Guide to operation/installation of Multiplus II

rh5555 · March 14

I have been upgrading our TAB 400 to Lithium (2 x LiTime 230Ah) and a new charger/inverter. I picked the Multiplus II 3000VA because I'd been happy with other Victron Products and I thought NuCamp had chosen it for their 400Ah lithium package (whereas it seems they used the older Multiplus). What I didn't realized was how complicated it could all get, and how confusing the documentation could be. The Multiplus II is a very versatile unit, and has many features way beyond TAB owner's requirements, which can make navigation of the documentation quite tortuous. I learnt the hard way (mistakes and buying unnecessary hardware) so I'm writing this up to aid future owners wishing to upgrade to either the Multiplus or the Multiplus II. It may also be useful for those of you who have a Multiplus installed at the factory as they are very similar to the Multiplus II.

120V Wiring:

I'm not going to go into any detail here. Just note that 120V input from shore power connector goes directly to the AC1 input (though technically it should go through a 30A breaker). If you want the inverter to be able to power everything on the TAB (including microwave and AC) then the L1 output from the Multiplus II will be connected directly to your original WFCO power center 120V input. The WFCO converter will need to be disconnected from the 120V system by removing its hot wire from the 120V breaker, and from the 12V system by removing the two 40A fuses.

Communications:

This is the area that confused me the most. The Multiplus II has a rocker switch with 3 positions:

Off (the middle position) which turns everything off. I'm calling this the Hard Off for reasons that will become apparent
On (the position marked "I") which turns everything on.
Charger only (position marked "II") which only enables the charger

It also has a bunch of LEDs that show the state of the charger/inverter.That's all very well for a unit mounted on a wall in your remote cabin, but for us the Multiplus II will doubtless be somewhere that you cannot reach the switch, let alone see the LEDs, so you will need some remote way of controlling the Multiplus II and seeing what it is doing. If you are doing a self-install, you will also need to program the Multiplus II to correctly charge the batteries that are connected to it.

I have uncovered 3 methods of communicating with the Multiplus II which don't seem to go overboard in terms of capabilities you'll never need:

MK3-USB and Victron Connect on a PC or Mac:

This requires a PC or Mac and is the only way to program your Multiplus II. The Connect program for the PC/Mac provides way more functionality than the Connect app for your phone. To access the additional functionality click on the cog icon, you'll need the password: It's "ZZZ".

VE.Bus Smart Dongle (bluetooth) and Victron Connect on a phone:

This is the only way to see what the Multiplus II is doing on your phone. It has very limited functionality. The dongle has to be connected to your battery with the included leads in order to function (and draws about 5mA). It can also measure the temperature of a battery by sticking it to the exterior of a battery or using an optional temperature probe. An added bonus of this unit is that it measures the battery voltage and passes this information back to the Multiplus II. The Multiplus II then automatically modifies its charge voltage to compensate for any voltage dropped in the battery leads. It is very important that you connect the Smart Dongle battery leads right at the battery. I've seen videos where installers connect the leads to the output terminals of the Multiplus II. This completely defeats the compensation feature.

Digital Multi Control GX:

If you want to have a wall display showing you what the Multiplus II is doing, then this is your cheapest option. It duplicates the LEDs on the front panel of the Multiplus II and gives you control over the features most relevant for a TAB owner.

All of these interfaces connect to the Multiplus II using CAT5 (or CAT6) cables. The Multiplus II has 2 RJ45 jacks for the CAT5 cables, so you can only use two at a time. Note that in normal networking use, CAT5 cables only use 4 of the 8 wires, whereas the Multiplus II seems to use all 8. You can have a CAT5 cable that works fine in your home network, but causes strange behavior with Victron components. Good quality cables are essential! Victron sell ones that are guaranteed to work.

Hierarchy:

If you set the switch on the Multiplus II to "Off", then all the communication devices listed above are disabled. You cannot turn the Multiplus II back on remotely.

If you set the switch on the Multiplus II to "On", then the operation of the Multiplus II can be overridden by any of the communications devices. The degree of overriding depends on the device:

MK3-USB and Victron Connect: This give you the most control. You can set the maximum current draw from your shore power by clicking the icon outlined in red (in pictures above). You can set the operation to "on", "off", "charger only" or "inverter only" by clicking the icon outlined in black (above), and you can disable the charger completely by going into the settings menu (cog icon) and selecting the charger tab where there is an option to disable the charger completely (as shown). When the Multiplus II is turned "off" using Connect, it can be turned back on again, so this is different to turning the Multiplus II "off" at its switch. I call this a "soft off".
VE.Bus Smart Dongle (bluetooth) and Victron Connect: This gives you the least control, you can just set the maximum current draw from shore power and the operation mode using the icons described above. There is no way to disable the charger.
Digital Multi Control GX: This lets you set the operation to "on", "off" or "charger only" (no "inverter only" option). The "current limit" knob lets you set the maximum current the charger will draw from your shore power. You can turn the charger off by setting this current to zero.

