LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[CatNewBee]

Originally Posted by john61ct

That is only relevant for charge sources that are both user-adjustable, and VE.Bus compatible.

Not all such Victron devices are.

Even SPI, I2C or CAN would be fine, but I suspect no adjustment is possible with this particular unit.

I'd be very happy to be proven wrong.

You are wrong. Most controllers have only a (sometimes optional) BT interface.

[Dockhead]

Originally Posted by newhaul

Upon further reading of the specifications page , I would personally have to recommend that you don't use this with Lfp for long term storage .

Lfp don't like being fully charged.

Storage Mode: Less maintenance and aging when the battery is not in use The storage mode kicks in whenever the battery has not been subjected to discharge during 24 hours. In the storage mode float voltage is reduced to 2,2 V/cell (13,2 V for a 12 V battery) to minimise gassing and corrosion of the positive plates. Once a week the voltage is raised back to the absorption level to ‘equalize’ the battery. This feature prevents stratification of the electrolyte and sulphation, a major cause of early battery failure.

Because of this statement in there
Once a week the voltage is raised back to the absorption level to ‘equalize’ the battery

And then there is this part
Also charges Li-ion (LiFePO₄) batteries LiFePO₄ batteries are charged with a simple bulk – absorption – float algorithm.

And the Lfp float is 13.5v or fairly close to what is normally considered by most of us using Lfp to be considered fully charged .

And we all know Lfp hate being kept fully charged for long periods.

OK, so how do we solve this? We've discussed it a lot, but I'm not sure we've come up with anything clear cut.


* At the dock, if I'm not on board I shut down the systems and isolate the batteries and shut down the charger. Disconnect shore power.



* Anticipating not being on board, I stop charging short of a full charge, by forcing the charger into float (can be done with any Victron charger/inverter even without the Venus control)



* If I'm on board and using some systems, I stop charging short of a full charge, by forcing the charger into float.


* Anticipating leaving for a long sailing passage, I will fully charge the battery by forcing the charger into bulk.




So far so good -- right?


But what about if I am using Power Boost? I think that's the big fly in the ointment. I don't see how I could hold the battery at partial SOC and be using Power Boost, because after heavy loads from the inverter, the whole normal charge routine will start, and I would have to manually force to float every time at the desired state of charge.


Unless perhaps I could get an automatic "force to float" command into the charger/inverter from the BMS. Based on selecting a target SOC.


That would be pretty simple to implement, but Batrium doesn't have any such function that I was able to find. I can imagine a toggle switch on the instrument panel for selecting 50% vs 90% or whatever target SOC, based on which the BMS would command the Multiplus to go over to float at the selected target.



Ideas?

[newhaul]

Originally Posted by Dockhead

OK, so how do we solve this? We've discussed it a lot, but I'm not sure we've come up with anything clear cut.


* At the dock, if I'm not on board I shut down the systems and isolate the batteries and shut down the charger. Disconnect shore power.



* Anticipating not being on board, I stop charging short of a full charge, by forcing the charger into float (can be done with any Victron charger/inverter even without the Venus control)



* If I'm on board and using some systems, I stop charging short of a full charge, by forcing the charger into float.


* Anticipating leaving for a long sailing passage, I will fully charge the battery by forcing the charger into bulk.




So far so good -- right?


But what about if I am using Power Boost? I think that's the big fly in the ointment. I don't see how I could hold the battery at partial SOC and be using Power Boost, because after heavy loads from the inverter, the whole normal charge routine will start, and I would have to manually force to float every time at the desired state of charge.


Unless perhaps I could get an automatic "force to float" command into the charger/inverter from the BMS. Based on selecting a target SOC.


That would be pretty simple to implement, but Batrium doesn't have any such function that I was able to find. I can imagine a toggle switch on the instrument panel for selecting 50% vs 90% or whatever target SOC, based on which the BMS would command the Multiplus to go over to float at the selected target.



Ideas?

no ideas as far as using a mains charger in those scenarios .

The only time I use a mains charger is the day I am leaving to top up with during my preps to get underway.

I have 2 settings normally used on my solar . ( considering all of the various discissions on the forum about Lfp )

new regime will be me on boat using systems charge to 13.8v ( one day a month to 14.45v top balancing) forstaling memory issues )

not onboard set controller to 12.8v ( I'm onboard 75% of the time so rarely set here ) .

