50A RV Install - Very Basic Questions (Pre-Purchase & Install)

[BobKones]

Hi Folks!

Hoping to get a little help prior to purchasing.

I have a Diesel Pusher that runs on both 30 & 50 Amp shore power and has a genset with an existing Trace Legend Series 1 Inverter from about 25 years ago. It’s an MSW unit. Shore power and genset are fed through an Automatic Transfer Switch.

I’m looking to replace it with a Victron Energy MultiPlus-II 2X 120V 3000VA unit, specifically a PMP122305102

I’m not an electrician but this should be a fairly simple install for me. I’m thinking it should be as simple as wire the new one as the old one and configure it and all is well

This brings up a couple of questions…

The old inverter has an AC feed side (IN) and AC Hot out 1 & 2 with the neutrals joined together on the output side. (see picture)

I’m guessing that what I would do when installing the PMP122305102 is to separate these output lines into AC Out 1 & AC Out 2. Would that be correct?

Lastly, am I buying the right inverter? I’d like to get this project done fast. IE, get the inverter coming and get it in there and configure it.

I’ve included a picture of the old inverter connections and the new Victron unit to make it easier for you.

[Netrange (Steffen)]

I think it’s the wrong multi.
Your old inverter only has 1 AC In BUT 2 AC outputs.
Do you have any more information about the current inverter… maybe a type label, etc.?

What kind of voltages are we actually talking about… what kind of power supply is available on site…

[BobKones]

Sure, it’s a Trace Legend L1512 which means 1500 watt / 12v charger. The two outputs feed two separate Inverter circuits in the unit (one dedicated Microwave) and various generic outlets.

As you can see from the picture, the PMP122305102 has one input and two outputs. Looking at the power flow diagram on the datasheet for the PMP122305102 it seems that if you feed it 120VAC (30A) it powers both AC outputs with 120VAC. \

The power supply on site will always be either 15A / 30A or 50A. Basically, you use 15A when storing the unit and either 30A or 50A when you’re camping.

Apparently you can feed the PMP122305102 any of the above but for the time being I would just install it as it is now, with a single phase 120VAC circuit and look to feeding it split phase 50A power later on down the road for maximum effect.

It seems to me this unit could be ideal, in that sense.

Interesting…I just saw this from the manual;

AC-out-2 (Maximum Torque: 2 Nm)

A second output is available that disconnects its load in the event of battery operation. On these terminals, equipment is connected that may only operate if AC voltage is available on AC-in-1, e.g. an electric boiler or an air conditioner. The load on AC-out-2 is disconnected immediately when the inverter/charger switches to battery operation. After AC power becomes available on AC-in-1, the load on AC-out-2 will be reconnected with a delay of approximately 2 minutes.

I wonder if that output is user-configurable?

[MiPaul (Paul Keberly)]

That Trace unit appears to be a 30A device, a 120V single leg AC in, with two AC outputs. I couldn’t find an output 2 in the manual. My guess is one is pass-thru only when on shore, the other is inverted/shore?

I installed the MP 2x120 (24V) in our old pusher, we love it. We did rewire the breaker panels to take advantage of the MP 50A pass-thru capability on both legs, with everything in the coach powered from the inverter. This does require a bit of user intervention to manage loads when on battery, which I have mostly automated now.

The MP has inverted loads on AC out 1 and shore only loads on AC out 2. I’d wager your panel has a 30A breaker to feed the inverter AC input and one of the AC outputs feed a subsection of the panel, or a separate panel as I had.

[BobKones]

Hi Paul - thanks for the reply and for taking the time to research it!

The manual for the Trace does not show the extra output terminal - I suspect it was an added feature that was not documented.

As you surmised, it is a 30A single leg in, but…both outputs are powered when inverting.

One is a dedicated circuit to the microwave, and the other feeds 5or 6 outlets. My guess is that the two circuits share the neutral, and probably this fits with a production change with respect to the inverter design, but it’s just a guess on my part.

Your bet paid off, I have a small breaker panel above the bed, and it does have a 30A breaker feeding the inverter. It’s the only panel installed in the unit.

