AGM still makes more sense than Lithium

Skyko

I have been reading a few dozen blogs about LiFePO4 tests and installations. They all tout the 2000 to 5000 cycle life and 80% depth of discharge, then say you can only use AGM for 50% depth of discharge and will get 500 cycles.

In the real world there are several problems with this.

1) People are getting way more than 500 cycles with AGM at 50% DoD

2) Nobody has documented (that I have found) a LiFePO4 installation with anywhere near 2000 cycles, much less 5000

3) LiFePO4 suffers from age loss of capacity issues even if unused, so I question if 5000 cycles is even possible before the battery has degraded. 5000 cycles at one per day is over 13 years.


Next is the issue of availability. I can find 20 local places and 200 online places where I can buy 10 different brands of AGM. With LiFePO4 I am stuck with a couple of Chinese manufacturers. How well are warranty issues handled?

There are descriptions on how to compress your LiFePO4 cells so they don't bulge as much. There are some who have had cells bulge even when never used just sitting on a shelf. This does not sound like market ready technology. I have a hard time seeing Sam's Club stocking swollen LiFePO4 packs next to baby diapers and Chickinubs.

Then there is complexity. With an AGM, you buy the battery, install it, and check it again in a few years. With LiFePO4 you buy the batteries, buy some rods and plates to compress them, buy battery monitoring circuitry, balance your cells, run a few cycles, check your cell balance...

Final is price. With the extra parts and battery monitors, I am seeing Lithium cells at 2x the price of AGM even if you equalize the amp-hour rating to 0.8 Lithium 0.5 AGM. With 1000 cycles of AGM and 2000 cycles of LiFePO4, price is a wash, although you have lost opportunity cost in the extra $$$ you spent on Lithium (you could have put it in Twitter stock and tripled your money instead of paying for those extra future cycles)

AGM still makes more sense. Unless you are *really* needing the lower weight.

techntrek

Re: AGM still makes more sense than Lithium

Neither makes sense for a stationary application with no unusual restraints (like no venting), FLA always wins $/kw.

Skyko

Re: AGM still makes more sense than Lithium

For batteries in confined living quarters in a mobile application like rv or boat, AGM or Lithium seem to make more sense to me (yes I know AGM can outgas but I don't think it can get to dangerous levels if you even have just a little vent).

If you limit the choice between those two, then AGM is the winner for now. When Duracell, Trojan, Lifeline start making a Lithium available at your local boat or rv dealer with at least a 1 year warranty and no more than double the price of AGM, then I may change my opinion.

PNjunction

Re: AGM still makes more sense than Lithium

For many, AGM makes perfect sense. Enersys TPPL agm's are my favorite. (street branded Odyssey is only one example)

I'm puzzled by what you've been reading about Lifepo4. One of the biggest mistakes is trying to apply mobile Electric-Vehicle or model Radio-Control issues to standard house banks.

Essentially what you have stated is much the same type of FUD that appeared when AGM's first appeared on the scene. You only stated a bunch of negatives - how about some positives?

No stratification. No sulfation. Extremely efficient charge and discharge (less fuel usage with a generator). Easy to charge - no lengthy absorb, IUI profiles etc. Not necessary to keep at 100% charge, in fact if not being used actively, then keeping them slightly discharged is better for cycle life. EV and RC balance obsession not necessary when banks are only running <1C, and not taken down past 80% DOD - which should be easily attainable if you allow for a little bit of autonomy or have any sort of decent monitoring. They are NOT the super sensitive COBALT-phosphate (LiCoo2) such as in your laptop or cellphone, but are IRON-phosphate which are much less sensitive. (the tradeoff for good safety is that they have about half the power density of sensitive cobalt-based types)

There's more to lifepo4 than just a weight savings.

The rules are the same for any battery - don't abuse them, don't buy junk, basically put the same effort into the care you would with your lead-based batteries. Puffing is the result of junk, abuse, or a combination of both.

If you don't want to get your cells from CALB, then look at Genasun for full packages to feel better about it.

Thing is, there are many misinformed sources out there with agendas that will do anything to sway your purchasing decision.

vtmaps

Re: AGM still makes more sense than Lithium

Skyko wrote: »

With an AGM, you buy the battery, install it, and check it again in a few years.