Seems like it would work good . We shall see in a year or so .

[CatNewBee]

Originally Posted by Dockhead

OK, so how do we solve this? We've discussed it a lot, but I'm not sure we've come up with anything clear cut.


* At the dock, if I'm not on board I shut down the systems and isolate the batteries and shut down the charger. Disconnect shore power.



* Anticipating not being on board, I stop charging short of a full charge, by forcing the charger into float (can be done with any Victron charger/inverter even without the Venus control)



* If I'm on board and using some systems, I stop charging short of a full charge, by forcing the charger into float.


* Anticipating leaving for a long sailing passage, I will fully charge the battery by forcing the charger into bulk.




So far so good -- right?


But what about if I am using Power Boost? I think that's the big fly in the ointment. I don't see how I could hold the battery at partial SOC and be using Power Boost, because after heavy loads from the inverter, the whole normal charge routine will start, and I would have to manually force to float every time at the desired state of charge.


Unless perhaps I could get an automatic "force to float" command into the charger/inverter from the BMS. Based on selecting a target SOC.


That would be pretty simple to implement, but Batrium doesn't have any such function that I was able to find. I can imagine a toggle switch on the instrument panel for selecting 50% vs 90% or whatever target SOC, based on which the BMS would command the Multiplus to go over to float at the selected target.



Ideas?

Use the programmable inputs of the multiplus along with a macro. You can do it by a switch, connected one side to the input of the multiplus, the other to a BMV, that delivers the SOC. Switching off, the Multiplus will run the normal settings and receive no cut signal, switched on, the bmv will trigger float or stop charge above the set value.

I would use a BMV that oversees all charging sources and loads instead of the multiplus internal SOC calcullation

[Dockhead]

Originally Posted by CatNewBee

Use the programmable inputs of the multiplus along with a macro. You can do it by a switch, connected one side to the input of the multiplus, the other to a BMV, that delivers the SOC, switching off, the the multiplus will run the normal settings, switched on, the bmv will trigger float or stop charge above the set value.

OK, so the programmable input on the Multiplus can be programmed to "force float"?


If so, then I see how this could work. Either the BMS OR the battery monitor could then be programmed to give a signal at a set SOC level, and this could be used to force the Multiplus into float.


If you want it to run the normal program, just interrupt that signal with a toggle switch.


Did I understand that correctly? If so, that sounds like the solution! That would work even when using Power Boost! Thanks!

[john61ct]

Originally Posted by CatNewBee

You are wrong. Most controllers have only a (sometimes optional) BT interface.

Sorry? don't catch your intent here.

Are you still thinking this charger does allow user-custom settings?

[john61ct]

Originally Posted by Dockhead

But what about if I am using Power Boost? I think that's the big fly in the ointment

Yes, combi inverter/chargers interfere with the usual LFP design modes, cannot separate loads buss from charge buss.

Keeping both Absorb and Float settings turned down to Storage voltage levels is one possibility.

A lead Reserve bank lets you completely isolate the LFP Main house, even if it is very small. Or Starter(s) can serve that function.

Or just let the LFP bank sit at Full and take the longevity hit, could well allow you to get a decade or more and KISS.

[Dockhead]

Originally Posted by john61ct

Yes, combi inverter/chargers interfere with the usual LFP design modes, cannot separate loads buss from charge buss.

Keeping both Absorb and Float settings turned down to Storage voltage levels is one possibility.

A lead Reserve bank lets you completely isolate the LFP Main house, even if it is very small. Or Starter(s) can serve that function.

Or just let the LFP bank sit at Full and take the longevity hit, could well allow you to get a decade or more and KISS.

A parallel lead bank wouldn't solve this problem at all.



You want your inverter connected to the lithium, not the lead bank.


Power Boost, by the way, murders lead batteries. It's how I ruined my latest set of lead batteries . Every time you draw power from the batts for power boost, a whole new charging cycle is initiated. Lead batteries don't like to see absorption voltages over and over again when they are more or less fully charged -- it corrodes the positive plates.


No, I think CatNewBee's solution is perfect. The Victron battery monitors have a programmable relay for SOC (intended for automatic starting of generators, but easily adaptable for this). So I can get a signal to force float at any given programmed SOC, from a 700-series battery monitor. Now to figure out how to program the Multiplus.

