Fast switching power doesn't need a ground or a common return to generate loud EMI and foul AM. In my old testing lab I had used an old transistor radio to locate noise that was fouling a turbine flowmeter output. The problem lies with rapid rising and falling voltage - something that is desired with some electronic switches that are inefficient during those transitions. That inefficiency comes out as heat that accumulates in in motors and degrades performance. We were using stepper motors that that had voltage rise like 20 V/nanosecond. They weren't large motors, but very loud in the EM noise department. It was a trick to solve.
transistor radios are a forgotten tech. They aren't to bad in a car, but in the home a drill or mixer can cause a lot of disturbance. On Sat, Nov 10, 2018 at 1:43 PM Bill Dube via EV <[email protected]> wrote: > There is no "ground" in a vehicle, only "chassis". (Unless the vehicle > is on charge and connected to the grid.) The drivetrain and the AM radio > share the chassis "ground", which is likely the root of the problem. > > The EMI comes from the controller PWM switching, goes into the chassis, > (and is radiated in general by the drive components,) and is received by > the AM radio. > > The AM radio can be filtered, but that adds cost, is difficult, reduces > the sensitivity, and likely the sound fidelity of the AM radio. The > drive train can be designed to reduce the EMI in the specific frequency > region of AM, which adds significant cost, and is _/very/_ difficult. > You can locate the sensitive components of the AM radio away from the > drive train, which is a bit difficult and adds cost. > > Is the cost worth the improvement of the AM radio reception? Most > folks don't care, and the added cost of clear sensitive AM reception is > not worth anything to them. Teslas answer is to "use streaming" instead > of the AM radio is probably the most sensible for most people. > > This problem is similar to acoustic noise in airplanes. It is quite > costly to reduce the cabin noise in airplanes, and it adds weight, which > reduces efficiency and reduces performance. In small airplanes, > helicopters, and military airplanes, everyone wears headphones (or ear > plugs). In commercial airplanes, the airplane itself is designed to > reduce the cabin noise. However, it is very expensive to solve noise the > problem at the source end. Much cheaper and lighter to solve the problem > at the relieving end. > > Do you _need_ an AM radio in your car? Probably not. You don't get > to your destination any quicker. > > Bill D. > > > > > On 11/10/2018 1:03 PM, Peri Hartman via EV wrote: > > Hmm, maybe cost savings of putting a grounded shield around the motor > > and controller. For the AM radio, what could the cost be? $1.00? > > > > Peri > > > > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20181111/48d25efe/attachment.html > > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > Please discuss EV drag racing at NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > -- Michael E. Ross (919) 585-6737 Land (919) 901-2805 Cell and Text (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Tablet, Google Phone and Text -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20181110/29984709/attachment.html> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
