Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

Cariboocoot

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

Blackcherry04 wrote: »

He can do that because he has a 20 amp hr 12v battery and a 40amp hr 12v battery that he posts about. If you have a 48V battery with 64 cells there no way to ever keep them balanced. His advise is to use a fluke meter and a single cell charger to keep them balanced, totally impossible to do with a Solar size bank. They probably do that over on the RC forums on a small battery pack.

I think the same problem would occur even with the BMS: 16 cells? Oh yeah I'd want all that extra wiring around to try and keep it evened out. Not.

Having seen so many lead-acid batteries destroyed by misuse I can just imagine the horror of burning up an expensive bank of LiFePo's by your average Joe. This is the main reason the chemistry is impractical at this point; the intense management isn't going to happen and the cells are not forgiving of mistakes.

Blackcherry04

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

Cariboocoot wrote: »

I think the same problem would occur even with the BMS: 16 cells? Oh yeah I'd want all that extra wiring around to try and keep it evened out. Not.

Having seen so many lead-acid batteries destroyed by misuse I can just imagine the horror of burning up an expensive bank of LiFePo's by your average Joe. This is the main reason the chemistry is impractical at this point; the intense management isn't going to happen and the cells are not forgiving of mistakes.

Your 100% right, without a technical expertise they are a disaster waiting to happen. At this point I don't think much about them, but I see where I will have to deal with them at some point, so I might as well learn as much as my customers will.

creeky

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

Thanks Karrak for the excellent posts.

Coot posts "At the other end of the spectrum is how low the Voltage will be at these lower SOC levels and how that will affect loads (especially non-inverter loads)." According to the available literature: at 80% dod a (12v 9kw) LFP battery bank is capable of delivering 350 amps. And indeed LFP offers 500 amps at 50% dod. A significant advantage over FLA battery banks. And the voltages at these dods, as seen in Karrak's original post, are much higher than with FLA.

Self discharge on LFP is almost non existent. Far far lower than FLA. So what other non-inverter loads there are I'm not sure.

I have a near 15kw FLA currently (sorry never gets old) and the most I ever draw from my system is 2kw, or call it >160 amps. I had a 3kw inverter previously, say 250 amps. So make my FLA a LFP and even at full load we're within the 80% dod capacity. And I almost never take my dod below 20%. It's FLA after all. And I wouldn't like to think what I would be doing to my FLA if I discharged at 2kw at a 80% dod. Or even 50. No?

Coot also asks "Now if the LiFePo is going to be 'kept' at, say, 90% SOC as a maximum (they don't suffer from the low SOC sulphation problem of lead-acid) just how low can they be taken and reliably recharged from without lifespan sacrifice? It would need to be 40% to make up the same range (40-90 = 50%). If they can go lower and still be brought back (it has been established there is less Voltage difference per SOC point than with lead-acid so the current increase per Watt is not an issue) then they have a capacity advantage."

And this appears to be the case. You can "reliably" discharge LFP packs to 40% and still receive 3650 cycles. If you discharge to 50% dod you should receive 5000 cycles. Destructive testing has taken LFP packs to 100% dod and received 2000 cycles. So yes. LFP has a capacity advantage.

These attributes are why LFP looks good for off grid.

Thanks again to Coot for bringing this up so concisely.

BC4 comments "It's your business if your a 95% to 50% or 100% to 80%, no one cares." I suppose no one cares except someone who relies on a battery pack (regardless of chemistry) to get them through the night. Then you care a great deal.

To put this in perspective. Take the a fore mentioned 9kw battery pack. If you can run 95 to 50 dod at 9kw. That's, eh, call it 4kw. Now 100 to 80 dod. That's less than 2 kw. So you must more than double your battery bank size to make up the difference.

So in one sense he's correct. If the size of the battery pack is a variable based on an imaginary number, then no one cares. But if you need your battery pack to produce electricity after 3 low input days (such as Alaska Man just experienced) then the lifespan vs dod makes a great deal of difference. And if you want to run a microwave, as Coot points out, then the amperage available at a low soc or deep into your dod also makes a difference.

