Parallel BMS's

[s/v Jedi]

DVCC - Distributed Voltage and Current Control.

This doesn’t mean it must control devices. It can mean a control system for reliably distributing accurate voltage and current information to other devices.

Yes you can do bluetooth smart networking but not all devices do this (Multiplus) while DVCC is supported by all. You can use it as a replacement for voltage sensing wires running to solar controllers, chargers etc.

There is a separate setting to give a BMS control of things and imo this should be off for self reliant long distance blue water cruisers.

[CaptainRivet]

Originally Posted by s/v Jedi

DVCC - Distributed Voltage and Current Control.

This doesn’t mean it must control devices. It can mean a control system for reliably distributing accurate voltage and current information to other devices.

Yes you can do bluetooth smart networking but not all devices do this (Multiplus) while DVCC is supported by all. You can use it as a replacement for voltage sensing wires running to solar controllers, chargers etc.

There is a separate setting to give a BMS control of things and imo this should be off for self reliant long distance blue water cruisers.

That's again the theory victron writes in their manual. In reality that DVCC works flawlessly (and nothing else you want) is if the cerbo/Venus OS given full control over BMS and a lot of other dependencies are met, many of them are scattered somewhere over forums all over the place where you by random find them like eg you cannot run BT connect and DVCC in parallel.
The root cause is that Venus OS got so huge and there are meanwhile so many also undocumented dependencies and so complex in setup (not just flipping that DVCC switch as manual states) that it only works flawlessly if you just handover all to cerbo.

Bt connect works also via BT dongle with Multi, I have it this way.

Andy from offgrid garage also discovered that and switch off long time ago DVCC and running BT connect to sync charge.
He also stated in one of his last video after a shutdown of the whole system by BMS that he tends more and more to cut the communication to venus/cerbo and just use it as monitoring due to all incidents that happened are caused by imporper communication.

[Dockhead]

Thanks guys, for being so patient with my ignorance. And it seems to be simpler than I thought. Let me add here that in my particular case, I will have so much battery capacity (3x what I used to have, even 5x if you discount the last 15% of the lead batteries which you only get from shore power) that there is no reason in the world for me to push the last 5% or whatever of capacity of the lithium.  So I will be perfectly happy programming this conservatively, shutting down charging early with a lot of margin to the kind of conditions which require emergency measures of whatever type. So now I understand that Nick has both alternator regulator and Multiplus managing themselves without any network functions.  So Cerbo in his system has DVCC off (right?), just like Cpt Rivet, acting as a battery monitor/system monitor. I see both of you are talking about tail current in the Multiplus charging algorithm, but I don't see a setting for that here:

[s/v Jedi]

Originally Posted by Dockhead

Thanks guys, for being so patient with my ignorance. And it seems to be simpler than I thought. Let me add here that in my particular case, I will have so much battery capacity (3x what I used to have, even 5x if you discount the last 15% of the lead batteries which you only get from shore power) that there is no reason in the world for me to push the last 5% or whatever of capacity of the lithium.  So I will be perfectly happy programming this conservatively, shutting down charging early with a lot of margin to the kind of conditions which require emergency measures of whatever type. So now I understand that Nick has both alternator regulator and Multiplus managing themselves without any network functions.  So Cerbo in his system has DVCC off (right?), just like Cpt Rivet, acting as a battery monitor/system monitor. I see both of you are talking about tail current in the Multiplus charging algorithm, but I don't see a setting for that here:

Attachment 295668

I have DVCC on. It uses the Smartshunt as source and distributes that info to all Multiplus and MPPT units. This works for everybody except Rivet

[CaptainRivet]

Originally Posted by s/v Jedi

I have DVCC on. It uses the Smartshunt as source and distributes that info to all Multiplus and MPPT units. This works for everybody except Rivet

DVCC is working now after a magical manual update from one of my 3 MPPTs, nothing else changed and where MVader said update has nothing changed regarding DVCC. But I don't use it as i don't trust it. And that's by the way the MPPT that failed going open voltage and current, random or coincidence????
I know many where DVCC doesn't incl. Andy from Offgrid garage. he had several issues with DVCC and doing it via BT connect too as simple and effective without side effects like DVCC. And BT to multiplus works too with the BT dongle for it and it's very comfy via BT connect to quickly change something like current for shorepower assist or switching to inverter only and cheaper then the remote.