With LiFePO4 you buy the batteries, buy some rods and plates to compress them, buy battery monitoring circuitry, balance your cells, run a few cycles, check your cell balance...

I think a battery monitor is even more important with AGM than flooded lead acid. When you buy an AGM you should commission it, which involves cycling and checking cell balance.

Skyko wrote: »

yes I know AGM can outgas but I don't think it can get to dangerous levels if you even have just a little vent.

AGM batteries have been involved in some impressive fires and explosions. The venting requirements are the same as for flooded batteries. Normally they don't gas, and for that matter normally fuses don't blow. When things go wrong, fuses can blow and AGMs can gas and burn.

--vtMaps

Skyko

Re: AGM still makes more sense than Lithium

vtmaps wrote: »

AGM batteries have been involved in some impressive fires and explosions. The venting requirements are the same as for flooded batteries. Normally they don't gas, and for that matter normally fuses don't blow. When things go wrong, fuses can blow and AGMs can gas and burn.

--vtMaps

Can you give a link of AGM fires and explosions due to outgassing? Any battery can cause a fire if you directly short the terminals or some such misuse.

Read this about the Lifeline AGM:

http://www.lifelinebatteries.com/safety_bull.php

"Under space available contract with the U.S. Government, each LIFELINE battery not only passed the gas emission test in MIL-SPEC B-8565J (Section 4.6.22), but no single unit generated over one percent hydrogen gas in any test section. That equates to over 99 percent recombinant gas efficiency even during a simulated-shorted cell overcharge."

vtmaps

Re: AGM still makes more sense than Lithium

Skyko wrote: »

Can you give a link of AGM fires and explosions due to outgassing? Any battery can cause a fire if you directly short the terminals or some such misuse.

Read this about the Lifeline AGM:

http://www.lifelinebatteries.com/safety_bull.php

"Under space available contract with the U.S. Government, each LIFELINE battery not only passed the gas emission test in MIL-SPEC B-8565J (Section 4.6.22), but no single unit generated over one percent hydrogen gas in any test section. That equates to over 99 percent recombinant gas efficiency even during a simulated-shorted cell overcharge."

I wasn't referring to shorting a battery. The problems I've read about are shorted cells, over voltages (due to human or charge controller error), and over current (usually an open cell in a one string causing all charging current into a parallel string). As far as providing links, I don't have a list handy, but I have read one account just a week or two ago on the RE-wrenches forum. That was caused by someone fiddling with the controls and setting the absorb up to 3 volts per cell. I don't recall what brand of AGM battery was involved.

I wasn't aware of MIL-SPEC B-8565J (Section 4.6.22), but this is from the lifeline manual:

Thermal runaway is a condition in which the battery temperature increases rapidly resulting in extreme overheating of the battery. Under rare conditions, the battery can melt, catch on fire, or even explode. Thermal runaway can only occur if the battery is at high ambient temperature and/or the charging voltage is set too high. As the battery accepts current, its internal temperature rises. The rise in temperature reduces the battery impedance, causing it to accept more current. The higher current further heats the battery, and so on, causing the battery temperature to “runaway”. An upper limit will eventually be reached when the electrolyte starts to boil, but once the electrolyte has boiled away, the temperature can climb even further to the point of plastic meltdown and possible fire.

As of this writing, Concorde does not know of any Lifeline® AGM batteries that have failed due to thermal runaway. To preclude the possibility of thermal runway, the charging instructions of Chapter 4 should be carefully followed, especially if the battery will be subjected to high ambient temperatures. Batteries should not be installed near heat sources or in direct sunlight that may artificially elevate their temperature. Also, there should be adequate air circulation around the batteries to prevent heat build-up.

--vtMaps

Skyko

Re: AGM still makes more sense than Lithium

"Concorde does not know of any Lifeline® AGM batteries that have failed due to thermal runaway."

This is a pretty telling statement considering how many (hundreds of thousands?) of Lifeline AGM batteries have been sold and are in use.

Here is what happens when you short a LiFePO4 cell (I know it is an extreme case of abuse, but imagine that explosion and toxic smoke in a truck camper)

http://www.youtube.com/watch?v=p21iZVFHEZk

vtmaps

Re: AGM still makes more sense than Lithium

Skyko wrote: »

Here is what happens when you short a LiFePO4 cell

What does that have to do with AGMs? AGMs also burn or explode when shorted. In the quote I posted, Lifeline is referring to overcharging, not shorting. (although they mention a shorted cell as a cause of overcharging in the mil spec). They are NOT saying their batteries are safe if shorted out.