It looks like the MP 2x120 can be wired up just as the old one is now, on a single 30A leg and that I could then feed it 50A at a later date and power the entire panel to improve it.

I was thinking that, for the time being, I could just buy an electrical junction box and tie three lines together and just feed one end of it to the AC OUT 1 on the inverter and I would have the same functionality as I do now.

So I’m guessing this is the correct inverter to buy for my unit. I’d appreciate any confirmation you can give me on that.

Have you ever used the PowerAssist feature? Right now I’m in a 30A park and my washer/dryer combo gets messed up during the dry cycle if the power sags too low. It’s very sensitive to that. So I was hoping that a new inverter would act like a line-active UPS and raise the power as needed when too much is being used or there is not enough present.

I’d also love to hear the short strokes on how you fed it 50A and what you did to the panel as it seems to be split between the two legs when on 50A.

Again, many thanks, it sounds like you’ve done what I have been thinking.

Btw, saw this about the Output 2 on the ‘net “AC output 1 is a primary and the secondary output is programmed to be a pass through only when shore is present however, you can reconfigure the functionality of this through assistants with Victron’s configuration tools.”

If that’s correct then I should be able to skip the junction box routine.

[MiPaul (Paul Keberly)]

Yes that inverter would work, and allows for future expansion when you’re ready to pull big wire. Yes power assist works great. UPS mode keeps our laundry combo going when shore goes away. We did an 8 week trip and the microwave clock kept time. It does not like to run on GFCI circuits, it will trip a North American 120V GFCI pretty quickly.

I don’t have any experience using Out 2, everything is on Out 1 for us.

#6/4 SOOW cable from the transfer switch out to the MP AC in, #6/4 from AC out1 to a 6 slot/12 circuit QO breaker panel that feeds everything in the coach. I use Shelly relays and a bit of Node RED code in a Cerbo GX to work both sides of the water heater, and the AC side of the fridge as needed. A separate I/O module handles DC/DC converters, gen start/stop, and the Domestic roof AC load shed option, also under NodeRED control.

[BobKones]

@MiPaul

6 slot/12 circuit QO breaker panel

Thank you Paul, that was exactly what I needed to know!

I replaced the Norcold fridge (24x7 500 watt draw) with a thrifty residential a while back and also ditched the water heater with an on-demand that runs on 12v and propane. I then replaced one of the AC units with the new 18K Chill Cubes which uses a variable speed compressor (apparently you can run 3 of those on a 30 amp connection). So the old 50A requirement for this unit should be down to 30A once the new inverter goes in…

My guess is that, because I’m on 30A for the time being, I will have to move the breaker for the washer/dryer to the inverter side of the panel in order for the power assist feature to work.

With respect to GFCI, do you mean the outlets in the unit? If so, I replaced them all with normal ones long ago.

[MiPaul (Paul Keberly)]

You’re welcome. We still have the gas fridge, great for boondocking. Just replaced our rear AC with a 24V unit. Frees up the inverter for other items. Been watching the Chill cubes, waiting for a heat pump model for the front. Those Dometics are noisy power hogs.

Yep that should do it for you. If you won’t ever need both legs of AC, the MP2 might be a cheaper option?

No, a GFCI on the shore plug. It seems ours are pretty sensitive, made to run a single item and not a coach full of stuff. I’ve had troubles, YMMV. Safe travels.

[BobKones]

We stopped using the Norcold (1200 LRIM) on gas when we saw how many units it burned down. We missed out on the class-action lawsuit though which was a shame because it would have paid for the new residential fridge, as it did for so many others. Lots of videos of Monaco’s on fire from this, and I talked to one fella that went through it, and to this day, he cannot enter someone else’s RV if it has a Norcold in it. He’s that emotionally scarred from it because it burnt up so fast he could only get one shoe on and lost everything as it was his home.

I ordered up the 120x2 as well as the USB programming interface so the project is a go I will start with just replicating the existing 30A inverter setup for expediency, and then upgrade to the 50A feed thereafter. That’s what I am looking into now.

