Lithium may require a real paradigm shift

[SHaley]

After designing my LiPo conversion circuit I realized that I was thinking about how the system was going to be used in the wrong way. I'm using the Lead Acid model in my mind of, Charge, use(discharge) recharge, store. It's totally different for LiPo. A couple of comparisons below and feel free to add or sub.

1. Lithium should be stored at a 50% to 60% SOC to avoid plating the anode.
This would require the ability to run the converter or Tow but select charge/no charge for the battery pack.

2. The last section of the charge (saturation) is what diminishes the cycle life.
When Li-ions are charged to 4.20V/cell like consumer electronics, every reduction in peak charge voltage of 0.10V/cell is said to double the cycle life but also less capacity for the trip. I charge my cell phone to 4.2v/cell but I need talk time and can buy a new one for $15. If I'm light boondocking for a weekend then charging to only 14V can prolonged cycle life to 1000–1,500 cycles. For LiFePo4 (LFP) my trailer battery charges to 3.5v/cell at 4 cells 3.6v/cell is max for LFP. If you later charge to a higher end voltage the cell will come right back to full capacity, no memory.
Most LFP chargers have a 14.0v EOC voltage but check yours.

More to come, got to take advantage of this weather.

[wulfraat]

Correct on 50-60%. Well, < 80% is what I have heard as well. But definetly do not store at 100% SOC for long term battery health. FYI Cictron Multiplus Converter/chargers allow you do manage charge rate to the batteries - IE can you can turn off charging, or put just enough charge rate to balance out the outgoing 12v demand.

Regarding saturation / float, you are correct there as well. However, to my knowledge, all of the 12v consumer grade batteries / BMS on the market use passive cell balancing, meaning, you must float at 100% for a somewhat breif (~15-60 min) amount of time for the BMS to balance cells in the pack.

That doesn't mean you need to go to 100% on each cycle / charge, however.

I generally store at 60-80%. I only float at 100% every 5-10 or so cycles. At the end of the day who knows if that really makes a difference or not..... Based on my usage patterns my 600ah pack will roll for 20+ years. I am 4 years in.....

[dznf0g]

Originally Posted by SHaley

After designing my LiPo conversion circuit I realized that I was thinking about how the system was going to be used in the wrong way. I'm using the Lead Acid model in my mind of, Charge, use(discharge) recharge, store. It's totally different for LiPo. A couple of comparisons below and feel free to add or sub.

1. Lithium should be stored at a 50% to 60% SOC to avoid plating the anode.
This would require the ability to run the converter or Tow but select charge/no charge for the battery pack.

2. The last section of the charge (saturation) is what diminishes the cycle life.
When Li-ions are charged to 4.20V/cell like consumer electronics, every reduction in peak charge voltage of 0.10V/cell is said to double the cycle life but also less capacity for the trip. I charge my cell phone to 4.2v/cell but I need talk time and can buy a new one for $15. If I'm light boondocking for a weekend then charging to only 14V can prolonged cycle life to 1000–1,500 cycles. For LiFePo4 (LFP) my trailer battery charges to 3.5v/cell at 4 cells 3.6v/cell is max for LFP. If you later charge to a higher end voltage the cell will come right back to full capacity, no memory.
Most LFP chargers have a 14.0v EOC voltage but check yours.

More to come, got to take advantage of this weather.

While the numbers vary somewhat among applications and manufacturers, this all is basically true. Some BMSs handle all this for you, but you need to study your particular equipment.

LI, in general, and in gross terms"

1) like to live in humanlike comfort zones. 40*F to 80*F. Heating and cooling may be required for maximum life.

2) don't like to be run down below 15-20% nor above 80-85% capacity levels, for maximum life. Again some BMSs take care of that and some don't.

3) should be stored (differs from your numbers) 60% to 80% of their full capacity.

And don't forget your E-bikes.....they typically have no BMS, or a rudimentary one.

