Connect bms serially for coms

[bruce_loco]

Hi Guys

So I see the rack mounted battery systems communicate between each other.
Which BMSs can communicate between each other via cambus/RS485/serial port to have this type of functionality?
Daly Smart BMS?
QUCC?
JK?
any others?
I haven't seen anything in the daly manual.

Thanks

 

[houseofancients]

Hi Guys

So I see the rack mounted battery systems communicate between each other.
Which BMSs can communicate between each other via cambus/RS485/serial port to have this type of functionality?
Daly Smart BMS?
QUCC?
JK?
any others?
I haven't seen anything in the daly manual.

Thanks

seplos

 

[bruce_loco]

seplos

I am looking at a 48V eve LiFepo4 280Ah 16s(per pack)
Wouldn't you need a BMS with Amps closer to the battery Amp?
I know it is a stupid question since in theory it will limit what the batteries can pull and also extract, it just means slower charging time, which is irrelevant because for solar you won't get that much juice in at once...

 

[houseofancients]

I am looking at a 48V eve LiFepo4 280Ah 16s(per pack)
Wouldn't you need a BMS with Amps closer to the battery Amp?
I know it is a stupid question since in theory it will limit what the batteries can pull and also extract, it just means slower charging time, which is irrelevant because for solar you won't get that much juice in at once...

200a continues at 51,2v is 10,2 kw.
why would one want more power to flow through 1 bms ?

 

[bruce_loco]

200a continues at 51,2v is 10,2 kw.
why would one want more power to flow through 1 bms ?

So if I connect 16 EVE 3.2V 280Ah -> this is 14.3 Kw
I don't think that I will every max out that type of power. So the 200a Seplos should suffice.
So this is the recommended one if you want to connect multiple ones battery banks?

 

[houseofancients]

So if I connect 16 EVE 3.2V 280Ah -> this is 14.3 Kw
I don't think that I will every max out that type of power. So the 200a Seplos should suffice.
So this is the recommended one if you want to connect multiple ones battery banks?

no saying forum recommended as this is not my place to do so, but yes that is possible and yes that is what i and others here use...

 

[jtvt]

I'm not sure what you are after, but you can get bms that can watch multiple strings like Batrium.

 

[bruce_loco]

no saying forum recommended as this is not my place to do so, but yes that is possible and yes that is what i and others here use...

You seem to be a fan of the seplos, I saw some videos about problems with diodes
What is the advantage of the serial connection between the bms's? detection and shutdown of events? passing info up to the inverter?
What do you see as the main advantages?
Thanks

 

[RCinFLA]

RS485 or CAN bus is just a physical interface. It does not specify what a given manufacturer does for actual messaging format and how these messages are interpreted by another device. There are some pseudo-standards on messages established by first manufacturers, but no guaranty another manufacturer's device follows it. General rule is if it does not understand message, it just ignores it.

The main benefit of having BMS communications is it can tell an inverter/charger to back off charging rate to allow more balancing time by BMS so there is less likelihood of cell overvoltage shutdown, or in a multi-battery array system if one BMS shuts down the other BMS's in system will also shut down so one battery array does not get hit with excessive discharge or charge current.

 

[burgerking]

The main benefit of having BMS communications is it can tell an inverter/charger to back off charging rate to allow more balancing time by BMS so there is less likelihood of cell overvoltage shutdown, or in a multi-battery array system if one BMS shuts down the other BMS's in system will also shut down so one battery array does not get hit with excessive discharge or charge current.

Agree. It makes for a smoother ride too.
Without communication, the Inverter would dump as much current then suddenly, the BMS cuts off power. not smooth transition IMO.

 

[rmaddy]

Agree. It makes for a smoother ride too.
Without communication, the Inverter would dump as much current then suddenly, the BMS cuts off power. not smooth transition IMO.

Any inverter worth buying would not do this. Any inverter that supports LiFePO₄ batteries will properly taper the charge current as the battery gets to 100% SOC. If an inverter triggers the battery's BMS then most likely the inverter isn't setup correctly for the type and size of battery. No communication between the inverter and the battery/BMS is needed for this. Such communication just allows for the normal charging process to be optimized to a higher degree. It probably also helps in multi-battery setups if one of the batteries is having an issue.

Remember, there are countless existing systems working out there just fine without any communication between the inverter and battery. My system is one of them.

