Welcome

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.

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:

Stay tuned, updates will be coming frequently now!

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.

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: