[RFI] Fwd: Undelivered Mail Returned to Sender

[Roger (K8RI)]

Switch mode power supplies and Pulse Width speed controllers can be made 
that do not radiate noise, but they cost more so those parts are often 
left out saving maybe 10 to 50 cents on the construction.  With the many 
millions of wall warts this can add up to millions of dollars in profits.

Like Jim, I say it's best to avoid them.  Last fall we replaced our 
furnace and central air conditioning. After discussions and the company 
agreeing to replace the system if it caused RFI (We added that to the 
contract) THEY suggested using a two speed AC motor instead of the PWM 
motor. That tells me they know the PWM speed controller creates noise

There are a number of after market switch mode power supplies for ham 
gear as well as some big amps using SMPS with no problems, but they are 
designed to be clean

When I worked as a tech, I designed and built some 3 phase, SCR power 
controllers for resistance heating elements. THAT was a comedy of errors 
and one of the most difficult projects I ever handled.  That thing 
developed interference with a vengeance!

73, Roger (K8RI)

On 4/30/2019 11:46 PM, Jim Brown wrote:
> On 4/30/2019 4:38 PM, Paul wrote:
>> I might call on the RFI audience to share their experience with 
>> regular electric motors versus the newer DC motors.  I am drawn to 
>> the energy efficiency of the latter but fear the control electronics 
>> may be RFI noisy as are our baneful “wall worts”.
>>
>> So, anyone have an opinion ?
>
> Not an opinion -- they have no place in scientific discussions. :)
>
> It is a FACT that the the electronic controllers for most variable 
> speed motors are quite noisy, for the same reason that the switch-mode 
> power supplies in today's wall warts are noisy -- poor design and 
> construction that fails to prevent radiation and conduction of RF 
> noise. In other words, best to avoid them.
>
> 73, Jim K9YC
>
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-- 
Roger (K8RI)