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douglane asked

Smart BMS 12/200 with Multiplus Compact 12/1600/70

I have a setup with a Multiplus 12/1600/70 and a Smart Solar 100/30 MPPT which I am planning to convert to lithium using Smart Lithium batteries and a Smart BMS 12/200. My question is about the System+ port on the Smart BMS. The documentation is unclear about how use the System port, and where charge sources should be connected. The manual shows the following two setups, which would seem to contradict each other. Which is correct? If I connect the charge sources to the System+ port, do I need to connect the load disconnect to the charge sources, or will the System+ port handle the load disconnect?

In the appendix, the manual says:

"If These MultiPlus models are not connected directly to the System+ port, they can also be controlled from the Load Disconnect and Charge Disconnect outputs by using the Smart BMS CL 12/100 to MultiPlus cable"

It is unclear in the manual which setup one should choose or what the benefits and drawbacks of each are. It is also unclear whether I can connect other charge sources such as the MPPT to the System+ port with no load disconnect. This is important as my MPPT does not have a remote disconnect port, and the VE.Direct port is already connected to a Cerbo GX.

Manual: https://www.victronenergy.com/media/pg/Smart_BMS_12-200/en/system-examples---smart-bms.html

Example 1 - Multiplus connected to System+ port, no remote disconnect:

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Example 2 - Multiplus connected to batteries w/remote load disconnect

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MPPT ControllersMultiPlus Quattro Inverter ChargerBMS
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3 Answers
bathnm avatar image
bathnm answered ·

@douglane The link gives me different scenarios!

1643038703686.png


That said, from my understanding both scenarios in your post are correct. They are just doing different things, because of the inverter verses inverter/charger.

When designing you need to remember that nearly all FET based systems, can only allow current to flow in one direction, in this case from the battery to the System + port. Therefore connecting a charge source to System + will create no end of problems.

In the first example in your post, their is a simple invert, as it is just a load source it can be connected to the system + port. In a load disconnect situation the system + port is disconnected and the inverter would just stop working as it has no supply.

In the second example in your post, it is an inverter/charger. Due to it's charging nature it CAN NOT be connected to the System +, as that is just for loads. It is therefore connected direct to the battery, this way it can be a load and a charger. Therefore how does it get signalled to stop charge or inverting based on the BMS. This is teh extra signal wires depicted. One will signal the Inverter/Charger that it should not provide any charge, the other is to signal a load disconnect. You additionally need to install assistances on the Multiplus, to watch for these signals and control the inverter/charger accordingly.

Regarding MPPT, your figure 1 is very clear. The MPPT is connected direct to the battery (as it is a charge source) and the charge disconnect from the BMS wired to the MPPT. This will signal it to shut down on a charge disconnect.

I can not remember, but I believe (so please do check documentation) that the charge disconnect is feed from the Cerbo to the MPPT over VE.Direct if and only if there is an inverter with the two wire BMS assistant installed. If this is not the case then what you can do is take a Smart Battery Protect; connect the MPPT to the supply side and the battery to the load side. Then connect the SBP load disconnect to the BMS charge disconnect. This then frees up teh VE.Direct port to wire to the Cerbo and the BMS will signal the SBP to stop passing current on a charge disconnect. When the SBP disconnects the MPPT will detect this and stop charging. This would be my preferred choice over relying on the Cerbo, as there are two many things that could cause a charge disconnect when not required, such as the inverter being switched off.

Which product and wiring topology to use, comes down to the products selected and what you are trying to achieve.

Hope that all makes sense and helps.


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douglane avatar image douglane commented ·
@Bathnm - Thank you so much! That is indeed a massive help. I completely missed the nuance of inverter vs. inverter/charger (which is what I have). I will double-check, but I believe form the documentation, the 12/1600/70 Compact does have the two wire BMS assist, so hopefully that will work, but I note the plan B there of the battery protect, which is good news.


As for the charge disconnect feeding to the MPPT via VE.Direct in the first scenario, I can't find that anywhere in any of the documentation, but I'll do some more Googling. It sounds like a small SBP might be a better option anyway.

