LiFeYPo4 questions

[PNjunction]

Tell ya what - I'll put my money where my mouth is.

My little Braille lifepo4 will be subjected to 14.2v extended charge from now on even when absorb is complete by at least 4 hours. This will simulate it becoming fully charged at the start of my typical solar insolation period. I'll report back. If it cuts the cycle life from 5K to 4.5K cycles, this might take awhile. With only 4 26650's inside, that is a mere 2.3Ah capacity so I should be able to run through those pretty quickly with my HF radio gear monitoring which is <1C current. This should be fun actually. I'll set my Xantrex pwm charger to 14.2v absorb AND float.

I can also force this with a Battery Tender charger designed for gel. It won't drop back to float once reaching the hvc and stays there until timeout. This is unlike my agm-specific Battery Tender which WILL reach 14.6v and once it senses about 100ma absorb, will drop back to float. So I'll use the gel model. I was going to throw these away, so thanks guys I found a new use for them.

Lurkers - ideally a charger should charge up to the HVC voltage and just stop, or better yet monitor the absorb current and stop at a low value, but these 1.25A BT's will drop back to a useless float voltage intended for Pb. Whatever you do, DO NOT use Schumacher speed-chargers, even if you set the chemistry / voltage correctly, as these units love to go to a high-voltage EQ charge, even if the voltage display says otherwise! Multimeters will reveal this behind the scenes helper which will destroy your lifepo4!

[Sunking]

PN what you are doing is no real test using solar as the source of power. You do not get enough hours to do much damage. If you are a ham I bet you have something like a Astron DC supply. Crank it up to to 14.2 and put a 3S pack on it over night. Just be sure to put the battery into a fire/explosion proof bag they sell for charging RC batteries.

Bottom line chargers are made to be autonomous. I understand you can do what you do, but only if you are there to monitor things and terminate charge when you see current taper off. But 99% of the public do not have the time, skills, or knowledge to do that.

[PNjunction]

The fireproof bag is overkill for lifepo4 if taken care of properly. Lithium-Cobalt like in RC modeling - yes of course. Lacking a bag, for RC modelers using Li-Cobalt then perhaps use the fireplace at least. The enhanced safety from Lifepo4 comes at a cost - it has half the power-density of LiCo02, but now you don't have to use a bag or fireplace to charge them. Lifepo4 can actually be used where they need to be, unless one does the "lets destroy one up reeaal good in front of the firehouse" video for dramatic purposes.

I went to the source of the internal cells in my Braille, and got much more information. Seems like my target voltage of 14.2 was pretty close if I needed to do a faux-float as would be done if my batteries were charged up very quickly, and my solar charge controller just sat there at 14.2v for the rest of the day.

http://www.buya123batteries.com/ALM_12V7_p/400520-301.htm

At the bottom you'll find the data sheets.

It incorporates an hvc, lvc, and internal bms. I am going to do all three manually on my Braille and Shorai's by merely limiting my charge voltage, discharge voltage, and perhaps use the Optimate TM-241 lithium charger as a faux-balancer once in a blue moon. Interesting is that they mention a float-voltage of 14.0, which implies that either they are planning on an external parasitic drain, say from an led or other circuit, or maybe they are implying that the internal bms itself is drawing a minute amount of power. The point is that the battery itself in bare form does not need a float, but constant parasitic external drains might make one want to incorporate that. Seems like they have no problem with them sitting at 14.0v, even though I won't be doing that in my solar application.

I do have Astrons and Daiwa power supplies - however again for lurkers - they need to be MODIFIED to be able to look into what appears to them as a direct short! The low-impedance of a lifepo4, agm, etc can make these throw their internal crowbar circuitry and worse if attached when the battery is at a low SOC. I'm also not going to dump more than 2C into these things, although I can, but for regular use a little Astron 4A - modified! - might do.

This is just making me jones out for getting my hands on some CALB or Winston large-capacity prismatics now. Nevertheless, I'm going to do this constant faux-float on my learner batts every time I charge and prove it to myself.

[Sunking]

My Astron has both voltage and current limit controls on the face so I can charge about any battery I desire usin ga CV with current limit which is basically what any Lithium uses. FWIW RC batteries are LiPo, not cobalt.

[SunEagle]

My Astron has both voltage and current limit controls on the face so I can charge about any battery I desire usin ga CV with current limit which is basically what any Lithium uses. FWIW RC batteries are LiPo, not cobalt.

