New to lithium

[Bluewatersailor]

Hi I plain to build a 12v 400ah lithium bank one concern I have is that at times will be drawing a heavy load over 210a for short times ,
Am I correct in thinking the BMS will shut the batteries if it unable to deal with sure a load ? And if so what is the way around this please .

 

[snoobler]

If you exceed the BMS current rating, it will disconnect the battery.

The solution is to get a BMS capable of handling higher currents. Daly makes models with current limits in excess of your needs.

 

[Deleted member 9967]

Some BMS also have the ability to set them ahead of time as to the amount of amperage at which it will say no to and click a relay and turn everything off.
But yes, you should start with a BMS rated for about one third more than what you want to expend. So a 300 amp BMS would work.

 

[Canuck_123]

Keep in mind there are two different types of BMS you need to consider (some of my terms may be incorrect but the idea is right!)
FET based BMS: All current flows through the BMS and the BMS itself interrupts the flow when it senses a low or high cell voltage (or low temp if capable of measuring). With this type of BMS you have to make sure it is rated for higher than your anticipated load as the previous posters said. The really cheap versions don't allow you to control many parameters, but most do today if you add bluetooth or a serial interface. Examples: Overkill Solar, Daly. Battleborn are a drop-in example of a battery assembled using this method.

For the second type, the current does not flow through the BMS, rather the BMS is used to control a separate relay through which the current flows (usually 2 relays, one for charging, one for loads). This allows you to buy a quality relay from the likes of Tyco or Blue Seas for whatever amp rating you need. You can source commercial, even military spec. This type of BMS tends to be more sophisticated with the ability to control many parameters via a bluetooth/PC/LCD panel, but also has a steeper learning curve.
Examples: REC BMS (popular with the marine crowd because they will config to interface natively with Victron GX devices), Electrodacus SBMS0 (inexpensive and can be confusing initially but really cool open source board and a very knowledgeable engineer backing it)

Hope this helps,
Don

 

[Bluewatersailor]

Could I use say a 100A BMS running that to my shunt and V+ busbar
and run the inverter straight off the lithium batteries as that will be the only thing useing a heavy load ?
It would mean monitoring the voltage while the load was being use but as I only be useing the big load for 20 mins at a time and only when the batteries are almost full , or would the BMS notice the load?

 

[Canuck_123]

I suppose, IF your BMS has a good display of the individual cell voltages and you were very diligent about watching it then yes, you are just replacing the automated on/off relay with yourself. But keep in mind that some inverters will have a small draw when not in use which you won't be protected against so if you do this, have a way to totally disconnect it from the battery.
I'm waffling between the two options and would use Overkill for inline or an SBMS0 if I want the power switched by external relays. If you absolutely want to go with an inline BMS, you may want to consider doubling the number of cells and running a 4s2p (two 12V packs in parallel) configuration with 2 BMS's. Ex, 2 x Overkill 120A = 240A continuous draw. This also adds redundancy - if one battery fails you may not be able to run your inverter, but you could run your DC loads off the other (auto-pilot, nav lights, etc.). That's why I keep coming back to this config as a possibility.

 

[Bluewatersailor]

I will only be useing the inverter to make water so it won't be left on all the time in which case there won't be a constant standby load .
I was plainning to use the smart 123 which has a Bluetooth so I could monitor the batteries while useing the big load.
Here a link to the BMS maybe someone someone could find another reason why my plan wouldn't work or would work with this type of BMS

123SmartBMS G3 4S, 1x I-sensor 2020

123SmartBMS gen3 is an easy to use yet advanced, modular BMS to keep your lithium batteries in perfect condition, increasing the lifespan of the battery pack.

123electric.de

 

[Canuck_123]

Lol. The 123Smart is a relay-driving BMS, not one that is inline with the current (ie, 123 is same as the SBMS0). You would use it to open or close a relay like this one that they sell: https://123electric.de/gb/123smartrelay/5-123smart-relay.html.
So yes, you could use the 123Smart to disconnect your DC loads via the relay I linked, and use the Bluetooth and app to monitor inverter loads, but you are so close to doing it all automatically via the BMS I think you should research some more options. For example I'm likely to use the SBMS0 because it has 4 I/O ports. I'll use:
1: Turn off Multiplus Inverter at cell level low voltage
2: Turn off Multiplus Charger at cell level high voltage
3: Switch off DC loads (via BP100) at cell level low voltage
4: Switch off DC charge sources (MPPT, DC-DC charger) at cell level high voltage (via 2nd BP100)

Out of curiosity how many watts is your watermaker? I have a Rainman 120VAC unit and it draws (per spec sheet, haven't measured) 1250 watts. I expect a start up surge but I'm buying a MutliPlus 3000 that will handle that.

Lastly, I have no experience with the 123Smart but have read a few forum posts where people talk of replacing them with something else. I'm not sure why they were unsatisfied but worth searching or asking about it on this forum.

 

[Bluewatersailor]

Lol. The 123Smart is a relay-driving BMS, not one that is inline with the current (ie, 123 is same as the SBMS0). You would use it to open or close a relay like this one that they sell: https://123electric.de/gb/123smartrelay/5-123smart-relay.html.
So yes, you could use the 123Smart to disconnect your DC loads via the relay I linked, and use the Bluetooth and app to monitor inverter loads, but you are so close to doing it all automatically via the BMS I think you should research some more options. For example I'm likely to use the SBMS0 because it has 4 I/O ports. I'll use:
1: Turn off Multiplus Inverter at cell level low voltage
2: Turn off Multiplus Charger at cell level high voltage
3: Switch off DC loads (via BP100) at cell level low voltage
4: Switch off DC charge sources (MPPT, DC-DC charger) at cell level high voltage (via 2nd BP100)

Out of curiosity how many watts is your watermaker? I have a Rainman 120VAC unit and it draws (per spec sheet, haven't measured) 1250 watts. I expect a start up surge but I'm buying a MutliPlus 3000 that will handle that.

Lastly, I have no experience with the 123Smart but have read a few forum posts where people talk of replacing them with something else. I'm not sure why they were unsatisfied but worth searching or asking about it on this forum.

The water maker use 11A @240v so I guess that's going to be more like 220A @12v seen a lot but if it's only used when the batteries are full and say 30 minutes at a time given me 50 lts of water that should be a problem 20% of the whole bank .
Seen I need to do more research, all new to me .