Hybrid FLA - Lithium circa 2022

[@Michael]

I ran across what I think is a way of building a hybrid lead-acid/lithium battery system similar to what's been proposed by @marcopolo, @hbn7hj and others.

The general idea is to directly connect the FLA and LiFePo4 battery banks when voltages are within a certain range and disconnect them from each other when not.

All charge sources are always attached to the FLA bank. The LiFePo4 bank is combined with FLA's when FLA's are charging and LiFePo4 is not fully charged and disconnected when the LiFePo4 is charged, but the FLA's are not charged. Connect/disconnect is via a mechanical relay.

During charge cycles, the concept relies on monitoring voltage to allow full charge of the FLA's without exposing the LiFePo4's to the excessively high voltage needed by the FLA's.

The concept takes advantage of the natural load-sharing feature of a hybrid bank, where the LiFePo4's charge the fastest and supply most of the current until they are nearly depleted.

See:

https://www.wildebus.com/hybrid-batt...-introduction/

and:

https://www.emilyandclarksadventure.com/bbms

Both of the sites sell a microprocessor controller to determine when to combine and disconnect the banks, based on charge status and voltage difference.

Interesting.

--Mike

[booster]

Originally Posted by @Michael

I ran across what I think is a way of building a hybrid lead-acid/lithium battery system similar to what's been proposed by @marcopolo, @hbn7hj and others.

The general idea is to directly connect the FLA and LiFePo4 battery banks when voltages are within a certain range and disconnect them from each other when not.

All charge sources are always attached to the FLA bank. The LiFePo4 bank is combined with FLA's when FLA's are charging and LiFePo4 is not fully charged and disconnected when the LiFePo4 is charged, but the FLA's are not charged. Connect/disconnect is via a mechanical relay.

During charge cycles, the concept relies on monitoring voltage to allow full charge of the FLA's without exposing the LiFePo4's to the excessively high voltage needed by the FLA's.

The concept takes advantage of the natural load-sharing feature of a hybrid bank, where the LiFePo4's charge the fastest and supply most of the current until they are nearly depleted.

See:

https://www.wildebus.com/hybrid-batt...-introduction/

and:

https://www.emilyandclarksadventure.com/bbms

Both of the sites sell a microprocessor controller to determine when to combine and disconnect the banks, based on charge status and voltage difference.

Interesting.

--Mike

That is similar to some of the initial concepts discussed here a few years ago when the possibility of hybrid first came up.


At that time using 14.4v for charging was not an issue, we were told, for lithium so common charging would be fine at 14.4 or even 14.7v without lithium damage. Those rules have changed now with many wanting 13.8-14v on the lithium max.


I didn't have time to go the links, but charging together at a lower voltage than is needed for the lead acid is going to leave them short charged as the lithium will get there quickly and there will be on absorption voltage or hold time done. They probably would not see more the 70% or so which will cause capacity walk down quite quickly.


On discharge, they won't share load very well as the voltage drop on the lead acid will happen a lot quicker than on the lithium. I don't know how much you would actually get out of the lead acid as it would rest even fully charged at a lower voltage than the lowest you would get on empty lithiums.


All of this kind of stuff is what lead to the use of B to B and other multiple charging in the combo systems that have been put together by folks on here.


There are several discussions that go into great detail on them on this forum.

[GallenH]

So I've been wondering for a while: Is this scenario possible/good?


charging sources-->B2B-->Lithium batteries-->B2B-->AGM batteries.

Obviously needs a lot of clarification

1. Missing switching; manual and/or relays.
2. Probably a separate shore AC charger for lithium using existing for AGM (a previous @Michael suggestion). Solar might be used for Lithium or AGM .

As in earlier hybrid discussions, Lithium would be the recipient of faster charging, then relegated (perhaps overnight) to charging the AGM.

[rowiebowie]

Something to ask yourself. If lead-acid/lithium hybid systems are a good idea, how come OEM's don't build them this way?

Another way to phrase it, if a lead-acid to lithium-only conversion were difficult, how come a dolt like me was able to convert my class b?

[booster]

Originally Posted by rowiebowie

Something to ask yourself. If lead-acid/lithium hybid systems are a good idea, how come OEM's don't build them this way?

Another way to phrase it, if a lead-acid to lithium-only conversion were difficult, how come a dolt like me was able to convert my class b?