[Dockhead]

Originally Posted by s/v Jedi

I have DVCC on. It uses the Smartshunt as source and distributes that info to all Multiplus and MPPT units. This works for everybody except Rivet

Originally Posted by CaptainRivet

DVCC is working now after a magical manual update from one of my 3 MPPTs, nothing else changed and where MVader said update has nothing changed regarding DVCC. But I don't use it as i don't trust it. And that's by the way the MPPT that failed going open voltage and current, random or coincidence????
I know many where DVCC doesn't incl. Andy from Offgrid garage. he had several issues with DVCC and doing it via BT connect too as simple and effective without side effects like DVCC. And BT to multiplus works too with the BT dongle for it and it's very comfy via BT connect to quickly change something like current for shorepower assist or switching to inverter only and cheaper then the remote.

Cool.


Does the Multiplus use current in its charging algorithm? I can't find anything about that in the manual.

[Dockhead]

And a question for Nick:


Why do you use BVM's instead of the BMS's, to trigger HVC and LVC? Or if you don't, then what do you need the BVM's for?

[s/v Jedi]

Originally Posted by Dockhead

Cool.


Does the Multiplus use current in its charging algorithm? I can't find anything about that in the manual.

Yes, it is used for tail current, to decide when to finish absorption phase.

Originally Posted by Dockhead

And a question for Nick:


Why do you use BVM's instead of the BMS's, to trigger HVC and LVC? Or if you don't, then what do you need the BVM's for?

Only the BMS can do HVC, LVC but also act on temperature, over current etc.

The BMV per battery: these can precisely and independently of the BMS show all important data like voltage, current, SOC and often even balance. This is presented in a standardized format regardless of brand/type of battery or BMS incl. on the Victron portal. Also, the BMV has the programmable relay.

The most cost effective batteries today provide o access to the BMS, which simply does its job inside the battery and that’s it. Just like an old fashioned LA and you can use these because you have the BMV.

[CaptainRivet]

Originally Posted by s/v Jedi

Yes, it is used for tail current, to decide when to finish absorption phase.



Only the BMS can do HVC, LVC but also act on temperature, over current etc.

The BMV per battery: these can precisely and independently of the BMS show all important data like voltage, current, SOC and often even balance. This is presented in a standardized format regardless of brand/type of battery or BMS incl. on the Victron portal. Also, the BMV has the programmable relay.

The most cost effective batteries today provide o access to the BMS, which simply does its job inside the battery and that’s it. Just like an old fashioned LA and you can use these because you have the BMV.

With the JK you don't need multiple BMV as JK report all data into cerbo and you don't have to deal with slightly different data from BMV and JK because they will never 100% align and which one is accurate now?
The mosfet BMS care about each battery and also do charge/load cutoff in case one battery has a problem. In charge you will have that one battery is more full then the other in the knee so one cuts charge while the other will take a tiny bit more charge to balance. In load this will not happen, also because you stay of the edges. Just watch Andy Offgrid video about his 3 battery bank and you see how that works in reality.
I would use one BMV for the whole bank als independent last resort cut off with its relay output. This also gives you combined SOC of both batteries and will be also show up from JK master as aggregated data. Cost less, in reality emergency cutoff will always be both batteries and you still have all data in cerbo.
I would use an 150A NH fuse per battery that's also the disconnect switch and one master relay as last resort cutoff. If something is wrong with the battery the NH will cut and emergency you cut both anyhow so 1 relay doing that is enough together with BMS. Smallest amount of contact points=failure points and voltage drop plus as side effect cheapest solution. Doesn't work with class T fuses as they are screwed and cannot be pulled easily, then best is to use 2 relays each also act as disconnect switch and both realys are steered by one BMV.

[s/v Jedi]

Originally Posted by CaptainRivet

With the JK you don't need multiple BMV as JK report all data into cerbo and you don't have to deal with slightly different data from BMV and JK because they will never 100% align and which one is accurate now?
The mosfet BMS care about each battery and also do charge/load cutoff in case one battery has a problem. In charge you will have that one battery is more full then the other in the knee so one cuts charge while the other will take a tiny bit more charge to balance. In load this will not happen, also because you stay of the edges. Just watch Andy Offgrid video about his 3 battery bank and you see how that works in reality.
I would use one BMV for the whole bank als independent last resort cut off with its relay output. This also gives you combined SOC of both batteries and will be also show up from JK master as aggregated data. Cost less, in reality emergency cutoff will always be both batteries and you still have all data in cerbo.
I would use an 150A NH fuse per battery that's also the disconnect switch and one master relay as last resort cutoff. If something is wrong with the battery the NH will cut and emergency you cut both anyhow so 1 relay doing that is enough together with BMS. Smallest amount of contact points=failure points and voltage drop plus as side effect cheapest solution. Doesn't work with class T fuses as they are screwed and cannot be pulled easily, then best is to use 2 relays each also act as disconnect switch and both realys are steered by one BMV.

