MultiPlus and transfer switch

[John L]

I need some help understanding a Victron MultiPlus 3000 inverter charger and transfer switch. I have a 2021Reflection 337 with 50 amp service.

I understand there is a manual switch and one by AM Solar (SPS), that is automatic, I understand these will allow me to use both legs of service. Are there any other choices? Does the inverter have anything built in?

Simplistically is a 50amp to 30amp dog bone basically the same thing? When off grid using the MultiPlus If I do not need the 50 amps but can get by on 30 amps would I need a transfer switch or do I need the switch because the MultiPlus does not allow me the ability to feed both legs? I know if I need to draw more than 30 amps from the MultiPlus (batteries) I would need the switch.

Thanks
John

[howson]

Whew....a lot of questions!

I have a 2021Reflection 337 with 50 amp service.

Let's start with the basics: "50 amp service" means there are two lines of 120vAC that can each supply 50 amps to your trailer. Potentially that means 100 amps from the shore connection. Based on your post I think you know this.

I understand there is a manual switch and one by AM Solar (SPS), that is automatic, I understand these will allow me to use both legs of service. Are there any other choices?

AMSolar's SPS and TucsonJim 's manual switch are the only two setups I am personally aware of that will allow a single inverter to feed both lines in a 50A trailer.

Does the inverter have anything built in?

Yes--when on shore power the Victron will pass ("switch") up to 50 amps through the inverter on one line. Of note the Victron must be on to pass shore power.

Simplistically is a 50amp to 30amp dog bone basically the same thing?

When you write Same thing are you referencing AMSolar's SPS and Jim's manual transfer switch? I think so...as the dogbone ties together the two "hot" lines. (I'm not an electrician so my terminology may be wrong--somebody will correct me if I have that wrong.)

When off grid using the MultiPlus If I do not need the 50 amps but can get by on 30 amps would I need a transfer switch or do I need the switch because the MultiPlus does not allow me the ability to feed both legs?

Without the SPS or Jim's setup, the issue becomes that the Multiplus will feed one line in the trailer. 50 vs 30 is not really the issue--the Multiplus will output a maximum sustained 25A (3000W/120v=25A). That's all you'll get--and even that won't last very long unless you have a really large battery bank. 25A of 120vAC is 250A of 12vDC. With three 100aH batteries, assuming 100% state of charge at the start, running at full tilt (250A coming out of the batteries) the 3 batteries will be exhausted in a little over an hour. I'm assuming LifePO4 (lithium) batteries.

So without the SPS or some other manual way of tying the hot lines together, can you live without one side of the panel (one 50A circuit) being powered? If "yes"--no transfer switch needed. Or if you can move lines on the Power Center's circuit breaker panel and keep the two 50A circuits balanced that would work, too, since you theoretically won't use anything on the "non shore" 50A leg.

I didn't want to choose, or wire in a sub-panel, or rewire the panel--I wanted to be able to pick and choose what I wanted to power (within the limitations of the inverter) when I wanted. The SPS is automatic and an elegant (albeit expensive) solution. It is not perfect, either--see my Inverter Overloading thread for more information.

I know if I need to draw more than 30 amps from the MultiPlus (batteries) I would need the switch.

Worth repeating that you won't pull 30A of 120vAC from the 12/3000 Multiplus when it is inverting (running on batteries). OK--for a very short surge it will allow this in an overload condition--but figure on 25A as your maximum.

Another way those with deep pockets (and 5th wheels, usually) get around the single line limitation is to run two 12/3000 Multiplus. There are YouTube videos with guys showing their setups (I can't access YouTube at work so can't link to them). The Multiplus' are networked together and each handles one line of the 50A trailer's circuits. This type of setup requires a lot of batteries and is very expensive.

A lot of info here to absorb. I hope some of it helps.

Howard

[ncitro]

I second everything Howard says above. I went the "one side" route and connected my Multiplus to just one side of my 50 amp panel. My non Multiplus side has just the electric water heater and factory converter (kept for a backup). I run everything else (including two AC units) on the Multiplus side. Theoretically I could draw more than 50 amps on that leg, although it would be unlikely I would need to run the fireplace and both AC units at the same time. Even if I did all of the wiring would be properly protected by the circuit breakers in the rig and the pole. The only downside is the loads on the other side are not shown in my total AC draw in Victron Connect, and therefore must be accounted for manually when considering Power Assist. Since its only the electric water heater, and if I have limited shore power I am probably running it on propane and its a non-issue. If your rig has additional loads, in particular three AC units this may not be an option, but for mine it has been fine.

[John L]

Thanks for the info Howard & Neil. This is helpful.