Charger works-Inverter Doesn't

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Charger works-Inverter Doesn't

Postby Steven_Cleary on Sun Jul 01, 2007 11:27 am

Hello,

I've installed a VFX4024M on a sailboat. It's AC wired through a switch I had custom made that has a "shore" position and an "inverter" position, as well as an "off" position. The AC from the dock is 50 AMPS at 220V (or 208, whatever it is...). The 2 hot legs are split at the panel into two 110V legs that power my 110 accessories. Some larger items are on 1 leg, some other larger items are on the other. I've taken one of the legs and run it to the inverter via the switch described above. When in the "shore" position, AC runs from the pole on the dock directly to the panel. When in the "Inverter" position one of the 110 legs runs to the Inverter, then back out of the inverter to the Switch which then feeds the panel. The switch was made to bypass the inverter, and to prevent "back feeding" to the output side of the inverter from the panel when bypassing the inverter.

The charger works correctly and the AC loads are properly fed from the output side of the Inverter (when it's connected to an AC source). I have the neutrals isolated for the items running off the feed from the Inverter as required (neutral goes from the pole through the switch to the inverter, the neutral coming back from the output side of the inverter is then connected to the AC loads).

My problem is that when I switch the AC supply off and want the inverter to supply AC, something isn't right. If I'm not mistaken, the only difference with an AC source and without is the ground switching mechanism in the Inverter. My understanding is that the inverter makes a ground to neutral connection when the AC source isn't present (the AC source makes that connection when it is present). I've tried pulling the shunt between the two chassis grounds, no difference. The inverter says it is putting out 120V, if I take a meter reading at an outlet I get voltage but only if I use the hot and ground for connection points, if I use the neutral and hot, I get random readings.

I've re-read all the docs and it appears everything is wired correctly. As I said, it's been working flawlessly via the transfer switch/battery charger mechanism for months. I'm actually posting while sailing off the coast of MA. No alarms or warnings on the Inverter. I've reset it, also disconnected the DC source and reconnected it. I have a 5yr old onboard and I NEED to be able to put on movies :). I do have an 8K generator onboard and the inverter works correctly for battery charging/AC loads when the generator is running...just like it does when the shore power cord is connected.

This has to be some type of ground switching problem. Do I need to "unisolate" the neutrals when using the inverter as AC source (ie tie the neutrals for the 'inverter served loads' back to the rest of the neutrals on the boat?) Appologies for the length, but I figured without a good explanation I wouldn't get any good advice.

Thanks,

Steve

Thoughts?
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Update...

Postby Steven_Cleary on Sun Jul 01, 2007 6:41 pm

I removed my panel and tied the isolated neutrals back to the main neutrals on the panel and it all works correctly. I've double checked the wiring and it is all correct. The neutral comes back from the FX and goes via the switch to the panel as it should.

I would bet money if I opened the lid to my shore cord connection and put a jumper from the neutral to the ground poles...it would work correctly as well.

Shouldn't the outback be providing the neutral for me when the AC source is disconnected?

In the short term I will use a jumper when the AC source is disconnected and I will remove it prior to reconnecting the AC source.

What am I missing??
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Postby sparky on Sun Jul 01, 2007 6:59 pm

Steven,

Tell us why you are using the custom switch? The Inverter has the logic to do the switching you know? Got to run but I "feel" the switch is your problem.

Have a good watch ! Check out Jupiter and Venus tonight !
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Postby The Electron on Mon Jul 02, 2007 10:34 am

This is a real common problem. And please be aware that as I post, I'm as much asking for insight myself!
Steven, it sounds like you have two problems. First, it's the NEC "impossibility" of having similtaneous power sources that share the same ground, and second, what you have tried to do to alleviate problem #1. Let me try to explain.
This matter of sorting out neutral-ground bond switching can be fun. When you have the capability(possibility) of having BOTH shore-power-only loads powered from shore power AND sub-panel loads SOMETIMES powered from the inverter AT THE SAME TIME, it becomes necessary to have the ability to isolate the neutral found in your sub-panel due to it now being it's own "utility company" and it must have a SEPERATE neutral-ground bond. But wait a minute- won't the two seperate neutrals now be connected due to the fact that the whole thing shares the SAME GROUND?!
And then we end up right back where we started.
Explained a different way, How do you keep the ground and neutral SEPERATE for the shore-power circuits while you have to keep the ground and neutral SOMETIMES TOGETHER for the inverter cicuits? Sparky's right about the inverter doing the switching between ground and neutral when it needs to, but that all gets defeated as soon as you introduce shore power input into the equation, (which WE HOPE has neutral and ground bonded at one point somewhere), AND you have an inverter with the capability to pass-thru.
I will refrain from trying to get into how to fix this, cuz the answer has to "violate code" one way or another. What I was hoping to do was have everyone take one step back from the chalkboard and see what we all come up with.
Thanks Steven for taking the time to describe your system so well. Please give us a closer look at this custom switch, as many of us are curious as to just what it's swithing.
Thanks all.

