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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!

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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.

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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:

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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

Revision A: Look for 3 groups of pins on the right.
Revision B: Look for one row of pins on the right.
Revision C: Look for 2 groups of pins, top and bottom.

Inside

If you have the chance to remove the old Tesla BMS board, It’s easier to see the differences.

Revision A: Soldered wires with molded strain relief.
Revision B: All 7 balance wires in one long connector.
Revision C: Note the ribbon cables top and bottom.

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:

Revision A modules, from eBay
Revision B module, from the same eBay listing

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.