Unveiling the Precision of the Fnirsi HRM-10 Battery Resistance Tester
- by Clemens Valens
- Reading time: 6 min
As the world shifts towards battery-powered devices, the demand for tools to test and repair these batteries is skyrocketing. After previously reviewing the Fnirsi SWM-10 spot welder, a must-have for assembling and fixing battery packs, it's time to take a closer look at another essential gadget: the Fnirsi HRM-10 High-Precision Internal Resistance Tester. This compact device is perfect for assessing the health and quality of your batteries with ease.
A Closer Look at the Fnirsi HRM-10: Impressive Features and Design
The HRM-10 is a sleek, handheld device, about the size of a standard multimeter. It has a solid, weighty feel, and its design features a classic combination of black and light blue, consistent with other Fnirsi tools I've used. Once powered on (after possibly needing to charge the battery), you're greeted by a sharp, colorful graphic display that shows two key readings: voltage and resistance. The device is operated via a 5-key keypad positioned below the screen.
You'll notice a round 4-way connector on the top side, where you attach the test lead. This lead, known as a Kelvin Plus test lead, has two clamps at the opposite end and is securely fastened to the tester with a screw-on ring, ensuring it stays in place during use.
Updating the Firmware of the Fnirsi HRM-10
On the right side of the HRM-10, you'll find an exposed USB-C connector, which serves multiple purposes: charging the device, retrieving data, and upgrading the firmware. Although the Fnirsi website offers firmware version V0.3 for download, my test unit came pre-installed with V0.4, so I didn't need to explore the update process. To check the software version on your tester, navigate to the ‘Factory default’ section in the ‘System settings’ menu.
Navigating the Tricky Process of Setting the Date and Time
When you power on the Fnirsi HRM-10, it displays the date and time, which are likely incorrect. Adjusting these settings in the ‘System settings’ menu can be more complicated than expected. The process involves changing the date and time digit by digit, with up/down icons indicating the active digit, but the navigation feels counterintuitive—up actually means down and vice versa. While this can be frustrating, it's worth setting the correct time, especially if you plan to use the Pass/Fail test mode, as it records the time and date alongside the test results.
Important Note on Using Kelvin Test Leads
Before you dive into testing batteries with the HRM-10, it's crucial to carefully read the user manual, as it contains a key detail hidden in the 'Precautions' section about the Kelvin Plus test leads. The manual specifies that the clamps must always remain open during testing for accurate measurements—the jaws should never touch each other directly. While this is easy to achieve when testing batteries with protruding contacts, like the positive side of an AA cell, it can be challenging with flat contacts, such as the negative side. It's important not to overlook this, as closed clamps can lead to unreliable results, especially when using the Pass/Fail test mode. This crucial detail should have been highlighted more prominently in the instructions.
Assessing Accuracy: How the Fnirsi HRM-10 Measures Up
Using the Fnirsi HRM-10 is straightforward, especially in auto-ranging mode—just clamp it onto a battery and read the results. But how accurate are those readings? The voltage measurement, displayed with four decimal places, is impressively precise. When connected to a bench power supply set at 5 V, the HRM-10’s reading differed by only 100 µV from my trusted Fluke 189 multimeter. Although my Fluke hasn’t been calibrated in over a decade, its reliability still holds up.
As for resistance measurements, the HRM-10 displays two decimals in milliohm mode, indicating a potential accuracy of 10 µΩ. I tested it with a 5 mΩ, 0.1% precision resistor, and the HRM-10 reported values fluctuating between 5.07 mΩ and 5.08 mΩ—slightly higher than expected, according to the resistor's manufacturer, Vishay Precision Group. However, when I switched to ‘Resistance calibration’ mode, the reading stabilized between 4.99 mΩ and 5.00 mΩ, which is spot on.
These results convinced me of the HRM-10’s accuracy, and I opted not to tamper with its calibration, trusting that Fnirsi’s tools are more precise than anything I have on hand.
Is the Fnirsi HRM-10's Accuracy Overkill?
As the saying goes, "with great accuracy comes great responsibility," and this is especially true with the Fnirsi HRM-10. When dealing with such minute resistance values, even the slightest contact resistance can impact your readings, making the placement of the leads crucial. This raises questions about the quality of the leads themselves and whether the precision offered by so many decimals is truly necessary. And how good are these leads anyway? I wonder if fewer decimals wouldn’t have been better.
Pass/Fail Testing
The Fnirsi HRM-10 features a convenient Pass/Fail test function designed for quickly comparing battery cells. By setting upper and lower thresholds for voltage and resistance, the device will indicate whether the battery passes (with a green light) or fails (with a red light). The results are automatically stored in a table, which you can review later in the ‘History records’ or export as a CSV file via the USB port. The device supports up to eight test presets, but it's a bit disappointing that neither the thresholds nor the preset number are saved alongside the results.
Conclusion
The Fnirsi HRM-10 Internal Resistance Tester is a user-friendly and highly accurate tool for assessing battery quality. It also doubles as a reliable voltmeter and milliohm meter, offering precision beyond what most multimeters can achieve, especially below 100 mΩ. The Pass/Fail test mode is particularly useful for those who need to sort through large batches of batteries quickly. From a mechanical standpoint, the HRM-10 is well-designed, featuring a stand for upright positioning and a hole for easy hanging. Overall, the device exudes quality and reliability, making it a trustworthy addition to any toolkit.