--vtMaps

Cariboocoot

Re: AGM still makes more sense than Lithium

vtmaps wrote: »

I think a battery monitor is even more important with AGM than flooded lead acid. When you buy an AGM you should commission it, which involves cycling and checking cell balance.

Well that last part is going to be impossible on account of the cells of an AGM not being accessible and not having enough electrolyte in them to measure anyway.

AGM batteries have been involved in some impressive fires and explosions. The venting requirements are the same as for flooded batteries. Normally they don't gas, and for that matter normally fuses don't blow. When things go wrong, fuses can blow and AGMs can gas and burn.

--vtMaps

Venting requirements may be the same by regulation, but in reality those regulations are wrong. In the normal course of use AGM's do not vent at all. As it is flooded cells really only require the venting because they are put in a closed battery box; in the open there is no containment for any gas produced and so it cannot reach dangerous levels. With an AGM this danger is even smaller as there isn't enough liquid inside to produce copious amounts of gas.

When things go wrong anything can be a problem, including any type of battery and any system component including the ones meant to keep us safe. When comparing one type of battery to another the safety differences are actually minor and not the most important thing to look at.

So far the ol' FLA's are still the most practical despite all their drawbacks (which obviously aren't as severe as some would have us believe; the huge number in use without incident is proof of this).

I have always said only pick AGM's if their advantages are needed for your system.

As it is, the alternate technologies such as LIFEPO4, NIFE, and lithium are not suited for the average Joe who just wants to get a system up and running. But if a few people don't take the chance on them these battery technologies will never advance to where they are viable for everyone.

PNjunction

Re: AGM still makes more sense than Lithium

Cariboocoot wrote: »

As it is, the alternate technologies such as LIFEPO4, NIFE, and lithium are not suited for the average Joe who just wants to get a system up and running. But if a few people don't take the chance on them these battery technologies will never advance to where they are viable for everyone.

Exactly, they aren't for everyone and one should always match the battery to their application. However the average joe that just wants to experiment with a simple 12v system can just put 4 of them in series (4S), or on a small scale deal with pre-built powersport batteries like Shorai, Antigravity, and others just to get your feet wet.

Unfortunately many look for drama rather than factual material. I could post a link to the guy whose face is burned off from that pesky battery acid hydrogen explosion underhood when he went to recharge his overgassing lead-acid in his truck.

The point however is just to look for the facts. And instead of repeating what one has merely read about, put a simple *quality* 4S Lifepo4 under your belt and get some hands on. You may be surprised.

Skyko

Re: AGM still makes more sense than Lithium

I went to West Marine and asked them if I could buy some LiFePO4 and got a blank stare.

It is not ready for the masses. Early adopters, yes.

Personally I would just go with LiPo...twice the energy density and cheaper than LiFePO4...only blows up if you don't know what you are doing.

PNjunction

Re: AGM still makes more sense than Lithium

Actually Lipo is a category without specifying the phosphate chemistry, although most associate that with the critical LiCo02 cobalt types.

For most, that would be a very bad idea, and is one of the reasons that LiFepo4 (IRON phosphate) is a much better deal in regards to safety for the common man.

One reason for banding individual cells together is that you don't want to place mechanical stress on the connector terminals and risk breakage, which are usually affixed with short rigid bus bars. Some have adopted flexible braid connectors to accomplish this. Even though a house-bank is not mobile, this is a very good idea. You'd want to do this lead-based cells too, so no surprise there.

I can say that these would make the perfect test bed for Mike's solar-monolith!

But yes, I'm not throwing my AGM's away either if they don't fit my application.

Skyko

Re: AGM still makes more sense than Lithium

Everything I have read seems to indicate people band the cells together to prevent swelling, which just seems insane. Either the design is flawed or the manufacturer needs to construct a better case to withstand the pressures without swelling.

Really makes me think the price of these things in China is about $10 per cell and they are trying to save $0.25 on case materials...then the exporters mark them up to $130 per cell.

bill von novak

Re: AGM still makes more sense than Lithium

Skyko wrote: »

I went to West Marine and asked them if I could buy some LiFePO4 and got a blank stare.

