Category: Pathfinder BMS

News and updates about the all new, designed in America, Pathfinder BMS

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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.

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New Self-Test feature

We added a super handy self-test feature to the Pathfinder terminal boards.

They now have a TEST button and fault indicator lights for each cell.

This feature will catch many of the wiring mistakes that can destroy the BMS before the damage can happen.

This test can detect swapped balance wires and open circuit cell connections, both of which would damage the voltage sensing inputs on the BMS main board if the terminal board was plugged in before fixing the faults.

The new 16 cell self-testing boards are finished and ready to ship with pre-orders.

(All of the terminal boards will have this feature at no extra cost)

Example Usage:

In this example, all of the balance wire connections are correct, and only the green LED lights when pressing the TEST button. This assembly is ready to connect to the BMS.

In this example, one of the cell terminal bus bars has been left off. Pressing the button lights up a single red LED corresponding to the open connection. If the BMS was plugged in like this, the full battery voltage would be present between 2 cell voltage inputs that are not tolerant of the full battery voltage.

In these examples, 2 balance wires are swapped out of position. The red LEDs will light even without pressing the test button. This may be the most damaging type of wiring fault because it puts negative voltage across several of the cell voltage inputs, which will destroy them if the connector is plugged into the BMS.

In this example, multiple faults are present and the red LEDs do a fun little dance. Might want to start over if it does this…

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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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16 Cell Layout with a Pathfinder BMS

While I’ve been working on the new user manual, the programmer is making great progress on the firmware.

I’m pretty happy with how the new illustrations are looking. Here’s a preview: The cell connections for a 48v 16 cell LiFePO4 battery:

Figure? Shows the general layout of a 16 cell battery. Note that the most positive terminal (BC16) on the group of cells is connected only to BC16 and the “+Cell” terminal of the BMS. The “B+” terminal connects to the positive side of your electrical system.

The most negative terminal (BC0) on the group of cells is connected to the negative (or ground) side of your electrical system. It is OK to connect this wire to a chassis ground, if applicable.

It is difficult to draw all 16 cells on a single page. See figure? For a zoomed-in view of the balance wire connections. All 17 balance wires (AKA voltage sensing wires) must be connected as shown. See note 1.

Note 1: Which stud to use? Where is BCx?

We usually specify that each balance wire should be attached to the positive terminal of the corresponding cell. 

For example, connect wire BC2 to the positive terminal of Cell 2. 

This is only for consistency in the instructions, because anywhere on the node between 2 cells is the same as far as electricity is concerned. 

For example, wire BC2 can be connected to the positive terminal of cell 2, or to the negative terminal of cell 3, or it can be bolted or soldered to the center of the bus bar connecting these cell terminals. In fact, attaching the wire to the center of the bus bar may be technically superior, but we don’t think it’s worth the extra effort in practice.