The BMS SOC data isn’t accurate enough. It is when it is empty or full, but not in the working range which is so important for a house battery.

You can’t correct it either. With a BMV you can tune it in to high precision because you can change every parameter.

The only failures I have had is with MOSFET’s in BMS’s. Maybe there was a power surge which caused that failure but nothing else failed so even though I got free replacements under warranty, this isn’t what you want for reliability and self reliance so I keep my recommendation for the BlueSea RBS with momentary remote switch control from the boat’s main panel and a BMS that can control it as well instead of MOSFET’s.

This makes the setup: battery - fuse in pos - shunt in neg - RBS in pos and then to the busbars.

[Dockhead]

Originally Posted by s/v Jedi

The BMS SOC data isn’t accurate enough. It is when it is empty or full, but not in the working range which is so important for a house battery.

You can’t correct it either. With a BMV you can tune it in to high precision because you can change every parameter.

The only failures I have had is with MOSFET’s in BMS’s. Maybe there was a power surge which caused that failure but nothing else failed so even though I got free replacements under warranty, this isn’t what you want for reliability and self reliance so I keep my recommendation for the BlueSea RBS with momentary remote switch control from the boat’s main panel and a BMS that can control it as well instead of MOSFET’s.

This makes the setup: battery - fuse in pos - shunt in neg - RBS in pos and then to the busbars.

I already ordered two Blue Seas bistable 500A contactors based on your recommendations. I will install one each on the positive lead from each battery before the bus bar

So -- One each 250A NH fused disconnect (Size 1, or Size 2 if I decide to upgrade the Multiplus) is first in line in the positive lead. Then the BMS, then the contactor, then the bus bar. Contactors are controlled by the BMS's.

Sounds like I don't need the BVM's.

Sounds like I don't need a CANBUS alternator regulator. So maybe the good old Balmar.

So we let the Cerbo handle the SOC calculation, and the alternator shutdown? Switch DVCC ON so that it feeds Multiplus with current and voltage data via CANBUS?

And have the Cerbo cut the alternator charging based on reaching 100% SOC, right? Or other parameters too? Will the Cerbo take a signal over CANBUS from the BMS's that a cell is too high, temp is too high, or something else which requires cutting charge sources? Can the Multiplus also work with such information?

[CaptainRivet]

Originally Posted by Dockhead

I already ordered two Blue Seas bistable 500A contactors based on your recommendations. I will install one each on the positive lead from each battery before the bus bar

So -- One each 250A NH fused disconnect (Size 1, or Size 2 if I decide to upgrade the Multiplus) is first in line in the positive lead. Then the BMS, then the contactor, then the bus bar. Contactors are controlled by the BMS's.

Sounds like I don't need the BVM's.

Sounds like I don't need a CANBUS alternator regulator. So maybe the good old Balmar.

So we let the Cerbo handle the SOC calculation, and the alternator shutdown? Switch DVCC ON so that it feeds Multiplus with current and voltage data via CANBUS?

And have the Cerbo cut the alternator charging based on reaching 100% SOC, right? Or other parameters too? Will the Cerbo take a signal over CANBUS from the BMS's that a cell is too high, temp is too high, or something else which requires cutting charge sources? Can the Multiplus also work with such information?

If you take the Jk 200A inverter BMS the NH1 or 2 fuse must be 150A, you need to derate parallel BMS. The fuse protects BMS from overload/damage plus the install if it gets an internal problem and has nothing to do with the multi. 2x150=300A is good for running the 5kw multi.
The multi goes with its own cable/s to the main busbar and the fuse need to be rated for the cable then.
The 300A relays would have been enough, cheaper and need less power. Who is steering both relay??
Jk is a mosfet and no contactor BMS??
You need at least one BMV 702 or 712 to steer both relay as last resort disconnect in case BMS fails.
Alternator cut at 13.6V or 27.2V with cerbo relay steering but for that you need to use large version and program with MQTT. Or the balmar soft/parameter for the regulator has a cut off, long time ago since I installed one...don't remember.