It is not ready for the masses. Early adopters, yes.

Well, if you walked into West Marine and asked them for a wind diversion controller you'd probably get the same blank look. But that doesn't speak to the readiness of diversion charge controller technology.

(They are, however, now selling them in at least one local auto parts store, under the name "Super B." Haven't used any yet.)

karrak

Re: AGM still makes more sense than Lithium

Skyko wrote: »

I went to West Marine and asked them if I could buy some LiFePO4 and got a blank stare.

That suprises me, the cruising boat owners are some of the most enthusiastic adoptors of LiFePO4 batteries. This is one of the best sources of information on LiFePO4 batteries I have found. http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html

Personally I would just go with LiPo...twice the energy density and cheaper than LiFePO4...only blows up if you don't know what you are doing.

Besides being more dangerous, they only have about one third the lifespan of LiFePO4s. Do you want to replace your batteries every 2-4 years?

karrak

Re: AGM still makes more sense than Lithium

Skyko wrote: »

Everything I have read seems to indicate people band the cells together to prevent swelling, which just seems insane. Either the design is flawed or the manufacturer needs to construct a better case to withstand the pressures without swelling.

The primary market for these cells is electric vehicles and other applications where size and weight are an issue. To make a prismatic case that would stop the bulging would require extra weight and size. You can pack the cells into a cylinder, but cylinders don't pack very efficiently.

As far as i can see the cases will only bulge if the cells are abused or charged at high current rates. My LiFePO4 batteries have no strapping on them and have been in use for nearly a year. To date I haven't noticed any bulging.

Really makes me think the price of these things in China is about $10 per cell and they are trying to save $0.25 on case materials...then the exporters mark them up to $130 per cell.

I calculate that $130 would buy a 100Ah cell in Australia, tell me where in China I can pick up 100Ah cells for $10 and i will pack my suitcase and get them in person. I thought the LiFePO4 market was quite competitive.

PNjunction

Re: AGM still makes more sense than Lithium

Skyko wrote: »

Everything I have read seems to indicate people band the cells together to prevent swelling, which just seems insane. Either the design is flawed or the manufacturer needs to construct a better case to withstand the pressures without swelling.

If you are swelling, then you are buying junk, (typically shrink-wrapped mom-n-pop garage built packs from substandard or reject cells), or have placed them into service that is totally inappropriate for their use. Guys who try to start their Harley Davidsons with $10 ebay lifepo4's run into this scenario.

Thing is, even today you can still run into marine outlets that don't know the difference between GEL and AGM. They end up installing gels, applying agm charging voltages to them, burn them up, and blame the "agm" batteries as being junk. Knowledge is key to success - otherwise you just play into the hands of the marketers, unknowledgeable bloggers and the like looking to make headlines.

Don't get too hung up on Chinese build quality. Like any country, you can get junk if you shoot for the absolute lowest price point. Take some care, and you can end up with batteries with the same quality as your Chinese built latest smartphone or tablet.

Another thing not mentioned about Lifepo4 is the ability to maintain voltage under extreme load due to their insanely low internal resistance. That means that you stand a better chance of starting motors and other high-current startup devices without having to resort to insanely oversized agm battery banks to handle that initially high power draw.

karrak

Re: AGM still makes more sense than Lithium

Skyko wrote: »

2) Nobody has documented (that I have found) a LiFePO4 installation with anywhere near 2000 cycles, much less 5000

This is true but there has been lots of testing which suggests these figures are attainable, only time will tell though ...

3) LiFePO4 suffers from age loss of capacity issues even if unused, so I question if 5000 cycles is even possible before the battery has degraded. 5000 cycles at one per day is over 13 years.

This is the elephant in the room. At elevated temperatures and high SOC, capacity loss is a severe problem but things are far less clear at normal temperatures and if we keep the SOC less than 90%.

Next is the issue of availability. I can find 20 local places and 200 online places where I can buy 10 different brands of AGM. With LiFePO4 I am stuck with a couple of Chinese manufacturers. How well are warranty issues handled?

If there are two LiFePO4 battery suppliers in Perth, Western Australia, there must be hundreds of companies in the US that are selling LiFePO4 batteries. Balqon is the distributor of Winston batteries in the US.

