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Old 05-12-2005, 02:35 PM   #1
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Inverter troubles

How did you wire the common ground in your AC circuit. We have the common ground wired to the negative side. Ive got 2 750W and 1 1000W inverters wires into the bus. The problem is is they output AC 60V on the positive side and 60V on the negative. So it shorts to ground either way. Im considering using isolation transformers, but was wondering what the rest have done?
Nicholas Frey
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Old 05-12-2005, 03:39 PM   #2
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You cannot have multiple inverters connected in anyway, they will be out of phase with each other and cause a short.

I grounded (green wire) the recepticles to the bus, which really doesn't do any good unless you also ground the bus in some way.

Then I ran run the black wire (hot wire) and the white wire (neutral or common wire) to the switches and outlets that a want that inverter to power. You must keep each of these circuits seperate between inverters. You will need to decide what you want each inverter to power and only hook up that one inverter.

Not sure what you are trying to do but I should point out that if you want to use multiple source (although you can only use one at a time as I pointed out) a transfer switch can be put inline to move your circuits between sources.

Lets take for example you have a circuit that runs all of your kitchen area appliances and it is plugged into a transfer switch. One one side your 1000W inverter is plugged into it. On the other side you have plugged in one of your 750W inverters.

Lets say you want to use this single inverter to power everything and only turn on the other two smaller inverters when you need the extra power. So you can have this 1000W inverter powering everything and if you know you are going to need some extra power when you use your microwave you can turn on that other 750W inverter. When you do this the tranfer switch will see that you are now supplying power on the side and it tranfer your kitchen circuit over to running off the 750W inverter, leaving the 1000W inverter to power everything else in the bus except this circuit. Then when you turn the 750W inverter back off it automatically tranfers over to the 1000W inverter again.

This is how most RVs switch between generator, inverter, and shore power. Tranfer switches are very handy and if you use them in the right places they can be very power tool. Also you can buy inverters with built in transfer switches, the one I have in my bus is one of these.

Here are some examples of just tranfer switches:
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Old 05-12-2005, 05:30 PM   #3
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I don't use shore power very often. I use either my inverter or generator. There really is nothing useful to do with the green wire. Every circuit in my bus uses only 2 wires. Every circuit in my bus does run through a GFI.

The transfer switches I looked at previously were rather expensive. So is destroying a generator or inverter by accidentally connecting either of them to shore power, or to each other for that matter.

To solve this dilema, i installed 3 outlets in my "power cabinet" (technically there are two outlets, and an inverter) Each outlet is connected to it's respective power source: shore, inverter, generator. The bus has two circuits that run all 110 volt stuff. Each of these circuits has a male plug. I can plug into the outlet that corrosponds to the power source i want to use. This makes sure that i NEVER connect two power sources together. It also allows me to use two different inverters at the same time if i want. Each inverter can be connected to a different circuit. IF everything is connected to one circuit, and the radio is blastin, the picture on the TV gets bigger/smaller with the music.

I'll try to take some pic's
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Old 05-13-2005, 08:43 AM   #4
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there are 2 circuits, with an inverter powering each. The shore power either plugs into shore or the generator. Then that all goes through a transfer switch to switch between inverters and the shore/gen power.
Nicholas Frey
Transportation Chairman
Society of Automotive Engineers
University of South Florida

The first requisite of a good citizen in this republic of ours is that he shall be able and willing to pull his own weight.
-Theodore Roosevelt
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Old 05-13-2005, 09:42 AM   #5
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Hi Frey,

Do you have the inverter's 115VAC grounded to the same ground as the battery? The AC should be isolated from the 12VDC system. Also make sure that there is no break in the AC cord. Make continuity checks on your wires (you might have an open), Also check and make sure that all of the wires are connected the same on the outlets and to each other(black with black, white with white, green with green).
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Old 05-14-2005, 12:36 AM   #6
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Make sure you neutral and ground are not bonded anywhere in the bus. It aint like a home system they must be seperate. Also check the genny beacuse many of them bond the ground a neutral which they need. You have the genny disconnected when you are using the inverters? The ground should be grounded to the bus frame and the neutrals must be isolated. You can get zapped if the ground the neutral are connected. You can run a volt meter between the earth and the bus body and if you get any voltage you have a ground/neutral bond somehwere. This very topic has come up on another board recently and it is very important to have it right. Stay safe
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Old 05-15-2005, 01:07 PM   #7
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Grounding and neutral on 120VAC systems in a bus

I second that. Everything I've read says that you should never bond the ground and the neutral in a motor home. If you do that, the body becomes electrified in the event of a short: think Disney's 20,000 Leagues Under The Sea, where the cannibals were on the hull of the Nautilus. Not something you want going on. The 120VAC neutral in a motor home should be "floating", that is, it only connects to the ground through the electrical hook-up at the campground's power panel.

I am also keeping my 12V electrical system separate from the chassis by running a negative wire instead of grounding to the frame. It takes twice as much wire (obviously), but it keeps the electrical systems isolated. This way I don't have to deal with isolaters, diodes, or any of that stuff -- KISS.
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