And this is the real crux. LFP seems to offer higher amperage discharge even at greater dod. In addition is appears to offer greater longevity even with higher dod over FLA.

The trick now is to find reliable and reasonable information about how to implement what looks like a real improvement for us off grid solar users. Thanks to P/K/R etc for showing us what can be done.

karrak

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

Cariboocoot wrote: »

Now if the LiFePo is going to be 'kept' at, say, 90% SOC as a maximum (they don't suffer from the low SOC sulphation problem of lead-acid) just how low can they be taken and reliably recharged from without lifespan sacrifice? It would need to be 40% to make up the same range (40-90 = 50%). If they can go lower and still be brought back (it has been established there is less Voltage difference per SOC point than with lead-acid so the current increase per Watt is not an issue) then they have a capacity advantage.

I would use the range 90-20% SOC for an LFP battery, Winston says 10%. The main thing is to keep the cell voltages above 2.8 volts (22.4 volts for 24 volt battery)

At the other end of the spectrum is how low the Voltage will be at these lower SOC levels and how that will affect loads (especially non-inverter loads).

Here is the logged data over about a month of use with my battery.

[alltime]
timestamp = '20141103094309 '
maxvoltages = [3.463, 3.49, 3.465, 3.503, 3.462, 3.462, 3.509, 3.501, 27.86]
minnoload = [3.235, 3.231, 3.235, 3.236, 3.239, 3.237, 3.247, 3.233, 25.92]
minvoltages = [3.114, 3.112, 3.093, 3.11, 3.078, 3.119, 3.117, 3.095, 24.86]
deltav = [0.004, 0.109, 0.109]
amps = [-35.0, 173.9]
ah = [-6.96, 104.07, 210.18, 28164, -1208.51, 1191.33]

maxvoltages is the maximum voltage measured over the time period of each cell and the pack as a whole
minnoload is the minimum voltage measured over the time period of each cell and the pack as a whole with a load of less than 10A
minvoltages is the minimum voltage measured over the time period for each cell and the pack as a whole
deltav is the difference in voltage between the highest and lowest cell in mV measured over the time period, the first reading is the lowest difference, the second in the maximum difference with a load less than 10A, the third is the maximum difference
amps is the maximum charge and maximum discharge current measured over the time period, negative is charge
ah is the DOD of the battery in Ah measured over the time period, my pack has a nominal rating of 360Ah, the first figure is the lowest DOD, with 0 being 'full', the second figure if the average DOD over the period, the third figure if the maximum DOD (360 should be empty), the forth figure is the number of samples the average is taken over, the fith figure is the total charge in Ah, the sixth figure is the total discharge in Ah. There is a minute between samples.

The important figures here are that my maximum discharge current was 173.9A or ~C/2, the minimum pack voltage of 24.86 volts and maximum DOD of 210.18Ah (~40%SOC). I cant be sure but it is most likely that the minimum voltage occurred at around ~40%SOC with the load around C/2. The reason I say this is that our highest power draw is at breakfast (toaster, microwave and Induction cooktop on together) when the battery is likely to be at its lowest state of charge.

Simon

karrak

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

Blackcherry04 wrote: »

If you have a 48V battery with 64 cells there no way to ever keep them balanced. His advise is to use a fluke meter and a single cell charger to keep them balanced, totally impossible to do with a Solar size bank. They probably do that over on the RC forums on a small battery pack.

48 volts is 16 cells (16s) not 64 and it is possible to do manually.

Cariboocoot wrote: »

I think the same problem would occur even with the BMS: 16 cells? Oh yeah I'd want all that extra wiring around to try and keep it evened out. Not.

A 24 volts battery BMS requires only nine wires, a 48 volt battery requires 17 wires if going to a central controller or a one wire loop between the cells if one uses something like the House Power BMS mentioned by Blackcherry04.

