I think the take away is variable speed motors are not "evil". Properly
engineered (like anything else) they bring a ton of benefits.
My 11 year old Bryant Evolution Extreme heat pump is RFI silent. It has
a variable speed compressor in the outdoor unit and PCM blower in the
indoor unit. Really high quality stuff and silent in the audio range as
well. One of the most energy efficient air-source heat pumps made.
73,
Steve
W1SRD
On 11/11/2024 1:14 PM, Jim Brown wrote:
Almost 30 years, Neil Muncy, W3WJE, (the Pin One Guy), showed me and
an pro audio RFI colleague an in-house engineering report from a mfr
of large variable speed drives. They were having problems with RFI
from the drives screwing up the control circuitry from those drives,
and identified the wiring between controller drive as a principal
mechanism. The common thread was that the controllers and motors were
widely separated.
We were interested because RFI from drives running elevator motors was
getting into microphone circuits in large sound systems. A system Neil
was working on was at large performing arts center in NJ.
A few years later, at a church in Dayton where I was inspecting a
sound system I'd designed, I ran into an EE who specialized in EMC. We
got to talking, and the conversation turned to variable speed drives
in large installations. He volunteered that interconnecting wiring was
the culprit, and we agreed that all of the current-carrying conductors
had to be twisted pairs, which was the same solution Neil found.
Obviously, making the controller and motor a single integrated package
is also a great solution for smaller systems.
73, Jim K9YC
On 11/11/2024 12:12 PM, Gary Johnson via RFI wrote:
I wanted to mention one other good strategy that these new
adjustable-speed drives are using: For most of the motors, they
integrate all the power electronics right into the motor assembly,
thus eliminating wires on the output side where the commutating
waveforms and high circulating currents are present. Then they are
applying proper RFI suppression to the incoming AC lines, again built
right into the motor assembly. So the potential antenna lengths are
greatly reduced and I’m seeing how effective this strategy actually
is. The only motor without this approach is the big compressor, and
that has a HUGE filter network nearby and also twisted wires to the
motor, all inside a steel enclosure. Carrier was not being cheap or
sloppy, and it shows.
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