And those LiPo's will eventually over heat and flame. They don't like physical abuse or over charging. The charging bag is a real cheap investment to keep the fire from spreading. I have seen them go off in a metal ammo can. Talk about letting the smoke out.

[Sunking]

And those LiPo's will eventually over heat and flame. They don't like physical abuse or over charging. The charging bag is a real cheap investment to keep the fire from spreading. I have seen them go off in a metal ammo can. Talk about letting the smoke out.

No worries about me my friend. I charge all my LiPo's with a Icharger fine tuned for whatever pack I put in it. I just use the Astron as the source. Bu tfor a large format 12 volt AGM, I use the Astron.

[PNjunction]

...FWIW RC batteries are LiPo, not cobalt.

Nope - the common Lipo battery IS primarily Cobalt oxide. At least the cathode is. The anode is primarily a solid polymer. But the dangers of super-critical charge requirements are still there, hence the need for bags and fireplaces when charging. You still have a temperamental Li-Cobalt battery on your hands.

Unfortunately for readers who may stumble upon this, they aren't aware of the unintended FUD by associating the much much safer LiFepo4 with Lico02 Cobalt / Lipo's.

You can take a 4S nominal 12v Lifepo4 to up to about 15.2v although that is NOT recommended, but is a good recipe for non-dramatic lithium plating, which raises the internal resistance and lowers capacity. Take it to about 30v, and then unsavory reactions will start occuring. This is very unlike Cobalt oxide, which a mere few 10ths of a volt of overcharge turns into a critical fire safety concern. Take a lead-acid flooded to 30v, and you'll get plenty of spewing battery acid and hydrogen, so yep - all batteries are a safety concern when abused.

The good news is that I've started the regimen of massively extended and unnecessary float voltages on my little Lifepo4 26650's. If / when I eat my hat, you'll be the first to know!

[SunEagle]

No worries about me my friend. I charge all my LiPo's with a Icharger fine tuned for whatever pack I put in it. I just use the Astron as the source. Bu tfor a large format 12 volt AGM, I use the Astron.

I figured you would have it all in control but I wanted to let anyone else reading these threads that charging LiPo's can be exciting at the least opportune time. Having a fire proof charging container or bag is little in cost then replacing fire damaged workshop or home.

I use my Revolectrix Cellpro Multi 4 charger. I like the multiple battery selection and charging profiles already installed. I also use the bag which I place on some ceramic tiles to keep it off the floor. Can't be too safe.

[SolarEU]

LiFePo4 (Iron) VERSUS LiCo02 (Cobalt)

Unfortunately for readers who may stumble upon this, they aren't aware of the unintended FUD by associating the much much safer LiFepo4 with Lico02 Cobalt / Lipo's.

How can an amateur like me recognize if a battery is the safer LiFePo4 (Iron) or the more risky LiCo02 (Cobalt)? Is there any way to detect it?

[PNjunction]

Wikipedia does a good job in the safety section of explaining and contrasting it with Lipo/cobalt:

http://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery

The main point being that it does not like to give up oxygen atoms, the fuel for fire. Other points can be seen, but the price for this added safety is less power density - which just means that for the same amount of power, Lifepo4 will be larger than LiCo02.

Admittedly it can be very hard to get to this information when the signal to noise ratio on the web and in the media tends to overlook it, and instead presents the drama of cobalt instead of iron-phosphate. Two other notable attack vectors are price and politics.

[inetdog]

How can an amateur like me recognize if a battery is the safer LiFePo4 (Iron) or the more risky LiCo02 (Cobalt)? Is there any way to detect it?

The best way to tell the difference is to look at the manufacturer's specification sheet for it.

If all of the original labels have been removed, you can get a good idea by looking at the fully charged voltage, the discharge voltage curve and the energy density per weight from a controlled discharge test. Just do not run the voltage down below the point of no return during the testing.

[PNjunction]

Just do not run the voltage down below the point of no return during the testing.

I'm glad you brought that up. Make sure that you are not confusing a hard-damage low voltage limit (if you stay there long) with a real-world 80% DOD limit, otherwise you'll be sacrificing cycle life akin to lead-acid and losing the benefits of Lifepo4 if you go below 80% DOD on a regular basis.