Think you better make now a curcuit diagram and publish it here before buying more stuff as you seem to miss some stuff even we explained it but in 5 different threads. It's time you put all that into one.

[CaptainRivet]

Jedi' s way is the 1000% perfection EE way that very expensive, creates dozen additional failure points and either based on a contactor BMS or totally dumb LI-time drop ins that has no way of communicating and every battery is on its own
Jedi has no glue about JK inverter BMS which is basically an expensive Epoch drop in with full communication. He is basically securing a 160Euro BMS with full communication and master salve mode with a BMV+blue sea relay which is 450Euro plus delelivering that data into cerbo (which it already has from JK) and that twice as per each battery. For a bank that's driven very hard and contains expensive cells that's OK but for Dockheads setup and plan to use of the bank total overkill in my eyes.
The way I showed you is optimised as less as possible failure points, much cheaper and using JK BMS as it has master/slave and cares about parallel BMS, with 150A fuse it makes sure the fuse blows before mosfet gets damaged so a disconnect for both with one relay steered by a BMV712 is 200% safe and much more securitythat 80% of installation out there have. This BMV you can tune if you want as perfect as possible soc and that's enough to have it for the whole bank with parallel batteries. All cutoff you do based on voltage, best on cell voltage as SOC can and will fade over time while cell voltage is 100% precise.
But Jedis way with expensive JK inverter BMS that you basically ignore what it does makes 0 sense. Then get the dumb JK 300A BMS and use Jedis way but make sure you do all 100% right as you have much more you can screw up.
You need to make a decision, jerry picking and try use both don't work.

[Dockhead]

Originally Posted by CaptainRivet

If you take the Jk 200A inverter BMS the NH1 or 2 fuse must be 150A, you need to derate parallel BMS. The fuse protects BMS from overload/damage plus the install if it gets an internal problem and has nothing to do with the multi. 2x150=300A is good for running the 5kw multi.
The multi goes with its own cable/s to the main busbar and the fuse need to be rated for the cable then.
The 300A relays would have been enough, cheaper and need less power. Who is steering both relay??
Jk is a mosfet and no contactor BMS??

So the JK will do the HVC/LVC via the Mosfet? We don't use the BMS's dry contact relay plus contactors for that? The JK manual is completely devoid of any information on this point.

Thanks for catching my mistake with the fuses. Brain fart on my part.


The contactors are bistable so consume no power except when changing state. They are not that expensive so I thought the biggest and most robust contacts would be best.

Originally Posted by CaptainRivet

You need at least one BMV 702 or 712 to steer both relay as last resort disconnect in case BMS fails.

OK, I'm starting to understand. So you wouldn't steer the contactors with the BMS, you'd use a BMV. But why not the Cerbo? Does the BMV do something the Cerbo won't?

Originally Posted by CaptainRivet

Alternator cut at 13.6V or 27.2V with cerbo relay steering but for that you need to use large version and program with MQTT. Or the balmar soft/parameter for the regulator has a cut off, long time ago since I installed one...don't remember.

Large version of what? Sorry, you lost me there.

Originally Posted by CaptainRivet

Think you better make now a curcuit diagram and publish it here before buying more stuff as you seem to miss some stuff even we explained it but in 5 different threads. It's time you put all that into one.

OK, good plan. I'll do that.

I'm not an engineer; I'm just a lawyer. So it takes me a while to absorb and understand this stuff. Sorry for being so dense.

[Dockhead]

Another issue which troubles me about this install is charging capacity.

I have a 100 amp hot rated heavy duty large case school bus alternator.

And a 6.5kW heavy duty low speed generator.

My Multiplus will only put out 70 amps.

The house bank will be 628AH. About 15kWH.

So it will be a hella lengthy session to charge up that bank.

Putting it into perspective I realize (breaking old lead-acid mental habits) that I am liberated from trying to get the bank full; now I will only care about putting in as much power as I need.

But still. Maybe I should upgrade the Multiplus to the 5000VA one, which charges at 120A? Or add a Skylla charger? The 120A charger would be nice -- that needs a bit over 3kW, so puts an optimal load on the generator.

Or maybe I shouldn't worry about it -- I will be harvesting power whenever I run the main engine, so maybe I won't even notice. I rarely stay at anchor more than a couple days before moving, and usually run the main engine for some time, if not for a whole passage, every time I move.

I'd be interested to from people with experience with this, especially those without solar.