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Pathfinder BMS firmware update: V_0.222_BETA July 5, 2025

Edit: We published another minor bug fix as V_0.222_BETA on July 5.

We have published the first firmware update for Pathfinder BMSs as V_0.221_BETA. All Pathfinders are set to load “STABLE” updates only, so if you haven’t already, please set your BMS to load “BETA” updates, and connect to WiFi.

If you prefer to update offline with the UF2 method, you can find the new file here: https://github.com/OverkillSolarLLC/UF2

The datasheet has been updated to go along with the new firmware: Pathfinder BMS datasheet PDF

Recovery Mode is here!

There are a lot of bug fixes in this release, and some new features including the addition of Recovery Mode. This feature allows you to manually start up the system after a discharge cutoff by enabling the predischarge circuit from the BMS controls. To use it, navigate to “Recovery Mode” on the screen, and hold the OK button. The screen will display the system voltage and you can easily see when your charger engages by the bump in voltage. If the loads on the system are still too high for the predischarge circuit, you will see the red “overload” LED on the main board light up. In that case you will have to shed loads from the system or connect a “dumb” power supply.

This update also includes improvements to the BQ34Z100 Learning Cycle, MQTT bug fixes, and other miscellaneous bug fixes.

Your feedback is valuable! Please send an email to Support@OverkillSolar.com if you have anything to say about this update, good or bad. Remember, if you ever need to roll back an update, or if you rejected an update and changed your mind, all versions are available in UF2 format forever.

Pathfinder BMS firmware change log July 3 2025

V_0.222_BETA

  • Bug fix: Prevent learning cycle instructions from repeating after the cycle is finished.
  • Added Learning cycle “Stage” to non-volatile storage. When the BMS reboots after this update, the stage variable will be lost, but thereafter it will be retained. This does not interrupt the Learning cycle but it will interrupt the sequencing of the on-screen instructions if a learning cycle is already active.

V_0.221_BETA

  • Bug fix: disabling radio power freezes the user interface
  • Don’t auto-start the Learning cycle. Added Start Learning Cycle button to Learning Cycle screen.
  • Changed Charge Overcurrent Recovery parameter default to -200mA from 0mA to prevent rapid cycling of a charge overcurrent fault. (not user adjustable)
  • Bug fix: changing protection parameters to overlap an existing fault condition caused the BQ76952 to crash. Added a partial reset of the BQ76952 after every parameter change.

V_0.215_BETA

Note: some BMSs were shipped with V_0.215_BETA, but the OTA and UF2 files were bumped up to V_0.221_BETA before publishing the update.

Learning cycle

  • Adjusted learn cycle termination voltages to narrower range to accommodate moderate cell mismatch. These parameters are still non adjustable in the field.
  • Added Learning Cycle Reset function to the RESET screen. This resets the BQ43Z100 and re-initializes the learning cycle. User parameters are not overwritten, but calibrations are erased. Null current calibration must be repeated after a learning cycle reset.
  • Added a warning when changing design capacity after learning cycle is started. Once started, the Z100 learning cycle must be reset before capacity can be changed.
  • Bug fix: Energy and current not scaled correctly for the learning cycle. This caused the reported measured capacity to be 5x too high. Scale factor for energy and current is now calculated when setting Design Energy. Current resolution will now change depending on the scale factor.
  • Improved on screen instructions for learning cycle.

MQTT

  • Add MQTT status screen.
  • Bug fix: MQTT was not indexing active cells if less than 16. High/low cell numbers were off by 1.
  • Bug fix: Cell delta incorrectly formatted for MQTT
  • Limit the retry rate for a disconnected MQTT broker to 5 minutes, or 5 seconds if the user cancels the warning popup.
  • Bug fix: MQTT broker disconnecting may cause OTA to fail due to memory leak. MQTT not properly handling broker disconnect events.
  • Bug fix: MQTT leaking memory during connect attempts if radio power is off.
  • Bug fix: MQTT power was displaying current instead of power due to wrong data variable- linked the correct data source.

Recovery Mode

  • Added Recovery Mode screen- Recovery mode is manual operation only, hold the OK button to engage the output via the predischarge circuit.

Misc

  • Added indicators around cell voltage on OLED cell voltage screens to show which cell is balancing.
  • Added function to load alpha OTA with secret code (UP-DN-L-R). Customers should not use this function unless asked to test a specific alpha build.
  • Display RemainingCapacity on SOH screen.
  • Bug fix: Idle calibration routine was overshooting and not getting fresh data during automatic calibration.
  • Bug fix: Wifi scan failed if radio power disabled. Added a warning and prevent starting the scan.
  • Bug fix: Antenna light sometimes stuck on when radio power is disabled.
  • Bug fix: restart BLE advertising after cycling radio power.
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Pathfinders are Shipping!