[2012FB]

Interesting! I have no idea why this did not dawn on me. I don’t charge my EVs more than 80% especially the Tesla which has no head room unlike my GM or Audi. I’ll have to get into the Multiplus II and set it for 80%. Thanks for the post!!

[SHaley]

2012 Make sure of your battery chemistry. Li/xxx lithium cobalt oxide, Lithium Manganese Oxide, Lithium Nickel Manganese Cobalt Oxide, Lithium Nickel Cobalt Aluminum Oxide, Lithium titanate, Lithium Iron Phosphate(LiFePO4) — LFP, Boiled shrimp, fried shrimp, steamed shrimp etc.
Apply the same principles but different volts/cell.

Okay, I really gotta say thanks to the father of modern lithium chemistry who is 99 years old (100 in July) and one hell of an engineer. You will not believe his name - but what he has brought to the field solid state physics is beyond words. His name is John B. Goodenough and he is a professor at UT Austin. I'm going to boonedock one day a raise a glass to this guy.

[AKNate]

I’ll largely repeat here what I said in another thread about this topic. Most EV, laptop, phone, etc batteries are a completely different chemistry than the LiFePO4 batteries we use in RVs. Having “lithium” in the name is about the only thing your Airstream’s batteries have in common with them. LiFePO4 batteries run at much lower voltage. Much of what you read about lithium batteries on the internet and even personal experiences with EVs, phones, or laptops is not specific to LiFePO4 and sometimes isn’t applicable. Most other lithium battery types have cycle ratings in the upper hundreds and are quite susceptible to degradation. Most LiFePO4 batteries are rated in the many thousands of cycles and don’t share all the same concerns, or at least not to the same magnitude. My Lion Energy batteries are rated for 3500 cycles at 100% DoD. BattleBorn’s are rated similarly.
There isn’t a ton of research that I’ve found that is specific to LiFePO4. What I’ve found doesn’t really give me cause for great concern. This paper compared capacity retention vs cycle SoC. After 1000 cycles the battery that was babied at 50-75% SoC had about 95% of its original capacity. The one kept at 75-100% had about 92% capacity. A loss of 3% in 1000 cycles isn’t really enough for me to worry about or make me cut off charging at 80%.
If someone knows of a study specific to LiFePO4 that looks at storage SoC, I’d be interested to know the results, but I have my doubts it would be anywhere near the degree of something to worry about as it is with other lithium chemistries, since the scale of the curves with LiFePO4 is an order of magnitude different. Sure, it probably shortens the life/reduces capacity. Enough that I’ll care? Probably not. Either way by the time I’ll need to replace the batteries I expect the replacements will be relatively cheap.
I think it’s still probably a good idea to run down your batteries a bit before storing and I’d make sure your “float” voltage isn’t set too high, but I’ve not seen anything from BattleBorn, LionEnergy, or any others that says you’re going to damage your battery or void your warranty if you sit at 100% SoC. That’s a pretty common thing to do in RVs.

[dznf0g]

Originally Posted by AKNate

I’ll largely repeat here what I said in another thread about this topic. Most EV, laptop, phone, etc batteries are a completely different chemistry than the LiFePO4 batteries we use in RVs. Having “lithium” in the name is about the only thing your Airstream’s batteries have in common with them. LiFePO4 batteries run at much lower voltage. Much of what you read about lithium batteries on the internet and even personal experiences with EVs, phones, or laptops is not specific to LiFePO4 and sometimes isn’t applicable. Most other lithium battery types have cycle ratings in the upper hundreds and are quite susceptible to degradation. Most LiFePO4 batteries are rated in the many thousands of cycles and don’t share all the same concerns, or at least not to the same magnitude. My Lion Energy batteries are rated for 3500 cycles at 100% DoD. BattleBorn’s are rated similarly.
There isn’t a ton of research that I’ve found that is specific to LiFePO4. What I’ve found doesn’t really give me cause for great concern. This paper compared capacity retention vs cycle SoC. After 1000 cycles the battery that was babied at 50-75% SoC had about 95% of its original capacity. The one kept at 75-100% had about 92% capacity. A loss of 3% in 1000 cycles isn’t really enough for me to worry about or make me cut off charging at 80%.
If someone knows of a study specific to LiFePO4 that looks at storage SoC, I’d be interested to know the results, but I have my doubts it would be anywhere near the degree of something to worry about as it is with other lithium chemistries, since the scale of the curves with LiFePO4 is an order of magnitude different. Sure, it probably shortens the life/reduces capacity. Enough that I’ll care? Probably not. Either way by the time I’ll need to replace the batteries I expect the replacements will be relatively cheap.
I think it’s still probably a good idea to run down your batteries a bit before storing and I’d make sure your “float” voltage isn’t set too high, but I’ve not seen anything from BattleBorn, LionEnergy, or any others that says you’re going to damage your battery or void your warranty if you sit at 100% SoC. That’s a pretty common thing to do in RVs.

