[RFI] Noisy Uninterruptable Power Supply (UPS)

[Gary Johnson]

Another vote for the Cyberpower consumer equipment noted by Jim as being free of RFI. They also make larger units that are FCC Part 15 Class B certified. Many larger UPSs are Class A (industrial) and more prone to problems. Also, external battery packs may aggravate things due to radiation from the wires; the charging waveforms can be quite dirty. If you want to read about a couple of RFI mitigations, see this: https://na6o.com/main/RFI_files/Tripp-Lite_UPS_RFI_Report.pdf

As for Eaton, I was responsible for EMC on the Gemini Planet Imager, and the one big problem we had was a very large Eaton UPS. When it switched to battery backup, it drove the 120V output differentially. That is, both the hot and neutral were at 60V with opposite phase. That energized neutral raised havoc with multiple pieces of equipment. We ultimately got another brand though I can’t seem to remember which.

Gary Johnson NA6O  
gwj at me.com

> From: Jim Brown <jim at audiosystemsgroup.com>
> 
>> On 6/12/2023 12:50 PM, RVZ via RFI wrote:
>> ?I'm wondering if there is a commercially made UPS (Uninterruptable Power Supply) that is RF quiet, or more RF quiet, than the average?
> 
> Yes, the CyberPower CP1500PFCLCD. I have five of them, first bought at 
> least ten years ago. In addition to being relatively quiet when in 
> standby mode, it has the MAJOR virtue of not overcharging the battery, 
> causing the battery to last a long time. Most UPS units DO overcharge 
> the battery, so you have to buy a replacement (from them, of course) 
> every year or two.
> 
> With ANY modern power supply, it's good practice to wind multiple turns 
> of the power cord through a big #31 clamp-on. Detailed advice in this 
> applications note.
> http://k9yc.com/KillingReceiveNoise.pdf
> and this slide deck.
> http://k9yc.com/KillingRXNoiseVisalia.pdf
> 
> 73, Jim K9YC