16 cells 12v 800ah

Hello everyone,

Thank you for an amazing forum.

Im about to build a 800ah bank, consisting of 16 cells in a 12v system.
I would like it to fit inside one compartment that i have that's 43cm wide and 60 cm long

So far by watching Wills videos i have come up with this drawing of how i could connect and place the cells/banks, would this work for me?
Or would it be better to build two banks of 8 cells and use two BMS's?

You may want to consider that you may want to move this around and 16 cells bundled together can be unwieldy to say the least. 8 cells per pack is a bit more manageable at 4s2p, 4 cells per pack much more manageable (and fault tolerant too if something goes amiss with one cell somewhere). I'm not one to put all the eggs in one basket so to speak.

Of course much depends on the BMS you are going to use (some allow for series & parallel and others don't allow parallel). Keep in mind the Amperage the BMS will have to contend with at maximum load demand, too many underestimate that.

Would you recommend it like this instead ?

Two long format packs would be more manageable …. think about lifting it all up and moving it around. You can go with 2 "short packs" by putting 4x4 side by side, shorter but double width obviously. You have to see for yourself what fits your spot and what works better for you to manhandle them. In that layout having a (+) & (-) BUS is the simplest for connections.

A "doodle" I'm working on as part of my own documentation but it's enough to give an idea of the bus.... Note as I use Chargery BMS with external relays & shunt.

Thanks Steve,
I have not decided on BMS yet for the two packs, i have some Victron stuff on the boat, and would like the BMS to communicate with that on the CAN bus.
Do you have any suggestions for an BMS, that works with Victron Multiplus and MPPT chargers ?

You might want to look at TinyBMS which can do CanBus. They are more expensive than the cheapo's but it's a damn good product from what I hear. CanBus is not something I deal with as my SCC, Inverter (does CanBus & Modbus) & Chargery BMS do Modbus and I am programming software for managing all that.

Hi Rocco!

I'm also building a LiFePO4 battery that will function with a Victron setup (EasySolar). From my research it seems that the only batteries and BMS that can fully communicate with Victron equipment out of the box are listed on this webpage (it seems to only be batteries though). As far as I understand, CANbus is just a protocol that says how the devices should talk to each other, but it doesn't specify what they're talking about. Therefore, the fact that the TinyBMS features CANbus communication is not sufficient to ensure that it can communicate with Victron devices. For that, both companies would have to coordinate their interfaces. I actually emailed the manufacturer of TinyBMS to ask whether they support Victron devices over CANbus but they told me they didn't ("Our CAN UART converter is capable of minimalistic command transmission. Currently, we do now know how it will operate with your specific equipment.")

However, Victron provides another way to synchronize with any thrid-party BMS: see here. Basically the BMS has to output 2 signals to say whether charge/discharge are allowed and they come as inputs on your Victron inverter (better to isolate the signals with intermediate optocouplers though). The inverter will do what the BMS commands. That's great if you only have AC loads, and that nothing else draws on your battery. If you have also DC loads, then you can add a relay that will be closed only when the "discharge allowed" signal from your BMS is up.

You could potentially wire any BMS to you Victron this way, but you won't have all the details displayed in your Victron frontend. So if you also want data such as precise SOC and temperatures, you can always add a BMV-712 that will interface nicely with your devices. Depends also on what you already have.

EDIT: Ok now I see a problem coming if your really want to go with two BMS: you won't be able to have 2*2 charge/discharge signal inputs on your Multiplus.

Yes you are right about the two bms's.

I was also looking at the 123 smart bms it has gained some Fame on different groups.

Rocco said:

i have come up with this drawing of how i could connect and place the cells/banks, would this work for me?
Or would it be better to build two banks of 8 cells and use two BMS's?

Click to expand...

It looks good to me. I'm not a fan of seperate strings. KISS.

Rocco said:

Yes you are right about the two bms's.

I was also looking at the 123 smart bms it has gained some Fame on different groups.

Click to expand...

LINK?

ghostwriter66 said:

LINK?

Click to expand...

Here is the link https://123electric.eu/

SolarRat said:

It looks good to me. I'm not a fan of seperate strings. KISS.

