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Old 07-27-2021, 05:26 PM   #1
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Victron Multiplus and the Existing Transfer Switch

I'm removing my lead acid batteries and replacing then with lithium. As part of the project, I'm using a Victron Multiplus 3kW inverter/converter. I've located the existing inverter. The wiring diagram says that the existing converter is wired internally to the power panel, so I'll need to dig a bit for that.


The question I have is whether I can/should remove the existing transfer switch. From the Victron datasheets, it appears that the Victron acts as a transfer switch in its "no break" main A/C output. (the second A/C output only has power when the unit has input A/C power) So it seems the existing transfer switch should be removed.


Thoughts?
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Old 07-27-2021, 10:58 PM   #2
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Yes, the existing inverter goes away along with the transfer switch.

Have you seen the new multiplus-II 2 X 120v?

It simplifies wiring a 50A trailer. Take a look.
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Old 07-28-2021, 06:42 AM   #3
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I'll remove the converter, of course, but what about the transfer switch? I think it too should be removed, but wanted to see what others had done.
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Old 07-28-2021, 06:55 AM   #4
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I just installed the “NEW” MultiPlus II 240/120 and we are using it the week for the first time. It’s performed flawlessly.
I will be using it extensively for the next 3 months and we travel the west.
I provide a detailed report once testing has some legs. #notsponsored
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Old 07-28-2021, 07:59 AM   #5
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The place I purchased the MultiPlus from didn't have any of the MultiPlus II in stock, so I ended up with the older model. We have a trip planned and since the batteries in the trailer we purchased are shot, I needed the upgrade sooner rather than later.


I'm hoping that we won't miss much by having the older model.
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Old 07-28-2021, 08:11 AM   #6
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Quote:
Originally Posted by wulfraat View Post
Yes, the existing inverter goes away along with the transfer switch.

Have you seen the new multiplus-II 2 X 120v?

It simplifies wiring a 50A trailer. Take a look.
We've got one of the Multiplus II 2 x 120v inverters fro Victron and I agree with you totally. It made the install on a 50-amp coach very simple, and it's great that it knows whether we're on single phase 30-amp or split phase 50-amp service.

Only downside I've found so far is that it only monitors the current flow on L1, not L2. On L2 it only passes it through to the breaker panel but does nothing else.
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Old 07-28-2021, 11:15 AM   #7
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If you have a plug on the front of the trailer for a generator you will need the original transfer switch to isolate the shore power from the generator. The viltron transfer switch isolates the inverter from the shore power. All this is designed to protect the grid from external power inputs. That is a very real problem for linemen working on the grid.
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Old 07-28-2021, 11:22 AM   #8
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Not sure if you have the second power outlet at the front of the trailer that is intended for connecting external generator. My 27FB does and that is what the transfer switch actually switches between. If you have this then I think that you need to connect your the power out of the transfer switch to the AC in on the Multiplus. I have a picture on another post of how I did it.
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Old 07-28-2021, 11:29 AM   #9
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He is a link to the other thread with pictures. Note I did not have factory inverter.


https://www.airforums.com/forums/f44...te-220486.html



I also left the factory converter in place and just disconnected the power to it. If the multiplus dies I like the option in a pinch to be able to swap back to stock.
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Old 07-28-2021, 11:37 AM   #10
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GusKMG and Peter C have the right of it. After I started taking things apart, I realized that the existing transfer switch isolates the two coach inputs (one on the side toward the back and the one on the front) from each other, which the schematic labels shore power and generator inputs.



What I need to do is relocate the transfer switch by the multiplus and have the output of the transfer switch be the 120 input to the multiplus and then the 120 output of the multiplus go to the distribution panel in place of the existing transfer switch output.
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Old 07-28-2021, 01:47 PM   #11
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Not to hijack this thread, but I have a situation where I think my transfer switch must have blown: I can use the generator input just fine, but the side input is shot. Is there any meaningful risk in running it like this? With the one side down, am on borrowed time with the other side?
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Old 07-28-2021, 03:19 PM   #12
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@SS-Housten:


If it were me, I would drag out my multimeter and test whether you have power coming into the transfer switch from the "blown" input. If not, then the problem isn't the transfer switch. It is somewhere between the transfer switch and the input.
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Old 07-28-2021, 10:56 PM   #13
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Transfer Switch removal

Guskmg & Peter C have it correct. Don’t remove transfer switch. If you want to take advantage of the “hybrid” function of the Victron-one of its coolest features (draws power from batteries when input AC is low) you must have ALL A/C devices (including all outlets) powered through the inverter.
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Old 07-31-2021, 07:22 AM   #14
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For those who care, here's how the multiplus will be wired. The factory wiring is shown by the dashed arrow between the transfer switch and distribution panel.


To wire in the multiplus, the output of the transfer switch is wired to the 120 input of the multiplus. The 120 output of the multiplus is wired into the distribution panel in the same way that the transfer switch comes from the factory.


Gulliver72 is correct in that you also want all AC power devices powered through the distribution panel. To accomplish that, in my panel I can use either circuit 2 or circuit 4.



Circuit 2 was used to power the old converter. When I removed the old converter, that circuit became an empty 15 amp breaker. To use that one, I'd need to run a wire from the circuit 2 breaker to the curb side, front corner of the coach where the wire that ties all the old inverter powered receptacles terminates and tie the two wires together in a junction box.



Circuit 4, also 15 amp, was used to power the old inverter as well as all the receptacles that were powered by the old inverter (i.e., via the inverter). The 120 wire that ties all the old inverter powered receptacles together and the old inverter power both terminate in the curb side front corner of the coach. It is a simple matter to tie the two wires together in a junction box, so that is probably what I'll do.


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