The key is that the cell electronics are the simple part. They don't
have to be very sensitive or selective at all. They are just listening
to a a 100 kW radio station that is transmitting FM on its PWM carrier.
It is actually difficult _not_ to listen.
The more sensitive receiver is the single central "brain" that is
listening to the messages that the cell electronics are transmitting.
This central brain is the most difficult part, but there is only one of
them, so the cost of the system can be low overall.
Again, you can _briefly_ pause the drive to listen, perhaps for a
several milliseconds out of every second, and it would be imperceptible
to the customer. I doubt that the motor would even notice. You might
even listen between "on" pulses of the ~20 kHz PWM base frequency. The
transmission band can be in the high MHz, or low GHz band.
While charging, which is much more critical for safety, you can
turn the charger off for much longer periods to get much more detailed
information from the cell, if you like.
When you are driving, you only need to hear from a cell when it is
too hot, too cold, or low voltage. You also need some sort of cell roll
call occasionally, but you can do that at a slow pace.
Bill D.
On 4/29/2020 5:30 PM, Lawrence Winiarski via EV wrote:
Isn't "Wide Band Noise" what RF guys overcome every day? The reason you tune
a radio is to ignore the 50 million otherchannels and the
sun/jupiter/everyelectronicdevice known to man and concentrate on your own..
I can use my cell phone in my EV just fine. If noise was really
insurmountable, then I wouldn't be able to do that.
Seems to me that with enough selectivity over enough time, you can ignore every
bit of noise known to man.
As I said the Ham guys can pick out signal in signal to noise ratios of -120db.
That's 12 orders of magnitude and they can detecta walkie/talkie on the
other side of the globe. It's amazing. Sure it's only a few bits/min, but
the point is that it IS doable.
It requires a different mindset than just straight digital manipulation. You
accept error rates and deal with them using math.
On Tuesday, April 28, 2020, 9:58:47 PM PDT, Offgrid Systems via EV
<[email protected]> wrote:
Yeah I'm gonna agree with Lee here. I've been thinking about this for
years also, going as far as testing some ac powerline comm chips adapted
to DC power busses. I found it's impossible with all the noise coming
from the drive on an EV. But Lee, you don't even need a spectrum
analyser, just fire up your EV drive train, looking at any of the phases
with a oscilloscope. It's wide band noise, and the motor control is
modulating to operate the motor, but with sinewave drives, or even the
old PWM drives, there is noise during the entire cycle, and the only way
you get a quiet time is if you actually shut off and short the motor for
a brief period. But if you do that there will be high peak currents that
will not be good for the efficiency of the drive. If reliability is the
key, you will not want to use the DC busses, unless it's a low noise
application, and you can control and build all of the power devices,
like maybe a powerwall with a pure sinewave inverter, and you make the
charger (solar charge controller) and the inverter. But for motor
control, it's a difficult problem to solve.
Tim Economu
On 4/28/2020 6:48 PM, [email protected] wrote:
It sounds easy; but put a spectrum analyzer on your battery leads to see
what's*really* there. I think you'd be shocked at the noise level.
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.
Same as above. Are you going to design a special charger that must be
used with your BMS?
There are lots of solutions that work*some* of the time. There are a
few that work*most* of the time. But it gets damnably difficult to find
schemes that work*all* of the time.
The problem is that a BMS is a safety system that you want to work*all*
of the time.
Lee Hart
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