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Equi=Core Hum & Other Issues

I’ve owned a Core Power Tech Equi=Core 1800 for 6 months. Recently the transformer has started to hum inside the chassis. It happens when components are on and also when sources are powered down. The transformer hum is intermittent. It ranges from multiple times per day to 3 or 4 days without any hum. I never had DC on my dedicated lines before, so I picked up a Klein Tools AC/DC tester... https://www.kleintools.com/catalog/electrical-testers/electronic-acdc-voltage-tester-12-240v-ac-15-2...
and when plugged into wall receptacles it indicated overload. Line voltage is steady at 122VAC and always has been.
What am I doing wrong, and how should I test for DC on the power line?

I discovered another problem when testing the Equi=Core duplex receptacles; they indicate inverted polarity. All house outlets measure correct polarity.
I’m looking for some assistance in diagnosing this hum. I’m not sure if it’s due to DC offset or if the torroid itself is vibrating in its mounting.

I know this is becoming a long thread, but I must mention that the Equi=Core now trips the breaker at the panel when powered on. It trips several times in a row, eventually allowing power-up. This is a 20A dedicated line from a subpanel which I’ve had for years.
Any advice is much appreciated.


lowrider57
lowrider57's avatar
lowrider57 OP
5,418 posts
 
Thanks @jea48 . I always appreciate your help.
I've read about mods where the torroid is removed from  the bottom of the chassis and a layer of cork or other substance is used for the transformer to sit upon.

I found this comment on a transformer hum thread...
Changes in acoustic buzz from a power transformer often indicate that the AC waveform is not a pure sine wave, but has harmonics. The cause of this is probably outside of your control - you may find the buzz comes and goes depending on demand on the grid. There are so many switching power supplies (including large industrial motors) that rip the **** out of a pure sinewave.

Jim, thanks for your thoughts. I'll have some time later this week to look at the conditioner. 
A massive transformer...
https://images.app.goo.gl/ZvE7yvoxRMrJcL3BA



gs5556
1,278 posts
 
Check both the main panel and subpanel to see if each phase is 120 volts and the neutral to ground is close to zero volts. 

erik_squires
17,574 posts
 
Try turning off all other circuits in your home next time. :)

Did you add any new light bulbs, computers, or fancy LED lighting??
lowrider57's avatar
lowrider57 OP
5,418 posts
 
@erik_squires , nothing has changed in the house. That's why I'm so puzzled. Just sitting here one day and heard the hum; and it's loud. Today, it was present for only five minutes and system was turned off.

Thanks @gs5556. I added your advice to my list.

lowrider57's avatar
lowrider57 OP
5,418 posts
 
Erik, I do wonder how valid the case for harmonics on the AC line is. 
I could turn off my fridge for a while since it's an older unit and the compressor kicks on and off frequently. And as you know, everything shares a ground.

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