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Old 01-19-2015, 01:58 AM   #1
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Ground Loop - Off Grid DC/AC Inverter wiring help

Hello, thank you for taking the time in reading my post.

Background: Like most, in my RV I have 2 AC "inputs" being generator or shore power. Since my rigs generator was ripped out years ago, I decided to install 4 trojan t-105's and a DC/AC inverter in its place with a couple solar panels attached.

Problem: Since I am using DC and AC systems at the same time, I am getting feedback through my speakers via the inverter.My inverter has your standard household 3 prong GFI outlet, that I wired using the old generator power wires that were cut, as I wanted to use the original AC fuse box. I followed the wires to my AC Fuse box, where I noticed the AC Ground Bus has a wire that goes directly to the chassis ground, which is what I am pretty sure is the source of my ground loop caused feedback.

Question: Are my suspicions correct? is that what is causing my ground loop? Can I remove the wire that is grounding the AC to my chassis? why would the AC ground be connected to a DC floating ground in the first place? Did it have something to do with the original battery charger/shore power converter? (I never touched my AC fuse box, but did remove the old battery charger/converter)

Shouldn't the AC and DC systems be isolated?

in either case the inverter will be grounded (not to be confused with its - DC input) which is basically the same thing, the chassis ground... will I continue to get a ground loop?

Oh and yes, I am not confusing a AC Ground with a AC Neutral. it is the bare or in my junction boxes, the green wire.

I know you can buy a ground loop isolator for your audio equipment that is receiving the feedback, but I am more interested in building a safer, proper system.

Or... Does any of this "matter"?

Sorry for rambling
Hope that all made sense,
Thanks for your time!
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Old 01-19-2015, 06:38 AM   #2
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I seriously doubt it since in most inverters the Ground pin is not connected.

However what kind of inverter did you purchase.. A True Sine Wave or a MSW.. MSW inverters are noted for not playing nice with audio gear, or with Radio gear, or digital timers, or .. Well a long list of things.

In days of old there was a document on the Xantrex MSW inverter web pages that listed some of the things that do not ALWAYS work well with MSW inverters.. (NOTE: some do some do not) It was a long list.

And I will add that different MSW inverters make a difference as well.

The list of things that do not work well with TSW inverters however was a bit shorter:

Anything needing more power than the inverter can provide

(That's the whole list).
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Old 01-19-2015, 10:36 AM   #3
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First that is safety ground so do not remove it.

Your 120 volt powered audio system should be floating and no path to ground unless something is touching.

Disconnect antennas first as they may have ground connection.

You also may have dirty output from converter on 12 volt for 12 volt powered items.

Things like this just take time to determine source.

Often disconnecting single eires and adding filter caps.
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Old 01-19-2015, 01:57 PM   #4
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I am positive it is a ground loop. My audio amp is 12v DC, and as soon as i turn it on the feedback is the exact same as the transformer noise coming from the inverter. When I run the amp through a 110 AC/DC adapter, the feedback is eliminated.

Not being a pro, but just knowing that the AC and DC are sharing the same ground, and knowing they are both at different frequencies....

Like I said, I know I can solve my audio issue by just buying a ground loop isolator, but I am more interested in making sure my system is safe and wired correctly.

My inverter is MSW, but like i was saying earlier in this post, I am experiencing feedback on my DC device. Here is my actual inverter: Industrial Strength Inverter 1250W 2 Outlets | PV1250FC | Tripp Lite
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Old 01-19-2015, 02:28 PM   #5
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Running via the adaptor isolates the device as you discovered.

There may be another path that is getting into the amp.

As suggested disconnect one wire at a time to see where it is.
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Old 01-19-2015, 03:01 PM   #6
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Running via the adaptor isolates the device as you discovered.

There may be another path that is getting into the amp.

As suggested disconnect one wire at a time to see where it is.
Yes as i stated earlier, there is another path getting to the amp, the AC and DC are sharing the same ground, which is causing a ground loop.

Can I isolate the AC ground from the DC ground? I am able to complete a DC circuit using my AC ground and a DC + lead.

I guess I should be asking the maker of my inverter...?
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Old 01-19-2015, 03:21 PM   #7
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I seriously doubt it since in most inverters the Ground pin is not connected.

.
I have confirmed the ground pin on my inverter is active, I can get a DC readout using the AC ground pin and the battery + without the actual inverter being grounded.
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Old 01-19-2015, 03:26 PM   #8
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The ground loop can be distant.

Your devices may not be designed for how you have them installed and creating issues.

Many have floating chassis fore isolation from high voltage then they have the floating chassis not isolated much from the antenna.

Antenna coax and audio cable shields often can create problems.

The ac grounds are there for safety.

Dc grounds to chasis to save weight and money.

In real cases the dc has hot and return wires from device to source so that is possible but may not help here.
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Old 01-19-2015, 04:20 PM   #9
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The ground loop can be distant.

