After installing AC line filtering on the blower motor and additional filtering on the AC input to the air handler I got the noise down to S6 on my HF radio, better but not good enough.
Hello all, I'm new here, and confess that I'm not a ham operator. I found this thread by searching about EMI/RFI problems caused on my home computing network by a new furnace motor. It seems that interference from these new ECM motors is a relatively common occurrence, and that ham operators are most susceptible. I can at least say I share your pain! I'm hoping we also share solutions to the problem, which is why I've joined the network here.
AB9SW mentions installing line filters on the AC lines to the motor, and I've seen this mentioned by others as well. I think this is where I need to start in my case, and am looking for a little assistance learning how to select the correct components, since I'm not an electrical guy. But if you use small words and speak slowly, my old courses might start coming back to me
I've isolated the problem to the new ECM fan motor I installed in an old electric furnace last week. When it turns on/off/changes speeds, my network traffic stops dead (for example, continuous pings suddenly become lost packets). When it resumes, the traffic moves again but I see a lot of scatter in ping times (latency).
Unfortunately a portion of my network relies on "powerline ethernet" (homeplug) technology, which uses the household AC wiring to carry the network signal. This is being used to get the internet connection from the 3.5 GHz radio receiver on my garage to my house about 100 ft away. Through testing I've determined that this is the only link in my network that is being (noticeably) affected by the motor. It's my conclusion then that the motor is injecting unwanted EMI noise back onto the household AC wiring that the homeplug system uses as a carrier, thereby disrupting it. Since all the Cat5e wired network in the house appears to be immune, it is also my conclusion that my network is not being affected by RFI from either the household AC wiring or the low-voltage thermostat wiring. That's my rationale then for focussing on filtering the AC input to the motor.
The motor has two high-voltage AC connections. The power connection is ~230 VAC, two wires connected to L1 and L2 of the AC wiring to the furnace. The on/off signal connection is 115 VAC, one wire connected to the fan relay on the furnace, which is ultimately connected to L1. (The remaining wires are the 24 VAC thermostat harness, which I'm ignoring as mentioned.)
Through searches here and elsewhere, again mostly ham sites, I learned that an "EMI powerline filter" might help, and that Corcom makes them. I've read up on their products, found a dealer, etc., and am now just trying to select an appropriate filter from their catalogue. I'm using their selector chart here:http://www.cor.com/Selector/Selector%20Chart.asp
I get stuck at the question "For switched mode power supply?". I don't know if that's intended for building an SMPS and preventing it from polluting the AC-in, or if instead it's just referring to any device that may have similar noise characteristics like those of an SMPS (high-frequency switching). My understanding is that the ECM motors contain a rectifier and inverter, with the inverter possibly controlling the motor by pulse width modulation (PWM), and thereby behaving like an SMPS. (All this is from wikipedia btw, so please correct me if it's totally out to lunch!
) I don't know whether I should treat the all-in-one ECM motor as an SMPS or not when selecting a filter. Any recommendations?
The next decision is the current rating. The motor's stated full load amperage (FLA) is 4 amps. I don't know what the 115 VAC signal line draws. I'm not sure how much above the rating I should select a filter. For example, some of the Corcoms are available in 5 and 10 A ratings. Is 5 A cutting it too close? Any guidance / rules-of-thumb on selecting a current rating? I don't mind the filter being a sacrificial fuse compared with the $400 motor, but I don't want to be cooking them unnecessarily.
There is a choice between low leakage current and not. I'm assuming this is not really a concern for a furnace motor. Agreed?
The rest has to do with the application, for example:
B-series: "Suitable for high impedance loads"
R-series: "Well suited for low impedance loads where noisy RFI environments are present"
Everything is relative, so where does an ECM furnace motor fall in the realm of low/high impedance loads? The R-series are supposed to be a more effective filter, but is an ECM motor too much to be considered "low impedance"?
So, if anyone could provide some guidance on the SMPS decision, the current rating, and whether I need worry about the leakage rating, that would be greatly appreciated. As you can see I'm as much interested in learning as getting "the answer", however if you're keen to put me (and this thread) out of misery, exact part numbers are also accepted
Thanks so much!