If you connect the Digital Multi Control GX and either dongle, then the GX overrides settings made with Connect using either dongle, and disables Connect from making any further changes.

Operation:

Mostly, this is really simple: Set the switch on the Multiplus II to "on". Override this setting using any of the communications devices to "charger only" mode, which won't drain the batteries if you don't have shore power, and will recharge the batteries if you do. It will also automatically pass through 120V power when you connect to shore power. If you need 120V power when boondocking, then you'd set the Multiplus II to "on" or "inverter only" (again using one of the communications devices) for as long as you need it. Be sure to turn the inverter off when you no longer need 120V power. It will flatten your batteries even if you're not using any 120V appliances.

Somewhat more subtle, it should be noted that the Multiplus II does not pass through 120V when it is turned off, either at the unit itself or via any of the communications devices. If your Multiplus II is only powering some of your outlets, this might not be an issue, but if your Multiplus II feeds your entire trailer this can be a problem: Suppose you're plugged into shore power and want to use your microwave, Alde on electric heat, your A/C or any other 120V appliance, then the Multiplus II must be set to "on" or "charger only" (it really doesn't matter which as the inverter won't come on anyway) for the 120V to be passed through. But this in turn means the charger will be engaged to top up your batteries or provide power for your lights. Be aware: The charger hums. The volume of humming depends on how much current it is delivering, but it is always there. If you're a light sleeper, or just sensitive to background noise, you may find this distressing and want to be able to turn the charger off when you need some peace and quiet. There are four ways of doing this:

If you have the Digital Multi Control, set the toggle to "charger only" and then turn the knob that controls the current that the Multiplus II will draw from shore power to zero. This will turn the charger off. The "mains on" LED will then be the only one illuminated, and it may blink.
If you're using the MK3-USB, hook up your PC and turn the charger off using the Connect program. The operation of the Multiplus II will show as "passthru".
If you're using the Smart Dongle, you can limit the input current to the charger to 1 Amp. This will greatly reduce the hum, but not completely silence the unit.
Install an independent switch between the Auxiliary Input 1 terminals. Install the Charge Current Control assistant using VE Configure and the MK3-USB on a PC (no Apple products). With the Multiplus II in "charger only" or "on" mode, close the switch and the charger will turn off. I will fully document the steps to enable this feature elsewhere.

Finally, if you're not using the VE.Bus Smart Dongle, then you'll need to connect some lightweight wires from your battery terminals to the Vsense input on the Multiplus. This connection allows the Multiplus II to compensate for any voltage dropped along its power leads letting you charge your batteries at the highest possible rate.

Current Limit:

All of the communication devices give you the ability to limit the current that the Multiplus II will draw to power its charger. I didn't initially see the point of this feature, but I now see it could be really useful: I always want to charge my batteries as fast as possible, but when charging batteries at 120A, the Multiplus II draws about 15 Amps from the 120V supply. This might trip the breaker of a 30A outlet at a camp ground if you're running your Alde on its 2kW setting at the same time, or if you're using a smaller generator you could overload it. So, being able to limit the current draw is really important. Note that the current limit is just for the charger, not for other 120V devices.

Conclusion:

If you're thinking about installing either a Victron Multiplus or Multiplus II in your TAB, you will also need to spend money on communications devices. You will need a MK3-USB interface for doing the setup (to tell the Multiplus that you're using Lithium Batteries, for instance). You could get away with using just that for everything. However, if you want to be able to check on the operation of the Multiplus or turn the inverter on and off, then the MK3-USB is unwieldy as you have to hook it up to a PC (or Mac) each time. So you'll also need either the Digital Multi Control (if you want a simple wall control) or the VE.Bus Smart Dongle (if you want an app on your phone). If you go the Smart Dongle approach (or that's all you got from NuCamp), then option 4 (above) for turning the charger off may be of interest.

Caveats:

My installation of the Multiplus II has not been without problems:

The units are beasts. They weigh in at about 40 pounds. You need an installation location that lets you firmly secure the unit. I had to change my original installation location because it couldn't support the Multiplus sufficiently for bumping down forest service roads.
The Multiplus II is noisy, especially when charging or inverting at high currents (I don't know how it compares to the original Multiplus). Even when both inverter and charger are disabled, there is still a gentle hum. Depending on where you attach the Multiplus II to your trailer, the unit can cause your trailer to resonate quite offensively when charging batteries.
The Multiplus II inherently seems to have quite a high leakage current to ground. I have measured this on 2 units and it is in the 2 to 3mA range. Add this to the inherent ground leakage currents of the TAB itself when situated somewhere damp (I live in the PNW) and the combination routinely trips a GFCI breaker. Not a problem if connected to 30A shore power, as these are not GFCI protected. I have no information about the original Multiplus, so don't know if they leak too.
My experience with the Smart Dongle on the second Multiplus II unit I tested was worrying: If there is only a very small load on the Multiplus II and the Smart Dongle is connected, then (after a short delay) the output voltage becomes unstable and swings dramatically from about 13V to 16V. This became apparent with my LiTime lithium batteries that incorporate a novel BMS that stops the batteries being charged when the BMS decides they're charged enough. Then the load on the Multiplus II dropped to the quiescent current of the trailer which was not enough to stop these wild voltage swings. Consequently, I'm not using the Smart Dongle at all to prevent such instability problems, and the risk of frying a 12V component.
For trailer installations, it is annoying that the Multiplus doesn't pass the 120V AC through when turned off. Unit has to be on with charge current set to zero if you just want AC in the trailer without the noise of the charger charging the batteries. I ended up installing a secondary relay to automatically connect the rest of the trailer directly to shore power when the Multiplus II is turned off.

