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Re: [RFI] Bosch Heat Pump

To: rfi@contesting.com
Subject: Re: [RFI] Bosch Heat Pump
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 26 Jun 2022 16:46:03 -0700
List-post: <mailto:rfi@contesting.com>
Hi Wes,

No experience to share, but I can share what I've learned about these systems in general from those who have experience with variable speed systems.

A common problem is caused by layout of the installation, where the controller is widely displaced from the motor, poor wiring practices are followed, creating both magnetic and EM fields. My first detailed info was from the late Neil Muncy, W3WJE, who as a consultant encountered strong magnetic fields from controllers for a large bank of elevator motors in at the NJ Performing Arts Center, for which he had designed sound systems. The trash was coupling into mic lines via Pin One Problems and a cable defect called Shield-Current-Induced Noise. Details of the latter mechanism in an AES Paper on my website. In the process of diagnosing and solving the problem, he found internal applications notes from a mfr of those control systems.

Solutions include twisted pair for all current-carrying conductors, and including bonding conductors that intimately follow the current carrying conductors, thus minimizing both the magnetic field and loops sufficient to act as antennas. One of the loops is formed bypass capacitors to building and/or frame ground; DC and mains fundamental follows the path of least resistance, while higher frequencies follow the path of least impedance; running that bonding conductor with the power forms a transmission line, providing that lower impedance. I learned this fundamental principle at an IEEE Engineering Conference many years ago.

An EE consultant I met nearly 20 years ago who was the father of my client contact at a church got to chatting about this problem, and we found ourselves nodding our heads in sync as to solutions.

In summary, it's related both to design/construction of the hardware and to how systems are installed.

Another thing I learned as a result of long experience in the EMC Working Group of the AES Standards Committee is that Europe pays a lot more attention to EMC than we do, with the result that some products designed and built there to sell there, and exported here, tend to be better than average EMC performers. I experienced that with HF radio in a Volvo S80 that had no problems, as opposed to my Toyota Sequoia (big SUV), whose computer went into "limp home" along I-80 in Northern NV. Luckily I had tools that allowed me to reboot it by disconnecting the battery.

73, Jim K9YC

On 6/26/2022 3:19 PM, Wes Stewart via RFI wrote:
I'm considering replacing my 15 year old Trane dual compressor, variable speed 
blower roof top packaged heat pump.  The ECM blower motor generates a little 
hash that I can hear on 10-meters with the beam pointed at the house, 100 feet away 
but it's not serious.
I'm considering a Bosch Inverter heat pump which gets rave reviews for being efficient and quiet but but I'm not sure it would be electrically quiet.

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