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
<[email protected]> 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
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