow for impedance experiments during the electrolysis of fuel cells. Electrolysis of the fuel cell utilizes the same cell connection scheme as for charging of batteries.
Fig. 41 EL1002 with serial supply
Note
The potential will be indicated as positive in the EL1002 (because the connection is reversed with regard to the sense cables)
The measured current must be positive (I ≥ 0).
Compensation for voltage drop (zero-volt option)
During regular operation of fuel cells, the typical current flowing through the cells is usually very high (a few hundred amperes). At such high currents, the potential drop (Udrop = R*I) is also significant. Fuel cells typically have a potential of around 1 V. Such low potential is usually consumed by the voltage drop in cables at high currents. If a current value is set in the galvanostatic mode of the EL1002 at which the voltage drop exceeds the fuel cell potential, the current value will not build up.
Fig. 42 shows the voltage drop across the resistance (R) of the system. There are some additional resistances within the EL1002 leading to further voltage drops. The Fig. 42 a illustrates this two-step voltage drop at very high currents. Since in this case the voltage drop is larger than the potential of the fuel cell, the set current cannot be achieved by the EL1002. To compensate for the voltage drop at high currents, a small additional potential is provided by the external power supply to the fuel cell (Fig. 42 b). This keeps the output potential between the + and - terminals of EL1002 positive (> 1 V), and allows for high current experiments.
Fig. 42 Compensation of the voltage drop in a system using an external power supply
In contrast to the arrangement in 7.4.1, the DUT is not reversed in the zero-volt option. The potential will be indicated as negative in the EL1002. The measured current must be positive (I ≥ 0).
Fig. 43 Compensation of the voltage drop in a system using an external power supply
Applications with an additional power supply in parallel using the EXT+ terminal
This configuration allows for the following electrochemical experiments:
Charging batteries
State of charge (SoC)
Discharging batteries
Fuel cell and electrolysis cell operation
In this configuration, the charging, discharging or SOC operations can be controlled directly by Zahner Lab software without altering the hardware settings.
Caution
The external power supply must operate in constant current mode.
Charging: current through DUT is NEGATIVE
SoC: current through DUT is ZERO
Discharging: current through DUT is POSITIVE
The current flow cannot be switched off by the EL1002 in this configuration, as it is also dependent on the external device which is controlled separately.
Fig. 44 Cable connection scheme of EL1002 with additional DC supply using EXT+ terminal
Follow the cable connection scheme shown in Fig. 44 to connect the power supply in parallel to the EL1002.
Note
It is recommended to use as short and thick cables as possible between the EL1002 and the DUT. Also, twist the cables around each other as much as possible to minimize mutual induction.
It is recommended to use long and untwisted cables between the EL1002 and the power supply. See chapter General notes for applications with external supply or load ideal current source.
Charging
Fig. 45 Current flow scheme in the system during charging
Warning
The power dissipation in EL1002 is limited to 1000 W.
The voltage used to calculate the power dissipation is the one that drops across the current controller in Fig. 19 , i.e., the voltage between the + terminal and EXT+ or - terminal, respectively.
If we assume, no voltage drop in the cables then the voltage of test object will be the same as the voltage drop across the current controller. In case of voltage drop in the cables, the actual power dissipation will be lower than what will be calculated using the test object voltage. Since voltage drop in cable varies from setup to setup hence, for simplicity, we will calculate the power dissipation using the voltage of test object.
The current used to calculate power dissipation is the current that flows through the current controller, which does not necessarily have to be the same current that flows through the current measuring unit if external sources or sinks are used.
In Fig. 45 , the schematic diagram shows the current scheme during the charging of a DUT (i.e., a battery). Here, the power supply is outputting 80 ADC, out of which a charging current of 60 ADC is flowing through the DUT. User can define the charging current directly in Zahner Lab software with the DC CURRENT. Since the charging current sign is negative so DC CURRENT in Zahner Lab software will be -60 A.
The rest 20 ADC (80 ADC - 60 ADC) is flowing to the + terminal of EL1002 where it will be used as buffer current for the EIS operation and then eventually sinked. The DC current in EL1002 must be higher than the AC amplitude for the EIS. The AC current between the + and - terminals of the EL1002 is only allowed in one direction (from + to -) and is therefore flowing in reversed direction with respect to the charging current.
In the above-provided scheme, the EL1002 is connected in parallel to the external power supply and when the EL1002 (galvanostatic mode in the Zahner Lab window) is turned off, all the current provided by the external power supply flows through and charges the DUT. Hence by turning of the EL1002, this scheme can also be used for charging batteries or for electrolysis and removing the EL1002 from the setup is not required.
Caution
The DC current flowing to the + terminal of the EL1002 must be higher than the EIS amplitude (A AC), as the EL1002 only allows current flow in one direction. If the DC current is less than the EIS amplitude then a complete sine excitation by the EL1002 is not possible.
It is recommended to test different DC currents of the EL1002, because depending on the setup the ratio of DC to AC current may affect the bandwidth of the EIS measurement or may cause interference with harmonics. A good starting value for the DC current of the external source is I DC EL1002 = 3*I AC EL1002 for measurements at the open circuit voltage/potential (OCV/OCV) of a DUT.
Discharging
Fig. 46 Current flow scheme in the system during discharging
The power dissipation in EL1002 is limited to 1000 W.
