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Old 12-14-2012, 11:45 AM   #1
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Help solve my inverter mystery

I recently watched my sunforce 1000-watt pure sine wave inverter go up in smoke and I'm baffled about the reason. I replaced the inverter and I'd really like to avoid a repeat.
Here is the setup:
the inverter is installed in the front storage compartment of my TT. It is wired to the battery bank via two bus bars, positive and negative. Positive lead has a catastrophic 120A fuse installed inline. The inverter is grounded to the trailer frame.
Inverter output goes directly to a dedicated outlet in the trailer. It is not connected to the trailer AC wiring in any way.
I use the inverter to run a HD TV and satellite receiver or blu ray player. Nothing else.
Worked fine until I fired up my generator after a cloudy day left the battery bank a little low.
The generator was plugged into the 30A trailer connection.
When I flipped the remote to turn on the inverter, it fried itself.
Now, the inverter had no direct connection to the generator output. The only thing they have in common is the converter connection to the battery bank. Yet the fuse in the 12V line to the inverter didn't even get warm.
Could it have been a coincidence? Am I missing something?
I dont dare repeat the steps for fear of destroying the brand-new replacement inverter.
Any ideas?
Thanks in advance for the help.
Dave in quartzsite
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Old 12-14-2012, 10:46 PM   #2
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This article shows you hook your cables directly to the battery, not grounding through the frame.
I am not sure if this caused your first one to fry or not. I just followed what the video said.
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Old 12-15-2012, 06:27 AM   #3
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one question, is the inverter grounded to the frame in any way? Other than the battery negative. Like the ground on the outlet.
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Old 12-15-2012, 08:03 AM   #4
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Ditto on "do not ground to the frame"
The black cable must go directly to the battery bank.
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Old 12-15-2012, 10:40 AM   #5
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Originally Posted by herk7769 View Post
Ditto on "do not ground to the frame"
The black cable must go directly to the battery bank.
. It is wired to the battery bank via two bus bars, positive and negative. Positive lead has a catastrophic 120A fuse installed inline. The inverter is grounded to the trailer frame.


Sounds to me he wired it properly, +ve and -ve to the battery bank via bus bars and the inverter itself is grounded to the frame which is standard practice. If you look at Xantrex Inverters as an example they recommend using 10 gage wire to ground the inverter.
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Old 12-15-2012, 10:53 AM   #6
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Sorry if I didn't make myself clear. The inverter is connected to the battery bank via a bus bar and two 4 ga cables. The frame ground connects to the grounding terminal on the inverter with 10 ga as per the manufacturers specs. Negative cable is not connected to the frame.
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Old 12-15-2012, 11:45 AM   #7
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Sorry if I didn't make myself clear. The inverter is connected to the battery bank via a bus bar and two 4 ga cables. The frame ground connects to the grounding terminal on the inverter with 10 ga as per the manufacturers specs. Negative cable is not connected to the frame.
I see.

How are the circuits you power from the inverter powered when running on generator?

If you hook the top two terminals of the duplex to the camper's AC circuit and the bottom two terminals to the inverter's AC output; nothing bad will happen as long as BOTH are never used at the same time.

Powering up the inverter while there is a higher potential on the output side will force juice to flow backwards through the inverter, letting the smoke out.

Could this be happening?

A solution would be to clip the tie metal between the top and bottom of the duplex, making the top outlet "house power only" and the bottom outlet to be "inverter only."

view Image
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Old 12-15-2012, 12:00 PM   #8
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Originally Posted by herk7769

I see.

How are the circuits you power from the inverter powered when running on generator?

If you hook the top two terminals of the duplex to the camper's AC circuit and the bottom two terminals to the inverter's AC output; nothing bad will happen as long as BOTH are never used at the same time.

Powering up the inverter while there is a higher potential on the output side will force juice to flow backwards through the inverter, letting the smoke out.

Could this be happening?

A solution would be to clip the tie metal between the top and bottom of the duplex, making the top outlet "house power only" and the bottom outlet to be "inverter only."

view Image

Thanks for the suggestions. I doubt that is the answer, though.
The inverter output goes into a dedicated line that runs to its own duplex outlet in the trailer. The generator powers all the other outlets. The inverter outlet is dead until the inverter is switched on.

There is no connection between these two AC circuits. Yet I can't run both at the same time. Voodoo electronics?

The only common connection is the charging circuit to the battery bank. It also shares this with my solar system. So why does a 12-volt feed from the converter fry the inverter, but the 12 volt feed from the solar regulator does nothing? And why didn't the fuse blow?
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Old 12-15-2012, 12:16 PM   #9
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So why does a 12-volt feed from the converter fry the inverter, but the 12 volt feed from the solar regulator does nothing? And why didn't the fuse blow?
I can answer the second question. The feed side fuse is designed to protect the battery from a short circuit in the inverter (not the other way around).

