In my intended use, there will be 4 18S battery strings each with its own independent BMS.
I don’t intend to use any fancy footwork if a string is disconnected, life will carry on until it behaves again and rejoins the party.
Hopefully, though with matched cells this will be a rare enough occasion.
So until I have an issue, I am not looking to overthink it.
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It may not be the best diode ever, but here is an example of the body diode specs. for a FET that I’m currently using. This is really not that bad compared to dedicated diodes with similar current ratings.
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@TheTerribleTriplet I have a question for you.
Regarding the BMS you are using through @Louisvdw app.
Am I correct in saying you have dialled in the settings now, so that the BMS contactor doesn’t actually operate?
In other words, the charging instructions given by the BMS to the Venus device deliver exactly what you want. The extreme measure of tripping out the bank is now unnecessary?
If you are not doing something funky with your settings, then there are no trips from the BMS as the inverter use is limited before that stage.
However when in a offgrid setup (or load shedding) the GX tries to gives power and then the BMS will trip at some stage.
If you question is related to TTTs settings for his 17s frankenbank then he would be better to answer that.
@Louisvdw Thanks for the reply. (No, my query is not 17S related).
It will be in a permanent off-grid situation.
I am not worried about tripping out if the battery gets too low which I am aware could happen off-grid. Presumably, the Victron’s own low voltage cut-off still provides this function as well.
However:
Are you saying that BMS could not stop the charging and trip because the batteries start to overcharge? I wasn’t aware of that.
Edit: " Presumably, the Victron’s own low voltage cut-off still provides this function as well." Or is this “always ignored” when DVCC is selected?
Edit Edit: The DVCC splurb states that with your app and a BMS:
“For such batteries, there is no need to wire allow-to-charge and allow-to-discharge connections to the AUX inputs on a Multi or a Quattro.”
My question is will these wired inputs still work, even if they are not necessary, do you know?
I do not know if those wire connections will still work. My guess would be that the one will take priority, and I would guess that is the DVCC when activated.
So the BMS will always be there to protect. Nothing in the GX side will stop that.
The BMS will request a stop to the charging and the GX will notify all charging devices. There could be a failure anywere (who knows what devices people plan to add to their ESS and what settings they are “trying” - this does sound like something @TheTerribleTriplet would try 
) and then the charge could potentially not stop and in that case the BMS will kick in.
But if you use only Victron devices they work very safe if something happens. For instance the MPPT will stop charging the battery and only give PV power for what the inverter is using when the connection to the BMS is lost. It then wait until the BMS is connected again.
So stay blue and it will all work as you expect it.
This set-up will be all blue barring the batteries and BMS.
The reason I asked…
Is that this particular BMS may represent an option that can not only report intelligently, and control charging rates, but instead of using contactors as the final line of defence, those BMS outputs could be used as the allow-to-charge & allow-to-discharge inputs to the Victron equipment.
Sounds similar to the ECS equipment I am currently looking at addin to the driver.
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I don’t know this one.
Yes, I edit the charge amps down to 1 amp when above 98% BMS SOC, instead of 5amps.
If the cells behave, it works, no need for more extreme measures.
Only manual intervention I found that helps a LOT, using what is there for this purpose on the Venus whilst cells “settle”:
When Delta is:
100mV< drop the DVCC charge amps immediately to like 3amps, even 1, give a warning.
<20mV. release all holds again.
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If I don’t need the contactors, then I just have to lie to the BMS about the shunt and the battery capacity and I can my overall battery bank 1000A BMS.
When ESS is used, then the dynamic cut-off curve is used instead of the low voltage cut-off. But in an off-grid system you won’t be using the ESS assistant, so yes… this still works. There is a feature in the BMS protocol where the battery can specify the lowest voltage… but it is not used at all.
Short answer: Yes.
You will have to install the two-signal BMS assistant to make it work (built into the ESS assistant for those who use that). This is where things get a little wonky at the moment. There has been some BMS-related changes in firmware 489.
The specific change is that the VE.Bus BMS is built into the main firmware (no more assistant required). The VE.Bus BMS is of course a kind of two-signal BMS (using the VE.Bus to communicate those signals). Now I have learned that when using this BMS, you cannot also use the can-bus control feature. It raises error Ve.Bus error #15. And I do not know if perhaps the same thing also happens with two-signal BMSes.
In short, before firmware 489 you can use both together, and the physical wiring takes priority. After 489, I do not know.
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Thank you, it is a challenging, but enjoyable thing, doing this jigsaw puzzle.
Hi @Phil.g00
Have you ordered these contactors before. I am keen to get my hands on 1 (in SA).
Regards
Mark
https://www.mouser.co.za/c/?q=EV200AAA
This one? You will be able to get free shipping with that price…
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Hi,
I am just back from SA, so I have been scarce on this board for a few weeks. To answer you question:
No, I am keeping my powder dry until I have to. The BMS world seems to be a fast-developing one. I have not bought the lithium batteries I intend to yet, because I want to buy a lot when I buy and I am saving up.
At the same time I am keenly following @Louisvdw 's progress on a BMS suitable for multiple banks.
With these things still up in the air I haven’t taken the BMS plunge yet.
OK, I pulled the trigger:
Shipping, handling and Alibaba fees bring it to a total of $1363
No doubt there will be customs charges & VAT coming up as well.
Anyway @TheTerribleTriplet I still see 72 batteries ( 4 x 18) in my future.
It’s 2 per BMS unfortunately. I will use something with less rating for the pre-charge contactor.
I am pretty sure these are clones and not the genuine article. But then again the genuine article is probably made close by anyway.
Here is an aliexpress link:
These were actually cheaper than mine, if you were to order 8.
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