Rec-BMS & Victron

[Rocketman]

Hello Everyone,

I have a LOT of Victron blue boxes already installed on my motorhome. CCGX, Mppt 100/50, Multiplus 3000 (12v) BMV-712.(I like them a lot).

Now I am interested in installing some Lithium batteries, thus I need a BMS. The battery will be a 12v 600Ah (or so - maybe more) battery - probably in a 3 or 4P 4S configuration. I would like the BMS to interface with the CCGX - with the CAN-BUS.

I have been looking at the REC-BMS. It seems to check all the boxes - I would like to hear from people that actually use it. How does it work for you? Any problems?

I have a few questions:
CAN Connection - From what I have read, it seems all I need to do is plug the BMS Can wire into a network cable that runs to my CCGX. Make a couple of easy software communication adjustments on the CCGX and it will work. Have I missed anything?

Charging the batteries: From my reading it looks like the BMS will be controlling the charging by sending signals to the CCGX, as it gets full, the BMS tells the CCGX to reduce the amps, and the CCGX passes that along to the MPPT's, then when totally full, the BMS says - no more power, and the MPPT's don't send any more power. Is that what actually occurs? Also, will the MPPT's produce power for the loads, so I don't keep cycling the battery between 99 and 100%?

Connecting the BMS to Connectors (Kilovolt EV200) I am a little confused about the connectors to the Kilovolt EV200. Is all I need to do is just the connect the two wires from the relay to the load EV200? Do I do the same for the charge bus? How do the digital relays work? This is probably the area that confuses me most.

Thanks for your help

 

[nebulight]

I don't have REC active, but looking at their larger unit for my 48v home unit. If you have Victron you should 100% use REC. A few things...

• You've got a pretty good understanding of how the CAN communications work. The MPPT and multi are directly controlled by the BMS so when the battery is full the REC tells the MPPT and multi to stop charging. If it's empty it turns off the inverter. As for floating the batteries when full, I'm not sure it works that way as the chargers really become slaves to the BMS and just do what they are instructed for both current and voltage. You might want to reach out to REC, but here is a snip from their manual:
  • The communication between the REC BMS and the Victron GX device is established through the CAN bus. All the parameters that control the charging/discharging behavior are calculated by the ABMS and transmitted to the GX unit in every measurement cycle. The charging current is controlled by the Maximum charging current parameter. It’s calculated as Charge Coefficient CHAC x Battery capacity. The parameter has an upper limit which is defined as Maximum Charging current per device MAXC x number of inverter devices STRN. When the highest cell reaches the voltage interval between Balance start voltage and Balance end Voltage, the charging current starts to ramp down to 1.1 A x Number of Devices until the last cell rises to the End of Charge Voltage. At that point the Maximum charging voltage allowed is set to Number of cells x (End of Charge Voltage per cell – 0.2 x end of charge hysteresis per cell). End of Charge SOC hysteresis and End of charge cell voltage hysteresis is set to prevent unwanted switching. SOC is calibrated to 100 % and Power LED lights ON 100 % Charge optocoupler is turned off. Charging is stopped in case of systems errors (See System Errors indication chapter). SOC is calibrated to 96 % when the maximum open circuit cell voltage rises above the 0.502 x (Balance start voltage + balance end voltage), minimum open circuit voltage above balance start voltage and system is in charge regime.
• You should buy their pre-charge circuit before using the EV200. It will precharge the capacitors in your multi before connecting the EV200. There are outputs from the BMS that will control the EV200, but the precharge box goes between the BMS output and the EV200.
• Also, you no longer need the 712 as the shunt for the BMS will pass along battery meter stats to the CCGX. But since you already have it, you can use the same shunt (just add wires to where the PCB connects to the shunt).

 

[gnubie]

What's the advantage of having the charger turn off? If the BMS isn't capable of disconnected under cell over voltage I can appreciate that it would be useful, but other than that does it actually do anything useful? Under normal operations the charger will bring the battery up to what ever target voltage is set, park it there for as long as it takes for current to fall of or until a time limit is reached, then release back down to the lower lithium safe float voltage.

If the charger is turned off you have to rely on the BMS telling the charger to turn back on when the system picks up a load, rather than the controller simply seeing the system voltage fall a bit and automatically supply current to prop it back up etc.

 

[nebulight]

The advantage is the charger is controlled by the BMS. The BMS knows the cell voltages so you never run into an over or under voltage condition because the BMS won't allow it. If by chance there is a failure in CAN communication, the BMS also has a EV200 500 amp relay that acts as a main disconnect.

And the charger isn't really turned off, it just stops charging so when it's ready to charge again, the BMS tells it to.

 

[Pierrot]

Hello - Here is a nice vidéo about the Rec Bms :

 

[Rocketman]

I have seen that Video (several times), in fact that video turned me on to Rec-BMS. I was just looking for more details and other experiences, before purchasing this more expensive BMS.

