Lithium iron phosphate batteries LiFePO4

[markopolo]

Just posting a few very interesting links re: Lithium iron phosphate batteries

First, a quick primer about the technologies:
(PDF file) http://www.righthandeng.com/hp153_pg86_ ... for_re.pdf

Note: Boeing is not using Lithium iron phosphate batteries

Second, if you like DIY projects then you can save a lot......
This update from Technomads after one year on Lithium iron phosphate batteries http://www.technomadia.com/2012/09/a-ye ... batteries/ includes links back to the start of their project and cost analysis comparisons etc.

Another DIY project inspired by Technomads http://marazuladventures.wordpress.com/ ... -research/
Be sure to download the PDF file: http://marazuladventures.files.wordpres ... eries8.pdf

and finally this blog - http://www.aboutrving.com/rr_one.php - the author had two production lithium ion batteries, coach and chassis, installed in his motorhome over two years ago and they are still performing well

[pattonsr]

Advanced RV has been using LiFePO4 batteries without any problems to the best of my knowledge.

[markopolo]

Just adding something I posted on Yahoo.

Re: LiFePO4 cost
They DIY approach to packaging the cells yourself can save you lots of money. All of the Lithium iron phosphate cells are made in China and are not that expensive but it is the combining and packaging of them with the mandatory protection circuitry / battery management sytem that into a useable unit for RV's and boats etc. and that only a few companies do it that allows for the very high retail pricing.

Also, one of the arguments in supporting their value as replacement batteries is that you would need only 70% or so of the ah capacity you previous had with lead acid batteries as they can be deeply discharged repeatedly (80%) whereas most lead acid battery users try to limit the discharge to 50%. LiFePO4 battery voltage doesn't taper off until they are basically discharged. Lead acid batteries discharge voltage drops as capacity is used.

Cycle life (80% discharge): lead acid 200 to 300 cycles, LiFePO4 1,000 to 2,000 cycles.

You can get considerably more useable battery capacity if you have LiFePO4 batteries rather than AGM batteries.

800ah LiFePO4 E-trek battery bank at 80% discharge equals 640 useable amp hours.
800ah AGM E-trek battery bank at 50% discharge equals 400 useable amp hours.

That's like 60% more useable amp hours!

Of course you can discharge true deep cycle lead acid batteries 80% but their lifespan would be greatly reduced as shown above.

Unless some other technology leap frogs over LiFePO4 adoption I think it will eventually be the RV battery of choice assuming prices come down of course.

[mlts22]

There are some other nice features. The LiFePO4 batteries don't gas, so they can be placed inside as opposed to a ventilated compartment. They don't need watering. They also can be mounted in any position.

Of course, the tradeoff is having to have circuitry to open circuits if a cell gets too hot or vents, as well as exact charging since these cells don't take to overcharging well, but those are not impossible, especially once China starts getting some experience in using these cells for in-town scooters and such as an effort to reduce pollution.

[markopolo]

Just bumping this old topic up to the top to see if we can continue the discussion.

I'd really like to know what the recommendations are for storing lithium batteries. I've read 80% SOC, 30% to 50% SOC, 40% SOC. I need help finding informative links on this topic.

Also, I'd like to see a definition of storage as it applies to lithium batteries. Is storage 1 day, 1 week, 1 month etc. of non-use?

[Davydd]

Advanced RV just sent out a news information sheet on their lithium ion battery system...

Go Farther off the Grid

They are using assembled LiFeP04 batteries in 400ah, 600ah and 800ah assemblies. They had been testing their systems since before May of this year that I know of for sure and they seemingly made the decision to go with it. I noticed previously they had been using lithium Smart batteries in some RVs.

I'm not sure exactly what you are asking about in battery storage.

[pattonsr]

I have no idea what Advanced RV recommends for Lithium in storage. My plan is to store the Sprinter with access to a 20 amp circuit. Set the inverter/charger to 15 amps incoming. Only use two stage charging. Set a wake up voltage to reenter stage one. Unless one has parasitic losses, the wake up voltage will probably never be reached if one stores the batteries full charged.