If you have time, feel free to comment, but if I’ve taken up too much already, feel free to ignore me Some other kind soul will likely help or I’ll figure it out myself as I go along. I’m trying to break it down into simple steps for clarity, work flow & sourcing/purchasing purposes.

This is what the OE wiring looks like with respect to the incoming 15/30/50A feed;

A) The panel appears to be fed 50A (120x2) directly from the transfer switch. Those wires (Red, Black, Green & White) currently go to a 50A breaker in the box providing full 50A power, if available, from either the pedestal or generator. (see second pic top right and bottom breaker)

This line should be replaced with #6/4 SOOW and run from the transfer switch to AC IN on the inverter, which would provide the full source power, including 120x2, to the inverter from either shore or generator.

B) OUTPUT 1 on the inverter should be #6/4 SOOW and run to the 50A breaker (bottom) just as it is now, with each leg on it’s own side of the breaker.

In this scenario, when supplied with reliable power, whether it’s 15, 30 or 50A, it will passthrough the inverter, to the breaker box, just as it does now. The only difference is that the electrons take a longer route to get there by going through the inverter.

If plugged into a 15A pedestal, as an example, and the inverter is set to 13A, and you draw 20A, then the inverter will add ~5A from battery power to make up the difference for as long as the load is present, or your batteries can hold up.

So the only difference from OE design to passing the the source power through the inverter first is that this makes the inverter a single point of failure.

If this is correct, I am unsure why you replaced your panel. According to Victron specs the max peak power the inverter can put out is 5500W or 45.83A That should be acceptably below the threshold of the 50A feed breaker.

I believe the loads in my breaker box are divided up such that L1 powers some, and L2 powers some. This is probably done to ensure things like the two AC units use their own leg and other, less load drawing devices share the other leg. Ie, for capacity reasons.

If the 50A feed breaker in the panel is wired the same way, and fed from the inverter instead of the transfer switch, then in a passthrough situation (15/30/50) nothing has really changed other than the power is passing through the inverter.

When on battery power, what has changed is that the inverter now powers the entire panel, and not just some outlets.

If I’m in error on any of this, please let me know.

One issue that comes to mind is this, the existing inverter has two 15A circuit breakers on it. Those breakers, and the inverter, appear to feed the inverter output outlets in the vehicle. As such, I doubt they go to the panel at all. In effect, it seems to me that the inverter with it’s two breakers acts as a panel. I could be wrong on that…but it seems like this would have to be dealt with, otherwise all of those outlets would not be fed power.

Update: It looks like AC-Out-2, which is normally turned off in the event that unit goes to inverter/battery power, can be configured with VEConfigure to be kept active based on battery voltage. Ie, if the battery voltage is >10v, AC-Out-2 is kept active regardless of whether the unit is inverting or not.

So that should solve the immediate issue of what to do with the 2 output circuits going to the old inverter.

[MiPaul (Paul Keberly)]

Not a problem, we have company in town for the holiday.

That’s correct, the inverter is right after the transfer switch. It is a single point of failure like most RV stuff, but I wager your transfer switch will fail before your MP does. My panel was wired similar to yours going to the inverter, but the inverter out went to a separate sub panel. It was easier to just replace both panels with a single that had enough space for everything, the new box size was the same size as the main. I was able to reclaim quite a bit of space in the process, we have a short coach, space is a premium.

Yes we feed the whole coach. IF you don’t have items that will overload the inverter, you don’t need to load shed, that wasn’t our case at the time of our install. I’m not sure about the MP output 2, we really don’t have a use for it. You would need breakers someplace for those 2 circuits to use Out 2, or I’m not following correctly? A junction box and romex could easily get them to your main panel to centralize things. A twin 20A breaker in the now unused 30A inverter slot would keep your old panel intact.

Power assist has a minimum output power it will assist with, the scenario you describe is correct, but the assist values might not be valid. It does work very well for us, it’s pretty seamless. UPS mode is the same way, unplug from shore pedestal and the laundry continues.

A Cerbo GX and an android tablet are a great way to monitor & control your system.

[BobKones]

This is great information - you’re picking up on things I had not yet thought of.