I don't know about a "study", but here is one manufacturer recommendations:

https://www.canbat.com/how-to-store-lifepo4-batteries/


Other recommendations:
https://explorevanx.com/blog/how-to-...-12v-batteries

https://www.evworks.com.au/page/tech...-lithium-batt/

[SHaley]

My major point that I was going to make is for us older AS people. Maybe the new AS design is the same. The converter terminal is tied to the batteries. Can't stop charging them even if you wanted.

Do we agree this is not the way to do LFO. Maybe a 1 by 2 battery disconnect where you select converter or battery?
Only the charger with it's own on/off connects to the batteries.

[AKNate]

Originally Posted by dznf0g

I don't know about a "study", but here is one manufacturer recommendations:

https://www.canbat.com/how-to-store-lifepo4-batteries/


Other recommendations:
https://explorevanx.com/blog/how-to-...-12v-batteries

https://www.evworks.com.au/page/tech...-lithium-batt/

Those seem to agree charging to 100% and storing is fine. You just shouldn’t store below 50% or the gradual discharge may eventually bite you.

When you store LiFePO4 batteries, it is important that you store them with a state of charge (SOC) of 50% or higher. A higher state of charge is recommended when storing for an extended period of time. If you want the battery to retain a good level of charge after the storage period is over, you should charge them to 100% and store them in that fully charged state.

[SHaley]

Originally Posted by dznf0g

I don't know about a "study", but here is one manufacturer recommendations:

https://www.canbat.com/how-to-store-lifepo4-batteries/


Other recommendations:
https://explorevanx.com/blog/how-to-...-12v-batteries

https://www.evworks.com.au/page/tech...-lithium-batt/

Am I reading this right, the canbat & exlorvax say to charge the battery before storage. Charge it to what 50% SOC or 100%?

[uncle_bob]

Originally Posted by SHaley

Am I reading this right, the canbat & exlorvax say to charge the battery before storage. Charge it to what 50% SOC or 100%?

Hi

What's being done here is to talk about two *very* different kinds of lithium battery. One is a cell found in things like laptops. They have specific charge issues. The other is a *very* different battery used in RV's. With the RV battery (LiFePO4) charging "up full" is fine. In fact, you very much need to do it to equalize the cells. If you don't, then *that* will be what kills you.

Probably the biggest manufacturer of RV lithiums out their right now is Battle Born. (at least in terms of RV's equipped with them). My guess is this is by a pretty wide margin. Their recommendation is a full charge and then put it in storage. Again, this is for LiFePO4 and not for other types of Li batteries.

Bob

[dznf0g]

Originally Posted by AKNate

Those seem to agree charging to 100% and storing is fine. You just shouldn’t store below 50% or the gradual discharge may eventually bite you.

Yes, for long term, disconnected storage. "Storing" with a maintenance charge applied at 100%, no. A 100% charged, disconnected batt will be at 90% in 5 months.

[SHaley]

So what about my original question. Does your LFP battery charge whenever you tow or plug into shore power or do decide when to charge?

[richard5933]

Originally Posted by SHaley

So what about my original question. Does your LFP battery charge whenever you tow or plug into shore power or do decide when to charge?

