I purchased a HRM-10 battery tester directly from the FNIRSI factory store. Based on information I already saw online, I anticipated the meter had good quality and would help me identify the condition of batteries and cells I have on hand.
While browsing the FNIRSI site, I was greeted with a coupon code for a discount off my first order and free shipping. I could have ordered from a popular third party retailer at a similar price. I thought it might be nice to support the company directly.
I used my own funds, and did not notify them I do reviews online when I ordered. So my review will be unbiased, and the unit should be representative of the typical consumer purchase.
Product Fulfillment
I received a confirmation email and a QR code to track my order with Shop .com, which I had to install. While I could see the order in the app, the tracking feature never worked, and the status was always shown as "preparing to ship". Regardless, after a couple weeks went by, my order arrived in excellent packaging and a sealed new box.
Day # 1
I looked the device over, with only one noticeable oddity: The connector pins inside the top connector were not at the same heights. I realize some connectors are made this way, so that the pins mate early or late for grounding purposes. I plugged in the supplied Kelvin leads and went about testing various cells in my collection. All seemed fine.
I went about putting the device through sample measurements. What I learned was very interesting, as will be detailed later.
The Following Week (Uh-oh)
I needed the unit to check some cells. After plugging in the cable and starting, I experienced out-of-range readings. I tightened the connector, and the readings were better at first, becoming problematic after a short while.
So I disconnected the cable and looked at both ends. One of the pins had dropped down very low inside the connector. I pulled it up with needle-nose pliers, and it reached a improved height, that was still lower than others. Reconnected the cable and things were OK for the remainder of the session.
Third time trying to use the unit, I couldn’t get valid results at all. I looked inside the connector to discover the pin had dropped down again, and this time tilted sideways. The mating end of the cable also had a dink mark.
Under higher magnification, I could see the connector plastic had distortion around two of the pin holes, worse on the loose pin.
I contacted FNIRSI by email asking for support on their 30-day return policy. I included the picture above and a description of my experience. Several weekdays later, I received a response. They told me the return policy only applies to an unused item. A return would not be authorized because I went about pulling up the pin myself.
They did offer me a 30% refund and implied I could keep the unit and fix it myself. I hesitantly agreed to it.
Their email offering me the refund included the grainy picture below, but no further information how to repair, which is how I knew they wanted to help me be able to fix it myself. Still, I needed to consult YouTube to find a person who had opened one up to safely get inside.
If I would do it again, I’d go with a third party seller. They have all the systems in place to give the buyer a modern day no-hassle experience. I would have been able to return the item using their free online returns system within 30 days for any reason.
Now onto my test findings...
Using the Cables
The 4-wire "Kelvin" clips are fine for batteries or cells with long nipples or terminals that can be grabbed onto with jaws. However, for opposing flat surfaces, it's difficult to make robust 4-wire connections to the flat ends. What I was able to do is piggyback spring-probe pens onto the standard cables. A picture shows how this was done. It worked perfectly to extend the 4-wire connection to a more appropriate interconnect.
Other reviewers have utilized a spacer to assist keeping the alligators open when pushing the alligator clip ends against the terminals. This didn't work very well for me. The two large clips are on short, thick, independent cables, not far enough away from the junction into one cable. As a result, it's awkward trying to spread the cables tips 180 degrees apart, aimed at the opposing ends of a 18650. My probe pen workaround got past this issue, leading to very stable 4-wire measurements.
This could be better.
As the cable exits the unit from the top of the unit, there is a long, stiff region, presenting a mechanical advantage over the base. The cables are soft - but thick, with memory of how they were bent when shipped. The unit's stability using the tilt stand is overpowered by moving the cable. Not the worst I've dealt with though.
Not sure why there needs to be a specialty connector, it's an unusual type few people would have on hand. As I found out, not the most reliable choice either. Because of the stiff assembly, the cable must be removed to put away in the original box or a typical short storage case. With frequent attachment cycles, I would not be surprised if other people's units could also fail due to pin retention issues.
I searched, but did not find any alternate accessory cables designed for this unit. There is no information about the connector type or part number, so building your own is not a straightforward task. I think it's a GX12-4.
I'd much rather have a unit with banana jacks on standard spacing, so that I can use industry standard 4-wire cables.
How it performed... It wasn't what I expected.
I was surprised how similar the IR readings were between known good cells will good capacity, vs. old weak cells which have poor test capacity. It seemed the internal resistance was arbitrary, unlike other testers I've used.
