SunGoldPower SPH10K48SP inverter output making my APC UPS give off a buzzing sound

[Gentleman Mike]

I've set up this SPH10K48SP and it works great, very impressive unit for the price except for one thing. It makes a downstream rack mounted APC SmartUPS give off a buzzing noise, like possibly from a transformer, whenever power is coming from the SunGold inverter. It still works, but the buzzing is constant until the SunGold goes back into grid passthrough mode.

What could cause this? I looked at the inverter output with a cheap handheld oscilloscope I have, and it looks like a clean sine wave to my eyes, but could there be some hidden harmonics causing the issue? If so, could this damage certain appliances in my house, like say the furnace blower, fridge compressor or sump pump motor?

Is it damaging the APC UPS, or does the annoying buzz have no ill effect functionally?

It doesn't have anything to do with the grounding or anything like that. The UPS would complain with a site wiring fault if there was a ground issue.

EDIT: At work we are also experimenting with using the 5 kW SunGold unit as a replacement for a standard UPS in the server room, and I also noticed the same issue when plugging our existing APC UPS there into the inverter.

 

[42OhmsPA]

Where is your neutral/ground bond?
What is setting 63 on the 10k?

Two things that I can think of that may have an impact but it's above my level of knowledge.
I wish I had a UPS here to test with my ASF.

 

[Gentleman Mike]

Where is your neutral/ground bond?
What is setting 63 on the 10k?

Two things that I can think of that may have an impact but it's above my level of knowledge.
I wish I had a UPS here to test with my ASF.

The bond is in the main electrical panel where the utility comes in, and 63 is set to disabled which is default.

 

[42OhmsPA]

That's how I have mine setup as well.

Have you metered voltages at the receptacle the UPS is plugged into when in inverter mode?
What about putting the UPS on a different leg?
Safe to assume frequency is set to 60hz.

 

[Gentleman Mike]

That's how I have mine setup as well.

Have you metered voltages at the receptacle the UPS is plugged into when in inverter mode?
What about putting the UPS on a different leg?
Safe to assume frequency is set to 60hz.

I did, it's getting spot on 120 volts at the receptacle, 60 hz.

I just ran an extension cord to another outlet to try a different leg but am still getting the buzz.

Weird!

The whole thing with an entirely different unit at work (the 5kw model) causing the buzz there too is interesting. It's either something with the inverters sungold uses, or I have the same problem with my setup at both locations.

Other than the UPS buzz, everything I plug in appears to function normally.

 

[Supervstech]

That's how I have mine setup as well.

Have you metered voltages at the receptacle the UPS is plugged into when in inverter mode?
What about putting the UPS on a different leg?
Safe to assume frequency is set to 60hz.

Never assume anything…

 

[42OhmsPA]

I did, it's getting spot on 120 volts at the receptacle, 60 hz.

I just ran an extension cord to another outlet to try a different leg but am still getting the buzz.

Weird!

The whole thing with an entirely different unit at work (the 5kw model) causing the buzz there too is interesting. It's either something with the inverters sungold uses, or I have the same problem with my setup at both locations.

Other than the UPS buzz, everything I plug in appears to function normally.

I would say it's definitely something with the inverters. They are made by SRNE if that helps you in troubleshooting. The 10kW is the ASF model and the 5kW should be the the HYP model.

There are a few other members running these models, hopefully they can chime in with some help.

 

[Gentleman Mike]

I wonder if any of those other members have one of those fancy expensive power quality meters.

 

[marionw]

I have an SPH10K48SP with a number of different APC UPS's including several RT 3000 SmartUPS rack mounted models and all work just great with no buzzing. In fact when my HVAC kicks on they don't event beep unlike when I am running off of my 10kw generator

 

[Gentleman Mike]

Interesting. Thanks. I wonder what I've done wrong.

 

[marionw]

I do have L1, L2, N and G from the Inverter connected to the appropriate points in the subpanel.
L1 and L2 power the subpanel through a 40 amp breaker. N and G connect to the neutral bar in the subpanel. As of yet I do not have grid power into the inverter from the main panel. Not sure how a main panel N or G gets connected to the Inverter AC output N and G (and then to the subpanel)

Don't know how your system is wired and whether you can isolate grid to inverter wiring.

Would it be possible to provide a block diagram and/or pictures. There are smarter folks on this forum that may see something in your wiring diagram.

 

[Gentleman Mike]

I will draw up a diagram, but I am using a manual transfer switch rather than a subpanel. Reliance 10 circuit 50 amp.

There's a dual pole breaker in the main panel that provides AC input to the Sungold, then AC output to the generator input on the transfer switch. Neutral and ground are bonded in the main panel only.

Could there be problems with the fact that the AC input and output neutrals are also bonded together in the main panel? The transfer switch doesn't isolate neutral between generator and grid. Not an issue for a true generator since it doesn't have an AC input, but maybe for these all-in-one inverters it is?

Also, for some reason the buzzing in the UPS stopped. But this still got me thinking if the neutral thing is a problem.

 

[JMACK61]

You have access to an oscilloscope? I have had experience with basically an Inverter (your SPH) powering another Inverter/ battery charger (your APC UPS). All my DIY Powerwall make the house run of the sun has been with two APC SU 2200’s I run one per 120volt leg and no they won’t synchronize to make 240 VAC and for you I have ran the output of one running on battery into the into the input of the other and I tell you from experience they did not like it. I’m pretty sure that’s when I fried relay 6. I don,t know why a APC does not like inverter output AC but I know I won’t do it again.