The issue has dealt with specific makes and models with and without RFI,
but as PWM is by its nature an RFI generator we need to stop and think
about how companies (any company) acquires the motors and speed controllers.
It's already been mentioned that one company was using PWM speed control
on a motor that ran at a constant speed.
Do each of these companies use the same controller on the same model?
Do they build the controller, or do they contract out the motor and
controller, or do they, like many stores contract out parts on a
periodic basis so that this year company A builds the controller for
company B's motors while next year company C builds the controllers. IE
can you, or can you not depend on the same motor and controller
combination for a specific model furnace/air conditioner?
Perhaps when purchasing a system we should contract it out and stipulate
that the system generate no RFI. I've had companies that would do it
for a complete GEO Thermal installation and some that refused. IE you
install it and if it works as the contract stipulates I'll pay you,
otherwise fix it or take it out. Turns out our old system is so
efficient that it'd take nearly 50 years (47 point something) to reach
the payback at current rates. With the average system life of 25 years
or less ... we kept the old system. OTOH with the extreme spring and
summer temps we've had this year it would have been quite a bit less,
but still not enough.
You might have to pay a bit more, but as long as the final price is
within reason it would be worth it and there would be no haggling about
whether their system created RFI or not.
73
Roger (K8RI)
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