 

[burgerking]

Assume:
16S, 3.65V max cell voltage
No BMS and Inverter communication. Inverter only knows 58.4V max charge voltage

While charging, one of the cell reached 3.65V faster than the others; the others are only in the 3.5xs
Battery Voltage at the Inverter port is only 57.5 (assume perfect connection)

What will happen when without communication?
a) BMS disconnects from Inverter because it already reached a limit.
b) Inverter tapers down to zero current

I've seen Daly, JBD disconnects the inverter (Deye, Growatt, Victron)

Disconnecting the battery to the charger is a protection, I agree. But if the BMS uses physical relay to disconnect (some JBD for instance) then it will trigger this multiple times in a day, contact will die fast.

Of course we can lower the max charge voltage at the inverter... this will lessen the problem until voltage delta increases...

 

[HRTKD]

@rmaddy already covered this. I have no communication between the BMS and everything else in my system that can charge the batteries. I have no shutdowns. High quality EVE cells, properly top balanced and well maintained. Configuring the charge devices and the BMS is important. A charger that charges to 3.65 volts is not what you want in your system.

Besides adjusting voltage, you can also reduce the amperage that the inverter/charger uses.

 

[rmaddy]

Inverter only knows 58.4V max charge voltage

Then that's not a LiFePO₄ friendly charger and shouldn't be used with LiFePO₄ batteries. There is no reason to charge a 48V LiFePO₄ battery at 58.4V. 56.0V - 57.6V would be the maximum for daily use.

While charging, one of the cell reached 3.65V faster than the others; the others are only in the 3.5xs

This is an exceptional case and the BMS will do its job of shutting things down. Do what is needed to get the battery properly balanced again which includes using a charger that can be set to a proper voltage for LiFePO₄ batteries.

If the BMS is causing multiple shutdowns a day then there is an issue with the battery that needs to be resolved. It's not a lack of communication with the charger, it's an imbalanced battery that needs to be rebalanced.

My two drop-in LiFePO₄ batteries have been getting fully recharged multiple times a day for the last 9 months. This is mostly from a stand-alone solar charge controller and on rare occasion from an inverter/charger. I haven't had a BMS shutdown ever despite the fact that there is no communication between the batteries and either charger. I attribute this to getting the batteries properly setup and balanced initially and by setting up my chargers such that they do not needlessly over stress the batteries with excessive charge voltage/current.

 

[burgerking]

Then that's not a LiFePO₄ friendly charger and shouldn't be used with LiFePO₄ batteries. There is no reason to charge a 48V LiFePO₄ battery at 58.4V. 56.0V - 57.6V would be the maximum for daily use.

3.65v max single sell LiFePo4 Voltage x 16 cells = 58.4V


But of course it is true, one should have lower vmax per cell voltage like 3.5V.

Of course we can lower the max charge voltage at the inverter... this will lessen the problem until voltage delta increases...

However this does not solve the issue of BMS disconnecting when one of the cells
reached VMax (now let us say 3.5v) earlier than the rest (which are still lagging at 3.45v).

And even if the battery is perfectly top balanced and well maintained, no way will all cells age equally.
Show me a 1 year old battery were all cells go up and down in perfect unison (within 10mv delta)?
One or more of the cells will degrade and reach threshold regardless how great the BMS' balancer is.
And once a threshold is reached, it will:

BMS cuts off power

By that statement what were you assuming I meant? That the BMS turned off the inverter?

In that statement, it was obvious the system is in the charging phase and not consuming battery juice phase.
"BMS cuts off power" was clearly referring to disconnecting the battery to the Inverter/charger:

I've seen Daly, JBD disconnects the inverter (Deye, Growatt, Victron)

Disconnecting the battery to the charger is a protection

Inverter/charger will still continue to run like a battery-less on-Grid inverter.

The problem is when using Physical Relay BMS like those big JBD or QUCC.
Closing and Opening degrades contacts of the contactor and it is a thing.
Try observing and you will hear the Contactor clicking during the upper part of the charge cycle.

 

[houseofancients]

3.65v max single sell LiFePo4 Voltage x 16 cells = 58.4V

Unless you have 15s...

but you don want to charge LiFePO4 to 100% as there is no real power to be gained from 90% onward

andy made a good and informative video about it, including testing graphs :