Then there is complexity. With an AGM, you buy the battery, install it, and check it again in a few years. With LiFePO4 you buy the batteries, buy some rods and plates to compress them, buy battery monitoring circuitry, balance your cells, run a few cycles, check your cell balance...

I am no expert on AGMs but i would think they need the right charge profiles to self balance and would have to be balanced at the start, if you get that wrong they won't last as long. If you start out with a balanced set of LiFePO4 cells and don't charge above 90%SOC or discharge below 10%SOC you could probably get by without any balancing or monitoring. Not something i would recommend. I think you would be crazy with any battery type not to check them on a regular basis.

Final is price. With the extra parts and battery monitors, I am seeing Lithium cells at 2x the price of AGM even if you equalize the amp-hour rating to 0.8 Lithium 0.5 AGM. With 1000 cycles of AGM and 2000 cycles of LiFePO4, price is a wash, although you have lost opportunity cost in the extra $$$ you spent on Lithium

I have calculated that the cost of storing power with LiFePO4 cells at between 15-30 cents per kWh which i think makes them cost competitive. For details see http://forum.solar-electric.com/showthread.php?19079-Alternative-to-Lead-Acid-Batteries&p=178256#post178256

One of the big advantages of LiFePO4 batteries over Lead Acid is that you don't need to keep them as full as possible to extend their life. During our last winter the batteries were less than full for around two months, and below 60% full for several weeks at a time. Good for the LiFePO4s, not good for Lead Acid. We don't need a generator to make sure the cells are kept topped up when the weather is bad or to give the cells a good charge to stir up the electrolyte etc.

If my assumptions about LiFePO4 battery life are correct, the cost of energy storage goes down with increased usage of the battery. This means we can use more power during summer when it is available without a penalty and make better utilisation of the solar panels and inverter.

Skyko

Re: AGM still makes more sense than Lithium

From the cruisersforum:

"Li cells need to be held in light compression to stop their sides from bulging. If the side bulge some capacity can be lost because the very thin plates that make up a cell start to separate and it's the close bond that makes these cells work so well. It's not a vice like crush, more a firm hold to keep the sides flat. The manufacturers make plate and band kits to bolt the cells together in packs but if you want to make a special configuration then some planning to include a side crushing mechanism is needed."

That was from a member with a lot of posts, T1_Terry.

I have played with Lithium Phosphate and they are great in my electric bike. I would not sleep near them though. I have Lithium Manganese in my Torqueedo 500 watt-hr electric outboard battery back and they also seem to work well (they use many cylindrical cells).

I guess the big issue I have with the LiFePO4 cells is the lack of guarantee when plunking down that much cash.

For a Lifeline AGM bank of 24V 300AH (150AH useable), it would cost $1600 for four 6V 300AH batteries wired in series. No BMS costs. I would get a 1 year/5 year warranty and could drive the batteries back to the store in my car.

For LiFePO4, I am forced to order from China if I want a reasonable cost, and there is a debatable warranty that would involve heavy shipping fees.

To get 150AH useable, perhaps I go with eight 180AH 3.2V cells. These are $250 each, or $2000 total, plus perhaps $200 for strapping and BMS. So we are at $2200 vs $1600, but the LiFePO4 are much lighter and perhaps longer life.

I would get 1000+ cycles out of the AGM and perhaps 2000 to 3000 cycles from the LiFePO4 (but I haven't found a ton of lab or real world testing of these figures since the technology is somewhat new)

It is *almost* there, but at the prices I mentioned, there should be an American company making a 24V 180AH pack for $3000 with all of the included safety features and offering at least a one year warranty. The only reason there is not is because they do not feel confident in the technology at this time....it isn't because they don't want to make a $1000 profit per battery.

Skyko

Re: AGM still makes more sense than Lithium

Ok, it looks like you can buy CALB 40AH 3.2 volt batteries from EVWest for $54 each. I am thinking about getting four of these and running some tests to satisfy my concerns. If I can run 2 cycles per day at 0.2C charge/discharge I could get a decent amount of data in a few months. If they stay in balance and don't swell, I would feel a lot better about spending 10x the amount on a 24V 180AH pack. I could always use the 12V 40AH pack for tent camping or something.

mike95490

Re: AGM still makes more sense than Lithium

PNjunction wrote: »

....I can say that these would make the perfect test bed for Mike's solar-monolith!.

