DIY Battery Resistance Tester with AD584JH

If you're interested in a DIY simple battery internal resistance tester and the AD584JH voltage reference, this article might be worth checking out.

If you want to build a basic internal resistance tester and use the AD584JH as a reference, you can assemble the components on a perfboard and power the whole thing with a 12V supply. For the 12V power source, you can use a lithium battery + boost converter + 7812 regulator. For voltage switching on the reference, a DIP switch will do the job, and for the power switch (K1), use a DP3T (double-pole triple-throw) switch. As for the casing, you can reuse an old radio case—or if you don't have one, feel free to repurpose any suitable enclosure.

Here's the schematic diagram of the circuit:

Working Principle:

The 555 timer generates a 1kHz square wave. In the circuit, C2 and R2 set the frequency with the formula F = 1 / (2 * 0.693 * C2 * R2). R2 connects directly to pin 3 of the IC, saving components and giving a 50% duty cycle. The signal from pin 3 goes through R3, C4, and C5 to inject a constant AC current into the battery being tested—around 100mA.

To measure, you need to set your digital multimeter to the 200mV AC range and read the voltage drop across points A and B. For example, a 10mV drop indicates a resistance of 100 milliohms. Maintaining a constant AC current is more complex than with DC, so this setup uses a DC constant-current method to power the 555 timer. An LM317-based constant current supply is used (with ADJ set to 1.25V and R1 = 25Ω), supplying 50mA to the 555 timer.

During testing, the voltage at pin 8 of the 555 IC will vary with the load resistance (around 7V), but the current across the load remains constant. To account for the 555's own power consumption, you can parallel a resistor with R1 (e.g., a 1K resistor adds ~1.25mA) to fine-tune the current.

You'll need to drill holes to install the power switch, voltage reference terminals, and the DIP switch.

Here's what the mounting panel for the voltage reference terminal and DIP switch looks like:

Here's the lithium battery and boost converter setup:

To improve voltage stability (since boost converters can have output fluctuations) and make future repairs easier, it's recommended to add a 7812 regulator circuit and a DC input jack.

This battery resistance tester is mainly for battery matching, so extreme accuracy isn't the priority.

Testing and Calibration Steps:

· Connect a current meter (set to 200mA) across points A and B, and adjust R1 so the AC output current is 100mA.

· Measure the signal frequency at that point; tweak R2 until the frequency hits 1000Hz.

· Connect a 0.1Ω resistor across A and B to simulate a battery. Adjust R1 until the meter reads 10mV (actual resistance = displayed voltage × 10).

Usage:

You need to set your digital multimeter to 200mV AC, connect the probes and the tester to the battery terminals, and you can begin testing.

Since the resistance being measured is very small, the connection method will affect the reading. For example, using alligator clips directly on the resistor leads gives a reading of 59 milliohms, but if clipped a bit away from the leads, it shows 60 milliohms.

This simple circuit is easy to build and can measure milliohm-level resistances—like wire resistance, switch contact resistance, etc.—and is also useful for pairing batteries based on their internal resistance.
However, since there’s no calibration against a standard internal resistance meter, the linearity and accuracy are currently unknown. If this is important to you, you’ll need to test and verify it yourself.

AD584JH Reference Issue:

If your AD584JH reference starts acting up, showing startup voltages like 9.993V, 7.492V, 4.997V, and 2.496V—but after 10 minutes, the 10V and 7.5V outputs drift (e.g., 9.8V or 7.4V with fluctuating last two digits), while the 4.997V and 2.496V remain stable—then you might need to troubleshoot the circuit or consider replacing the AD584 module.

Done.