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PWM Motor Controllers and QRM




 
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Author Topic: PWM Motor Controllers and QRM  (Read 302 times)
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WA2SQQ
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« on: July 04, 2018, 03:21:18 PM »

So last weekends heat wave claimed the life of my AC system. It was an old R22 system that served me well for 18 years. Iíve been hearing a lot of talk that the newer ďenergy efficientĒ air handlers use PWM motor speed controllers that generate lots of noise.  Any suggestions or feedback would be appreciated. Ironicly im in Florida this week where itís cooler than NJ!
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WD5JKO
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« Reply #1 on: July 04, 2018, 10:34:51 PM »


I had a similar experience last July here in Texas. I replaced my 18 year old American Standard system with a Lennox system with PWM motors outside and inside. I have the XC20-048-230A outdoor unit, and a SL280UH090V60 indoor Furnace.

From an operational standpoint, this system is fantastic, and a big step up from the older OFF or ON at 100% capability. It also has a humidity control capability where the system can run at a low level such that the humidity drops to a preset setpoint (AC Mode) without going more than 2 degrees F below setpoint. I shoot for 73 degrees F at 50% RH. With the temp at 105 outside, I can meet those setpoints with ease, and the electric bill is about a 3rd less than my old system which strained to cool to < 77 degrees.

From an EMI standpoint, my system has been a big disappointment. On a SDR set to 20m, when the system comes on, I see an S4 spur every 17 Khz across the band. Using a Sony BC-SW receiver in the master bathroom with a whip antenna / loopstick, the Lennox wipes out the BC Band > 1 Mhz, and if I listen to 75m on or next to a spur, then that wipes things out as well.

Help from the Installer has been zero. So far I am living with it. In the shack though, on 75m and 40m, I see the spurs, but they are below the power line noise. On 20m though, the spurs are well above the noise.

Jim
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WA2SQQ
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« Reply #2 on: July 05, 2018, 02:44:43 PM »

Iíll give up the higher efficiency. Got a few companies scheduled for estimates. I plan on having it in the contract, any noise any you fix / replace or Iím not interested. Thx for your feedback.
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KB2WIG
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« Reply #3 on: July 05, 2018, 02:56:23 PM »



FWIW,   I'd get some baseline recordings/ measurements of your current qwerm levels.

KLC
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WA2SQQ
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« Reply #4 on: July 05, 2018, 05:37:31 PM »

Good idea. Interesting, I had one AC guy call me back. When I brought up the topic he said, you donít want any unit that uses that technology, unless you have lots of money to spend on repairs!
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KD6VXI
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« Reply #5 on: July 05, 2018, 06:25:24 PM »

Good idea. Interesting, I had one AC guy call me back. When I brought up the topic he said, you donít want any unit that uses that technology, unless you have lots of money to spend on repairs!

Run from that guy.  It's HIS responsibility to install an rfi quiet device.  Proper bonding and shielding goes a LLLOOONNNGGG way towards limiting your rfi.

When the superstations are running rfi quiet variable speed systems, they can be done.  It takes ferrite.  43 and 61 mix.  It takes twisted pair wiring.  It takes a clause in the contract that if it doesn't meet residential rfi guidelines the contractor must repair or replace at their expense.

If your contractor even has the slightest jiggle about any of what I just said, tries to get you to pay for repairs (it was an improper installation.  That IS what you paid him for!!!), politely ask him to GTFO your property.

Seriously.  You don't have to settle for inefficient crap made decades ago because the contractor doesn't understand the difference between grounding and bonding.

Also, if a contractor is trying to out on you, he's an installer.  Nothing more.  Every contractor that is signed up with a manufacturer will already know how to fix this, mitigate the issue, or at least k owns its the manufacturers responsibility to meet relevant fcc guidelines.  If he doesn't know this, he has no relationship with the manufacturer, other than its what the parts house he has a line of credit at is pushing this week / month.



Ask me how I know......

--Shane
KD6VXI
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WD4DMZ
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« Reply #6 on: July 10, 2018, 12:46:29 PM »

Both of my Trane units have PWM air handler motors and fortunately cause me no problems. They are both about 9 years old. Perhaps the issue is related to the manufacturer's design. They are the hi-efficiency designs. When they need replacing I will stick with Trane.

Rich
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