You would be correct about needing breakers on the two circuits the existing inverter is feeding, and, using the existing panel with a double 20A breaker in place of the inverter’s 30A is brilliant! I will roll that into the design and it will free up output 2 again when it is in place.

You brought up a great point, monitoring. I only have the USB dongle coming with the unit for programming and this got me thinking about monitoring. The Bluetooth adapter is reported to be useless in that it cannot be used to configure anything and a waste of money.

That got me looking at the Cerbo GX but the panel for it it something like $700 (!!) and the unit itself is apparently $350 or so, and then, it seems you need to run a cable from the Cerbo GX to the panel and this is not easy. Not by a long shot.

Are you suggesting that you can get a Cerbo GX (only) and wirelessly connect to it with an Android tablet to have the same functionality of the panel? If so, that sounds like the way forward. Speaking of which, I only have the inverter and dongle coming, what else should be added, with respect to options, for full effect?

[MiPaul (Paul Keberly)]

Yep, I have a Cerbo in the basement near the inverter and a 10” Galaxy Tab A7 on the wall, connected using the coach WiFi. Victron supports a kiosk mode app for the tablet, got a wall mount on Etsy. The wall tablet does need wires for power, but not going to the Cerbo.

Currently we have a DIY communicating lithium battery, GPS module, and 4 solar MPPT connected to the Cerbo using Victron USB, also 3 Smart Shunts using VE.Direct cables. If you have internet, you can view, log, and control your coach remotely using VRM.

If you can find a Cerbo-S GX, it’s a bit cheaper, but doesn’t have analog tank or temperature inputs. The Garnet SeeLevel (RV-C version) tank system connects to the Cerbo with CAT5 cable. It’s light years better than the old MODA foil sensors, and it can use the same sensor wires. I use an Arduino to gather temperature data from 6 sensors and send it to our Cerbo-S for display You can see all of that on VRM too. Next up is to link in control for our new DC air conditioner

Cerbo can do remote firmware updates on connected devices, and change the config of your MP with VEConfigure from a PC/laptop. I’ll save the NodeRED pitch for later.

Where are you located?

[BobKones]

I’m probably very far away…on an Island on the far left side of Canada

I too have seen some posts about the add-on’s for the Victron and was quite amazed. I’ve been RV’ing for the better part of 10 years now and I think it’s coming to an end at some point (right after I finally got the unit sorted, of course!).

Believe it or not, the main reason for replacing my otherwise great Trace inverter is due to my new washer and dryer. It’s a combo unit, it’s electronic, and it’s very sensitive to low voltage. What it does is dump water in the tub during the dry cycle whenever it encounters a voltage issue

I just moved into a gorgeous, brand new park, but….it’s limited to 30A. I figured it’s new 30A so it should be OK but that is not the case even though I’m just about the only person here.

The other side of it is, because I replaced the fridge, went on-demand hot water, and put in an variable speed compressor AC unit, the motorhome should actually be 30A friendly. I really should not need 50A at all. So I’m thinking of the future owner as well with respect to the Victron, but this is the perfect test bed for the new inverter. I bet there are times when I’m using 5kw and I’m not using propane for heat this winter - it’s two 1,500 watt heaters.

I’m guessing a ‘kiosk mode app’ is a 3rd party app that Victron works with so that you can run it on your tablet? If so, does it expose all the same features the Victron color display does? I have excellent Internet in the Motorhome as I have a 28dBi wifi dish mounted on the old TV antenna and it does 30km’s

So my question remains, I thought it was the head/display unit that has the WiFi card built in but it sounds like its the blue Cerbo unit itself. If the tablet does everything the Victron head unit does, I have no problem with buying a dedicated tablet for it. Way cheaper and better then a $700 LCD screen that cost $23 to make!

Hang on a second, you mentioned you can use VE Configure with Cerbo using a laptop? If that’s the case I should send back the USB cable I bought and put that $100 towards the Cerbo. I need the VE Configure because it’s how you re-task the AC Out 2 port. Can VE Configure run off a laptop wirelessy when connected to Cerbo?