Your devices may not be designed for how you have them installed and creating issues.

Many have floating chassis fore isolation from high voltage then they have the floating chassis not isolated much from the antenna.

Antenna coax and audio cable shields often can create problems.

The ac grounds are there for safety.

Dc grounds to chasis to save weight and money.

In real cases the dc has hot and return wires from device to source so that is possible but may not help here.

When I run my amp DC i get the feedback, when I run the amp through a small AC/DC power adapter, the feedback is eliminated, so I know the audio cables are not picking up the interference.


Since the inverter output has a AC ground, wouldn't removing the chassis ground at the AC fuse box not remove the safety features of the ground plug since the inverter itself is grounded, along with the battery bank?

Thanks for your input!
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Old 01-19-2015, 05:00 PM   #10
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For ground loop to happen you need a loop.

Running on the adaptor cuts the loop in one place.

There is another path.

Either just run it from the adaptor or look for the other part of the loop.

You may need to add a ground to something else.

Do not disconnect any ac ground as they are there for a reason.
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Old 01-20-2015, 01:19 PM   #11
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"Low-current wiring is particularly susceptible to ground loops. If two pieces of audio equipment are plugged into different power outlets, there will often be a difference in their respective ground potentials. If a signal is passed from one to the other via an audio connection with the ground wire intact, this potential difference causes a spurious current through the cables, creating an audible buzz at the AC mains base frequency (50 or 60 Hz) and the harmonics thereof (120 Hz, 240 Hz, and so on), called mains hum."

direct from wiki...I don't understand how this isn't a ground loop.

Finding out that my inverter is giving my AC ground directly out of the inverter.

The AC ground line goes to my AC fuse box.

The AC ground line gets "grounded" AGAIN in my fuse box to the chassis ground.

Can anybody please explain to me why or how removing the 2nd chassis ground that is attached to my AC ground bus will no longer keep my AC grounded?

Im asking why the sky is blue, and people are telling me the color of the grass.... thanks for the replies i guess.
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Old 01-20-2015, 02:58 PM   #12
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Simple...the connection to ground from whatever it is has the function of safety ground.

Remove that connection and in the event of a failure all bets are off.
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Old 01-20-2015, 03:21 PM   #13
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1) Are the audio source and amplifier connected to a common ground source or are they grounded at different points? Not the main power grounds, but the ones at the units.

2) Are they getting power from the same source?

3) Do any of the audio cables run parallel to the power source?

4) Are the cables run in a coil or loop upon each other?

5) Are there any other wires from the coach running parallel to the audio cables?

6) Are you certain one unit is not pulling its ground source through the audio signal cables?

These are things we look for when dealing with audio in vehicles. 20+ years of chasing audio noise in cars, trucks and coaches tells me to eliminate these things first.

I would next try and use either direct to battery, direct to AC via inverter, direct to 12v power supply such as batteries or triplite type supply. Battery chargers hum and are very dirty so don't use those for testing.

I'll be watching for replies.
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Old 01-21-2015, 01:44 AM   #14
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1) Are the audio source and amplifier connected to a common ground source or are they grounded at different points? Not the main power grounds, but the ones at the units.

2) Are they getting power from the same source?

3) Do any of the audio cables run parallel to the power source?

4) Are the cables run in a coil or loop upon each other?

5) Are there any other wires from the coach running parallel to the audio cables?

6) Are you certain one unit is not pulling its ground source through the audio signal cables?

These are things we look for when dealing with audio in vehicles. 20+ years of chasing audio noise in cars, trucks and coaches tells me to eliminate these things first.

I would next try and use either direct to battery, direct to AC via inverter, direct to 12v power supply such as batteries or triplite type supply. Battery chargers hum and are very dirty so don't use those for testing.

I'll be watching for replies.


1/2) The audio source is 110v (over the air hdtv converter) and the amplifier is 12v. The amp is a small 20 watt amp designed to power bookshelf style speakers (as stated earlier, when i run the amp through a small AC 12v power adapter, the feedback is eliminated) OR if the amp is hardwired DC, there is no feedback as long as my inverter is turned off, but ultimately they both come from my battery bank.

3/4/5/6) there are no cables run or next to any of the audio cables, I am talking a small bookshelf speakers to act as my "TV speakers". I am aware of running power wires on the opposite side of a car to eliminate feedback. Is that what you mean when you say "coil and loop"? I am experiencing feedback through the speakers immediately even without any audio input wires present, as soon as i turn the amp on DC (with no RCA or aux input) i hear the hum from the transformer of my inverter. When wired DC, it is through my chassis wiring, not directly to the batteries.

I have not tried to wire the amp DC directly to the batteries and other various configurations you were talking about, I will definitely try those options tomorrow to see if I find different results.

I am not using a battery charger, it is strictly a DC/AC inverter as my system is off-grid and powered by solar. although the inverter is made by tripplite.
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