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MultiPlus-II knows that LiFePO4 battery is connected and has the temperature sensor working.
I know that BMS should control charging, but since MP-II knows the temperature and knows what type of battery is connected to it, why not use this info and act on it?
Remote Control gives me notifications about "Temperature sense error" when temp drops below 5C, so why not act on this error?
Hi @MarekP My personal view is that typically it is good practice to have only one single reliable "source of truth" and with modern LifeP04's, it is either an integrated or external BMS. It is also highly likely that it will have the most accurate readings, often at cell level so. Finally, why not keep things simple as that contributes to increased reliability and system stability. Just my personal design philosophy ;)
Thank you for your view on the subject of my question, but reality is not ideal.
We live in the real world.
My Victron dealer told me abut his client who lost his expensive battery because BMS, he bought with this battery, failed. He had to buy new battery for another 10000Euro, because vendor of this battery (and the BMS) did no honor the warranty on the battery.
Battery was damaged by the BMS so battery was not replaced under warranty.
The funny part is hat they replaced BMS under warranty.
So, going back too may original question.
Why MultiPlus-II cannot be set up to stop charging the LiFePO4 battery when its sensor tells it that the temperature is below 5C?
I am not personally aware of an assistant, which allows this functionality today, but maybe someone knows better.
As for the real world, even a Multiplus and temp sensor can fail.
If writing a dedicated assistant would give this functionality, why Victron is not doing it?
Statistically is less probable that two systems fail a the same time.
I cannot speak for Victron, but development and testing is a huge investment and I personally just don't a see a huge demand for this feature to justify it given this is in my experience an isolated incident and I'd may have recommended another battery chemistry if low temperatures present an ongoing concern. LTO I think is the future.
Hi,
I agree that LTO is the future.
Charging and discharging speeds, longevity are awesome, but are you sure that you can charge them below freezing?
You would probably point me to specification for this chemistry but, do you believe that the manufacturer of LTO batteries is telling the truth in the spec sheets?
As an example let me bring the Victron Lithium batteries that were never allowed to be charged below 5C even when they were build with Winston cells.
This limitation was in contrary to Winston spec which allow charging down to -25C. All because they are LiFeYPO4 and not LiFePO4.
Are you willing to risk thousand of Euros or Dollars spent on those batteries and charge them (Winston) at -25C? :)
This is why I am surprised that there is no assistant that prevents charging LiFePO4 below 5C without relaying on external BMS, when all, including Voctron, stress that charging below 5C is deadly for those cells.
Best Regards,
Marek
Some spec sheets for TTO suggest charging and discharging in temperatures as low as -50, but I cannot see that indoor installations locations will ever get that cold. If it works at -5C that is already an advantage, otherwise it simply is the wrong solution, at least for now.
I would like to see this very useful feature as well. For now, for redundancy, I add the BMV temp sensor and relay using two programmable relay assistants and one red assistant as found here: https://www.victronenergy.com/live/dc_coupling:using_bmv_soc_in_a_vebus_assistant_setup
Hi @Stephen Kunkel @MarekP Sounds like a feature request then, which is done in the modifications section.
Hi. I know that Victron wants to add this very feature because they have already semi-implemented it. If you refer to Victron Connect3 and select "Lithium Battery" the Multi's are supposed to do it already as defined there. Problem is, it does not work yet. Patience is the approach I take here.
@Stephen Kunkel, When using the Victron Smart Lithium batteries, the MultiPlus will stop charging when the battery itself reaches 5C. You can see the Smart Lithium battery temperature when you connect to it through Victron Connect. The battery sends a signal to the Victron BMS, which will then signal a charge disconnect to the MultiPlus.
But why is not stopping charging the Lithium battery when its own temp sensor indicates temp below 5C?
@MarekP I cant answer why Victron has made the design decisions they have. It may well be down to simply component and system design philosophy. Maybe the MultiPlus dose not have the ability to interpret itself the temperature value coming off the probe and react within an Assistant to that value, I cant find any assistant that has a linkage to temperature value.
However, I would rather the battery decide on the temperature than the MultiPlus. The battery is more aware of and able to monitor the actual cell temperature more closely. The challenge then comes when you have a Battle Born or similar battery with integrated BMS that dose not allow you to get any control signals.
Maybe something to consider is a heat mat under the battery to ensure it does not get below 5C, then there is no shut down of the charging required.
I am sure that MultiPlus-II has the ability to "interpret itself the temperature value coming off the probe".
It does that when has to control voltage of the Pb batteries, in relation to the their temperature, when is charging them.
Why would the temperature probe be included with the MultiPlus-II unit?
I would rather have more than one system to control safety of my expensive batteries.
Heating system for batteries is a good idea but when it fails, what than?
I agree it can be used in charging and reporting over the VE.Bus. My point was about it being included in logic within the Assistants. It is clearly not available and there maybe good reasons why not.
That is my question.
Why MultiPlus-II can adjust charging, based on temperature of the Pb battery, and it cannot do that when connected to Lithium battery?
Using it within its own charging algorithm to adjust voltage output is one thing, shutting down charge is another!.
There are plenty of other methods of shutting down charge based on temperature including the batteries own BMS. I am sure Victron would argue they should be used, especially as multiple charge sources could exists and just shutting down one will not protect the batteries.
if you are after multiple control systems for safety, then clearly you do not trust the BMS, which is your primary safety system and if that fails then you have far more challenges than stopping charge at 5C.
"Using it within its own charging algorithm to adjust voltage output is one thing, shutting down charge is another!."
Why?
What is the difference between lowering charge current to, let say, 10A or lowering it to ZERO Amps.
"There are plenty of other methods of shutting down charge based on temperature including the batteries own BMS."
BMS is is not a charger. The Charger needs to be "in charge" because it has the info (temp sensor) and means (charging circuit).
"If you are after multiple control systems for safety, then clearly you do not trust the BMS, which is your primary safety system and if that fails then you have far more challenges than stopping charge at 5C."
It is just a matter of cost.
If BMS or charger fails, cost of replacing them is not even close to 1/10 of the cost of replacing 20kWh in batteries.