 

[gnubie]

The advantage is the charger is controlled by the BMS. The BMS knows the cell voltages so you never run into an over or under voltage condition because the BMS won't allow it. If by chance there is a failure in CAN communication, the BMS also has a EV200 500 amp relay that acts as a main disconnect.

And the charger isn't really turned off, it just stops charging so when it's ready to charge again, the BMS tells it to.

That's what the BMS disconnect is for, under and over cell voltage protection. If the BMS is capable of doing this I still don't see any advantage to turning off the charger. Perhaps, at a stretch, it would be an advantage in that the battery would still remain operational and capable of supporting loads but given the circumstances of a) the charger manages end of charge cycle itself in normal conditions and b) if your cells are that far out of step something is wrong in the first place and for a reasonable quality battery or collection of cells, not necessarily top shelf either, is not likely to even be an issue. I'm still not convinced. Note, not trying to say that people shouldn't do it, just that I can't see the advantage of it.

The charger output is off. It doesn't just 'stop charging'.

 

[nebulight]

That's what the BMS disconnect is for, under and over cell voltage protection. If the BMS is capable of doing this I still don't see any advantage to turning off the charger. Perhaps, at a stretch, it would be an advantage in that the battery would still remain operational and capable of supporting loads but given the circumstances of a) the charger manages end of charge cycle itself in normal conditions and b) if your cells are that far out of step something is wrong in the first place and for a reasonable quality battery or collection of cells, not necessarily top shelf either, is not likely to even be an issue. I'm still not convinced. Note, not trying to say that people shouldn't do it, just that I can't see the advantage of it.

The charger output is off. It doesn't just 'stop charging'.

That's what a basic BMS is for. This can do so much more, like ramping down charge voltage at the top end to allow the cells to balance properly instead of just disconnecting the chargers and not getting a good balance. It can also adjust your charge rate in unfavorable temps (freezing or too hot). It instructs the inverter to shut down properly rather than just disconnecting the battery or limit the output of the inverter if you can't support the loads.

 

[toms]

As mentioned by others, the REC activates a precharge unit that switches the contactor.

I use the REC with a Sunny Island.

The main advantage for me is this setup allows me to bulk charge with DC coupling, and then hold at 3.5V (cell level) with AC coupling.

 

[luckybeanz]

I have a LOT of Victron blue boxes already installed on my motorhome. CCGX, Mppt 100/50, Multiplus 3000 (12v) BMV-712.(I like them a lot).

Have you got it all set up with REC yet? I'm looking at them for a boat conversion and will use all victron devices. Though need a 12v and a 48v bank, REC says to have two separate networks for this, though I think victron can handle them on a single network...

 

[Rocketman]

I decided not to go with Rec for the BMS. I decided on Batrium. (Although I am using Rec’s pre charge controller).

Batrium seems to be fit better for me. The software and making changes is MUCH easier. It also has the CAN bus setup to Victron.

It will probably be early spring before the battery project is setup and done.

Why 2 different voltage systems on lithium? Is the 48v for the inverter and a charger for the 12v (which is what your unit was originally)?

 

[luckybeanz]

It is on a boat 48v is to run inverter and electric motor, 12v is to run house electrics, lights etc.

 

[Rocketman]

Here is an idea to simplify the system. (Something I have thought about doing on my next RV. )

Run the 48v for inverter & a 48/12 converter set the 12v side to 13.2 volts. Then use a single AGM deep cycle battery for the 12v.
The real juice for all your 12v stuff comes from the 48v battery. Then if you need it you have a reserve from the 12v battery. I was thinking about this setup because there are a couple of items that would exceed the needed amps from the 48/12converter. (Plus emergency start boost on the big diesel).

In your case maybe you could not even have the12v battery hooked in all the time - just keep it for emergency power to run electronics.

If later you decided to make the 12v battery lithium a separate bms would probably be the way to go.
(Just an idea - I don’t know that much about boat power draws).

 

[luckybeanz]

un the 48v for inverter & a 48/12 converter set the 12v side to 13.2 volts. Then use a single AGM deep cycle battery for the 12v.
The real juice for all your 12v stuff comes from the 48v battery. Then if you need it you have a reserve from the 12v battery. I was thinking about this setup because there are a couple of items that would exceed the needed amps from the 48/12converter. (Plus emergency start boost on the big diesel).

I've already purchased the batteries as wanted to have the 12v (house bank) separate for redundancy. I'd be happy to stay at anchor and let the motor battery charge, but would not like to be at anchor without the house running. I know all the energy is coming from the same place but I feel it is just easier to manage with two banks, albeit a more complicated system. I'm going to have two BMS and basically two systems, though what I can't seem to have is being able to display the info from both systems on a single screen.