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Old 07-09-2020, 04:17 PM   #1
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Question Adding Inverter to Existing Transfer Switch

Hello all,

Is it possible to wire my inverter directly into the existing AC transfer switch without causing issue?

Existing switch transfers between Generator and Shore power, i am thinking that I will wire directly into the Generator side, and have both the generator and inverter connected.

I will turn the AC>DC converter off at the breaker and only use it when the inverter is off. I will only use the generator then the inverter is off. and i will have the transfer switch automatically go from shore to inverter.

Or, is it better for me to have shore and inverter together and generator on the other side?


thanks for your thoughts!
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Old 07-09-2020, 04:30 PM   #2
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Hello all,

Is it possible to wire my inverter directly into the existing AC transfer switch without causing issue?

Existing switch transfers between Generator and Shore power, i am thinking that I will wire directly into the Generator side, and have both the generator and inverter connected.

I will turn the AC>DC converter off at the breaker and only use it when the inverter is off. I will only use the generator then the inverter is off. and i will have the transfer switch automatically go from shore to inverter.

Or, is it better for me to have shore and inverter together and generator on the other side?


thanks for your thoughts!

The inverter would normally go on the output side of the transfer switch after going through the breaker panel, and with the genny and shore power on the input side.



Without knowing the model of the van, how the AC is wired, and what inverter/charger it is, hard to know for sure how it is made to work.


Some details would be nice.
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Old 07-09-2020, 04:32 PM   #3
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Does your inverter have an internal transfer switch?
If so, just feed shore power to the AC input of the genset's transfer switch, and the genset's output to the AC input of the inverter. That way, everything is automatic.
If your inverter doesn't have an built-in transfer switch, you could accomplish the same thing with a second external transfer switch.
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Old 07-09-2020, 04:36 PM   #4
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After re-reading my post I see where it is a bit ambiguous.

I am adding a new inverter to my existing electrical system that does not have on today. The idea here is to power all the outlets and AC appliances via the inverter when not on Shore, or Generator power.

I have an existing 2-way Transfer switch factory installed that transfers between Shore and Generator power, and I am looking to patch the new inverter into the existing system.

I see your point though, if I wire the inverter on the output side, I don't have to do anything special with the transfer switch at all.
I can leave that system alone, and just make sure the inverter is off when using the Shore or Generator power.

This is a 2016 Winnebago ERA 70A, by the way.
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Old 07-09-2020, 04:40 PM   #5
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if I wire the inverter on the output side, I don't have to do anything special with the transfer switch at all.
I can leave that system alone, and just make sure the inverter is off when using the Shore or Generator power.
It really depends on the inverter. High end ones have built in transfer switches, so you can just wire them in series after your existing transfer switch. With such a unit, the inverter can be set to come on automatically when no power is available from the other two sources.

Lower end inverters can be made to work this way with a second external transfer switch.
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Old 07-09-2020, 04:42 PM   #6
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Does your inverter have an internal transfer switch?
If so, just feed shore power to the AC input of the genset's transfer switch, and the genset's output to the AC input of the inverter. That way, everything is automatic.
If your inverter doesn't have an built-in transfer switch, you could accomplish the same thing with a second external transfer switch.

Not sure, but I think some of the safety types might take issue with possibility of the generator and shore power being connected at the same time and such. If the inverter is a standalone and not an inverter/charger, you would fine. This is the big downside of the all to common practice of calling and inverter/charge an inverter or a charger, as it changes everything when they are combined like they commonly are now.
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Old 07-09-2020, 04:44 PM   #7
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Not sure, but I think some of the safety types might take issue with possibility of the generator and shore power being connected at the same time and such.
But they are NOT connected at the same time. His existing transfer switch decides whether shore power or the genset feed the inverter, and the inverter's internal transfer switch decides whether to use the output of the external transfer switch (it can't tell whether the power is coming from the genset or shore power) or to enable the inverter.
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Old 07-09-2020, 04:59 PM   #8
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But they are NOT connected at the same time. His existing transfer switch decides whether shore power or the genset feed the inverter, and the inverter's internal transfer switch decides whether to use the output of the external transfer switch (it can't tell whether the power is coming from the genset or shore power) or to enable the inverter.

Gotcha, but you said connect the output of the genny to the inverter, which is fine if it is an inverter, but not if it is an inverter/charger. If the genny goes through the transfer switch all is good as both can't be on at the same time.