Nope, the monolith relies on the battery being 50# of ballast at the base to prevent tippage in wind (sort of like a sailboats' weighted keel)

Skyko

Re: AGM still makes more sense than Lithium

Actually a little more thought and I have an idea that might be a great way to test LiFePo4 without breaking the bank and still provide some benefit.

I may post this on the sailing forum as they have extensive experience with this technology.

Since we will have 1000 watts of solar and a 24V battery bank, but need 12V for some house items, I had planned to use a DC-DC or a battery balancer to obtain 12V from the 24V bank.

The new idea is to use 24V 300AH of lead acid as the main battery bank, then tap off of this bank with a 24V to 14V DC-DC converter (or off the shelf charger like the iCharger 208B 1-8 cell 20 amp charger I use for my RC LiPo). I would also have a tiny solar cell attached to the main panel that would tell me what the current level of insolation is. I would build a microcontroller to monitor and control the 4 LiFePO4 3.2V series cells and control the 24V powered DC charger that charges them.

The plan would be to bulk charge the main 24V lead acid pack during the high power sun part of the day when the most current is available, then when the lead acid batteries are in the absorption phase and not using the available current I would turn on the LiFePO4 charger to soak up this excess current. This might require some research into the Midnite Classic 150 I plan to use for the lead acid charging, as I do not know what it would do if it was charging the lead acid in absorption mode and the load on the batteries suddenly jumped by 10 to 15 amps.

If everything worked like my vision, I would have a 24V main storage system, a 12V LiFePo4 house battery, and the ability to efficiently use the maximum current from my solar panels during the day. It would also be an inexpensive way to test the LiFePo4 without sinking $2000 to $3000 in a full 24V pack.

zoneblue

Re: AGM still makes more sense than Lithium

Skyko wrote: »

The new idea is to use 24V 300AH of lead acid as the main battery bank, then tap off of this bank with a 24V to 14V DC-DC converter (or off the shelf charger like the iCharger 208B 1-8 cell 20 amp charger I use for my RC LiPo). ...

That will work ok, providing your charger is realtively efficient.

The plan would be to bulk charge the main 24V lead acid pack during the high power sun part of the day when the most current is available, then when the lead acid batteries are in the absorption phase and not using the available current I would turn on the LiFePO4 charger to soak up this excess current.

Classic has a large range of aux relay output functions. Waste not Hi, is an opportunity mode that goes hi whenever the classic thinks it has power to spare. It has adjustable hold and delay hystersis settings to prevent it oscillating. Plain Float Hi goes hi in float. There are others, but thats where to start looking. There will also soon be SOC based Aux modes, which will also work there.

This might require some research into the Midnite Classic 150 I plan to use for the lead acid charging, as I do not know what it would do if it was charging the lead acid in absorption mode and the load on the batteries suddenly jumped by 10 to 15 amps.

No probs, its like any other load. If the load is small, absorb will continue. If the load is big enough that it takes more than present solar less present charge acceptance , the voltage will drop, and it will kick back into bulk, voltage rise more slowly, and repeat. That isnt an issue, happens almost every day anyway. A medium sized load that kicks in once absorb setpoint is reached would effectively slow down the absorb stage initially until the charge acceptance falls away naturally, then speed through the last part to float. That, is the beauty of true ending amps, and among many reasons why the classic is your friend. You always get the correct absorb time regardless of what shenanigans you get up to.

PNjunction

Re: AGM still makes more sense than Lithium

Notes -

If you want to deal with CALB cells stateside, you can also get them from Calibpower in Pomona, Ca. Supposedly the gray cells have better performance than the older blue cells especially in cold climates. Don't forget the cell interconnects.

Quick qualification test:
If you are experimenting with a nominal 12v pack like a simple 4S, then once you charge the bank fully to 14.6v, you should see them drop to 14.2v ocv after 8-12 hours. Another 8-12 hours after that, the ocv will settle to 13.3v and stay there forever - well maybe a year. BUT you do not want to store them in a fully charged state. If you are not going to use it for more than a few days to perhaps a week, then discharge them down to about 80% SOC or more. Many thanks to CY at advrider!

