Lithium battery charge profiles

[tecnodave]

Jimbo,

IMHO, you are not exercising them enough, if you only use the top 20 % they will not get a good deep charge that will stir up all the electrolyte. Stratification will result and the acid in the bottom of the cells will be stronger than that in the top of cells....eventually sulfation will result......this is especially true for tall battery types.  I feel it is better to use 60-70 % of ampacity before recharging then recharge at 20 % of the 20 hour a.h. rate of the battery. If you only use a small percent of a battery's capacity it will eventually lose amp hour capacity. Get the manufacturers charging schedule for your battery type.


td

[jimbo]

When i was living there it was easier to give them a deeper discharge but now that it is rented i rely on my SMA inverter to start the gen at lower SOC.

Do you equalize only when necessary or at a given interval? Raylite recommend a 2 hr equalize every 20 days. 

[tecnodave]

Living there makes a big difference, you are not doing too bad with even s.g. readings After 6.5 years.  it all depends on the loads and how you use your system. I am very frugal with electricity , it's part of my lifestyle. Born on a homestead in rural Alaska ,  never saw grid electricity till I was a teen.
You will take better care of your system than any renter will with few exceptions.

I equalize all my new batts every two weeks, on the recycle ones I eq them more until I get s.g. variation down to < .020 between cells sometimes using high frequency desulfators and other techniques , mind you I am picking up batteries that are on the way to recycle and getting years out of them , certainly not something that most people do but I do work on traction vehicles and swap out a lot of batteries for reliability issues.

The ray lite recommendation sounds reasonable, I have never heard of that company though.

td

[vtmaps]

IMHO, you are not exercising them enough, if you only use the top 20 % they will not get a good deep charge that will stir up all the electrolyte. Stratification will result and the acid in the bottom of the cells will be stronger than that in the top of cells....eventually sulfation will result......this is especially true for tall battery types.  I feel it is better to use 60-70 % of ampacity before recharging then recharge at 20 % of the 20 hour a.h. rate of the battery. If you only use a small percent of a battery's capacity it will eventually lose amp hour capacity.

I totally agree that repeated shallow discharges are not good for the battery, but I'm not sure that stratification is always the reason.  I think it depends on your charging protocol. 

If your charge protocol causes the battery to spend enough time gassing, there will be no stratification... no matter what the SOC was when you began charging. 

Some charging protocols use the amount of time in bulk to determine the amount of time in absorb... if the battery starts out at a high SOC the bulk will be short and the absorb may be too short to stir the electrolyte.

If you use end amps to terminate absorb, you may also develop stratification if the charging current is too low.  Charging current often starts out low as the sun rises in the morning... if you start at a high SOC you may get to absorb without ever achieving a high enough current to properly charge the battery.

Let your hydrometer be your guide... it will tell you whether you have stratification or sulfation.  Technodave is quite correct that repeated shallow discharges (even if you manage to avoid stratification) are not good for the battery.

--vtMaps

[tecnodave]

vtMaps,

I agree totally, I do have WBjr,s on my Classic 150 and kid as well as TriMetrics on each system but I always go back to the hydrometer no matter what anything else is telling me.  I scored a two bulb hydrometer/thermometer.   WWII Navy Radiomans "B" battery tester that has two separate floats, one for s.g. And one for electrolyte temperature.  Very accurate and in good shape as it is 70 plus years old, wood box and all.

When I learn how to reduce iPad pixel count I will post a pic as this unit belongs in "what is it" or maybe in TJ's OP Antique collection.

td

[Alaska Man]

wait wait wait,

LiFePO4 cost competitive with lead acid?

Where?

Do tell, please!

I've got some medium scale liFePO4 stuff on my bike, and it's really agreeable.
but i never ever considered it for PV solar use, way too spendy.

4500 mAh - Proprietary Battery Size - Lithium Iron Phosphate (LiFePO4) - 6.4 V DC   $61.00 at Overstock.com


http://www.overstock.com/Electronics/WorldCharge-Lithium-Iron-Phosphate-LiFePO4-UPS-Battery/8726293/product.html?cid=225772&fp=f&mr:referralID=0127267a-fd60-11e3-8bdb-001b2166c2c0

[vtmaps]

4500 mAh - Proprietary Battery Size - Lithium Iron Phosphate (LiFePO4) - 6.4 V DC   $61.00 at Overstock.com

If you think 4.5 ah of LiFePO4 for $61 is a competitive with LA, I can hardly imagine what you are paying for your LA.

