PDF Download
This is the first version of the Pathfinder BMS datasheet. (The file will update when we revise the datasheet, so link to the file URL if you want to share it, and your link will stay up to date)
Datasheet: Pathfinder BMS
Author: overkillsolar
Mailing List
Be the first to know when the Pathfinder BMS is up for sale!
Pathfinder BMS Demo Video
First, sorry for the quality. I tried 3 times to get the GoPro to focus, and I have a lot of other work to do. I will try again.
This video demonstrates the onboard controls on the Pathfinder BMS. All functions can also be controlled by mobile app or PC app.
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.
2 ways to use the OKS BMS Mobile App on Amazon Fire tablets
Tested on:
- Fire HD 10 (11th Generation)
- Fire 7
Amazon Fire tablets are cheap, yet they look and feel like a far more expensive tablet. In fact they are the best cheap tablet we have tried using by a wide margin. The screen is high resolution and its responsive, and the battery life is excellent.
So what’s the catch? The tablet is basically an Amazon ad delivery platform. It has a special version of the Android operating system and it has a lot of built in junk that you can’t delete. It also has it’s own version of an app store called the Amazon App Store. It does not come with the google play store, so you can’t load most of the apps that you are used to having. Unless, of course you hack it!
(We have not tested our app on older generations of Fire tablet hardware. If you encounter an incompatible device please let us know.)
Method 1: Sideload the Google Play Store APKs
We followed this guide on Howtogeek.com and successfully loaded the Google play store on our Fire HD 10 tablet. (Here’s a PDF of the instructions, in case the link breaks in the future) It’s a bit of a PITA because you have to identify 4 different APKs that match your hardware version and sideload them on the tablet. It’s worth the effort though, because then you can install any Play Store app normally, including the Overkill Solar BMS Mobile app. When tested on the Fire HD 10, the app performed flawlessly. You still need a google account to use the play store
Method 2: Sideload the Overkill Solar APK
The Overkill Solar BMS Mobile App can be sideloaded from the .APK file on Fire tablets just like any other Android device. Grab the latest release from our Github, enable permissions for installing 3rd party apps on your device, and install. HowtoGeek.com also has a helpful guide for sideloading apps. (click here for PDF copy)
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.
Pathfinder BMS Prototypes!
Good news, I finally have a complete Pathfinder BMS on my desk!
Status
I will be putting these up for pre-sale ASAP, but there is still work to do.
At a minimum, the datasheet needs to be finished before pre-sale can start.
After that, the firmware needs to be finished.
These BMSs are capable of OTA online or offline (UF2- drag-n-drop) firmware updates, but we will not ship them until the firmware is fully functional.
Pathfinder BMS feature list:
• 170 amps continuous duty rating.
• M10x1.5 solid brass studs with stainless hardware.
• Screw terminals accept up to 14ga wire for the balance wires. (18ga wire is recommended)
• Works with LTO, NMC, and LiFePO4.
• 3-16 cells LiFePO4 or LTO, 3-12 cells NMC.
• Cell count is field configurable, with various pre-set configurations available. (4s and 16s pictured above).
• Battery voltage up to 64v, and as low as 7v.
• Advanced State-of-Charge monitoring algorithms via a Texas Instruments BQ34Z100 Fuel Gauge chip.
• Positive-side switching (More intuitive, allows a chassis ground to the cell negative)
• Base plate with mounting ears and optional DIN rail mounts.
• 1 amp high current passive balancer built into the base plate.
• Modular open frame design, integrated air cooled copper heat sink.
• 2 external cell temperature probes + 2 internal temperature sensors.
• Wired discharge shutoff switch.
• OLED display and button pad.
• USB-C For wired monitoring and updates.
• Bluetooth and Wifi remote monitoring via optional internet connection.
• Password protection and encrypted wireless data.
• NO user accounts, NO spyware, always free monitoring applications.
Stay tuned, updates will be coming frequently now!
New BMS current ratings
TLDR: 175 Amps
We are in the process of testing prototypes of the new Nomad and Pathfinder BMS to find the thermal limits and current ratings. (The current rating is determined by temperature limits)
In this test we have a constant current flowing thru the BMS main board. The target temperature for the advertised current rating is 50c, while sitting flat on the test bench at an ambient room temperature of 23c.
The BMS has a temperature sensor in the center of the MOSFET array (in addition to 2 external probes to measure cell temperature), and it will have a default cutoff temperature of 85c to protect the BMS. The BMS hardware can operate safely up to this temperature limit, so there is considerable headroom over the base current rating to account for higher ambient temperatures or temporary surge currents.
In this thermal camera photo, the temperature has stabilized at 50c with a constant current of 175 amps.
Tentatively, based on this testing, the base model Pathfinder BMS will be advertised with a 175 amp constant current rating. The Nomad BMS will be offered with fan cooling, which can as much as double the free-air current rating!
As this testing program continues we are gathering data for derating (and up-rating) curves based on ambient temperature and duty cycle.
New BMS Dimensions
Our old lineup of JBD BMSs is now out of production. Rather than adapting to a new JBD design, we are finishing our new BMS design ASAP.
JBD has new models available, but we have rejected all of their offerings for various reasons, mostly due to the complete lack of security on their built-in bluetooth connection.
The new BMS is named The Pathfinder BMS by Overkill Solar. It is entirely designed in America by Overkill Solar, and programmed mostly in Canada. We will be doing final assembly, programming, calibrating, and testing here in Naples, FL. The components are sourced globally.
Here are the physical dimensions of The Pathfinder BMS:
How to identify Tesla Rev. A-B-C modules with photos
Battery modules from Model S and Model X cars come in several revisions, known as Rev A, Rev B, and Rev C. They look very similar in photos, but the balance wire connections differ. Use this guide to identify your revision before ordering a BMS kit.
Outside
Inside
If you have the chance to remove the old Tesla BMS board, It’s easier to see the differences.
Misidentification or Misrepresentation?
Unfortunately it seems to be quite common for sellers of these batteries to send a different revision, or even show photos of different revisions on the same eBay listing. If you end up with a different battery that doesn’t match your BMS kit, contact support@overkillsolar.com and we will exchange the adapter board.
For example, I found these photos on eBay- one shows a pallet of Rev A modules, and the next photo is a close up of a Rev B module:
Tesla battery capacity
Each car battery can be broken down into 16 modules. Each module is a 6 cell Lithium-ion battery that puts out 24 volts, and they weigh about 65 pounds each (30kg).
The capacity of each module when new can be found by dividing the car’s advertised battery size by 16. Example: for an 85kWh (kilowatt-hour) battery pack, each module holds 5.3kWh when new. The capacity degrades with age, as all batteries do.
We have also seen examples of modules that were damaged by leaking coolant, which corrodes the bond wires to each of the individual 18650 cells. Modules in this condition will have a significantly lower capacity than a healthy module from the same car.
Model 3 / Model Y batteries
Model 3 and Model Y cars have a different type of module. The car battery contains 4 large modules, each of them has 24 cells and they put out about 96 volts. We do not recommend these modules for DIY projects due to the extreme danger of working with 96 volts DC.