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.