All three of our charging methods (DC-to-DC, solar, and 120v converter) will start at bulk and then drop to float. The 120v converter will run through an initial bulk till voltage hits the bulk voltage and the amp draw drops below a set threshold, and then it switches to float. The other two devices are Victron and they also use an adaptive bulk phase which is slightly quicker to drop to float if the batteries are already charged.

I was told by the tech support at BattleBorn that it's okay just to let the system(s) do their thing when we're camping, but when we're between trips to just disconnect the batteries and let them sit.

Not sure there is really that much of a paradigm shift necessary other than not having to stress over keeping the batteries plugged in during the time between trips.

[SHaley]

Thanks Richard, my concern is, and I think I'm going to still do this, is move the tow vech wire over to the DC-DC input. As it is I'd be charging against it.

[richard5933]

Originally Posted by SHaley

Thanks Richard, my concern is, and I think I'm going to still do this, is move the tow vech wire over to the DC-DC input. As it is I'd be charging against it.

I disconnected the 12v+ wire from the 7-wire harness. The tow vehicle does not provide any charging to my trailer through the 7-wire. Instead, I ran a pair of 6ga wires directly from the TV battery to an Andersen connector on the rear of the TV, and then another pair of 6ga wires from the positive & negative bus bars in the trailer to the tongue terminating in another Andersen connector.

When I hook up I connect the 7-wire and the Andersen connectors. The 6ga wires allow my 12/12-18 DC-to-DC charger to provide the full 18 amps to my two lithium batteries while driving down the road, pulling about 22 amps from the truck alternator while doing it. Because of the 6ga wires, we have no voltage drop to worry about between the TV and the trailer. I could probably have gone larger with the DC-to-DC charger but didn't feel it necessary - since our 400w solar is also able to charge while driving the DC-to-DC is really there as a backup for traveling at night or rainy days.

[uncle_bob]

Hi

Both on the trailer and the van, I run a very normal hookup via the 7 pin. No special wires or anything weird. The charging current is limited by programming the DC/DC at a level that is not blowing fuses. Both the Classic and the trailer behind the van very much benefit from charging while driving. If we drive for 6 hours a day and get 15A, that's about 90AH each day. With our usage profiles, that alone will keep the lithiums happy. Yes, there's solar. Get a couple cloudy / rainy / yucky days driving through the forests and you won't get much solar. I have data on this ....

Bob

[1StreamDream]

Originally Posted by dznf0g

Yes, for long term, disconnected storage. "Storing" with a maintenance charge applied at 100%, no. A 100% charged, disconnected batt will be at 90% in 5 months.

Along these lines, I have solar, and it’s always connected, always providing some daytime charge, even when my trailer sits unused for a couple months. Is this a bad plan, to constantly keep them “topped off”, even in storage ? I thought it was the optimal plan …. I now have 3x100ah of battleborn lifepo4 for this scenario. Should I disconnect my solar panel charging path when my trailer sits idle/unused in order to maximize battery longevity?

[2012FB]

Ok, so my solar via the Multiplus II keeps the Battleborn batteries at 100% constantly year round. This is the best method??

[uncle_bob]

Originally Posted by 1StreamDream

Along these lines, I have solar, and it’s always connected, always providing some daytime charge, even when my trailer sits unused for a couple months. Is this a bad plan, to constantly keep them “topped off”, even in storage ? I thought it was the optimal plan …. I now have 3x100ah of battleborn lifepo4 for this scenario. Should I disconnect my solar panel charging path when my trailer sits idle/unused in order to maximize battery longevity?

Hi

If you have the trailer/van in storage, the best approach is to do a full battery disconnect. Put in a switch or solenoid/relay that completely removes the battery from everything. Just let it sit there. No charge / no discharge / no top off to 14.4V. Let it drift around and do its thing. Maybe a year or two later it will take 10% of the rated amp hours to top it off .... maybe less ... like a lot less.

Bob