As an example Magnum calls their two stage charging Constant Current/Constant Voltage (CC/CV) which is an easy way to setup two stage charging.

[Davydd]

The Advanced RV charges the batteries from shore power. I would hope they have an intelligent battery charging system figured out because one thing you cannot do is overcharge lithium batteries because once done and out.

[pattonsr]

As long as an Outback, Magnum or Victron is used, no problem with lithium overcharging when using shore power.

The real question is how well they control overcharging driving down the road with a large second alternator. The exact details of this process is not documented yet .

[markopolo]

With lead acid you could say a fully charged battery is a happy battery. You can maintain the battery in a fully charged state at a float voltage. 13.1v or 13.2v etc.

In one example I read that lithium batteries should be either charged to 50% state of charge or discharged to 50% state of charge (depending on the starting point) prior to storing the batteries. That would be very different than what we do with lead acid batteries.

Another way to ask the question is - what is the storage or float voltage for lithium batteries? Is there such a thing?

Some links:

trickle charging is not acceptable for lithium batteries

http://www.powerstream.com/li.htm

2) Trickle charge not supported. The LiFePO4 batteries will be damaged when left on charge with the trickle mode charging. Most automotive 12V battery chargers have the trickle mode as a default setting. With LiFePO4 batteries, the charging must be stopped and the charger needs to be disconnected after the charge cycle is finished. If the charger unit disconnects (stops) after reaching the full charge, it may be used with LiFePO4. It is a must to avoid the trickling charge mode.

http://gwl-power.tumblr.com/post/631443 ... e-used-for

Store at 40% charge in cool place

battery lasts longest when operating in mid state-of-charge of 20–80%

http://batteryuniversity.com/learn/arti ... tery_table

[markopolo]

Another question......

How do LifepO4 battery Ah ratings compare to a lead-acid battery Ah ratings?

[bobojay]

Have to keep my eye on this thread as it's fascinating to me....

[Davydd]

Is there any difference? Isn't an amp hour an amp hour? The only thing that I've read is LiFePO4 batteries can be discharged at a higher rate and last longer without diminishing its capacity. That and they recharge faster with higher voltage and no float time. I'm studying up as much as I can. I think I know how Advanced RV has set up their battery banks of 400ah, 600ah and 800ah and what batteries they are using. At least I know they were testing the GBS Elite Power Systems batteries. Once installed one will never see them as they are under the floor in a sealed box.

If the Roadtrek videos are not doing a sleight of hand, it appears they are using Prismatic LiFePO4 batteries. I would guess they are using 180ah 3.2v batteries and putting 32 together to get 1,440 ah in a maximum configuration. It takes 4 cells to build a 12.8v battery assembly equal to 180 ah. That configuration would weigh almost 400 lbs. and depending how they are put together could create a bank of batteries measuring a minimum 22.4" x 28.8" x 11" high. Each tray you see in the video might latch under the floor as well and each tray of 8 cells would then be in approximately 24" x 8" metal boxes and would equal 360 ah. See the latches? It looks like they will hang. It would take four of those boxes to get to their maximum assembly. That's just a guess on my part from the visual clues.

[markopolo]

Originally Posted by Davydd

Is there any difference? Isn't an amp hour an amp hour? The only thing that I've read is LiFePO4 batteries can be discharged at a higher rate and last longer without diminishing its capacity. That and they recharge faster with higher voltage and no float time. I'm studying up as much as I can.................

I'm studying LifepO4 too.

For lead-acid the amp hour rating varies. I copied the following from another topic.

Look at the ratings here:
http://www.trojanbattery.com/products/deep-cycle-agm-2/

Batteries typically have three ratings: 5-Hr Rate,20-Hr Rate & 100-Hr Rate
Take the Trojan 31-AGM:
5-Hr Rate: 82 Ah (16.4 amps delivered per hour for 5 hours)
20-Hr Rate: 100 Ah (5 amps delivered per hour for 20 hours)
100-Hr Rate: 111 Ah (1.11 amps delivered per hour for 100 hours)

Same battery, 3 different amp-hour ratings.

In RV discussions we mostly use the 20 Hr rating for lead acid batteries.