If the feed wires were directly wired to the battery and the ends were somehow shorted the current would be so great it most likely would start a fire or blow up the battery. The fuse is designed to sever the connection between the battery and the inverter if that happens (and sized so "normal use" will not).

As to the first part of your question, I am at a loss right now. You have wired it correctly as far as I can determine and it could be (as much as I hate them) a coincidence.
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Old 12-15-2012, 01:07 PM   #10
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how is the ground terminal of the outlet grounded?

also, unless your inverter batteries are isolated from the camper battery, the negative IS tied to the frame, and IS grounded when plugged into the shore power.

Here's what I'm getting at. I installed an inverter that say explicitly that the inverter is not to be grounded on the neutral side as it was already grounded thru the battery negative. Doing do would cause the inverter to self destruct. Possibly, somehow, maybe yours is similar, and when you plugged into shore power, the neutral became grounded. I dunno.

I did find out why it says not to ground the neutral side of the inverter. The inverter puts out 65 volts on both the hot leg, and the neutral. Anything plugged across would "see" 120volts. I found this out quite accidentally. I installed a flip-flop switch on the hot leg of a circuit. We wanted to be able to change from shore to inverter easily. Well, after installation, we tested the inverter part, ok. then I went to plug into the shore power, I happened to wipe off the plug end and was shocked pretty good. Here, because I didn't isolate the neutral of the switch to the inverter, the neutral side of the camper was energized 65 volts to ground. Had I actually plugged into the shore power, I'm certain the inverter would have been destroyed.


This may or may not be your case.
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Old 12-15-2012, 01:21 PM   #11
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Originally Posted by RPAspey View Post
how is the ground terminal of the outlet grounded?

also, unless your inverter batteries are isolated from the camper battery, the negative IS tied to the frame, and IS grounded when plugged into the shore power.

Here's what I'm getting at. I installed an inverter that say explicitly that the inverter is not to be grounded on the neutral side as it was already grounded thru the battery negative. Doing do would cause the inverter to self destruct. Possibly, somehow, maybe yours is similar, and when you plugged into shore power, the neutral became grounded. I dunno.

I did find out why it says not to ground the neutral side of the inverter. The inverter puts out 65 volts on both the hot leg, and the neutral. Anything plugged across would "see" 120volts. I found this out quite accidentally. I installed a flip-flop switch on the hot leg of a circuit. We wanted to be able to change from shore to inverter easily. Well, after installation, we tested the inverter part, ok. then I went to plug into the shore power, I happened to wipe off the plug end and was shocked pretty good. Here, because I didn't isolate the neutral of the switch to the inverter, the neutral side of the camper was energized 65 volts to ground. Had I actually plugged into the shore power, I'm certain the inverter would have been destroyed.

This may or may not be your case.
Any chance you can make a "visual" of what you are describing? I can assimilate better with a "pointy-Talky" better than reading about a subject.

I think you have found realrotor's issue, I just need to see it in a drawing to understand it myself.
Lou
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Old 12-15-2012, 01:47 PM   #12
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Quote:
Originally Posted by RPAspey
how is the ground terminal of the outlet grounded?

also, unless your inverter batteries are isolated from the camper battery, the negative IS tied to the frame, and IS grounded when plugged into the shore power.

Here's what I'm getting at. I installed an inverter that say explicitly that the inverter is not to be grounded on the neutral side as it was already grounded thru the battery negative. Doing do would cause the inverter to self destruct. Possibly, somehow, maybe yours is similar, and when you plugged into shore power, the neutral became grounded. I dunno.

I did find out why it says not to ground the neutral side of the inverter. The inverter puts out 65 volts on both the hot leg, and the neutral. Anything plugged across would "see" 120volts. I found this out quite accidentally. I installed a flip-flop switch on the hot leg of a circuit. We wanted to be able to change from shore to inverter easily. Well, after installation, we tested the inverter part, ok. then I went to plug into the shore power, I happened to wipe off the plug end and was shocked pretty good. Here, because I didn't isolate the neutral of the switch to the inverter, the neutral side of the camper was energized 65 volts to ground. Had I actually plugged into the shore power, I'm certain the inverter would have been destroyed.

This may or may not be your case.
The outlet ground terminal is connected to the corresponding terminal on a 3-prong plug at the other end of 10-foot cable. That plug goes into the outlet socket on the inverter.

Sunforce is very specific that the grounding lug on the inverter must be connected to the vehicle chassis.

Despite that, I think you might be on to something. Thinking back, i realized that when the inverter started smoking the first thing I did was pull the plug from the outlet. The smoking stopped. Seems odd though. There was nothing plugged into the outlet at the time.