Having seen so many lead-acid batteries destroyed by misuse I can just imagine the horror of burning up an expensive bank of LiFePo's by your average Joe. This is the main reason the chemistry is impractical at this point; the intense management isn't going to happen and the cells are not forgiving of mistakes.

I would think there would be well over one billion devices in the world, from phones to computers to power tools being powered by more dangerous versions of Lithium Ion batteries than we are talking about. This is possible because each has a tiny embedded safety circuit that makes sure it can't be mistakenly overcharged or discharged. If the market takes off for large prismatic cells I am sure the same thing will be developed. I would like to see a situation where each cell talks via wireless to a central controller/logger which then talks via wireless to other components in the power system like Charge Controllers and Inverters so the only system wiring would be the main power feeds. This is not rocket science, all the technology is there it just needs a market.

At the moment we are stuck with BMS systems needing wiring between the cells and a controller and for full protection two or three relays, one in the feed between the solar panels and charge controller, one to shut down the loads, and an extra one if we have another power source like a generator. Not ideal but not very complicated either.

Blackcherry04 wrote: »

Your 100% right, without a technical expertise they are a disaster waiting to happen. At this point I don't think much about them, but I see where I will have to deal with them at some point, so I might as well learn as much as my customers will.

Any installer with enough electrical knowledge should be able to put together a user proof off-grid power system using LFP batteries that looks like a 'black box' to the user with the equipment I have outlined above.

Simon

PNjunction

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

Blackcherry04 wrote: »

He can do that because he has a 20 amp hr 12v battery and a 40amp hr 12v battery that he posts about. If you have a 48V battery with 64 cells there no way to ever keep them balanced. His advise is to use a fluke meter and a single cell charger to keep them balanced, totally impossible to do with a Solar size bank. They probably do that over on the RC forums on a small battery pack.

Sorry - not just RC'ers do this. EV'ers do the same with much more voltage and many many more cells. Running conservatively, they don't need the risk of the balance boards failing, and rely on their own manual initial balancing and conservative charge voltages. EV'ers would LOVE to run a mere 48v and the simplicity of operations that entails. See the EVTV stuff if you like.

Because I actually HAVE hands-on experience with lifepo4, if I had to build a 48v housebank tomorrow, and maintain it with conservatism, I could. This is why I wanted to get some real world experience and walk the walk, and not just stir endless forum theoretical talk.

Think of balancing like a EQ in FLA, your using it to balance cells, you do it with a over voltage, then you can do it with balancing boards as necessary. The board will start shunting the current as each cells voltage reaches the set point, while the others come up.

Yeah, and then one of the shunts fails, draining your cell to nada, or taking a bit longer to do it UNbalancing your battery. All that you have accomplished goes out the window. But this has all been rehashed over and over on the EV forums. I'll stick to conservatism but understand those that want/need the added circuitry.

PNjunction

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

Cariboocoot wrote: »

At the other end of the spectrum is how low the Voltage will be at these lower SOC levels and how that will affect loads (especially non-inverter loads).

That's the part that catches one off-guard. Unlike the early-warning signs of the voltage drop of lead-acid, there is very little voltage drop under heavy load right up to nearly the very end with lifepo4, and EV'ers in the early days found out the hard way when drawing hundreds of amps. One minute you seem fine, and the next - kaput. If the cells weren't balanced to begin with, one or more got damaged from cell reversal.

This is why these guys "bottom balance" to make sure that all cells reach the low voltage disconnect at the same time, especially when being able to draw hundreds of amps just before falling off the discharge cliff, as opposed to our top-balancing scheme.

Fortunately, we aren't pulling hundreds of amps in the typical solar setup and drawing cells down past 80% DOD - that is if you intend to make it through the night with an appropriately sized battery to begin with. But that higher overall voltage, ie 12.8v (maybe 12.7v under heavy load) as your lvd for 80% DOD takes some getting used to - as 12.8v is perfectly fine under lead-acid.