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just feed shore power to the AC input of the genset's transfer switch, and the genset's output to the AC input of the inverter. That way, everything is automatic.
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Old 07-09-2020, 05:01 PM   #9
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But they are NOT connected at the same time. His existing transfer switch decides whether shore power or the genset feed the inverter, and the inverter's internal transfer switch decides whether to use the output of the external transfer switch (it can't tell whether the power is coming from the genset or shore power) or to enable the inverter.
This is all true, except for the inverter. The new inverter does not have an internal transfer switch, it is also not a combination inverter/converter.

My plan right now is to have the inverter wired in after the gen/shore transfer switch and just manually make sure it is off when using gen/shore power.

So, when on inverter power, no gen no shore plugged in, and converter breaker switched off.

When on either gen or shore power, inverter off and converter switched on.
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Old 07-09-2020, 05:22 PM   #10
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This is all true, except for the inverter. The new inverter does not have an internal transfer switch, it is also not a combination inverter/converter.

My plan right now is to have the inverter wired in after the gen/shore transfer switch and just manually make sure it is off when using gen/shore power.

So, when on inverter power, no gen no shore plugged in, and converter breaker switched off.

When on either gen or shore power, inverter off and converter switched on.
hmm...
In that case, I think I am with Booster. I don't think it is good practice to depend on user care to prevent two unsynchronized AC sources from being connected at the same time.

If it were me, I would invest in a second transfer switch (not that expensive). If you don't want to spend the money, you could add a SPDT switch to select the AC source (inverter vs shore/genset).
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Old 07-09-2020, 05:28 PM   #11
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Gotcha, but you said connect the output of the genny to the inverter, which is fine if it is an inverter, but not if it is an inverter/charger. If the genny goes through the transfer switch all is good as both can't be on at the same time.
Why does it matter if it is an inverter/charger or not? As far as I can see, the only thing that matters is whether the inverter has an internal transfer switch or not. (or perhaps you are assuming the presence of another charger. I was assuming that if it was an inverter/charger, it would be the ONLY charger).
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Old 07-09-2020, 05:52 PM   #12
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Why does it matter if it is an inverter/charger or not? As far as I can see, the only thing that matters is whether the inverter has an internal transfer switch or not. (or perhaps you are assuming the presence of another charger. I was assuming that if it was an inverter/charger, it would be the ONLY charger).

I think we are thinking similar things in a different order maybe.


The internal transfer switch in an inverter/charger has only one AC input, so it that input comes from the transfer switch, output, if you wire the generator output straight to it also, both could be on at the same time, unless the generator also goes through the same transfer switch as the shore power.


If it is a standalone inverter with a transfer switch, I think it will also only have one input that is DC for the inverter AC. and one for AC. I think it would need to have a 3way internal with two AC inputs and at that point you wouldn't need the original one. Again it could be on from the genny when you were on shore power unless both shore and genny went through the original transfer switch.


The way we had ours when we had standalone charger and standalone inverter, without a transfer switch in it, was to just wire the inverter AC output to a second transfer switch input and the first transfer switch output to the other input of the added transfer switch. Output of the second switch to the van. That gives 3 sources of AC that can't be on at the same time, if I am looking at it right.



If it is a standalone inverter it has no
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Old 07-09-2020, 06:44 PM   #13
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I think we are thinking similar things in a different order maybe.


The internal transfer switch in an inverter/charger has only one AC input, so it that input comes from the transfer switch, output, if you wire the generator output straight to it also, both could be on at the same time, unless the generator also goes through the same transfer switch as the shore power.
OK, now I am confused.
The purpose of the "first" transfer switch is to decide whether the AC power in the van comes from shore power or the genet. It has two inputs (a) shore power, and (b) the genset. It has a single output "power out". One of the inputs is the "priority" input (usually the genset). When input power is present on the priority input, the transfer switch automatically connects it to "power out" and simultaneously disconnects the non-priority input. There is no possibility for both shore power and the genset to be connected to "power out" at the same time.

You may then install a "second transfer switch" to the van (which may or may not be part of the inverter). It, too, has tow inputs. The first one is the inverter's AC output, the second one is "power out" from the first transfer switch. So, it's "power out" (which is connected to the van's outlets) can only have one of the three available sources connected to it at a time. I.e., the first transfer switch decides between shore power and the genset, and the second transfer switch decides between the first transfer switch and the inverter.

Quote:
If it is a standalone inverter with a transfer switch, I think it will also only have one input that is DC for the inverter AC. and one for AC. I think it would need to have a 3way internal with two AC inputs and at that point you wouldn't need the original one. Again it could be on from the genny when you were on shore power unless both shore and genny went through the original transfer switch.
No. Inverters with internal transfer switches are not DC, they are AC. Obviously, inverters are connected to the battery via a DC terminal (to power the inverter and possibly also to charge the battery), but this has nothing to do with the internal transfer switch. It also has an AC input, which comes either from shore power or the genset's transfer switch.

