On 26/11/2014 11:15, Phil Allison wrote:
Jeff Layman wrote:

Some modern ceiling fans use low voltage( ie 24V) BLDC motors
operating from a SMPS - all crammed into the same housing.

Why one would run in the wrong direction before correcting itself is
a tad mysterious.

Puzzled me too so I Googled for the explanation. I have no idea if it is
accurate, but see the final paragraph in this section:
https://en.wikipedia.org/wiki/Brushl...lementat ions

No. The 999kHz local radio transmitter (1kW) is about 15 km
away..

** So the available signal is weak.

Fairly so, but reception is quite acceptable when the fan is off.


** You have missed the point.


The fan is in a new metal-framed conservatory.

** So the signal inside is very weak.

Indeed, even with a loop aerial connected.


** Assuming the fan has not developed a fault since you installed it,
the RFI you are hearing may well be within legal limits for such
appliances.

The AM and HF (short wave) bands do not enjoy the same regulatory
protection as FM and TV reception does - so things like SMPSs and
motor drives are permitted interfere somewhat with AM receivers in
the same premises.

I don't know if it is. It should fall within Directive 2004/108/EC, but
it isn't CE marked, and compliance with that Directive isn't mentioned
in the manual.

Having only weak signals available in the vicinity makes it so much
worse.

Is the fan motor in a plastic enclosure ?

A grounded, metal one would be far better at supressing AM band
noise.

I think it is plastic.

Anyway, I was able to try a few things today, and the interference has
been reduced to almost zero. Firstly, the earth appears OK. Just in
case, I connected another earth lead to a known good earth, but it made
no difference. Next I fitted the delta filter, which suppressed the
interference almost completely - result! Next I pulled the power
connector plug apart and wound the lead a couple of times through a
large ferrite ring (the only one I could get easily), and that cut out
almost completely what little noise was left. There is slight
interference when the fan is running at full speed, but I never use it
at that. speed.

So that's a good result without dismantling and returning the fan - thanks.

But here's something odd I found on the way. I got the MW on the
mains-wired radio in the conservatory working pretty well with only a
metre of wire connected as an aerial. It wasn't bad, but a bit quiet.
Well, the signal was weak. Fair enough in the metal conservatory. But
that was with the fan power connector unplugged (for fitting the ferrite
ring). As soon as put the power connector back together, so I could run
the fan (this is with the main power still disconnected at the wall
switch), the radio reception improved tremendously - loud and clear!
When I pulled the connector it went back to fairly quiet again. Weird -
something is acting as an aerial, but how?

--

Jeff