Blackcherry04

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

Same stuff - Different day. All this has been around before, The Ni-Cad and NiMH batteries were going to revolutionize the Battery storage world, then it was gel batteries and the AGM's. Now it's the LiFep04 promoters looking for someone else to share in their misery and expand into a new market. Next it will be the Sodium / Carbon with the Aquion batteries. The good thing is, this too shall pass and the FLA battery will still be trucking along.

Cariboocoot

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

karrak wrote: »

Any installer with enough electrical knowledge should be able to put together a user proof off-grid power system using LFP batteries that looks like a 'black box' to the user with the equipment I have outlined above.

Simon

You haven't met enough users otherwise you'd never say something like that. :roll:

PNjunction

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

Blackcherry04 wrote: »

Now it's the LiFep04 promoters looking for someone else to share in their misery and expand into a new market. Next it will be the Sodium / Carbon with the Aquion batteries. The good thing is, this too shall pass and the FLA battery will still be trucking along.

Thing is, I'm not promoting nor advocating the overthrow of FLA. You have nothing to be scared of from me. What I'm doing is sharing my own experience for those that may choose to run lifepo4 if it fits their situation. Unfortunately, lifepo4 has a lot of "too good to be true" aspects to it that touch off hot-buttons for many, and for some reason feel threatened by it. Instead of exploring the possibilities, there is only an endless parade of negativity missing the forest for the trees.

In my own case, it upset the apple-cart over what I thought I knew coming solely from a lead-based background. Ironically, I started my investigations with that mindset to "save" others from all that misery. My misery was short lived.

In fact, lifepo4 cheerleaders and salesman don't like me since I have proven to myself and show others that with a touch of conservatism, you don't need to obsess over balance. LVD and HVD like any battery installation - yes.

BALANCE - one reason not to obsess over balance is that the ONLY thing you are achieving by top-balancing is mere exposure to the same voltage at the end of charge. It has nothing to do with capacity balance because each cell has it's own slight differences in both manufactured capacity and internal resistance.

I proved this to myself by swapping out one of my 20ah cells into the 40ah battery. Yes, I was able to "top-balance" in this condition, but no sane person would run this way. That single 20ah cell gets hammered doing all the work and limiting the overall capacity of the entire battery, despite the perfect balance charge I'm able to provide across the entire set of cells.

Thus, by being conservative and giving myself a little headroom, the normal set of cells with roughly the same capacity and IR, can be easily maintained by using lower SOC charge voltages and making sure that none go over 3.6v. Sure, WIDE voltage differences are to be avoided and a reasonable sense of balance should be done, but it proved that endlessly driving these things into shunt-balancing voltages, or sweating out minute differences in SOC charge voltages is not doing anything for you.

It is this kind of actual hands-on that I wanted to share as it may save someone YEARS of forum speculation from those who are only spectators, and not active participants in the game.

karrak

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

Cariboocoot wrote: »

You haven't met enough users otherwise you'd never say something like that. :roll:

I understand what you are saying, making things 'user proof' is a major part of any design effort. I made a living designing, manufacturing and selling specilised electronic equipment predominantly to the police and mining industry. We used to have a term that the police agreed with, "has to be copper (police) proof":roll:

Simon

Reed

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

I remember the term "GI Proof" and it was generally accepted that there was no such thing. "This side towards Enemy" "hmm, which side is which?"

PN suggested I look at Cruiser and Sailing Forum. The thread on using LFP is now 270 pages of posts, and there are over 4300 posts on this thread. I have started on page one which dates back about three years. May get an education.

Reed and Elaine

westbranch

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

If they use the same VBulletin (SP?) program that this forum runs on, you will be able to read a full page or 2 and it will remember where you stopped and went on to something else when your head spins or you eyes grow weary.. have fun...4300 phew!

PNjunction

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

You mean this thread that will require a week's vacation to read:

http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html

It is a good example of getting the general debate about the merits of lifepo4 out of the way, and allows those who are actually using them to help each other. They also aren't concerned with manufacturing issues, like making them bulletproof for the guy next door, or other distractions.