I guess we really need a diagram...
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Old 07-09-2020, 08:54 PM   #14
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I added a transfer switch in the generator line and connected the added inverter to it. Works fine.
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Old 07-09-2020, 09:05 PM   #15
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OK, now I am confused.
The purpose of the "first" transfer switch is to decide whether the AC power in the van comes from shore power or the genet. It has two inputs (a) shore power, and (b) the genset. It has a single output "power out". One of the inputs is the "priority" input (usually the genset). When input power is present on the priority input, the transfer switch automatically connects it to "power out" and simultaneously disconnects the non-priority input. There is no possibility for both shore power and the genset to be connected to "power out" at the same time.

You may then install a "second transfer switch" to the van (which may or may not be part of the inverter). It, too, has tow inputs. The first one is the inverter's AC output, the second one is "power out" from the first transfer switch. So, it's "power out" (which is connected to the van's outlets) can only have one of the three available sources connected to it at a time. I.e., the first transfer switch decides between shore power and the genset, and the second transfer switch decides between the first transfer switch and the inverter.


No. Inverters with internal transfer switches are not DC, they are AC. Obviously, inverters are connected to the battery via a DC terminal (to power the inverter and possibly also to charge the battery), but this has nothing to do with the internal transfer switch. It also has an AC input, which comes either from shore power or the genset's transfer switch.

I guess we really need a diagram...

First part, that is just what I am saying to do two transfer switches. First one shore/genny, second one is output of first one/ inverter.


Second part I don't get. A standalone inverter with a transfer switch is primarily a DC device that changes power to AC output, so I supposed you could call it half and half if you want. The AC input to an inverter without charger is just passed through the inverter so you really have two AC inputs to the internal transfer switch, one from the DC generated inverter section internal to the unit, and one from some other AC source. I don't get how you are going to get 3 independent AC sources (shore, genny, inverted) that way, unless the AC input to the inverter is the output of another transfer switch with two inputs.


Time to sketch the diagram
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Old 07-09-2020, 09:22 PM   #16
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This is how I would see it would work without relying on operator shut off of the right things to not have two AC inputs at the same time.


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File Type: jpg inverter genny shore power.jpg (71.7 KB, 113 views)
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Old 07-09-2020, 09:25 PM   #17
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It also has an AC input, which comes either from shore power or the genset's transfer switch.
Quote:
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...unless the AC input to the inverter is the output of another transfer switch with two inputs.
These two statements are equivalent, n'est-ce pas?
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Old 07-09-2020, 09:32 PM   #18
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This is how I would see it would work without relying on operator shut off of the right things to not have two AC inputs at the same time.
[/IMG]
I agree with your diagram (except for the minor point that "DC in" and "DC out" are the same wire).

But I still don't understand why you said this:

Quote:
Gotcha, but you said connect the output of the genny to the inverter, which is fine if it is an inverter, but not if it is an inverter/charger.
Your diagram illustrates that it works either way.
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Old 07-09-2020, 09:41 PM   #19
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Hello all,

Is it possible to wire my inverter directly into the existing AC transfer switch without causing issue?

Existing switch transfers between Generator and Shore power, i am thinking that I will wire directly into the Generator side, and have both the generator and inverter connected.

I will turn the AC>DC converter off at the breaker and only use it when the inverter is off. I will only use the generator then the inverter is off. and i will have the transfer switch automatically go from shore to inverter.

Or, is it better for me to have shore and inverter together and generator on the other side?


thanks for your thoughts!
I added an inverter to an ERA 170c. The inverter has it's own transfer switch so the input to the inverter is the output of the Line/Generator switch in the RV. The inverter output now supplies the AC instead of the RV transfer switch. I also added a optical relay with a 115 AC control input and a SPST output. Ran the RV battery charger AC input through this relay. The control for the relay is is output of the RV transfer switch. Thus, the charger works with line input or generator but not when the inverter is the AC supply.
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Old 07-09-2020, 09:46 PM   #20
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I also added a optical relay with a 115 AC control input and a SPST output. Ran the RV battery charger AC input through this relay. The control for the relay is is output of the RV transfer switch. Thus, the charger works with line input or generator but not when the inverter is the AC supply.
Ah. Good point.

OTOH:
Couldn't you have also simply connected the charger upstream of inverter (i.e., between the output of the external transfer switch and the input to the inverter?
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