It's different for LifepO4. Here are the questions from the previous pages of this topic: (I replaced lithium with LifepO4)

What is the storage or float voltage for LifepO4 batteries? Is there such a thing?
What are the recommendations for storing LifepO4 batteries?
What is the definition of storage as it applies to LifepO4 batteries? Is storage 1 day, 1 week, 1 month etc. of non-use?
How does a LifepO4 battery Ah rating compare to a lead-acid battery Ah ratings?

[Davydd]

When I say is there a difference I mean this stuff is all averages and guesstimates it seems. When they put meters on this stuff the readings are generally close and not exact. In other words if you had a choice between 400 ah battery banks in AGM or LifPo I am going to expect pretty much the same draw down at the same speed but will know if I want to preserve the life of my batteries I will have to re-charge sooner with the AGMs than the LifPos and it will take longer. There is a considerable cost difference too. So, my decision is more based on how I will use them, maintain them, etc. and will that make a difference. You could life cycle cost the batteries as well but maintained correctly I expect the LifPos to outlast my ownership but my personal experience and reading of others is you can run through AGMs in a season if you try continuously boondock. Even those life cycle and battery efficiency degradation numbers are just assumed averages.

So is an AGM ah the same as a LifPo ah? Yes as in an amp hour is an amp hour drawn and used by a device. No as an aggregate of ah in a battery bank. No matter what the rating, if you call an AGM battery 400 ah you have about 200 ah at your disposal. If you call a LifPo battery 400 ah you will have about 320 ah at your disposal. And if treated equally well as recommended you can generally expect four times the life using LifPo batteries (500 cycles vs. 2,000 cycles). My auxiliary AGM did not last anywhere close to 500 cycles. At the other end of the spectrum, because of how Advanced RV has set up parameters and limits with BMS governors on the LifPo batteries they are confident you could go 5,000 cycles but that doesn't mean you will have 400 ah at your disposal at the end. With all batteries they lose efficiency.

I am under the understanding there is no float period. You charge steady until 100% charged or some rate under 100% because you cannot (absolutely should not) overcharge a LifPo battery.

As for LifPo storage, that is on my list of questions I will go over in my orientation. There is a sitting discharge rate but I haven't investigated it yet. So, I don't have any answers.

[markopolo]

The AGM that prematurely failed probably rarely, if ever was fully charged. And I mean fully charged, not 90% or 95% etc. I think you'd have to use a good 3 stage charger and to plug in for 24hr at least once per month to make sure it gets fully charged monthly. It's possible to do it off an alternator if a proper charging voltage gets to the battery terminal but often there are losses due to the length and gauge of wire and the isolator used. It can be .5v loss so the battery never gets 14.4v. A chronically undercharged battery will suffer from sulphation of the plates and lose capacity. This is just a guess because I don't know how you maintained that battery.

That's one area where LiFePO4 will be fantastic in RV's. The battery can sit at 80% charged and not be damaged.

A quality 400 Ah AGM can go 1,000 cycles if limited to 50% DOD, 500 cycles if 80% DOD. http://www.trojanbattery.com/markets/re ... energy-re/
If you use 320 AH from either then the 500 vs 2000 cycles is valid.

........But lead acid batteries suffer from something known as Peukert's law.

Peukert's law expresses the capacity of a battery in terms of the rate at which it is discharged. As the rate increases, the battery's available capacity decreases.

Here's an older post about running a small window type A/C off batteries: http://www.classbforum.com/phpBB2/vi...p=12025#p12025

The example was for a 900 Ah bank. Look at the 90 amp draw on the chart and you see the Peukert corrected amps to be almost 106 amps. That's the "penalty" with lead acid batteries. From what I've read the Peukert's exponent for a LifepO4 battery is much lower, almost negligible.

That indicates that you can get more out of a 400 Ah LifepO4 battery bank than a 400 Ah AGM battery bank so there's another advantage

This brings us to the quality of the LifepO4 cells. The discharge C-rating differs greatly depending on the quality and the intended use for the LifepO4 battery. They can be formulated to be more like starting batteries or deep cycle batteries depending on the the intended use.

