By Pass Multi Plus II pros and cons

DIDDLYV

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Planning on installing a new victron multiplus II 3000 12 volt. Is it a good idea to wire this in with a by pass or just run the shore power directly to the Multi plus II directly then bring the AC back to the distribution panel? Think a couple of those 1-0-2 switches would get the job done wire one to split shore power to 2nd Switch and the other leg to the Multi Plus then wire the 2nd to accept shore power or multi power and deliver either to the distribution panel. Doing this or just putting a 60 AMP junction where the current converter is under the distribution box will allow me to get by with about 10 to 16 foot of 6 guage cable vs going thru the hassle of re running all the way from the shore power plug on the back of the trailer to the Multi and then back to the distribution panel.
As an aide the 8 Exliporc lithium iron phosphate calb lifepo4 310ah batteries arrived 2 days ago very well packed in box of four cells each measured 3.30 volts the other box of 4 each measured 3.28. Appear to be brand new shiny cells with intact qr codes and straight flat sides.

Probably have 2 months to get the cables switches fuses solar panels terminals etc as well as the painted uni strut and angle brackets together as the Multi Plus 2 seems to be back ordered until July. Want to run the Unistrut to mount the solar panels so i have a good chance of getting 4 screws on each strut into a roof rib vs just into the roofing material. Hopefully my stud finder can find the ribs when the time comes.
 

DIDDLYV

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Is it a good or bad idea to wire a Victron Multi plus II 12 /3000 with a bypass switch or am I better wiring in directly??
 

rmaddy

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Normally you connect the shore power directly to the MultiPlus AC In and then the AC Out to the AC breaker panel. And of course the MultiPlus also gets connected to the battery busbars. With that setup your AC circuits will run whether you are connected to shore power or not. If you are connected, then the MultiPlus can charge the batteries as well as directly send the shore power AC to the AC breaker panel. If you are not connected then of course the MultiPlus goes into Inverter mode and powers the AC from the battery.

Can you explain the perceived benefit of having the bypass switch? Most likely the MultiPlus already does what you might be considering the bypass switch for. Though after rereading your original post for the third time maybe this has to do with wiring hassles.
 

DIDDLYV

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The main reason I asked about the by-pass is the Victron Multi Plus II documentation shows the Multi Plus II wired in with a by-pass. Initially I had planned on running new wire all the way from the Shore power connector to the Multi Plus II. That will take something like 27 - 28 feet of cable if I pull the existing cable from the shore power connector and connect the multi plus using that wire already connected to the distribution panel and making a 6 to 10 ft run to where the multi plus is. If I use a junction in the vicinity of distribution pannel I probably need 16 to 20 ft of new cable vs 28 ft for the short run to the multi plus II and back.

The only good reason I can see for the by pass is that if the multi plus II crapped out one can run off shore power at the flick of a couple of switches vs pulling panel and wiring the 50 amp breaker directly to the shore power cable.
 
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HRTKD

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My plan is to run shore power and generator through the Multiplus. I have an Automatic Transfer Switch already in the system, so power will come directly from that to the Multiplus. My run is much shorter than yours, so I have not worries about voltage drop.

If I were to go with the Quattro instead, then the ATS would be eliminated. Shore and generators wires would go directly into the Quattro since it has two AC-in ports.
 

DIDDLYV

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I run my portable generator directly into the shore power connection. I think I liking the multi plus power boost mode. with something like 600 AH of battery avail, even my 2000 watt generator will run anything for short periods supplemented by batteries and the 840 watts of solar.
 

imval

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Sep 20, 2020
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A transfer switch could be interesting in case you want to update your Multiplus (which you shouldn't need to except if you have an issue specifically solved by a new firmware or need a specific new feature available only in a new firmware, because the software update will reboot the Multiplus and switch off the output for a minute) and only have a desktop computer or if you are afraid that the Multiplus will crap on you (unlikely).
 

frthompson

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May 29, 2021
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I've thought about this too. The possible advantage of a manual bypass is you could be on AC power with the Multiplus turned off, because to pass AC power thru the Multiplus it has to be on. But I don't know if there is any real benefit to that?
 

imval

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Sep 20, 2020
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The bypass circuit is probably not that expensive to implement and would be interesting.
It all depends on what you expect to do on your system. If you want to fiddle around and try things on your system, probably best to have the bypass switch (will help your wife accept it as well ^^).
On a RV, a bypass switch could be interesting if you want to run your vehicle only off the shore and get rid of the inverter humming.
 
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