Then I switched from high-quality 18650's to cheap, low capacity cells, I did indeed find a definitive difference in internal resistance. High-quality cells always had a lower result than bargain cells, even if the higher quality would not hold much capacity anymore. After doing some research, I found out that the AC method the HRM-10 uses has a significant limitation. It is designed to measure ONLY the electrical resistance present in the metal pathways of a battery, not any opposition to current demand. If there are defects in the wired connections to the cell, this meter would readily catch the defect.
In contrast, other devices I have used compare the DC loaded resistance against the open circuit resistance. This does a quick performance check how well the cell maintains it's voltage as current is drawn. For this method, there is a pronounced correlation between cell aging and total internal resistance calculated inside the unit.
Not so with the HRM-10. The ionic resistance portion is not part of the measurement.
Total Effective Resistance = Electrical Resistance + Ionic Resistance
Only the ionic resistance portion of the measurement correlates strongly to the cell's ability to hold or maintain a charge. As the rechargeable cell is cycled hundreds of times, the total effective internal resistance goes up measurably. This resistance increase leads to more heat during charging and discharging.
Because of this lack of loading of the cell, the test result may have limited usefulness to most consumers, who generally need the total effective resistance to better evaluate the goodness of a cell.
The results on the HRM-10 will reveal the cell build quality, but not the chemical health.
Until going through this discovery, I never knew there are different types of internal resistance! If you want to learn more, follow the links at the end of the page.
What is this unit for then?
This unit is obviously designed for the final quality check at the end of a cell manufacturing line. The sorting feature helps to "weed out" defects in cell construction and chemistry, by checking the AC impedance and voltage.
Perhaps it can be used to troubleshoot problems with a battery pack, build new balanced packs, or to evaluate the current carrying ability of a cell.
Personally, now that I have both types of devices, I would perform both an AC and DC load test on each cell to fully characterize the internal resistance caused by both wiring and chemistry. If I only had one device, I would rather have one that performs the DC method.
Beyond Batteries?
As a dedicated battery tester, it works as it should. However, I know many persons want to know how this device works as a voltmeter, as an ohmmeter, and as a capacitor ESR checker. I will discuss my impressions based on testing I have done.
As a Voltmeter
Overall, this unit is poor at being a voltmeter in the typical high-impedance realm. When used directly on the output of a low impedance power supply, the results are good. When the output of the power supply has higher impedance, the voltage result was strangely changed at the output terminals when the HRM-10 was connected . My observation is the measurement technique alters the condition of the circuit being measured. Also, anything below about 0.1V was reported as 0.0000V.
For another scenario, I used two 4K resistors to make a series voltage divider across the power supply output. I set the power supply to 2V, expecting to find 1V across each resistor when measured. Unfortunately, the FNIRSI unit measured 0.0000 across each resistor. A standard voltmeter found 1V, but the HRM-10 failed this task entirely.
Could it be that the voltage isn't reported at all when the source impedance is over 200 ohms? To check this, I made my voltage divider using 50 ohm resistors. This time, voltage measurement worked fine.
Side note- the resistance reported during this measurement was just over 25 ohms - not 50 ohms. This was because I effectively had two resistors in parallel. The power source alone only had 26 milliohms according to the HRM-10. That is effectively a short circuit, using AC internal resistance method. The diagram below can help you picture in your mind why it's two 50 ohm resistors in parallel.
As a milli-Ohmmeter
For resistances below 200 ohms, this is an outstanding tester. The resistance is reported accurately and precisely. Resistors should be tested out of circuit. Wire-wound resistors may respond differently than expeced: Keep in mind a 1V AC waveform is being used - so any introduction of inductance, capacitance, protection circuits, or external noise can influence the result.
The low resistance capabilities of the HRM-10 is my favorite feature!
Many ohmmeters drop the ball below 10 ohms. This meter is the better option for that range. Here's my error chart "out of the box" No resistance calibration was done.
By grabbing onto an adapter board with gold-plated headers, I can extend the supplied cables to many scenarios. Below is shown a test setup that enables me to test all common types of USB cables. One end of the cable connects with the adapter board, the other to a shunt. The HRM-10 reports the total path resistance from the V and G pins of the source connector board down the red wire and back up the black wire inside the tested cable.
