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Old 10-23-2021, 12:30 PM   #1
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Inverter

Our boat has a switch for shore power and one for ships power and I plan to connect both the generator output and the inverter output to the ships power switch, when the generator is running then the inverter will not be operating but when the generator is turned off then the inverter will turn on automatically and send ac to the ships power circuit. My question is will the generator be damaged by the inverter sending out 120 v on the same circuit as the generator which will not be running.
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Old 10-23-2021, 12:38 PM   #2
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DON'T DO IT!!!!

Many, maybe most inverters will be damaged if their output is connected to another power source like your generator.

You need either a three source selector switch: one position for shore, another for generator and another for the inverter, or an inverter with an internal transfer switch that passes through power if available or inverter power if not.

Perhaps a good marine electrician can help you with this.

David
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Old 10-23-2021, 12:50 PM   #3
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Inverter

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Originally Posted by DavidM View Post
DON'T DO IT!!!!

Many, maybe most inverters will be damaged if their output is connected to another power source like your generator.

You need either a three source selector switch: one position for shore, another for generator and another for the inverter, or an inverter with an internal transfer switch that passes through power if available or inverter power if not.

Perhaps a good marine electrician can help you with this.

David
But the inverter see’s shore power when that is on, why is that any different to seeing the generator power when that is running. My question was would the generator be damaged.
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Old 10-23-2021, 01:47 PM   #4
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There is a right way to do this and a wrong way. If you do it the wrong way you destroy things.

If you buy the correct Inverter and you wire it correctly it will know when shore power is available and when the generator is available and it will only step in when neither is available.

Since you are asking this question, it is a sure sign that you need to continue educating your self about inverters. There is a way to accomplish what you want to do but its dangerous to experiment. Keep learning.
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Old 10-23-2021, 02:59 PM   #5
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Does your inverter not have a battery charger integrated? If it does than you want the inverter on when the generator is running so the batteries will be charged. This can all be accomplished with the correct wiring. My inverter is on 24/7 and has been for 5 years now. It is never turned off. Dig out your owners manual or download one off the internet to see how it should be done.
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Old 10-23-2021, 03:05 PM   #6
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Generally shore power and the generator are setup so that only one source is useable at a time.

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From there an inverter with a transfer switch and maybe a battery charger is connected. The inverter switches to battery charger and the load is switched when the inverter senses shore or generator power.

If your inverter doesn't have this transfer switch and shore power / generator input, it needs to be wired separately.

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Old 10-23-2021, 03:31 PM   #7
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You have to have some sort of transfer switch, so when one source is on its not backfeeding the other. Same reason you can't just plug a generator into your house panel during a power failure. It would backfeed the incoming line and kill the guys down the road trying to restore the power. I don't know if it would damage the generator, but it would be very dangerous wired that way. That's why you normally see a shore/gen selector switch. The inverter/charger would be wired in after that switch so it would pass through and charge off which ever source was switched on and supplying power.
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Old 10-23-2021, 03:44 PM   #8
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Quote:
Originally Posted by yamabuki View Post
But the inverter see’s shore power when that is on, why is that any different to seeing the generator power when that is running. My question was would the generator be damaged.
Not on the output side.
Otherwise why have a switch in the first place?
Get a new switch for all three selection or another two position. Wire inverter and generator inputs to new switch. Output it to existing two position input where you moved the inverter from. avoids any two feeding at same time.
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Old 10-23-2021, 03:51 PM   #9
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Virtually all quality inverter/chargers have an integral ATS (auto transfer switch). Finding a standalone inverter with one is a bit more difficult, but possible.

Installing a manual selector switch isn't difficult. This Blue Sea 3-pole with panel is made for your exact application

https://www.bluesea.com/products/836...%2B_OFF_2_Pole

Good luck.

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Old 10-23-2021, 04:47 PM   #10
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Quote:
Originally Posted by yamabuki View Post
But the inverter see’s shore power when that is on, why is that any different to seeing the generator power when that is running. My question was would the generator be damaged.
The inverter doesn't see shore power at its output. I don't know if it will harm your generator, maybe. But I am pretty sure it will destroy your inverter.

This is too serious to debate on this forum. Find good marine electrician and let him sort it out for you.

David
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Old 10-23-2021, 05:07 PM   #11
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Quote:
Originally Posted by DavidM View Post
The inverter doesn't see shore power at its output. I don't know if it will harm your generator, maybe. But I am pretty sure it will destroy your inverter.

This is too serious to debate on this forum. Find good marine electrician and let him sort it out for you.

