It's about source and receiver and signal strength. Ham guys don't' have
their radios in the bowels of the machine, they have their antenna (and
a power amp) outside the noise envelope. We are talking in dB of signal
to noise ratios, you just don't have the luxury of having your power amp
(much at all) and antenna outside the package. There is an acceptable
error rate, and no usable signal. If you do the measurements and tests,
I think you will agree.
t
On 4/28/2020 10:30 PM, Lawrence Winiarski wrote:
Isn't "Wide Band Noise" what RF guys overcome every day? The reason
you tune a radio is to ignore the 50 million other
channels 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 detect
a 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]
<mailto:[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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--
With hope,
Tim Economu
Offgrid Systems LLC
7664 Hellman Road
Clinton, Wa 98236
[email protected]
360-630-1962
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