[MiPaul (Paul Keberly)]

That is a ways off for us, interesting looking area out there.

I believe the app was released by Victron. I don’t know what features the color display has but I suspect the tablet would be a direct replacement. One thing I wish the tablet app had was an audible alert…maybe.

Yes the Cerbo has the connectivity and the smarts. VEconfig on a Windows laptop, yes. I don’t know what other platforms VEconfig supports, I never looked. I configure our MP from a Win desktop while the coach is out in the barn. VRM downloads a MP config file, uses VEconfig to change the file, VRM uploads the changed file back to the MP. It’s still unclear what using Out 2 buys you?

[BobKones]

I did some more research on the Cerbo and display panels and the like. The conclusion I’m coming to is I probably could have skipped buying the USB dongle and just went straight to the Cerbo and done the remote editing of the config file as you suggested and downloaded it back into the Victron inverter. Cerbo and a laptop, that’s what I’m getting at for both config and monitoring.

It’s really hard to get simple answers on Victron gear from the company but I think everyone knows that

With respect to re-tasking AC Out 2, if you see the pic of the original inverter above, it feeds two separate circuits for the motorhome that go to wall outlets. One circuit is dedicated to the microwave outlet, and the other is shared among numerous outlets for whatever you plug into them.

So the idea is this, for the time being, I’ll do a quick and dirty inverter install. Move the existing power feed from the old inverter to the AC In on the new one and use AC Out 1 for one of those feed circuits and AC Out 2 for the other. This should make the entire install a 30 minute affair plus configuration for the batteries etc.

My thinking is to do it in two stages, that’s one, and the second will be to run a proper feed from the transfer switch to the inverter, AC Out 1 from the inverter back to the panel, increase the panel breaker to 75A, and then do what you suggested, replace the existing 30A inverter breaker with a dual 20A and run wire back down to a junction box to feed the former inverter-only outlets.

At least that’s what the plan looks like now. It does mean I will be running those two circuits sans breakers for the time being but I’m not sure that will be dangerous for a short period.

As always, correct me if I’m wrong!

[BobKones]

The inverter should be here tomorrow or the next day so I was looking at VE Configure to pre-familiarize myself with it when I discovered something cool (you probably know about this but I was surprised). The default for AC Out 2 from Victron is de-energized when running on inverter in the event of a power failure (battery operation). This seemed like a deal-breaker to me but it can be reconfigured with the VE Configure by making it always on by a number of conditions you can choose, such as battery voltage.

As such, I can set it to keep that relay energized if the battery voltage is above 10V. In other words, always on.

The existing inverter has two AC outs, each one is a circuit powering some of the inverter outlets inside the unit. I realized that I could use AC Out 1 to feed one circuit and AC Out 2 to feed the other.

The existing unit has two 20A circuit breakers on the inverter for each of those outputs. So I was planning on doing a ‘quick & dirty’ install for right now, and coming back to creating a proper L1 & L2 feed from the transfer switch later, as well as a proper feed from the inverter to the breaker box such that the entire unit is run off the inverter as you suggested earlier. This is ideal but, it’s December and I can only do so much at one time as the unit is in service and it’s cold out

So my assumption was that I would run AC Out 1 & 2 without the 20A breakers for the time being, which kind of bothers me as you don’t have the safety of those 20A breakers.

But…I see that in VE Configure you can set both AC Out 1 and AC Out 2 to ‘break’ depending on the load. In other words, you can set each one to shut off if the load is higher than 2,400 watts. In other words, virtual breakers!

To me this is pretty darn cool because it means, even doing a ‘quick & dirty’ install, I can re-configure AC Out 2 to be permanently on, but can also set both outputs to break if the load exceeds 20A.

So I can start with replicating the existing inverter, which makes wiring it a 5 minute job, enjoy the power assist feature, and proper charging algorithms, along with pure sign wave and perfect preset 120v voltage, which will fix my washer/dryer voltage issue, and…come back later and do the proper L1 & L2 power feeds etc as time permits. And all that with, likely a 30 minute install time to get me through the winter.