I'm wondering whether sun force failed to consider an RV application where a separate AC source exists. Their documentation seems to refer only to vehicles, not trailers.

Maybe I should pull the ground wire.
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Old 12-15-2012, 01:55 PM   #13
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here you go, in a perfect setup, this is what you would have.

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Now say there is a device plugged into the isolated outlet fed only by the inverter. This device has a neutral that is grounded like a power strip with a shorted MOV or a miswired cord or outlet. The neutral of the inverter would be shorted to ground thru the neutral bond at the house panel. It would only cause a problem if camper was plugged in to shore power and the inverter turned on. Now the OP was on a generator. So, the generator ground is tied to what? the neutral. Some generators will do the same thing ad the inverter, put halve voltage on the neutral. not a problem normally. but tie it to an inverter that is sensitive to a grounded neutral, and you might have a problem.

of course without seeing the OP's setup its very hard to prove.

edit: Wait a minute....I mis-spoke the generator outlet ground is tied to the frame of the generator but to get a 120 volt to neutral, the neutral would have to be grounded.
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Old 12-15-2012, 02:00 PM   #14
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Has anyone used two 6 volt gel batteries instead of the one 12 volt installed in there tt?
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Old 12-15-2012, 02:21 PM   #15
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Quote:
Originally Posted by RPAspey
here you go, in a perfect setup, this is what you would have.

Now say there is a device plugged into the isolated outlet fed only by the inverter. This device has a neutral that is grounded like a power strip with a shorted MOV or a miswired cord or outlet. The neutral of the inverter would be shorted to ground thru the neutral bond at the house panel. It would only cause a problem if camper was plugged in to shore power and the inverter turned on. Now the OP was on a generator. So, the generator ground is tied to what? the neutral. Some generators will do the same thing ad the inverter, put halve voltage on the neutral. not a problem normally. but tie it to an inverter that is sensitive to a grounded neutral, and you might have a problem.

of course without seeing the OP's setup its very hard to prove.

I'm becoming more convinced that the frame ground connection is the answer.
What do you think of installing a fuse or circuit breaker in the ground wire? Would that protect against a repeat?
Or what about eliminating the ground completely?
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Old 12-15-2012, 02:30 PM   #16
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if you would plug the camper into the inverter, it should work. I have a buddy that does this with his grounded neutral sensitive inverter.

never fuse a ground.

At home, the neutral and ground shouldn't be tied together except at the main panel in the house. the neutral carries current at no potential.

With an inverter, the chassis of the inverter is grounded and is bonded to the outlet ground. the inverter neutral carries current like in a house, but it could have potential as it's not grounded.

A generator is just like the inverter.

As an aside, there was a safety meeting at work where the speaker, an expert in electrical accidents, said more people are killed by getting across a neutral circuit than contact with a hot leg. current kills, not voltage.
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Old 12-15-2012, 02:54 PM   #17
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I just went out and checked my generator. I have 90 volts neutral or phase to the ground terminal. but 123 hot to neutral. since nothing was plugged in, this doesn't surprise me.

with a heater plugged in, I get 74 volts hot and neutral to the ground of the outlet.
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Old 12-15-2012, 03:01 PM   #18
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I just went out and checked my generator. I have 90 volts neutral or phase to the ground terminal. but 123 hot to neutral. since nothing was plugged in, this doesn't surprise me.

with a heater plugged in, I get 74 volts hot and neutral to the ground of the outlet.
I am really confused. These numbers do not sound right to me.
What am I missing?
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Old 12-15-2012, 03:12 PM   #19
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my point is that, without grounding the neutral, there is potential on the neutral as well as the hot leg.

the amount of potential to ground I measured means nothing really. just that my generator is working. What really matters is hot to neutral potential.


my inverter style generator essentially no different than a normal inverter. Go ahead and measure the potential voltage from the hot and neutral to the ground on your inverter.

now if th OP has his neutral from the inverter grounded, and his generator is like most....problems.
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Old 12-15-2012, 06:46 PM   #20
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my point is that, without grounding the neutral, there is potential on the neutral as well as the hot leg.

the amount of potential to ground I measured means nothing really. just that my generator is working. What really matters is hot to neutral potential.

my inverter style generator essentially no different than a normal inverter. Go ahead and measure the potential voltage from the hot and neutral to the ground on your inverter.

now if th OP has his neutral from the inverter grounded, and his generator is like most....problems.
Maybe a dumb question. What is neutral? Would that be the ground terminal?
Should also point out that my generator is an inverter type. AC to DC and back to AC. So with both the generator and inverter running I have two inverters running in tandem. Could that be a Bad Thing?
I have in the past connected the inverter to the camper 30 W connection with no problem.
Also, why does the manufacturer warn of shock hazard if the inverter is not grounded to the vehicle frame?
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