EDIT- Wanted to add that it looks like the boat doesn't have a sub-panel, but a "split" panel with no 240v loads. Is that right, Steven?. I mentioned sub-panel above for illustrative purposes. Thanks.
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Postby sparky on Mon Jul 02, 2007 11:55 am

Is it safe to say you never tested this before ? If yes, a very common problem is the solenoid/relay has a bad contact on neutral.

Since there are no fault lights and nothing smells fried can you verify at the Inverter that the unit is making AC from the batteries. A 100 watt light bulb should be a good load.

Sorry if I am missing something from your post but it was long and well written. Probably need to read it again..............
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Postby SteveHiggins on Tue Jul 03, 2007 9:26 am

Steven,

It sounds like the switch is causing your issues.

The way this needs to be installed is to ABYC code, because it is a marine vessel. The Code is different for Marine/RV then homes.

I'm assuming that you have a main panel on the boat that is normally powered by shore or your genertor?

What you need to do build a Sub Panel for the inverter that is completly isolated by the inverter.

This means that you install a breaker in the main panel, that breaker breaks the hot line going to the inverter input. The Neutral, and ground then travel to the inverter as well. You MUST run all lines to and from the inverter in a Marine/RV installation, if you bypass the inverter, the Neutral ground switching of the inverter will be disabled.

You then connected the Sub panel to the inverter Output, this Subpanel must be compleatly isolated from the main panel AT ALL TIMES unless the inverter is making the connection thru the inverter.

The main panel loads should only be powered up when connected to shore power or the genset is running, the inverter will power the subpanel loads at all times with either inverterd power from the battery bank, or power passed thru from the main.
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Postby The Electron on Fri Jul 06, 2007 1:19 pm

Thanks Steve for your post. I have a weakness in making things too complicated when I try to explain something! The key to fixing this boat seems to be *Need a sub-panel for all inverter cicuits & *Use your switch as a transfer switch to select main input from shore/gen (if you haven't already done).

No matter what, all inverter ckts. HAVE to have thier own neutral ckt. which the M-style FX can bond when inverting!

I was tempted to try to salvage the "split-panel". I know better!

Let us know what you do/did Steven. Thanks!
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Postby Steven_Cleary on Mon Jul 23, 2007 9:19 pm

Hi Folks,

I apologize for the long delay in replying. I didn't get any notifications that anyone had replied. When I got back from vacation I took a look only to find all this great help.

In any case, during the trip I just ran a jumper from my isolated panel back to the main neutrals and it worked fine.

I'd like to revisit the design:

For all practical purposes I do have a sep panel. The only thing that would make a panel separate would be isolated electrical connections. My panel is setup with busses, which isolate some items on the panel from other items. I will try to either take some pics or make a diagram and post it on my boat website.

The switch I had made (i designed it and had built by a switch manufacturer for me) does the following (sparky, reason for the switch was so I could service the inverter without losing access to the items it would normally power..and so there wouldn't be the potential for back feeding the inverter from the panel..which would happen without a switch between the panel and the output side of the inverter):

It has 3 positions, shore/off/inverter. It only relates to the "isolated" items on my panel that I run with the inverter. It has terminals for shore hot and shore neutral, and inverter "in" hot and neutral, and inverter "out" hot and neutral and "out to panel" hot and neutral. When in the "shore" position it connects hot and neutral from the pole 'shore' directly to the panel. In this position, there is NO connectivity at all TO the inverter or FROM the inverter output to the panel, the inverter is completely isolated when the switch is in this position. It allows me to remove or service the inverter without losing the ability to use the items that the inverter can provide power to. When in the "off" position there is no connection from either shore or inverter to the panel. When in the inverter position it takes the hot/neutral from the pole and sends them to the "in" side of the inverter hot/neutral and also takes the "out" hot/neutral from the inverter to the panel hot/neutral. This creates the isolated neutral called for in the instructions.

This all works exactly as you would expect when the shore power is connected. When I disconnected shore power for the first time, the items that should have been powered from the inverter would not operate. The inverter showed it was putting out 120V, no errors or warnings. When I tied the neutral for the isolated panel back to the neutral on the main panel everything worked correctly. It certainly appears to me that the outback is NOT making the ground to neutral connections like it should when AC is not present from shore power or generator.

Thanks for all the comments, and here are some answers:

There are no 240v loads, all loads are 120v. (i'm sure it's painfully obvious I'm not an electrician :)) I have a 50AMP 240V service that is split into two legs of 120v which each go to a 50amp breaker, those in turn feed my loads.

SteveHiggins- I do have the system setup exactly as you describe. The switch isolates exactly as you suggest...the caveat is that the switch also allows the shore pole to feed the sub panel and isolate the inverter completely.

One last question, how can I test the ground switching on the inverter?

Thanks!

Steve Cleary
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