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Old 09-09-2012, 11:04   #1
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AC Outlet Wiring / Inverter / Generator

My setup right now:

- 1000w Xantrek pure sine wave inverter. The output goes to the 120 outlets onboard.
- Shorepower (120) is routed directly to the charge controller.
- I have 260 watts of solar but run my Honda 2000 every now and again to top off batteries or handle some power tools.
- For big loads (angle grinder, heat gun) I'll just plug directly into the generator.

My question is about running the 120 shorepower (coming from the generator) to the outlet circuits in addition to the inverter outputting to that circuit.

I don't think I'm actually going to do it, but was wondering if there was a problem combining two different AC sine waves or anything of the sort. In the DC world a load is a load and an amp is an amp, if you know that you have a "pure" sine wave is that enough to combine circuits in the AC world?
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Old 09-09-2012, 11:11   #2
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Re: ac outlet wiring / inverter / generator

It's a BIG no no.
Sure, the voltage is the same and so is the waveform, but they are not necessarily in phase.
If you want to let out the magic smoke, go ahead, but wait until the 4th of July!

IOW, NOOooo!
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Old 09-09-2012, 11:23   #3
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Re: ac outlet wiring / inverter / generator

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Originally Posted by rebel heart View Post
I don't think I'm actually going to do it, but was wondering if there was a problem combining two different AC sine waves or anything of the sort. In the DC world a load is a load and an amp is an amp, if you know that you have a "pure" sine wave is that enough to combine circuits in the AC world?
No, no, no! You cannot combine two AC output devices. In fact if you combine the inverter output with either your genset or shorepower output you are almost sure to fry the inverter.

AC has a waveform and the two waveforms must be synchronized for this to have any chance of working. Some inverter models, the Victron and MasteVolt do this, but most others don't.

Your description of your AC system was a little fuzzy (the shorepower going to a controller?) but what you need is a transfer switch to transfer the inverter output.

David
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Old 09-09-2012, 11:26   #4
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Re: ac outlet wiring / inverter / generator

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Originally Posted by senormechanico View Post
It's a BIG no no.
Sure, the voltage is the same and so is the waveform, but they are not necessarily in phase.
If you want to let out the magic smoke, go ahead, but wait until the 4th of July!

IOW, NOOooo!
This is exactly right.!!

You can put in a DPST NC relay, Connect the output of the inverter to the non-entergized side and the AC shore power on the entergized sized with the outlet AC on the common lugs. Its a safe break then make arrangement thats safe to use. Some larger inverters do that.

In commercial land, and solar land there are inverters to sync the outputs, but lots O $$$..

Not syncing the inverter would let the smoke out for sure.
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Old 09-09-2012, 12:12   #5
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Re: AC Outlet Wiring / Inverter / Generator

You need one of these to avoid EVER having two AC source on at the same time.

AC Toggle Source Selector 120V AC 30A - PN 8032 - Blue Sea Systems

Blue Sea also make a rotary version, I forget the model #.
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Old 09-09-2012, 12:28   #6
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Re: AC Outlet Wiring / Inverter / Generator

The only thing I might add to Sailorchics, suggestion is. Connect the relays trigger source to your external input contacts on the relay so that it will energize any time external power is available also make sure that the relay windings are rated for your input voltage be at 120 or 240 V. Also hook all of the plugs that you do not want to run on your inverter before the relay output. This will make sure that the inverter does not try to run the battery charger etc. This will basically make it foolproof, if anything can be foolproof. Just my two cents, Mike.
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Old 09-09-2012, 12:55   #7
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Re: AC Outlet Wiring / Inverter / Generator

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Originally Posted by Stu Jackson View Post
Blue Sea also make a rotary version, I forget the model #.

The original installation on my boat used a rotary. Fine idea. No slider/lock-outs to deal with -- I've seen a few of these broken aboard boats over the years.
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Old 09-09-2012, 13:06   #8
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Thanks folks, I figured ac had some more magic going on.
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Old 10-09-2012, 09:24   #9
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Re: AC Outlet Wiring / Inverter / Generator

There is an additional complication when setting up multiple systems. For correct operation the neutral and ground should be connected together when running on an inverter or genset but they should be separated when on shore power. Many modern inverers already include an automatic relay for doing this.

A double pole change over relay lets you make the connection on the soruce side of each individual device, With other selection systems additional relay(s) may be needed.
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Old 10-09-2012, 09:44   #10
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Re: AC Outlet Wiring / Inverter / Generator

In addition to being a big no-no in terms of syncing the AC (which is what grid-tied inverters in homes/utilities are all about), how do you keep your inverter from powering the marina?

If you aren't using a lot of power and your inverter is synced, it is entirely possible that you will end up using your inverter to power the fridge or battery charger on the next boat over. Unlike water and DC, check valves (diodes) are really uncommon on AC stuff and electricity can go out just as easily as it can come in. If your inverter is synced (in-phase) but a couple of volts higher than the incoming line you will instead have an outgoing line

Maybe not a big deal if you just want to run in parallel with the generator, but you still need to sync the AC and marine inverters aren't made for that.
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