The first batch of Pathfinder BMSs have shipped. Pre-orders up to #9025929 from April 15 are on the way.

The remaining pre-orders starting from #9025933 will ship in the next batch.
They are being manufactured now, and are expected to be here in 2-3 weeks.

When you get your new BMS, make sure your Overkill Solar mobile app has updated to version 2.0.0 (It might say V1.7.42beta until it gets an OTA update). Prior versions don’t support the new Pathfinder BMS.
The APK can be side loaded.
Also download a fresh copy of the Pathfinder datasheet, which has been updated recently.

We also have a new USB app for the Pathfinder.
The new USB app opens directly in a browser (Chrome, Edge, or Opera. Firefox needs a Webserial plugin to work)
The full step-by-step instruction manual has not been published yet.
If you have questions that are not answered in the datasheet, please email Support@OverkillSolar.com
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Pathfinder Schedule Update (It’s Late)

Well, April has come and gone and the Pathfinder BMS is not ready to ship yet.

Most of the components are finished and in our shop. We have the Balancer boards, User interface boards, all the revisions of the balance wire terminal boards. We do not have the main boards yet.

At the start of April I finished revising the main boards and decided to order a prototype instead of pushing the changes to a full run. Its a good thing too, because I have more changes to make. The predischarge circuit on the prototype is overheating when the system load is too high, and the load resistors were placed too close to the control circuits. I repositioned the load resistors away from the sensitive components, next to the FET temperature sensor, and added self resetting PTC fuses to prevent the predischarge circuit from melting down when the output has a short circuit. I also added a red “Overload” LED to give a clear indication that the load needs to be reduced.

The good news is under normal conditions predischarge is working GREAT. I have been testing with a big 48v inverter and without predischarge the BMS detects a short circuit from the inrush current. You can even hear the hard start noise, which is always a bit scary coming from “solid state” components. With predischarge enabled, the system starts up softly in about 1/2 second, with no stress. This is great because now we can leave the short circuit delay set at zero seconds for the fastest possible detection of actual short circuits, and have no issues with cold startup.

When the output has too much load or is actually shorted, the BMS will cancel the predischarge routine after an adjustable timeout, then retry after another adjustable delay. The output voltage target is also adjustable in terms of percent of battery voltage.

I have fixed the issues with the main board prototypes, and I am ready to order the full production run. The factory that makes them is on vacation the rest of the week, so I have all weekend to think about the changes.

BTW, so far we have not had to pay any new import taxes, so the presale price remains at $199. It looks like these parts actually fall under one of the exempted import codes for consumer electronics, so that’s nice.

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USB signal interference

I’ve been testing the pathfinder BMS with various equipment, and found that the USB connection is vulnerable to electrical noise from a big cheap inverter. We noticed this problem in the past with the JBD BMSs as well. (This doesn’t affect Wifi or Bluetooth)

This interference causes the USB port to stop communication, and the BMS must be rebooted to get it going again. We are working an getting the firmware to automatically restart the USB connection, but it doesn’t work yet. Remember, all Pathfinder BMSs can get firmware upgrades via OTA or UF2, so everyone will be able get the firmware solution later.

Other than getting a better inverter, the best solution seems to be adding ferrite chokes to the USB cable. I found that 2 or 3 snap on ferrite chokes is enough to stabilize the connection. Wrapping the cable 3 times thru a large ferrite ring had the best results, almost completely eliminating the interference when measured on the PC side.

Our very noisy inverter. This thing is crap, but great for testing interference.
Ferrites added to the USB cable. The large ring gave the best results.

We will do some experiments with adding common mode chokes to the Pathfinder circuit board and possibly add them to the next revision.

Better quality inverters produce far less noise, so this isn’t an issue for most customers. For example in the past we found that a Renogy inverter produced the least noise out all the units tested in our shop.

Details and scope traces:

I measured the signal interference using an oscilloscope at the PC end of the USB cable. Not much to see here. Yellow and Blue are the signal lines, Data+ and Data-.

The Inverter produces pulses of RF interference, and between pulses, the USB signal looks fine.

Inverter off, no chokes.
Inverter on, no chokes.

Here, I’ve zoomed out the time scale and added the purple trace on the inverter’s DC terminals. The pulses are happening at 21kHz, which is the inverter’s switching frequency. On the left side you can see a USB communication packet, which occurred between pulses of interference.

The real problem happens when the pulse of interference causes ringing on the USB signal lines as seen here. USB signals are mostly differential, but both lines pulled low means EOP or end-of-packet. This time, the ringing interference pulled the blue trace low enough that the USB controller would read an EOP signal.

Here, I added 3 snap on chokes (left), or wrapped the cable thru a large ferrite ring choke (right). In both cases the interference is dampened enough to prevent spurious EOP signals, but the large ring has the best results by far.

USB cable with 3 snap-on chokes, inverter on.
USB cable with Big ring choke, inverter on.