--vtMaps

[Alaska Man]

Everything costs twice as much in Alaska. I dropped $2,500 for 8 AGM 6v 220ah batteries I use. That's getting real close to making the (4) Li 3.2v I'm seeing on the net equal in pricing. With this plant being open in 2015 I think it would beat the LA bank.

[vtmaps]

Everything costs twice as much in Alaska. I dropped $2,500 for 8 AGM 6v 220ah batteries I use.

8 X  6 volt X 220 ah =  10,560 watthour for $2500...  That's about 25 cents per watthour for AGM

6.4 volts  X  4.5 ah =  28.8 watthour for $61... That's over $2 per watthour for LiFePO4

--vtMaps

[RossW]

Everything costs twice as much in Alaska. I dropped $2,500 for 8 AGM 6v 220ah batteries I use.

8 X  6 volt X 220 ah =  10,560 watthour for $2500...  That's about 25 cents per watthour for AGM

6.4 volts  X  4.5 ah =  28.8 watthour for $61... That's over $2 per watthour for LiFePO4

--vtMaps

Lets look at it another way shall we? In real practical application....
I've been buying 500AH/2V AGM second-hand for $110/cell. That makes $2640 for a 500AH bank. But in reality, I tried to never discharge them more than 20%, so 4800 watt-hours of usable power = 55c/Wh SECOND HAND.
Increase that to $600 ea or $3/Wh usable for new cells.

(I had three, then two, then finally only one) bank in order to get a comfortable 200AH drawdown.

I replaced those with a bank of 300AH LiFePO4 cells. They're rated for >2000 cycles @ 85% discharge. 200AH discharge is only 66% DoD, so should see significantly better life.
They cost $1.10/AH, and I need 16 cells. So 200AH*48V = 9600 watt-hours usable for $5280 = $0.55/WH usable NEW.

So even paying top dollar for brand new LiFePO4 cells, I get twice the usable capacity for the same price per WH in a smaller, lighter package.

[Cniemand]

Thanks Ross,

I rarely see people discussing/examining what is actually being used in battery banks. The need to double your bank size due to Pb restrictions changes the dynamics to make Lithium an option. As you can use much smaller banks. With batteries, it really does come down to long term usable aH.

[cpm]

wait wait wait,

LiFePO4 cost competitive with lead acid?

Where?

Do tell, please!

I've got some medium scale liFePO4 stuff on my bike, and it's really agreeable.
but i never ever considered it for PV solar use, way too spendy.

4500 mAh - Proprietary Battery Size - Lithium Iron Phosphate (LiFePO4) - 6.4 V DC   $61.00 at Overstock.com


http://www.overstock.com/Electronics/WorldCharge-Lithium-Iron-Phosphate-LiFePO4-UPS-Battery/8726293/product.html?cid=225772&fp=f&mr:referralID=0127267a-fd60-11e3-8bdb-001b2166c2c0

Fwiw, that's not a very good price all in all, unless it's a drop in replacement for some system where the oem is much more $$$.

the  traction battery on my e-assisted cargo bike is the equiv of 12 of these, which would cost $732, but I get my 9.5ah/36v from Li Ping for $318

[Alaska Man]

For me it is all about energy storage and life cycles. 

When I first decided to take the plunge I thought (-220AH 6V batteries would last me for days.

Well at 1760AH it would have. I had no idea about only being able to use 50% (880Ah) and then if I didn't want to drop 3 grand every two and half years, I really only have 440ah of useable storage.

So any LI/LA characteristic or any new Dodad that increases any of this is where I go next.

We can already produce relatively cheap and clean energy, the future of Solar is in storing it. IMHO

[lestef]

Hy all,
I'm about to buy the last piece for my PV system, the batteries... I read the discussions about LFP on this forum and I have noticed that you prefer the new gray Calbs instead of other brands, also on the other forums I have read that the Winston lifeYpo4 will have more cycle life by using yttrium in their chemistry...
For my system I don't need big discharge currents where Calbs have better results, the only parameter that I consider is the life of the cells...
What you think about this ?

[zoneblue]

Unfortunately i just dont think theres enough history to show any clear winner. Much of it will depend on freight and  finding a dealer you are happy with. These guys seem to have reasonable prices and frieght for mainland US.

http://www.balqon.com/store-2/#!/200-Ahr-Battery-Lithium-Iron-Phosphate-6-Week-Lead-Time/p/11906020/category=2736691