Actually, Hymer in Europe did make such a system that combined AGM and lithium just before they went under in this country. It was not very well done, it appears and faded out. The systems in use here appear to work much better because they match the voltages better.


I wouldn't say converting to lithium is easy as you have to replace pretty much everything, provide heat if you are in the cold, limit current on some, and do full shutoff charging, plus provide recovery methods in case of shutdown to activate chargers. Doable, sure, but especially if someone is doing a best practices setup like Avanti will have and ARV does, it gets very complex. IMO, the term "drop in" replacement does not really apply.

[avanti]

There is a scary but very important thread over at Sprinter-Source comprising a first-hand account of a serious LiFePo4 battery meltdown event in a DIY install:

https://sprinter-source.com/forums/i...hreads/106906/

Well worth reading.

[rowiebowie]

I was very thoughtful and cautious with my lithium conversion, but at it's most basic, it is replacement of batteries and charging sources. Much easier for me perhaps, because I stayed with a modest battery pack which kept my install to the coach area with no modifications under the hood.

Starting with the existing Battery Isolation Manager, I re-routed the wiring from it to my new components. Yes, an error could have been disastrous, but I maintain it was more plug & play than hard.

[GeorgeRa]

Originally Posted by avanti

There is a scary but very important thread over at Sprinter-Source comprising a first-hand account of a serious LiFePo4 battery meltdown event in a DIY install:

https://sprinter-source.com/forums/i...hreads/106906/

Well worth reading.

Thanks for posting. I have seen some substandard electrical conversions on the Sprinter Forum including adapting Tesla batteries. I am glad that the owner of the failed battery shared his troubles openly, good for other folks not to take electrical systems negligently.

[booster]

Originally Posted by GeorgeRa

Thanks for posting. I have seen some substandard electrical conversions on the Sprinter Forum including adapting Tesla batteries. I am glad that the owner of the failed battery shared his troubles openly, good for other folks not to take electrical systems negligently.

Ooooh, using the Tesla more dangerous chemistry and doing it any way but perfect is a recipe for disaster.

[GallenH]

Was one of the problems here that the OP was building his own lithium from interconnected cells? IOW would the same concerns be present buying a brand name 12v lithium battery?

[hbn7hj]

Originally Posted by rowiebowie

Something to ask yourself. If lead-acid/lithium hybid systems are a good idea, how come OEM's don't build them this way?

The reason for the hybrid system is to adapt a former FLA system. The battery box is in the cold and alternator charging system already set up. When I got to 400AH of lithium I don’t use the FLA part much. 100AH of lithium I used both. FLA for furnace and lithium for electronics.

The main remaining advantage is I can start the generator without knocking all the electronics off line. Another is if either system has a failure the other still works. That happened once when the FLA battery aged out.

No need to use a hybrid for a new system.

[booster]

The original premise on the hybrid system was to make it so those with lead acid battery banks that were recharging them from a generator could shorten the generator run time and still gets the lead acid batteries full.


The idea was to use a lithium battery that was smaller than the lead acid bank by quite a bit to do the finish charging in the long slow absorption stage of charging. It can take many hours to do and is at very low charge rate.


You would run both the lead acid and lithium to about 80% full on the AGM and stop the generator charging. Then you would finish charging the AGM bank the last 20% from the lithium. You could then quickly charge the lithium back up off the generator.

[Bud]

"No need to use a hybrid for a new system."


As booster mentioned earlier, Hymer...........

Today lithium is almost cheap compared to when Hymer was doing their whatever in Europe. There are very few applications left for expensive agm's - inexpensive marine deep-cycle or inexpensive agm or lithium.

[@Michael]

Originally Posted by booster

I didn't have time to go the links, but charging together at a lower voltage than is needed for the lead acid is going to leave them short charged as the lithium will get there quickly and there will be on absorption voltage or hold time done. They probably would not see more the 70% or so which will cause capacity walk down quite quickly.

They disconnect the lithium when the combined bank hits 14.x volts, then continue charging the FLA's to 100%. In their schema, both banks get charged to 100%.

Originally Posted by booster

On discharge, they won't share load very well as the voltage drop on the lead acid will happen a lot quicker than on the lithium. I don't know how much you would actually get out of the lead acid as it would rest even fully charged at a lower voltage than the lowest you would get on empty lithiums

True that the load sharing favors the LI's - they have a higher resting voltage and lower internal resistance, but the FLA's do contribute significantly once the combined bank voltage gets low enough (approx 12.8v). There is a thread on this forum with test data[link], and I did an experiment myself a couple years ago.