For Lifepo4, That would about 3.2v per cell, or 12.8v for a nominal 12v pack for 80% DOD. Ie, if you see it drop to 3.1v, stop and recharge, even though the specs may say that 2.5v / cell is the low-voltage limit. Just because you can go there, doesn't mean you should, otherwise you'll pay the price with cycle life akin to lead-acid. Twice or more basically (at current prices) when you have to replace your lifepo4's.

It is somewhat akin to not letting your lead-acids drop to 10.75v, although no experienced person would ever want to take their Pb batteries that low, unless they were unconcerned about cycle life.

I've had guys thinking that their 12v nominal drop-in lifepo4 pack state that 9-10v is the low voltage limit, but had to warn them that if they do that often, they are no better than they were with Pb in regards to cycle life. So if you are going to test, do not take it to the hard-limit low voltage point, but to the one you'll actually use, which should be about 3.2v at the lowest per cell.

Also forgotten is that once below 3.2v per cell, you can't just jam current into them - if you do go lower, then your best bet is to apply .01C until your cells reach 3.2v, and THEN you can apply a normal charge current. Many forget this and a double-whammy is now occurring. Cells are taken too low, and an application of full current in the sharp discharge knee hurts them further.

[inetdog]

I'm glad you brought that up. Make sure that you are not confusing a hard-damage low voltage limit (if you stay there long) with a real-world 80% DOD limit, otherwise you'll be sacrificing cycle life akin to lead-acid and losing the benefits of Lifepo4 if you go below 80% DOD on a regular basis.

For Lifepo4, That would about 3.2v per cell, or 12.8v for a nominal 12v pack for 80% DOD. Ie, if you see it drop to 3.1v, stop and recharge, even though the specs may say that 2.5v / cell is the low-voltage limit. Just because you can go there, doesn't mean you should, otherwise you'll pay the price with cycle life akin to lead-acid. Twice or more basically (at current prices) when you have to replace your lifepo4's.

It is somewhat akin to not letting your lead-acids drop to 10.75v, although no experienced person would ever want to take their Pb batteries that low, unless they were unconcerned about cycle life.

Definitely different from Lead Acid in one way, in that leaving the battery at a low charge level for awhile is not going to cause damage similar to the sulfation problem with lead acid.

So you really do need to calculate from the life cycle curve of your particular battery type whether you get more total energy out of the battery over its lifespan by only doing mini-cycles or by dropping them lower each day or waiting to recharge them.

Some Li chemistry batteries, not sure if it also applies to the iron phosphate family, even deteriorate faster when kept at full charge than when kept at 50-75% charge.
For those cells, cutting off the charging early and doing fractional cycles, say ranging between 50% and 75% SOC might give a longer working life than cycling between 75% and 100%. Do you have hard facts on that to share?

[PNjunction]

For storage recommendations, I guess longer than a few days or a week maybe, then 50% DOD seems to be about the norm. However, I have seen them arrive anywhere from 20% to 60% DOD depending on the manufacturer and application.

For example, the Shorai Lifepo4 powersports batteries are typically kept in "storage" at about 20% DOD. Their own charger has a function to either bring the battery up or down to this level before storing the bike - very handy. Presumably, one will be riding it in a week to a few months.

My Braille lifepo4 battery, which was over 2 years old, (26650 A123's inside) was sitting pretty out of the box at 13.3v! That's pretty high for long term storage, although I'm sure that the company didn't think this would end up being a shelf-queen and would sell quickly. That may mean that I'm going to suffer reduced cycle life by it sitting around at a high SOC for so long. We'll see.

These high SOC's during storage may be indicative of powersports lifepo4's being able to sit around like that, whereas low-rate prismatics designed for capacity rather than power, may be the ones that really need to be stored much lower. The Shorai's are prismatics, but apparently are tweaked.

I'm going KISS and just keeping them at 50% DOD for any long term storage that will be longer than a week. Still, I can't find any qualitative comparisons other than being at the extremes.

[Sunking]

Some Li chemistry batteries, not sure if it also applies to the iron phosphate family, even deteriorate faster when kept at full charge than when kept at 50-75% charge.

Pretty close and it is called Storage Voltage. For LiPo it is 3.85 vpc. Just about all the smart chargers for Lithium today have a storage setting. It will either charge or discharge to the right voltage. I keep mine in a warmer part of my refrigerator in a zip lock bag with silica gel packets.