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douglane avatar image
douglane answered ·

@Bathnm On review, I'm not sure that your assessment is correct, at least based on my read of the manual for the Smart BMS 12/200. In all the examples the documentation refers to a Multiplus, which is by definition an inverter/charger. Also, in section 6, it specifically states in the specifications that the System+ max discharge current AND charge current is 200 Amps. That would seem to indicate you can charge via the System + port as long as your total charge current is under 200 Amps. Here is the excerpt:

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bathnm avatar image bathnm commented ·
@douglane Sorry I do not have an answer. Looking at the data sheet, it shows a MultiPlus attached to the battery and not System +, maybe that is not due to the 120A charge capability but the potential load being greater than 200A.


The Appendix A off the manual has more information. Particularly point 6. It seems depending on the type of the MultiPlus, the connection design does change.

I would make contact with a local dealer and seek their support.

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douglane avatar image douglane bathnm commented ·
@Bathnm Thanks, I will definitely speak to them about it. I think you may be on to something with the charge/load capability. With the Mutliplus I have the peak output is 3000 watts, which is 234 amps at 12.8 volts. The peak discharge current of the Smart BMS is 400 amps, so that should be no problem. The continuous rating of the Multiplus is 1600, which is 125 amps at 12.8 volts, also well within spec. Thanks for helping me figure it out!
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douglane avatar image
douglane answered ·

I thought I'd add some additional detail about my installation experience as there is very little information about the Smart BMS 12/200 out there, and the manual does not explain the reasons behind the different options for connecting loads and charging sources.

In the end, I connected my Multiplus Compact 12/1600/70, my Smart Solar 100/30 MPPT, and all of my DC loads directly to the System+ port. The System+ port supports up to 200A charge/discharge current (peak 400A), and if your system fits these requirements, this is the simplest setup. The System+ port independently switches off charge sources and loads when the voltage or temp of the batteries is too low or too high. This means that you do not need to buy a Battery Protect to control your DC loads or charge sources, and you do not need to connect control cables to your MPPT or Multiplus. This significantly reduces cost and complexity, and is a big selling point of the Smart BMS 12/200 over the Smart BMS CL 12/100 which does not have a System+ port.

If your inverter, charger, or loads exceed 200A continuous, then you also have the flexibility of controlling some or all of your loads or charging sources (except for the alternator) directly to the battery rather than the Smart BMS 12/200, and using remote cables to control them. This gives you a ton of flexibility, but it could certainly be better explained in the manual!

I have included a diagram of my install in case it helps anyone, or someone wants to pick it apart :-)


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netweb avatar image netweb commented ·
Thanks for this update, helped clarify a few things and convince me to purchase the Smart BMS 12/200


Details on this BMS is few and far between in these forums, once I've got a few more things worked out in my setup I'll share my wiring diagram


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kljung avatar image kljung commented ·

Great information.


I am setting up a similar configuration but in your system there is a risk that the bow thruster can discharge your starter battery, I will probably use my current Argofet battery insulator to prevent this.

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douglane avatar image douglane kljung commented ·
Yep, I'm aware of that possibility, but the relatively long cable run and smaller diameter of the cable means that resistance will limit the discharge in terms of total AMPs. I actually installed a battery isolator between them when I bought the boat, but I couldn't get it to work right. I finally decided that, if it had been wired that way for 15 years, it's probably fine.
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svf5 avatar image svf5 commented ·

Dear douglane, thanks for this post. I plan to make a similiar install however i would connect the solar to the lead side then connect the lead bank to the systems port. Is there a reason you connected the solar directly to the systems port? Are your lead batteries charged via the alternator only ?

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douglane avatar image douglane svf5 commented ·
Yes, my lead batteries are only charged by the alternator. I am not sure if what you describe would work or not to be honest.
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nate-reid avatar image nate-reid commented ·
@douglane I am designing a similar system, was wondering what the purpose of the load dump battery is in your design?


Also, wondering if you thought of running the bow thruster off the lithium battery?

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douglane avatar image douglane nate-reid commented ·
The purpose of the load dump battery is to absorb the current spike that would be generated if the BMS disconnected the alternator while it was charging. Without a battery to absorb that spike in voltage, it would blow out the diodes in the alternator causing it to fail. I think this might be avoided with a smart regulator, but I had the lead acid battery so it was the simplest for me.


In order to run the windless off of the lithium, I'd need a very expensive cable, as my boat is 12-volt and it would need to run half the length of the boat. Also, there may be an issue with the current draw from a bow thruster. I know it's high, but I can't remember how high. I know that the current draw required to start an engine is definitely too high for lithium batteries. My plan is to disconnect the load dump battery from the BMS and use that to jump start the engine if I ever need to.

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