[john61ct]

Originally Posted by Dockhead

A parallel lead bank wouldn't solve this problem at all.

I was only talking about when you want to keep the LFP in "storage mode", their energy not required for cycling purposes, the shore power being sufficient to carry the loads.

Of course never mind, if using the (very versatile) programmable relay feature of the BMV-712 works better for you, many ways to skin the various cats to suit different use cases.

[Dockhead]

Originally Posted by john61ct

I was only talking about when you want to keep the LFP in "storage mode", their energy not required for cycling purposes, the shore power being sufficient to carry the loads.

Of course never mind, if using the (very versatile) programmable relay feature of the BMV-712 works better for you, many ways to skin the various cats to suit different use cases.

I don't think you understood the issue then -- it's being dockside with shorepower but using Power Boost.


This is a VERY COMMON situation in Northern Europe where shorepower may be as little as 6 amps (i've even seen 4 amps).


If you're hooked up for a long time, you won't want to hold the battery at 100% SOC, but you will be drawing from the battery to supplement shore power as often as every few minutes. An auxiliary lead bank will not solve this.



It would be really useful to be able to limit the charging to some set % SOC. I can get an output from a 7-series Victron battery mon, but still don't see how to use that signal in the Multiplus -- maybe CatNewBee has some ideas.

[evm1024]

I've been looking at the (non victron) lithium assistant. No experience with it yet. It appears to set the multiplus to accept charge on / charge off signals from a BMS or another source for that matter.

IT is called the Two signal BMS support assistant...

https://www.victronenergy.com/upload...uattros-EN.pdf

[newhaul]

Originally Posted by john61ct

Yes, combi inverter/chargers interfere with the usual LFP design modes, cannot separate loads buss from charge buss.

Keeping both Absorb and Float settings turned down to Storage voltage levels is one possibility.

A lead Reserve bank lets you completely isolate the LFP Main house, even if it is very small. Or Starter(s) can serve that function.

Or just let the LFP bank sit at Full and take the longevity hit, could well allow you to get a decade or more and KISS.

So now your advocating for a lead reserve / starter
What had changed since
http://www.cruisersforum.com/forums/...ml#post2972968
About 4 pages back when you were not wanting lead based in the system at all is this new charger the reason for the change in theoretical battery setups ?

[Dockhead]

Originally Posted by evm1024

I've been looking at the (non victron) lithium assistant. No experience with it yet. It appears to set the multiplus to accept charge on / charge off signals from a BMS or another source for that matter.

IT is called the Two signal BMS support assistant...

https://www.victronenergy.com/upload...uattros-EN.pdf

Bingo!


That's it exactly, and must be what CatNewBee was talking about.


It's not in my Multiplus manual -- guess it's a feature of newer ones, than mine:

[john61ct]

Yes I did not infer that Power Boost, or even any particular vendor's gear were essential elements to the current discussion.

Originally Posted by Dockhead

It would be really useful to be able to limit the charging to some set % SOC.

It may seem crude, but just setting Absorb and Float voltages to between 13.1 - 13.2V, 3.27 - 3.31Vpc should accomplish that.

By default start testing at the low end. If the Ah draw required from the bank is high, then stick to the higher end.

[Dockhead]

Originally Posted by john61ct

Yes I did not infer that Power Boost, or even any particular vendor's gear were essential elements to the current discussion.

Well, I mentioned Power Boost in every post. It's a fundamental function on my boat, and probably any other boat with any gear which will do this (Victron, Magnum, Mastervolt, etc.). This is an exceptionally useful function.

Originally Posted by john61ct

It may seem crude, but just setting Absorb and Float voltages to between 13.1 - 13.2V, 3.27 - 3.31Vpc should accomplish that.

By default start testing at the low end. If the Ah draw required from the bank is high, then stick to the higher end.

It does seem crude, and this does not achieve the described target functionality.


First of all, I am skeptical whether with lithium you can hit some partial SOC, whether it's 50% or whatever, or anything close, with voltage setting alone, although I will defer to those with experience (I have none).


But secondly, I am after a SWITCH to allow me to select target SOC with on flip. I don't want to go into a programming menu and reprogram charging voltages every time I change regime.