Interesting discussion here: (even gets into Peukert)
http://endless-sphere.com/forums/viewto ... =14&t=6559

They're indicating that you can replace a lead-acid battery with a lower Ah rated LifepO4 battery if good quality.

I can't wait for Davydd to report back after he's used his new Advanced RV for a bit. I suspect that power is just not going to be a concern at all in his RV.

Originally Posted by Davydd

So is an AGM ah the same as a LifPo ah? Yes as in an amp hour is an amp hour drawn and used by a device. ...................

Probably have to change that to no after factoring the Peukert "penalty" on each amp hr drawn from lead acid batteries. Advantage LifepO4.

[Davydd]

Marko,

I'm not an expert on this stuff. But yeah if one reads my analysis it doesn't seem I could use all that battery power. It is going to be interesting. There are some Advanced RVs already out in the field but I am not hearing any real life experiences about them for batteries and power usage. Maybe they just work and they don't think about it. One guy boondocked on the city streets of Manhattan for three days and I don't recall any comments about the power in the feature video they did. I'm not sure what he had installed. Most all the Advanced RVs have high amp battery systems. I believe out of the first couple of dozen very few had generators. Maybe just one.

[markopolo]

I saw this on Advanced RV's site: http://www.advanced-rv.com/go-farther-grid/

But it’s not just the weight savings. Compared to traditional AGM batteries, lithium batteries with the same amp-hour rating supply up to 40-percent more power between charges. Plus, they can safely charge at a much higher current than AGMs, so recharge time is shorter.

Note: assume that is for the products they have tested

I've read elsewhere of ratios as high as 2 to 1 depending on the application so the up to 40% more power seems possible in RV use. I've also read that quality matters. Don't expect great performance out of cheap cells.

I'm still reading up on this but it looks as though I could replace my 180 Ah lead acid battery bank with maybe a 130 Ah LifepO4 battery bank..... for example Or double the current "useful" capacity - just because - with a 260 Ah LifepO4 battery bank.

We need reports from RV'ers using LifepO4 batteries to get a better understanding of appropriate battery bank sizing.

[booster]

I have seen similar statements elsewhere about the extra power from the same AH capacity, but I think they were just referring to the going to 80% discharge compared to 50%, IIRC. As was mentioned earlier, Peukert might give you even more on top of that, especially if it was high load.

[Davydd]

The ARV release was specifically addressing the available amp hours between charging needs based on the recommended draw downs of 80% li-ion vs. 50% AGM. There are people that say you can draw down AGMs 80% as well but it has been pretty well documented it will reduce the life of the batteries. Of course, you could if you had to on occasion, but we are talking day in and day out general practice. Then on the other hand you can draw down li-ion batteries 95% if you chose and gain more. Advanced RV with its BMS has chosen to govern it at 80% draw down - a built in safety factor.

The weight savings depends on the batteries and manufacturers. Nominally a 100 amp hour 12v AGM will weigh about 67 lbs. The li-ion batteries ARV uses weigh about 28 lbs per 100 amp hour 12v block. The li-ons weigh about 42% of the AGMs. Factor in the useful amp hours of each you would have to use more AGMs to get an equivalent amount of energy between charges. I'm putting in an 800 ah battery bank. The weight will be 227 lbs. I will get a useable energy return of 640 ah. To get a return of 640 amp hours with AGMs I would have to install at least a dozen 12v 100 ah AGM batteries (1200 ah with 600 ah useable) and they would weigh 804 lbs. That is 577 lbs. difference for the same energy. Roadtrek uses 6v batteries. That may help AGMs in the differences but I haven't looked at it. I believe they don't go as high as 1,200 ah at 12v either because it is probably impossible to do so in a Sprinter because of space and weight.

I think if you want to go to these super high amperages li-ion is the only way. Since Roadtrek is pushing the envelope to achieve 24/7 air conditioning they had to do so with built up banks of 3.2v li-ion cells like ARV to achieve weight and space savings. They are doing so supplementing more solar and that means getting the air conditioner off the roof. With the air conditioner I am guessing they are using a 12v model that draws about 85 ah when running instead of the more common 125-140 ah draw rooftops.