Despite having 4000+ messages, overall lifepo4 IS simple to operate and maintain - whether you use a bms or not - it's up to you. The key issue is that they stick to the application at hand, that is a "Sub-C" application like ours, and are not going on tangents by EV, RC modeling, or other applications which require different handling and techniques.

One might think of it as a great resource for ideas that can be brought back here pertaining to our use.

One of their members has written up a GREAT lifepo4 article "Lifepo4 thoughts & musings" which can be found here although you'll have to manually click on the "How-To" category first and there is more than one page!

http://www.marinehowto.com/

Good stuff from which we can ALL benefit.

Blackcherry04

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

We've heard the proponents extol all the virtues of LifeP04 batteries and we get it, where they fall short is how anyone without a lot of technical expertise is going to manage them. In the real world most would be heading for a disaster. If you have deep pockets and time to babysit a battery bank, you might do ok. Being called a Naysayer or a Leaddie is a compliment, this is not speculation, it's the fact's.

Prime example :

" Been using them for well over a month and they function excellently, but do have one problem with charging, one cell line always goes over 3.6 volts during charge and the others are still at 3.3-4v. "

Answer Given :

"You've GOT to monitor each cell during this charge procedure with a battery with so many cells. During the charge, have you actually measured the voltage of each and every cell, and not just the line itself. "

How many cells is that in a 48v bank ?? This what your going to see over and over again.

The only difference between these and FLA batteries is the smoke from the money leaving your wallet if you don't watch them closely. You are trading a hydrometer and distilled water for a DVM and individual cell charger and lot of work keeping them balanced. Depending on the number and the size of the cells, size of the bank and how many parallel connections it contains. A properly designed BMS ( if you could find one ) can help, but a shunt type boards only drain less than 1 amp and unless you have one for each cell ( $10 - $15 per cell ) it's not likely to work and even then it has be verified to be working correctly often. Parallel connections have all the same issues with LiFeP04 that FLA batteries have, but they are a death sentence with LiFeP04 cells and do not get better on their own, it will cascade on to other cells and destroys them through uneven cell voltage in charge and discharge cycles.

Based on the quote above, can anyone guess where this persons bank is heading ?? It takes a whole more than a Fluke DVM and a Single Cell Charger. What is he going to do if he's off - grid ?? He's got to shut the system down, tear the bank apart and try to balance the cells manually using a charger ?? Where is the power going to come from to do this ?? If he has a bad cell or group of cells, what's he going to do ?? I'll tell you, he's up the creek and if he doesn't take action soon he'll end up with a smoking wallet. There 100's of way to lose these cells, even with the best designed system and equipment.

I don't see anyone here that has the expertise that is going to do it for people that get the idea from these threads they want a LiFeP04 bank.

Reed

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

PNJunction

Read that article and it is the best I have ever read. I anyone is seriously interested in LFP than they should read this article. I would strongly suggest that the naysayers also read before they attempt to rebut in the future.

One of the naysayers on this thread did post a photo of a damaged LFP battery bank but did not read the words. Below is what was said in the article.

"*These cells were in parallel which means a 3.2V nominal pack
*A 12V charger was used instead of a power supply or charger capable of LIMITING the voltage to 3.XX
Cells hit 4.55VPC!!!!!!!!!!!!!!!!!!!!!!!!
*Cells DID NOT EXPLODE, Catch fire or do anything other than get very hot!
*The cells did not even smoke!
*Two of the four cells actually survived this abuse!

If you believe LiCoO2 & LiFePO4 batteries are the same PLEASE STOP READING HERE and go back & hug your lead acid batteries.....(grin)
A lot of LFP is simple common sense..."

Reed

Cariboocoot

Re: Comparative specifications of LIFePO4 & Flooded Lead Acid batteries

Blackcherry04 wrote: »

I don't see anyone here that has the expertise that is going to do it for people that get the idea from these threads they want a LiFeP04 bank.

And I will thank the LiFePo cheerleaders to STOP recommending these as though they are viable for anyone and everyone who is trying to construct a solar electric power system.