In practice, there is no need to fully charge them to 100% SOC at 14.6v all the time. 90-95 percent will do just fine and extend cycle life. I normally only charge my lifepo4's to about 14.1v from my charge controller, although some might take it to 14.4v. The typical "gel" setting on a lead-based solar charge controller does fine since they top out at 14.0 - 14.1v absorb anyway. Ending-amps is a joke since it is so fast - get distracted with a phone call, and you'll notice you are sitting there with barely any current being drawn in the wink of an eye. Well, relatively that is.

The hardest thing to get used to is not doing any sort of float (unless you have a parasitic draw), not charging them to 100% all the time, not storing them fully charged for long periods of time, and the extremely flat charge discharge curve. Since that curve is so shallow, an accurate DC voltmeter is a must - something with the accuracy of a Fluke 87V or better is recommended. If your existing solar CC has temperature-compensation, you may want to take that into account and perhaps disable it for the lifepo4 so you don't have voltages wandering around, especially if you initially set it for 14.4v and a deep cold snap makes the temp comp shoot those voltages higher than 14.6v! Just something to be aware of. Or get a lithium-iron specific charge controller, however my lead-based Morningstar pwm's do nicely when set for the lower voltage.

Some manufacturers list a "recommended" 0.3C charge / discharge. However, they typically can handle 1C charge/discharge or more as long as you are aware of it. Something only my beloved Enersys AGM's would tolerate with ease. Be sure to consult manufacturer data sheets for the *current* model, as voltages listed in internet forums from 4 years ago or so are WRONG. And as always, be aware that well-meaning individuals often confuse LiCo02 (lithium-cobalt phosphate) voltages with LiFepo4 (Lithium-Iron phosphate) We want the lifepo4 specs!

One thing I use instead of a dedicated top-balancing system for small stuff on occasion is a Tecmate / Optimate Lithium-Iron TM-291 charger. I'll spare all the feature details, but one thing I do like is that it will help balance cells that are not extremely out of whack by using an oscillating absorb voltage charge between 14.0 - 14.4v. The trick as I understand it, is that this takes advantage of the quick individual rise-time window of the highest capacity cell to get the lower-capacity cells charged and balanced - rather than just sitting at a static absorb voltage. They do the same thing with their latest model LEAD-SPECIFIC versions for agm's. But so far, I've not really needed or noticed a major balance problem, since I'm usually discharging at 0.1C in my application.

PNjunction

Re: AGM still makes more sense than Lithium

Thought I'd better clean up my OWN act first after more hands on! Feels strange to quote myself...

PNjunction wrote: »

If you are experimenting with a nominal 12v pack like a simple 4S, then once you charge the bank fully to 14.6v, you should see them drop to 14.2v ocv after 8-12 hours.

Bad idea, not only from the standpoint that the voltage is too high on a practical level, but also does not take into account verifying initial pack balance. 14.0 - 14.2v is fine. Initial balance should be closely monitored to make sure that no cell reaches 3.6v before the total pack voltage reaches 13.8v and starts moving a bit beyond. Because we are doing low-current, low voltage duties, a balance of no more than 0.050v (50 millivolts) between the highest and lowest cell is adequate at a lower overall voltage of 14.v.

About the only time you'd want to run with a pack voltage as high as 14.4v, is if you had individual balancing boards that needed to see that high voltage to kick off the balancers. You can certainly do this if you place your faith in those boards. There is also no rule that says you have to stay at that voltage all the time - ie once you are satisfied that a balance has been achieved with these, then dropping down to 14.0 - 14.2v for more normal use, with occasional checkups once in awhile is ok. Or you could perform the balance, and physically remove the boards, keeping an eye out that they are not exceeding 0.050v spread.

You can do a quicker balance with an adjustable bench power supply, or my favorite, an "individual cell" charger rated to no more than about 3.6 to 3.7v without any external boards. Pull when individual cell voltage reaches 3.55v.

One thing I use instead of a dedicated top-balancing system for small stuff on occasion is a Tecmate / Optimate Lithium-Iron TM-291 charger.

The individual cell charger will get you there faster. Lately, I feel it is great for "drop in" powersports replacements that may already have closely matching cells, and tends to keep them that way, but for real world house banks that use larger prismatic cells (like GBS, CALB, and Winston), getting them balanced quickly with other methods is a lot faster and a bit more precise.

