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bathnm avatar image
bathnm asked

VE.Bus BMS verses smallBMS

As I continue to investigate and systems test to decide if I stay with the VE.Bus BMS to meet my needs, I have run into a question related to the Mains Detector. I am hop[ing someone might be able to answer.

Clearly in a load disconnect situation the VE.Bus BMS sends a signal over the VE.Bus to the Multiplus and the MultiPlus Assistant then switches the inverter off. It must switch it off in such a way that connecting the mains does not trigger the charger. Therefore the mains detector is required to switch the Multiplus back on, so it can charge the batteries.

If the smallBMS is used with the two wire assistant, does the two wire trigger a slightly different shut down of the Multiplus, such that when mains is connected it will start charging, or is the mains detector still needed.

MultiPlus Quattro Inverter ChargerBMS
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Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @Bathnm,

Check out this Victron Lithium battery training,

BMS discussion starts at about 8 minutes in, and in more detail in 16 minutes. Though of course if you are considering Victron Lithium I would suggest watching the whole thing.

https://vimeo.com/456522354

The VE.Bus BMS allows a lower power state, so low that it will not detect AC without the Mains detector. It is the recommended BMS if you have a Multi.

Note the training mentions miniBMS this was recently renamed to smallBMS.

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bathnm avatar image bathnm commented ·

@Guy Stewart (Victron Community Manager), Many thanks for the link. A great video and learnt a few things. I already have my setup of Victron Lithium batteries and associated equipment am going through integration and system configuration on my yacht at the moment.

I understand that the VE.Bus BMS is recommended with a Multiplus, but that comes with trade offs, such as when a Cerbo is part of the system there is no ability to change the inverter status (on / off / Charge Only / Invert Only). This is important to me due to it's location. I have done various bits of testing and heading towards using the 2-Wire Assistant rather than VE.Bus Assistant. This gives me the charge and load disconnect along with remote control from the Cerbo. What I was unaware of was what other features/benefits one looses. It seems that going 2-Wire BMS I will loose the low consumption mode in load disconnect.

In addition going to a smallBMS also gives a lower parasitic load as it draws less than the VE.Bus BMS.

Like everything there are trade-offs. I would love to use the VE.Bus BMS, but I can't accept the loss of remote control from the Cerbo. Unfortunately I have no space to install a DMC, which would give me that control but also at an extra cost

If Victron has any plans in the short term to address what I consider a major limitation of the VE.Bus BMS then I suspect I and others would be really pleased. If you need some beta testers please make contact with me as I would be happy to help.

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