Click to expand...

What bms would you use ?
I will use this on my boat I have a 3000w inverter and plan to do cooking on induction plates plus run a microwave etc etc. So the bms would need to be able to handle a high amp draw.
I also like to keep it in one large bank, i can always reconfigure to another setup if needed.
I'm not going to move the banks around they will be very stationary.

If you want to run thousands of W on a 12V system you will have very quick hundreds of amps going through... So I believe you should go directly for a BMS commanding relays. The 123 Smart BMS is made for that, like the Chargery and the TinyBMS. Price wise the Chargery is the cheapest, but might not have all the fancy settings of the other two. TinyBMS looks cool and has many options but that may not be the easiest to configure. I would say the 123 looks like the fanciest and best designed, and for you with a 4p4s setup it does not end up to be so much expensive (with a 16s setup the price starts to be high). So if I were you I would go for the 123 Smart BMS.

EDIT: Actually the 123 Smart BMS does not seem to have so many settings you can tweak (like balance voltage and so on), so it will fit your needs if you want something simple to configure, but if you want something more flexible go for Chargery or TinyBMS.

astronom said:

If you want to run thousands of W on a 12V system you will have very quick hundreds of amps going through... So I believe you should go directly for a BMS commanding relays. The 123 Smart BMS is made for that, like the Chargery and the TinyBMS. Price wise the Chargery is the cheapest, but might not have all the fancy settings of the other two. TinyBMS looks cool and has many options but that may not be the easiest to configure. I would say the 123 looks like the fanciest and best designed, and for you with a 4p4s setup it does not end up to be so much expensive (with a 16s setup the price starts to be high). So if I were you I would go for the 123 Smart BMS.

EDIT: Actually the 123 Smart BMS does not seem to have so many settings you can tweak (like balance voltage and so on), so it will fit your needs if you want something simple to configure, but if you want something more flexible go for Chargery or TinyBMS.

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Thanks for your recommendations astronom. Do you have any experience with the rec-bms, i have seen some boaters going for that particular BMS.

/Rocco

The REC BMS looks like serious stuff too although I didn't dig into the specs and manuals. Maybe you've seen they are compatible with Victron GX stuff via CAN, and it seems you're looking for that. I had in mind they are quite expensive and looked more targeted towards pro setups but I don't know. If you dig into those BMS that would be interesting for many here when you report what you find.

In the end the best person to chose your BMS will be you anyway, none of them have exactly the same functionalities and you might prioritize them differently than someone else. All what we can do here is give some feedback about some BMS's that have been tested by people (few actually, appart from Daly and Chargery and other Bluetooth BMS's on this forum) and how they came to chose it. Going around the forum you'll see the perfect BMS doesn't really exist ^^

Something we didn't talk about here was the precharge of the capacitors of your inverter, that would be good to have in your case, so try to use a BMS that does that (more info on other threads). I know that Chargery (with dedicated extension) and TinyBMS can do it, it doesn't seem the 123 can. And I don't know for the REC but I bet they have a solution for that.

First thank you for the feedback its really appreciated, getting into this DIY can be quite frightening so always good to have some knowledge to lean up against .
I saw that on the rec bms page there are accessories and there is a precharge unit there listed plus also a contactor that might be a good idea to install also.

Thank goodness I have a Samlex Inverter, it's a Soft Start System that prevents a large inrush load on startup, not many inverters have that feature which seems like an obvious one to have. Some folks think that the Samlex' are expensive but when you get into the nitty gritty details, you find that you get a lot more for the price than imagined off the top. Unfortunately, people trying to save a buck often miss the details only to discover later they have to make it up somehow somewhere else at an additional cost and that adds up too darn fast.

Rocco said:

First thank you for the feedback its really appreciated, getting into this DIY can be quite frightening so always good to have some knowledge to lean up against .
I saw that on the rec bms page there are accessories and there is a precharge unit there listed plus also a contactor that might be a good idea to install also.

Click to expand...