Wow, that felt really weird.

inetdog

Re: AGM still makes more sense than Lithium

PNjunction wrote: »

If you are not going to use it for more than a few days to perhaps a week, then discharge them down to about 80% SOC or more.

While we are on the subject of fine tuning:
Some would say 80% SOC or less or would say discharge them more than to 80% SOC (which is a really awkward though correct statement.)

PNjunction

Re: AGM still makes more sense than Lithium

Yes! Kinda' wrapping my head around that.

What we are finding is that like with the early days of AGM, the big marketing bullet point was the magical 80% number for DOD. In practice, many applications could not deal with a voltage less than 12v at low DOD's, but internal cell balance if bad, could easily put one cell into the deep discharge knee on a regular basis, and subsequent high-current recharge would damage that cell over time. We just didn't know or care about balance, and couldn't EQ anyway, and tossed the battery and got a new one until we all figured out that 50% DOD was more reasonable - albeit conveniently covering up balance issues.

Lifepo4 should be fine tuned for the environment. If you are an EV'er, then yes, charge at high-voltages, use your bms/balancer system, and take the system from perhaps the middle of the charge and discharge knees.

For guys that want to go simplistic, we'll voluntarily give up a bit of SOC range, and worst case not exceed the *start* of the knees. It may be a fine point, but it can let one go without having to use external balancing and the like. Of course LVC is a desired feature either way. Balance issues are magnified greatly when running very high current like in an EV application, but when we do house-bank stuff, what, maybe 0.1 to 0.2C max to ensure we can get through the night?

The conclusion I'm coming to is that for me, a more realistic expectation is 70% overall SOC range, and not the 80% range used to attract EV'ers or the drop-in-replacement crowd. My voltages are lower, balance is not super-critical, and while daily cycling capacity is not as big, the payoff is a huge increase in overall cycle life.

I don't know if I'm expressing it right - the warning to not confuse DOD with SOC, especially when using voltage solely as a source is taking it's toll.

PNjunction

Re: AGM still makes more sense than Lithium

How about this:

When I design my system with LiFePo4, I'm going to calculate my needed battery capacity at 70% of rated value instead of 80%, and run with no more than 14.v after an initial balance to 3.55v per cell, easing my needs for external balancing hardware. That gives me some headroom (barring out right cell failure) for balance skew at the bottom, which I will diligently try not to reach anyway. The limits at the bottom are 12v under load, and 12.8v when rested. I will routinely (but not obsessively) check that when at top of charge, my maximum cell deviation is no more than 0.050v.

Sounds like a motto for a diy lifepo4 club. No wonder - it's 115F in the computer room!

feedhorn

Re: AGM still makes more sense than Lithium

My theory of AGM may be different from yours:

AGM batteries work best in UPS or Grid Backup situations where the batteries are charged to 100% and maintained there for the life of the batteries.

New AGM batteries need to float at proper voltage for about 6 months to reach initial 100% charge. Its important to reach a true 100% charge.

Any portion of their capacity less than 100% will eventually turn to hard sulphate and that capacity will be lost.

Daily cycling of AGM batteries makes it impossible to reach a 100% charge and their capacity deteriorates day by day. Total capacity levels off at about the daily cycling capacity.


As for Lithium batteries:

Cycling is better than not cycling, they are not so good as backup batteries.

Capacity deteriorates over time. I have some 20 year old laptop cells that still have about 30% capacity.

High current discharge rate also deteriorates over time but the batteries are still useful way into the future.

Satellites use Lithium batteries and have expected lifetimes of 15-20 years when deep cycled and recharged every 88 minutes.

I use lithium for their long term survive-ability.

zoneblue

Re: AGM still makes more sense than Lithium

Interesting. Do you have a source for this material?

feedhorn wrote: »

My theory of AGM may be different from yours:

AGM batteries work best in UPS or Grid Backup situations where the batteries are charged to 100% and maintained there for the life of the batteries.

New AGM batteries need to float at proper voltage for about 6 months to reach initial 100% charge. Its important to reach a true 100% charge.

Any portion of their capacity less than 100% will eventually turn to hard sulphate and that capacity will be lost.

Daily cycling of AGM batteries makes it impossible to reach a 100% charge and their capacity deteriorates day by day. Total capacity levels off at about the daily cycling capacity.