Category: Status_Updates

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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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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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First batch is sold out!

Sorry, I should have made this post 2 weeks ago: The first production run of Pathfinder BMSs is sold out!

Orders after order number 9025792 (from March 16) will ship from the SECOND production run of Pathfinder BMSs, so they will have some additional lead time beyond the original April 30 estimate.

Pre-order now to save your place in line!

The orders keep coming in, so the lead time will continue to increase for new orders until we get caught up. (Ramping up manufacturing is hard!)

Big thanks to everyone who has placed a pre-order, we really appreciate your support and patience.

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Quick Start Guide (bottom cover)

Pre-sale Update:

Some of the boards for the first run of Pathfinder BMSs have been ordered and are currently in production. A big thanks to everyone who has put their orders in!

I just finished the quick start graphics for the bottom cover of the BMS, what do you think?

The full user manual will have more example drawings for other cell counts.

While working on revisions to the main boards, I decided to add a wiring test feature that will detect faults in the battery wiring before the BMS is even powered up. This should help prevent a lot of mistakes that we have seen in the past when wiring up DIY batteries.

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Pathfinder BMS update: Still programming

Since the last update We have been coding the Pathfinder BMS firmware every day. It looks the same, but it does a lot more stuff.

What works:

  • Automatic cell detection from 3 to 16 cells- one BMS model covers it all.
  • Positive side switching- Easier to set up, and fully compatible with chassis ground electrical systems.
  • Advanced State-of-Charge monitoring via the BQ34Z100 “fuel gauge” chip.
  • OTA updates: Over-the-air firmware updates via WIFI.
  • UF2 Updates: Load new firmware with a drag and drop USB interface.
  • Bluetooth app.
  • USB app: no extra dongles- USB-C is built in.
  • All of the data monitoring is available on the built in OLED screen.
  • Manual control of the outputs via the screen
  • All parameters can be set up via the free Bluetooth or USB apps

What will work soon:

  • Home Assistant integration: The pathfinder will be automatically discoverable by Home Assistant via MQTT (looking into Solar Assistant too)
  • All parameters can be set up via the OLED screen

SOC: State of Charge

This screen takes data from the fuel gauge chip and displays State of Charge with a confidence level. When all parameters are set correctly for the cell chemistry and the chip has completed a learning cycle, the confidence level will approach 100%. This is much better than other BMSs, which use a oversimplified voltage lookup table. It also calculates the Time to Full and Time to empty based on average current and battery capacity.

SOH: State of Health

The state of health is the ratio of design capacity to measured capacity

Manual Controls and MOSFET Status

This page allows you to manually switch off the charge or discharge MOSFETs (The solid state main outputs), and it shows the actual status of the outputs and the discharge switch input.

Session Values

The max and min for battery voltage, current, and power since the last reset

Battery Voltages

This page monitors the voltage of the cell stack, as well as the system voltage on the output side.

All Cell Voltages

This screen monitors all the individual cell voltages, and indicates the high and low cells and the delta. A similar screen displays all of the cell inputs even if the BMS is configured for fewer cells, and allows manual testing of the balancer for troubleshooting.

WiFi Setup

These screens let you set up the WiFi SSID and password. To use OTA updates or MQTT, WiFi must be connected. The Pathfinder is built with a focus on privacy- the WiFi connection is only used to check our Github for firmware updates or for local network monitoring. Remote monitoring can be relayed through Home Assistant, and in a later firmware update we plan to set up remote monitoring in the mobile app via a relay server, probably using the MQTT protocol. It should also be possible to do this via a local MQTT relay, if you want to set it up on your network.

Firmware Updates

The Pathfinder BMS firmware can be updated in 2 ways: OTA (Over-The-Air) or UF2 (USB Flashing Format).
The Overkill Solar website will have the change log for each release, and past releases will be archived in UF2 format.

Over-the-Air updates can update the BMS firmware via WiFi if it is connected. This screen lets you set it for automatic updates, or to always ask first (default), or to never check for updates. You can also opt in to Beta versions of the new firmware.

To flash a firmware update, plug the BMS in a PC via the USB-C port, and put it into UF2 mode via the onscreen menu.

A new USB drive will appear on the computer. Copy or drag-n-drop the .UF2 file into the new drive.
When the transfer is finished the BMS will reboot into run mode with the new firmware.
The firmware version is displayed during boot up.

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(Oct. 13 update, back to normal-ish) Delays due to Hurricane Ian

As you may have seen on the news, most of southwest Florida got trashed recently. The Overkill Solar main office and warehouse are undamaged, owing to their bomb-shelter-like construction. Unfortunately, the shop is without power (ironic, we know). UPS, USPS, DHL, etc are not making pickups because all the roads are flooded. When the flood waters recede and the carriers start moving again, we will get back to work shipping out your orders, so that you may be better prepared. In the meantime, cells will continue to ship normally from the California warehouse and customer support will be online from the St. Louis office.

Updates

1.) It’s the morning of Friday September 30, 2022. The Overkill Solar Naples office weathered the hurricane beautifully. Parts of Naples have heavy damage from flooding. We got lucky, as 30 miles to the north, large areas of Bonita Springs, Fort Myers, Cape Coral, Pine Island, and Sanibel Island are totally destroyed. We are starting to fill orders today with the office running on Overkill Solar batteries. I don’t know whether any of the carriers will actually be picking up packages today.

2.) It’s the morning of Monday October 3, 2022. Our electricity came back on last night and we are catching up on all of the orders. We expect to be up to date by Tuesday.

3.) Thursday Oct 13, This part of Naples is back to normal, and we are up to date on fulfilling orders.