The clip jaws tend to bend the pins inward. After these pictures, I pushed an additional 2x5 header without the pins over the tips of the pins of each header to prevent bending in and to protect from damage. Makes a cage shape where the clips can still grab onto
As an ESR Meter
When checking a few capacitor ESRs, I achieved acceptable results. Great results when comparing results against my LCR meters which were set to the same AC frequency the HRM-10 uses (1 kHz). However, the frequency cannot be adjusted on the FNIRSI. Therefore, in cases where you would use 100 Hz or 120 Hz on a LCR meter to check ESR on high-capacitance polarized capacitors, this meter produces less accurate but still very useful results.
Even more important is the lack of DC bias in the test waveform. AC reverses the polarity every half cycle, which can degrade the capacitor. For that reason, I cannot recommend this device for checking polarized capacitors such as electrolytic and tantalum.
Wrap-up of Initial Testing
The software has good menus, and the operation has snappy performance. The battery life is outstanding, and the USB data download works perfectly.
Unfortunately the internal resistance measurement the HRM-10 shows has nothing to do with battery age. Moreover, there is no education of the user how to interpret the meaning of the AC internal resistance reading. I suspect the void of information may lead many consumers buying a unit which doesn't serve their needs.
I found the connector system is neither industry standard for testers, nor is it reliable. When mine failed, the unit could only be fixed by disassembly.
Other than the connector, the unit itself has very good quality. I found clean, professional workmanship inside the unit during the repair.
Accuracy? As shipped, my unit's voltage readings were 0.16% high, and resistance readings on precision carbon resistors have near zero error. After voltage calibration, I didn't any error worth mentioning anymore. Here's how the voltage-calibrated meter performs:
User calibration is available in the menu for both voltage and resistance, requiring ±1V, ±10V, and ±60V inputs. This was straightforward, just follow the prompts. It shows both the setting voltage and the uncalibrated voltage on the screen. Ignore the second number, it's just for reference. You'll want to have an accurate voltmeter across the HRM-10's terminals to precisely tune your power supply. Once you get the value (such as 1.0000 V) on that voltmeter, press OK and it's confirmed. Thanks to FNIRSI for allowing the user to calibrate!
The Repair
In order to get my unit working again, I had to disassemble it. Sorry I didn't capture any images - there are videos online how this is done and what it looks like inside.
The plastic around the bad pin was blossomed/bubbled outward on the back side, which is evidence of melted plastic around the pin, likely due to overheating during soldering. The wires that attach from the connector to the board are several gages too thick. The wire is larger than the solder cup on the terminal pin. It seems that a lot of time needs to be spent applying heat to melt the wires to form a joint.
The terminal pin itself is entirely smooth, with no barbs or catches against the plastic to assure no backwards movement during plugging. It's only a friction fit keeping the pins in place during mating, and perhaps the inflexibility of the thick gage wire. This fit is gone after the plastic is compromised by high temperature.
After determining the problem, I decided to try to fix the pin into place. I mated up the cable, which pushed the pin some distance out the back side into the unit again. I put a very small amount of 2-part epoxy around the exposed base of the pin on the back side of the connector, then pushed it up into the correct position to match the others around it.
I verified the unit operates, then reassembled with cable still attached.
I found a longer case for the unit. This allows me to leave the cable attached when in storage. That way, I'm not risking the chance of a recessed pin from happening again. I don't think I'll ever detach it again. Hopefully the epoxy will hold if I do.
The Verdict
I like the FNIRSI HRM-10. It is a good overall value and has a professional feel. Only the poor connector design and lack of usefulness of the AC method internal resistance measurement detract from an excellent product. This will probably see more milli-ohmmeter use in my lab than battery testing.
I've wanted to buy a FNIRSI item for a while now. Just recently I watched dozens of online reviews of their tweezers, transistor testers, multimeters, radiation detectors, and oscilloscopes. I observe they achieve 95% of quality precision in build quality I look for. They are amongst leaders in combining many useful features into economical products. They definitely have some talented young Engineers and designers working on their products, more experience with practical use might help.
My wait on purchasing any devices from FNIRSI until now? Most items usually have direct equivalents from other companies, and those other products are usually more practical & polished by a small margin.
The deficiencies arise from being too fancy and trendy instead of concentrating on usability and function. Hopefully FNIRSI can start doing some "version 2.0" of their products with improvements in place to increase usability and reliability.
I would not buy directly from the factory again. It just wasn't the type of experience I have become accustomed to. If I had bought from a third party seller, I would have had a better fulfillment experience and an easier path to returning the unit. It's not that there isn't good people supporting the product, it's just not as easy as a consumer when things go wrong.
Links to the Subject of Battery Internal Resistance
https://batteryuniversity.com/article/bu-802a-how-does-rising-internal-resistance-affect-performance
Comments