Always nice if this can help you and others as well In your case I would say that the simplest and most effective for you would be the REC BMS, because it seems you will just have to plug in the CAN connector and wire everything to the battery and you will be all set. The Victron equipment will communicate with the battery and limit the current it's drawing or charging on its own. That would end up being as if you had an assembled plug and play lithium battery, like a Pylontech for instance (but they only exist in 48V as far as I know...). There should be no need for relays, precharge circuits or other stuff, the battery will directly command the Victron devices and tell them what to do.

All this holds if and only if you only have your Victron inverter (the Multiplus) and your Victron MPPT connected to the battery. If you have other charging sources (shore, alternator...) or loads (12V appliances...) that don't go through the Multiplus, you will have to add relays to be able to cut them out of the circuit. That should not be to hard to do, either with relays or Battery Protect modules from Victron.

Small downside for me of the REC BMS is its price, especially when you want to have accessories (doesn't seem required in your case though). But definitely it seems to be a very good value for money ratio in your case considering you'll just have to plug it to the Victron and follow setting instructions in the manual to have a great system.

Thanks Astronom.

I will have shorepower at times, but that will go into the Multiplus, i plan also to install the new DC/DC charger from Victron on my alternator. And the 8kw onan cummins generator will go into the Multiplus also because of the 220v it generates.
But the whole 12V system in the boat will be on the other side of the battery, so yes the Victron Battery protect should be in place there.
Im not 100% sure how well the Rec BMS connects with Victron on the CAN bus, but i can see there are some documentation for it on their site.
I friend shared the setup that he is doing on his boat, i plan to follow it where it makes sense. Please if you have some comments on it i would appreciate the feedback thank you.

Forgot to mention that i will be using the new Cerbo GX from Victron and the Smart solar MPPT controllers 100/30 for my 3x320w Solar panels
/Rocco

Ok I see that your friend has designed some serious setup here. He uses a relay as the way the BMS cuts current through the battery. However there are no separate circuits for charging and discharging (hard to do because the Multiplus does both on one bus. So if the BMS wants to forbid discharge it will cut all connections to the battery, and your friend will have to manually do something to charge it up again I guess. So I believe he designed the system with the idea in mind that the BMS is only there as a last resort to protect the battery if all the rest goes wrong, and I feel it's a sound idea. All the rest of the setup must already have the right under or over voltage limits for the battery, and Victron equipment seems to do that very well. But that maybe a bit suboptimal in some cases: if the BMS wants to shut off charge because of the low temperature of the cells, it will also have to forbid the discharge which is a pity because the battery could handle it. Then maybe he doesn't expect many low temp cut off, so that may be fine for him.

For how the REC BMS communicates with Victron you can see also this little thread here: https://community.victronenergy.com/questions/9952/rec-bms-ccgx-multi-plus123000120-settings.html

In this case the BMS will directly give all Victron equipment the limits they have to comply with in regard to the battery: essentially charging intensity max and discharging intensity max. I know that for instance on the Pylontech batteries I was talking about above, the charge amperage limit varies with temperature and goes to zero at around 5°C, but is already not so much at 10°C. It's an example, and the Multiplus and all MPPT that are connected on the same GX bus will know about what the battery wants and comply. However if something goes wrong and the Multiplus or another equipment starts to draw power even though the battery is empty, you won't have the same security as your friend with the BMS being able to open the relay and hard shut all current. Nevertheless, it seems to me that Victron products are qualitative enough so that you can trust them.

I can tell you what I intend to do for my setup (rather similar): I will wire the charge signal from my BMS to the Victron equipment and that will tell the MPPT to stop charging. I will count on the settings of my Multiplus to have it not overcharge the battery in the rare instances the generator should run. For the loads I prefer to play it safer (over discharge is much more damaging to the cells than over charge). I will have a bit of DC but mainly the Multiplus, and I will put a relay. Actually a latching relay controlled by the REC driver circuit to have minimal wasted power there. And I will have a precharge circuit thanks to the delay board of the Chargery BMS.

If you can trust in the communication between the REC BMS and Victron I think you are golden because that would be a very well synchronized system with no problems of precharge circuits or other pains, and it should behave very optimally (like keeping discharge possible in low temp) once setup properly.

Maybe you can ask your friend why he doesn't want to take advantage of the CAN communication between REC and Victron? I would be interested to know what he thinks.