High Voltage Measurements: Characterization of NiMH Batteries with Autolab PGSTAT302N in Combination with Voltage Multiplier

Significance of the topic

Nickel metal hydride (NiMH) batteries are a mature rechargeable technology with wide applications in hybrid vehicles and consumer electronics. Accurate characterization at voltages above 10 V is essential for evaluating battery pack performance, longevity and safety.

Objectives and overview

This study demonstrates how to extend the voltage range of the Metrohm Autolab PGSTAT302N potentiostat using a voltage multiplier to fully characterize an 8.4 V × 2 NiMH battery pack. Both DC charge–discharge cycling and AC impedance spectroscopy were performed to assess the device under test (DUT).

Methodology and instrumentation

Instrumentation and setup used:

• Metrohm Autolab PGSTAT302N potentiostat
• External voltage multiplier providing ±30 V compliance
• DUT: Two 8.4 V, 250 mAh NiMH cells in series
• Galvanostatic and potentiostatic modes for DC measurements
• Electrochemical impedance spectroscopy (EIS) with 16.8 V DC bias, 0.1 V AC amplitude, 100 kHz–100 mHz

Experimental procedures:

1. Initial charge: 100 mA for 600 s
2. Discharge sweep: 0 to –150 mA at 1 mA/s
3. Repeated charge/discharge cycles at ±100 mA for 10 cycles
4. Potentiostatic cycling at ±0.5 V vs. OCP

Main results and discussion

Key findings from DC tests:

• Open circuit voltage ≈19 V; final voltage ≈17.2 V at –150 mA
• Cycling showed stable charge (max 18.6 V) and discharge (min 17.7 V) profiles over 10 cycles
• Potentiostatic ±0.5 V vs. OCP yielded charge at 18.3 V and discharge at 17.3 V with reproducible currents

EIS insights:

• Bode plot revealed impedance modulus and phase angle characteristics, confirming reliable measurement up to 100 Ω total impedance

Benefits and practical applications

The voltage multiplier broadens the PGSTAT302N’s potential range to ±30 V, enabling:

• High-voltage battery pack analysis beyond standard 10 V limits
• Seamless switching between galvanostatic and potentiostatic modes
• Use of all AC and DC electrochemical techniques for comprehensive diagnostics

Future trends and possibilities

Emerging directions include:

• Multi-channel high-voltage modules for large battery arrays
• Advanced EIS protocols for state-of-health and state-of-charge mapping
• Extension to next-generation chemistries such as lithium-ion and solid-state cells requiring higher potentials

Conclusion

Integrating a voltage multiplier with the Autolab PGSTAT302N provides a versatile platform for detailed NiMH battery pack evaluation at voltages up to ±30 V. The approach yields reliable DC cycling profiles and impedance data, supporting both research and industrial quality control.

Reference

1. Metrohm Autolab PGSTAT302N Application Note AN-BAT-001, April 2019
2. Metrohm Autolab PGSTAT302N Product Documentation