Fig. 46 shows the current scheme during the discharging of a DUT (i.e., a battery) with electrical connections among the external power supply, EL1002 and DUT. Here, the current is read as a positive value in the Zahner Lab window, translating to a discharging current of 20 ADC.
The schematic diagram shows that both the 80 ADC (used in section 7.5.1 for charging) from the external power supply as well as the 20 ADC from the battery flow towards the + terminal of the EL1002. Here, the discharging current and the AC current from the external source flow into the same direction, opposite to the current flow in the charging setup. The 100 ADC current flowing to the + terminal of the EL1002 will be used as buffer current for the EIS and will eventually be sinked in EL1002. Here, if the EL1002 is turned off, the power supply will start charging the DUT at a charging current of 80 A.
State of charge (SoC)
Fig. 47 Current flow scheme in the system at SoC
The power dissipation in EL1002 is limited to 1000 W.
Fig. 47 illustrates the current scheme during the state of charge (SoC) measurement of a DUT (i.e., a battery) with electrical connections among the external power supply, EL1002 and DUT. In SoC, the DC current through the DUT is zero, which is set in the Zahner Lab Window. Here, the current provided by the external power supply completely flows through + terminal of EL1002 where it is sinked and used as buffer current for the EIS excitation. DC current provided by the external power supply should be higher than the AC amplitude used for EIS excitation.
Here, if the EL1002 is turned off, the power supply will start charging the DUT at a charging current of 80 ADC.
Note
In all three configurations charging, discharging and SoC everything is kept the same and only the DC CURRENT in Zahner Lab software is changed which leads to switching between different operation modes.
Summary parallel power supply with PAD4
The PAD4 card can in this setup also be used to analyze individual parts of the DUT. The schematics below illustrate the connection schemes using the PAD4 card within charging, discharging and SoC scenarios.
Charging
Fig. 48 Charging
Discharging
Fig. 49 Discharging
SoC
Fig. 50 SoC
Specifications
The following section lists the specifications of the EL1002.
Ranges and tolerances
Voltage Ranges |
||||||
|---|---|---|---|---|---|---|
Voltage Range |
Range Standalone [V] |
Range IM7 [V] |
Tolerance |
|||
Index |
Factor |
min |
max |
min |
max |
|
0 |
1.0 |
-5.0 |
5.0 |
-4.0 |
4.0 |
±500 µV ±0.1% of reading |
1 |
0.4 |
-100 |
100 |
-100 |
100 |
±12.5 mV ±0.1% of reading |
Current Ranges |
||||||
|---|---|---|---|---|---|---|
Shunt |
Range Standalone [A] |
Range IM7 [A] |
Tolerance |
|||
Index |
Resistance [Ω] |
min |
max |
min |
max |
|
0 |
5m |
680 |
-680 |
680 |
-680 |
±680 mA ±0.1% of reading |
1 |
50m |
60 |
-60 |
60 |
-60 |
±68 mA ±0.1% of reading |
General specifications
Potentiostatic Modes |
Potentiostatic, Galvanostatic, Pseudo-Galvanostatic, Off |
Cell Connection |
2-, 3-, 4-Terminal Sensing |
Ground Reference |
Floating |
Maximum Measurable Voltage |
±100 V |
Maximum Measurable Current |
±680 A (with 3rd party power supply/sink) |
Maximum Sink Current |
200 A |
Output Power |
0 W |
Power Dissipation |
1000 W |
Input Impedance |
100 kΩ |
Equivalent Input Noise |
< 10 µVrms |
Memory |
64 GB |
Interface |
USB, Ethernet2 |
Additional IOs |
52 |
Additional Analog Outputs |
12 |
Additional Analog Inputs |
42 |
Temperature Sensor Interface |
Type K2 |
Ambient Temperature |
10 °C – 25 °C |
Maximum Humidity |
60 % |
Dimensions (H x W x D) in mm |
160 x 470 x 485 |
Weight |
21.5 kg |
Zahner Lab / SCPI 3 |
|
ADC Resolution |
24 bits |
Voltage Input Resolution |
0.596 µV |
Current Input Resolution |
11.9 µA |
DAC Resolution |
18 bits |
Voltage Output Resolution |
38.14 µV |
Current Output Resolution |
763 µA |
IM7 3 |
|
ADC Resolution |
24 bits |
Voltage Input Resolution |
0.596 µV |
Current Input Resolution |
11.9 µA |
DAC Resolution |
16 bits |
Voltage Output Resolution |
250 µV |
Current Output Resolution |
2.44 mA |
Impedance Frequency Range |
10 µHz – 100 kHz |
Impedance Range |
1 µΩ - 100 Ω1 |
Safe operation conditions
The maximum power dissipation (sink) of the EL1002 is 1000 W. Fig. 19 is important for determining the power dissipation, which can be simply calculated by the formula P = U * I. It is important to always use the correct voltage and current that applies for the specific setup.
The voltage used to calculate the power dissipation is the one that drops across the current controller in Fig. 19 , i.e., the voltage between the terminal + and EXT+ or -, respectively.
EXT+ and - are only connected via the current measuring unit, the electrical resistance is negligible for the voltage calculation.
The current used to calculate power is the current that flows through the current controller, which does not necessarily have to be the same current that flows through the current measuring unit if external sources or sinks are used.
If you have connected an external source, as described in Applications with an additional power supply in parallel using the EXT+ terminal, the EL1002 can display 0 A, although the output stage consumes the entire current of the source - this must then be considered in the calculation of the power dissipation.