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Old 10-23-2021, 05:20 PM   #12
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I have posted on this topic before. If your inverter is an inexpensive device commonly sold for vehicle use you need to be very careful. if you wire the inverter's so called grounded conductor (which it is not) to your boat's grounded conductor circuit you will not be able to connect to dock power with a 4 prong power cable that features an isolated grounding conductor.

The reason is at an external power's electrical load center the wire (grounded conductor) and the green ( grounding conductor) are tied together. THERE IS NO GROUNDED CONDUCTOR IN SO-CALLED INVERTERS DESIGNED FOR VEHICLES. Each of the output terminals changes between 0V and 160-165V at a 60 Hz rate.

What will happen is immediatly after making the connetion to dock power you will create an electrical short circuit on the inverter's output. It will either trip your boat's DC circuit breaker powering the inverter OR the inverter may just burn up.
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Old 10-23-2021, 05:27 PM   #13
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when you say "ships power" i assume you mean the generator output.
it's been correctly pointed out that you can't wire the inverter output to the generator output. it's also correctly been mentioned that you should have a transfer switch that keeps you from turning on both the shore input and the genset input at the same time. when i say input, i mean input to the ac load center. (breaker panel)
typically, an inverter is wired to the load side of that transfer switch. if it's a very large inverter you can transfer the whole ac load through it. otherwise, you can split the ac load center into non-inverter loads and inverter loads. this gives the opportunity to separate out things like water heaters, heaters, a/c systems. run all the rest of the load center through the inverter transfer switch. the whole thing will be totally automatic.

this advice only applies if it is a real marine duty inverter with a transfer switch.
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Old 10-23-2021, 05:28 PM   #14
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You may want to look into something like this... Simplifies everything and you can set up your boat correctly. This allows any shore/gen/inverter/charge setup...
I also have an AGS setup and configured to kick in if my batteries get to a certain "low" set-point. Idiot proof as much as I can...

https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1
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Old 10-23-2021, 08:32 PM   #15
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Inverter

Quote:
Originally Posted by Soo-Valley View Post
Not on the output side.
Otherwise why have a switch in the first place?
Get a new switch for all three selection or another two position. Wire inverter and generator inputs to new switch. Output it to existing two position input where you moved the inverter from. avoids any two feeding at same time.
I should offer more info, the inverter charger has an internal switch so that when shore power is not available the inverter side is activated, the generator and inverter will not be active at the same time as when the generator is running the inverter charger acts the same as when shore power is available but the inverter ac output is not connected at the moment so I want to correct that.
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Old 10-23-2021, 09:07 PM   #16
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Quote:
Originally Posted by yamabuki View Post
I should offer more info, the inverter charger has an internal switch so that when shore power is not available the inverter side is activated, the generator and inverter will not be active at the same time as when the generator is running the inverter charger acts the same as when shore power is available but the inverter ac output is not connected at the moment so I want to correct that.
Thanks.
But to get on the same page I knew that. You are proposing to have three sources of AC supply whereas you only have two now. None of them must be connected at input or output and thus a need for a switch to isolate shore from Gen as both would go into Inverter for the charger function. No two should be able to supply power at the same time. Yes the inverter has auto switch to pass through or invert if no input supply of AC. The Inverter AC can get that input from Shore or Gen via switched.
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Old 10-24-2021, 12:16 AM   #17
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If you have an inverter/charger with a transfer switch, all of the loads should be connected to the output of the inverter. The shore power and genset will be connected to the input of the charger inverter, with a switch to chose between them depending on which is active. So no two AC source outputs are ever connected together, active or not.
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Old 10-29-2021, 04:07 PM   #18
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DavidM has it right. You don't want a system where it is possible to accidentally parallel any two sources of AC power.

Paralleling was done with many models of large 3 and 4 engine turbine aircraft in the past by utilizing some very expensive and complex circuitry. With most being twin-engine today they are set up generator to bus direct. If an engine fails or is shut down that load automatically transferred to the APU which starts up when an engine-driven generator fails.
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Old 10-29-2021, 07:51 PM   #19
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Our boat has a switch for shore power and one for ships power and I plan to connect both the generator output and the inverter output to the ships power switch, when the generator is running then the inverter will not be operating but when the generator is turned off then the inverter will turn on automatically and send ac to the ships power circuit. My question is will the generator be damaged by the inverter sending out 120 v on the same circuit as the generator which will not be running.
The answer is YES, the generator will be damaged.
Stop immediately.
I say that simply as the fastest way to cut through to avoid you trying this silliness.

I don’t think you will need to worry too much about the generator, at some point someone is likely to be found lying unresponsive next to the generator.

There are ways to accomplish what you want but your original question doesn’t explain end result you require.

Please seek professional help.
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