RS485 Connection when ESP is powered from the Battery?

[kinsi55]

I am wondering how the wiring is supposed to look when the ESP is powered from the battery itself (Using a buck converter). Would you still want to connect ground together? (And thus, connect the P- to the GND pin of the RS485 connector).

[syssi]

Sorry, I cannot support here. I'm a software developer. ;-) I hope someone else could step in here.

[kinsi55]

Ok I found the answer to this question myself: When you power the ESP from the Battery output (After the BMS), absolutely dont connect the GND, otherwise the coprocessor for handling RS485 (And I guess the LCD too seeing as I cannot start / turn off the BMS with the included button any more) will die a quick death (Sizable spark when connecting, for a reason that I dont fully understand).

Luckily it can still be started with the old "jumpstart" method and seems to otherwise function fine. oh well, I guess I wanted to use BLE anyways (I didnt)

Edit: I'm starting to even doubt that this would work without connecting GND as the tx pin would of course get pulled to the "Ground" in communication. I guess one would need to use optocouplers or an isolated DC:DC converter

[kinsi55]

Good news however, I have chatted with the seller (Hankzor) and it seems like they are willing to provide a replacement. I will be keeping this unit for now as other than the afformentioned problem, it seems to still work perfectly fine. They would offer a replacement for the entire warranty period (1 year) so if any issues should arise at a later point (Or somebody smarter than me figures out this problem) I still have that option.

[kinsi55]

To add a bit more to the postmortem: To make absolutely sure that I'm not a complete idiot, nor that I received some weird unit, I just measured the other side of the connector and it indeed is VBAT - However, unlike before, there is no more continuity between GND and B-. I wonder if the GND of that connector is somehow isolated in some special way and I managed to fry just that. The CPUEXT anomaly alert that I had after the incident was gone after restarting the BMS. I wont bother testing that theory for now tho as I'd like to avoid sending the BMS to heaven all the way.

[syssi]

@kinsi55 Could you contact me via mail ([email protected])? I'm still looking for some more details.

[kinsi55]

@syssi Do you happen to have Twitter or Discord? I'd prefer that over mail

[syssi]

@kinsi55 I'm available via the Home Assistant and ESPHome discord (Nickname: syssi, #5175) or twitter (@syssi84).

[logmod]

@kinsi55 Previously you wrote that you connected the buck converter between B+ and P-. Later you write that you checked the connection between GND and B- and found that they were linked. Did you also measure a link between P- and GND?

The fact that you now see a different connectivity could just mean this is the result of the destroyed chip. BTW, did you connect your P- to the earth ground of your house (which you should absolutely do)?

JK chose to expose the full VBAT on the GPS plug, probably because they wanted more flexibility to use the power as needed in different external modules. Their RS485 module comes with an isolated DC converter and an isolated RS485 driver. If you want to power your ESP though a battery powered DC converter you probably should use the same approach and convert your DC from this port.

[kinsi55]

Yeah had I done that, I would probably have been fine, but in that case in rare circumstances (Say, the battery goes completely flat and the BMS turns off) the ESP could, unless extra measures are taken (And those actually work), kill the battery as it would not be turned off

[logmod]

Not sure to understand the risk of this scenario. If the BMS turns off the inverter due to low voltage it will do this at a threshold defined by you. Let's assume you defined it to leave 5% SOC. Then you have around 500Wh left assuming a typical battery size. Your ESP will run for months on this.

[kinsi55]

The BMS has two "Low voltages" - One is where it turns off discharging, and another, lower point where it turns itself off entirely (Usually, the absolute minimum of the batteries) and you need to start it again manually.

How likely is this to happen in a stationary setting with a reasonable minimum voltage? Not very, regardless I still think its not exactly good practice to power something directly off the batteries, not just because of low voltage protection but also because of all the other faults that can occur.

[logmod]

If you use the GPS port VCC pin to power your device I would strongly assume that a BMS shutdown cuts that voltage, too.

[kinsi55]

Thats a good point, I'll have to test that theory if / when I should ever get a replacement unit :D

[gepetto666]

same question. have powered the d1 with dc dc converter. B+ and P- , but if turn off from bms discharge , the d1 still remain powered whit ground from rs485 connector.
has anybody try to use optocoupler ?

[lucize]

ok, sa inteleg ca nu ai investigat chip-urile de pe placa, din păcate tot eronat îmi arata temperatura si la ora asta nu m-as pune sa reconectez esp-ul. deconectasem anterior cateva secunde, aveam ceva speranțe ca își revine daca tin mai mult deconectat.
mersi de input! as mai avea si portul de CAN sa merg pe RS485 nativ daca nu reușesc cu ttl-ul

[meccip]

Unde arata temperatura eronat, in app-ul bms sau in datele din esp ?
Am desfacut bms-ul dar nu am descoperit nimic.

[lucize]

prin Bluetooth, ttl nu mai citește nimic..

[meccip]

si in app-ul jkbms pe telefon, temperaturile arata bine ?

[lucize]

nu..
tot ce arata in app arata si in Bluetooth, dar acum am măsurat pinii si nu-mi mai dau -1.5v, incerc mâine(azi pe lumina) sa conectez esp-ul

[paulsteigel]

Regarding powering of the ESP module, why dont we use a buck converter DC-3.3V (VCC) from the B+ and B- of the battery pack to avoid turning off of the JK-BMS. Put the converter and the ESP module in a safe box outside nearby the JK-BMS. Also use a relay to trigger the BMS starting up when needed using VCC wired to B- and GND to P-.
I am using ESP8266-01S (with only 4 GPIO available)

[meccip]

It is a strange thing powering esp from battery. First time i use buck converter from battery and i burn bms communication. Second time i use issolated source powered from lcd 12v output and my bms shutdown from time to time without reson. In this moment i use 220v/5v transformer with common ground and past more than 8 month without any issues.