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offshore asked

LiFePo4 Smart Battery with multiple VE.Bus BMS allowed?

Hello,

the short question is: is it allowed to use in one system multiple VE.Bus BMS?

My Plan is: One VE.Bus BMS is connected to a single 25,6V 200Ah Smart Batteries, and this I have 6x. So in total 6 BMS systems and 6 Batteries. All 6 BMS Systems are connected with Ve.Bus. The Relay for the Load disconnect in case of a low voltage I want to install on each batterie, so the batterie can disconnect from the system and not the load! Will this work? How this Bank will then displayed on the Color Control GX?


We are building boats with an AGM bank and I want to change this to LiFePO4 Batteries. The reason why I didn't do this was, because I don't like the logic of the Victron BMS system. I checked a lot Victron battery circuit suggestion and the logic was to be able to shut of the charge sources with a signal and the loads with a relay. Other manufacturers separate the battery from the system with a relay, which I like more because one bad batterie doesn't turn off the hole system.

The system now:

  • Battery Bank: 24V AGM 14 x Victron 12V 200Ah
  • Inverter: Quattro8000VA
  • Charger: Skilla-i 24/100
  • Alternator 2x 110A
  • Display: Cerbo GX with Touch GX
  • DC Loads 7x 300A to 600A each!


When I have to follow the Victron circuit suggestion for the Smart LiFePo4 Batterie, I have to use to each load a separate big relay, but for this I don't have the space! So I want to put the Relay on the Batterie, this means the batterie is disconnecting from the Batterie Bank, not the loads.


If this is not possible, do you have other ideas? I Could use the Victron 25,6/50 Super Pack with a build in BMS, but to reach 30kWh I need 30 batteries and for this I don't have the space.


Thanks!

Lithium BatteryBattery Protectve.bus bms
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2 Answers
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bathnm answered ·

Unfortunately what you are seeking to do will not work. I am not sure you would even get this to work with a smallBMS using the two wire assistant in the MultiPlus.

However, if something goes bad, disconnect the bad battery manually and remove it from the BMS Signal wire chain. Yes I know the system, will be out of action while you do this.

One thing to think about, what is your biggest load?

It is likely the MultiPlus. That dose not need a disconnect relay as it is controlled (discharge and charge) by the signals between the VE.Bus BMS and the MultiPlus.

All other loads can then be connected via a Smart Battery protect. The largest one available can handle 220A, probably plenty for all other loads and that can be controlled by the land disconnect signal from the BMS.

Yes I know the entire system will be out of action due to one battery failing, until it has been removed. Consider however a battery removed from the system can impact battery monitors, charge loads and a number of other critical data inputs. How many places do you enter the size of your bank? How many parts of the system are dependant on this for SOC, charging, etc.

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offshore avatar image
offshore answered ·

Thanks for the answer. This is really sad to hear. Are you sure this will not work?

The biggest load will be the hydraulic pump. Also a big load is the 8000VA Quattro but for this I don't need a relay like you wrote correct. Nearly All loads are in the range of 300 to 600A so the Smart Battery protect will not work. Also I don't have the space to do this for all loads.

That one battery failure can cut off all DC loads is in a boat from this size not allowed because people's lives can depend on it. In a motorhome for example I would have no problems with it.


For me the Victron BMS logic is really strange, because this means you cannot really use LiFePo4 for larger systems.

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bathnm avatar image bathnm commented ·

One thing to think about with the hydraulic pump. Do you need to control the pump itself, or can you shut down the control circuits on load disconnect. If the control circuits which draw small currents are shut down the main high draw hydraulic pump will not run. As an example with electric winch, rather than switch the supply to the winch motor, I cut the low current control circuit with a battery protect.

I understand the space issue, but once the high loads are sorted, Multiplus through it's native control and hydraulic pumps through the control circuits, what loads are left. These remaining loads can probably be controlled by the same Smart Battery Protect that is being used for the hydraulic pump controls.

I guess it depends on how you look at the system. I know for instance that Mastervolt inserts relays between each battery and the buss, but what are they actually protecting? The batteries send messages to stop charge or stop load to the rest of the Mastervolt devices. One thing to ask yourself, what events trigger the Relay. Will those events really just trigger for one battery or all batteries?.

If you get a load disconnect due to low cell voltage, will it impact one battery or all in the bank? Likewise If you get a charge disconnect, do you impact one battery or all? Low or high temperature, again one battery or all batteries? In general it will be the the bank that is low or high, not an individual battery. So is it easier to control a bank or the individuals? Just different ways of looking at the problem and solution.

Every design we do needs compromise and a balance of decisions. Maybe thing about why your are looking at the Victron battery rather than others that do support individual switching and ask can you compromise on the different approach ;)

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offshore avatar image offshore bathnm commented ·

To disconnect only the control supply for the hydraulic pump or the winches is an option but then the standby current is still too high. (We have customers who let the system run completely low for 2 months)

My only idea now is a to use a heavy duty relay, with a manual operation, in the negative line after the shunt to the negative busbar. This would kill all DC-Loads. The Problem is, that I need then a second busbar before this heavy duty relay, where the charging devices are connected all the time like the Quattro, Skylla and the alternator.

Another idea: what if i have on each battery a Ve.Bus BMS and connect this to a relay on the battery, and don't connect everything with the VE.Bus? Then I don't have the signal for the Charger/Inverter, but the battery is save. I think this would accept Victron too?

Do you know which values I see on the color control display when its connected to the VE.Bus BMS? I think when I connect the BMS not with the display, I will not miss a lot of functions, because a Shunt I have in any case.


I used on bigger systems often LiFePo4 Batteries, but not from Victron and on nearly every system there is in the first 3 years one dead cell, and this single damaged cell had only disconnect 4 batteries from the bank and not all loads. Thats why I can't really get used to this logic with a single BMS.


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