elbolillo · March 14

@rh5555 Very nice write up. I have the older Multiplus and have not noticed any problems with the Smart Dongle.

I agree that when the Multiplus is connected to shore power and is actively charging it does produce a noticeable hum but not something that is bothersome to me. However, it charges so fast that once charged it quiets down. Once the battery bank is fully charged I can barely hear a slight hum from the unit when connected to shore power. For me, the sound of the refrigerator cycling is much more noticeable. And while inverting, again the hum is gentle enough that I don't notice it much.

mjwaldner · March 14

@rh5555 Thank you very much for this info. I have been planning this same upgrade for a long time. I have read through so much documentation from Vitron now. It's nice to see that someone has done it. Do you have any pictures of your installation you can post?

rh5555 · March 15

Mine will be an unusual install, as I have the AIR8+ air conditioner to work around. By trimming back the sewer hose tube I was able to cram in 2 x 230Ah LiTime lithium batteries, the Multiplus II, new battery switch, BMV-712, breakers for 120V, trailer 12V and solar input, fuse (300A) for Multiplus and a changeover relay.

I chose to use 2 x 4AWG wiring between Multiplus II and the batteries rather than dealing with 2/0 AWG cables. The current rating is quite similar. This also allowed an A/B switch to select none, either or both batteries.

Image: https://us.v-cdn.net/5021717/uploads/editor/ft/ptsl28r6dk4q.jpg

Image: https://us.v-cdn.net/5021717/uploads/editor/s8/atlbzshefq7u.jpg

I get the feeling from the Victron fora that the Multiplus II is noisier than the original Multiplus, but for me the form factor forced the decision. If you can manage with either, then you should look carefully at the original Multiplus.

mjwaldner · March 15

Thanks for the info. I was seriously considering going with the Multiplus II before I saw your post.

Hammick · March 16

The VE Bus BT Smart Dongle on our '23 TAB 400 with the factory Lithium upgrade allows the Multiplus to be controlled via the Victron Connect app on an iPhone, Android, MAC or PC. We have the ability to select the current input, On, Off, Charger only or Inverter Only.

A few days ago I installed an MK3 USB adapter and realized some settings were not ideal on our Multiplus. Most notably temperature compensation was enabled which is not proper for lithium batteries.

I updated the firmware on the Multiplus and was pleasantly surprised to find a new feature under the advanced settings. It enables a "Sustain" feature which disables the Multiplus charger after the voltage reaches a user configurable setting. This allows the solar to finish the charging or can be useful for storage where you don't want your batteries at 100%. Once enabled the "Sustain" feature can be controlled via the smart dongle in the Victron Connect app. The re-bulk setting also continues to work.

So the way I have ours configured is the Multiplus charger is automatically disabled when the battery voltage reaches 13 volts. The solar charging continues uninterrupted. Every 20 days the charger will automatically charge the batteries to 100% then go back to disabled. I have the ability to initiate a 100% charge at any time using the Connect app.

Some screenshots attached of this new feature.

rh5555 · March 16

This is great information! Not sure I can take advantage of it as I cannot use the Smart Dongle.

Hammick · March 17

rh5555 said:

This is great information! Not sure I can take advantage of it as I cannot use the Smart Dongle.

The sustain feature is also available when accessing the Multiplus with the MK3.

rh5555 · March 17

Yes, but such a pain to pull out the PC to hook up...

When the Multiplus enters "Sustain" mode, does it fully turn off the charger? And make it near silent?

Hammick · March 18

rh5555 said:

Yes, but such a pain to pull out the PC to hook up...
When the Multiplus enters "Sustain" mode, does it fully turn off the charger? And make it near silent?

I have the USB C version of the MK3 and just use an old Android phone I had laying around to configure the Multiplus. Once you enable the "Sustain" mode you can toggle it using the VE Bluetooth Smart Adapter on iPhone, Android, MAC or PC. No need to plug in. You could use a USB A to USB C adapter if you have the older MK3.

Yes when "Sustain" is enabled the charger is completely off. I've been using this feature for a couple weeks and my 400ah of Battleborns have been between 70% and 85% SOC depending on how sunny the day was.

I snaked the USB C cable from the MK3 to the passenger side of the mattress.

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