[@Michael]

Originally Posted by hbn7hj

The reason for the hybrid system is to adapt a former FLA system. The battery box is in the cold and alternator charging system already set up. When I got to 400AH of lithium I don’t use the FLA part much. 100AH of lithium I used both. FLA for furnace and lithium for electronics.

The main remaining advantage is I can start the generator without knocking all the electronics off line. Another is if either system has a failure the other still works. That happened once when the FLA battery aged out.

No need to use a hybrid for a new system.

I still have the onboard generator, so a means of starting the generator is useful. Extreme cold also makes the AGM's useful. But I agree that in a new build, there is no reason to go hybrid.

I'm a bit jammed up because of space. My OEM AGM's are mounted underneath the camper directly exposed to road debris, salt, mud, etc., so directly swapping them for lithium is problematic - I'd have to build a pair of insulated, heated weathertight boxes (or give up interior storage space...)

[hbn7hj]

Originally Posted by @Michael

I'm a bit jammed up because of space. My OEM AGM's are mounted underneath the camper directly exposed to road debris, salt, mud, etc., so directly swapping them for lithium is problematic - I'd have to build a pair of insulated, heated weathertight boxes (or give up interior storage space...)

Lithium batteries belong inside. Just a strong opinion.

[booster]

Originally Posted by @Michael

They disconnect the lithium when the combined bank hits 14.x volts, then continue charging the FLA's to 100%. In their schema, both banks get charged to 100%.

Exactly the point of what the original idea was, except that if you have to continue to charge the AGMs anyway, why have the lithium? You are then just back to saving a little weight for a lot of money back then. You lose the fast charging, which was one of the big points of having lithium, you don't get any real sharing as all you get is sort of load staging with the lithium discharging first and the AGM second. You might just as well go all AGM.



A 50% down AGM is going to take upwards of 8-10 hours to fully charge depending on bank size and charger size to a small degree only. Running a generator that long is noisy, stinky, gas using waste for most of that time. By running the generator for an hour or two and then topping the AGMs from lithium then run the generator again to recharge the lithium you can cut the run time by over 50%.


Times have changed since all that was tried. It did work, but the cost reduction of the lithium and lower charge rates of many of the lithium batteries have diminished the benefits of doing the hybrid setup greatly. It is now better to go one way or the other with a one chemistry bank, IMO, especially with no generator rules getting more and more common.

[booster]

Originally Posted by @Michael

They disconnect the lithium when the combined bank hits 14.x volts, then continue charging the FLA's to 100%. In their schema, both banks get charged to 100%.

Marko did lots of great testing and experimenting back then and got good results. But those tests also showed exactly the point of what the original idea was, that if you have to continue to charge the AGMs anyway, why have the lithium? You are then just back to saving some weight for a lot of money back then. You lose the fast charging, which was one of the big points of having lithium, you don't get any real sharing as all you get is sort of load staging with the lithium discharging first and the AGM second. You might just as well go all AGM.



A 50+% down AGM is going to take upwards of 8-10 hours to fully charge depending on bank size and charger size to a small degree only. Running a generator that long is noisy, stinky, gas using waste for most of that time. By running the generator for an hour or two and then topping the AGMs from lithium then run the generator again to recharge the lithium you can cut the run time by over 50%.


Times have changed since all that was tried. It did work, but the cost reduction of the lithium and lower charge rates of many of the lithium batteries have diminished the benefits of doing the hybrid setup greatly. It is now better to go one way or the other with a one chemistry bank, IMO, especially with no generator rules getting more and more common.

[hbn7hj]

Originally Posted by booster

Times have changed since all that was tried. It did work, but the cost reduction of the lithium and lower charge rates of many of the lithium batteries have diminished the benefits of doing the hybrid setup greatly. It is now better to go one way or the other with a one chemistry bank, IMO, especially with no generator rules getting more and more common.

Gotta agree. For me the FLA is now only there to interface with the alternator.

[GallenH]

Yeah. I'm just not wanting to waste my LifeLine AGM. Plus my current alternator seems sized to only handle 200AH of batteries. A sleeker system would be to do 300AH of Lithium, upgrade my alternator, and nix the B2B that would be dedicated to charging the AGM off the Lithiums. That would cost c.$1k more than the hybrid (the cost of the new alternator+additional lithium minus the cost of the B2B dedicated to the AGM).