Awesome. I like the idea of the transmitter in the charger, but it would also be cool to make it an add-on with an existing charger. I would think you would want the frequency to be well off the freq of the charger switchers. Any ideas on that? Have any idea what the small signal impedance vs frequency is for lifepo4 100ah batteries? I would think that batterieshave high impedance at high freq regardless of SOC. Chemistry just doesn't happen that fast.
I think a possibility would be to have a synchronizing pulse sent from the "master" and use time slots for each bms slave to respond. I would think that making the BMS as a slave saves energy too. It doesn't waste energy talking unless ithas too. On Tuesday, April 28, 2020, 4:38:16 PM PDT, Bill Dube via EV <ev@lists.evdl.org> wrote: I have thought about doing this for perhaps 20 years. It may well be possible to communicate via the traction conductors. It is probably worth the effort to do so because it would allow you to incorporate the BMS in the cell. Sealing the BMS inside each cell could be very useful, especially from a warranty/liability angle. The cell manufacturer would love to have a log of the SOC history of the cell. Communicating _to_ the BMS is simple. You have two VERY large transmitters, the charger and the inverter. Simply frequency modulate the pwm of the inverter and/or the charger and put an FM detector in each BMS on the cell level. You turn the "noise" source into the communication transmitter. Done. Communication _from_ the cells is not quite as simple, but doable. Use the by-pass circuit to talk to the outside world. Put a capacitor in parallel with the by-pass resistor so that when you switch on the resistor, you get a spike. Again, you can transmit via FM using "spikes" generated by switching the by-pass on and off briefly. There are a few clever tricks you can employ. During charging, you can have the charger pause for a regular "moment of silence" in which the BMS can communicate quickly and in the clear without having to "shout" over the charger PWM. Perhaps the same thing could occur to a lesser extent with the inverter. Also, cells that are in a high SOC or low SOC have a high impedance, which would tend to make the BMS signal "louder". Since this is the most critical time for BMS communication, this helps quite a bit. During these times they can "scream" to the inverter to stop for a moment so they can give details about the problem. Just a thought.... Bill D. On 4/29/2020 9:35 AM, Lawrence Winiarski via EV wrote: >> Because there are no "mains" in a vehicle.??? > Is it really "That" Noisy? I suspect it is very doable, it's just that no > one has done it yet.The trick is probably using signal processing to get rid > of the noise and doing extremelylow bit rates, which is fine for a BMS. > Ham radio guys can send stuff over the entire earthon 10 watts using > techniques like jt65. I expect they can deal with a little noise. it's > justnot going to be trivial, but it would be doable. > > IMHO the main use for the BMS is in charging anyway. > > On Tuesday, April 28, 2020, 2:12:26 PM PDT, Lee Hart ><leeah...@earthlink.net> wrote: > > Lawrence Winiarski wrote: >> Anyone know anything about data over powerlines? Why can't the BMS >> communicate over the mains? > Because there are no "mains" in a vehicle. > > That said, it is possible to communicate via the DC power cables already > connected to each cell. But this is an extremely noisy environment. It > would require substantial filtering and protection to keep driving > currents from trashing data transfers. Some chargers are also extremely > noisy, and could block data transfers while charging. > > Lee _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/index.html INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20200428/3fa80aba/attachment.html> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/index.html INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
