LiFEPo4 sitting several months NOT hooked up = freaking about self discharge = Brick?

[Sunking]

Only problem with this charging regime is that it only charges the battery to around 80% so you are wasting about 10-15% of your accessible storage capacity. The vast majority of currently installed systems that I know of charge to around 3.45 volts/cell (55.2 volts) which will charge to above 90% with no ill effects.

You just proved you do not know what you are talking about.

[karrak]

You just proved you do not know what you are talking about.

Please elaborate

[SunEagle]

Please elaborate

I believe Sunking is correct in that the discussion concerns LiFEPo4 battery chemistry. You are talking about a different type battery.

[karrak]

I believe Sunking is correct in that the discussion concerns LiFEPo4 battery chemistry. You are talking about a different type battery.

I am talking about LiFePO4 batteries, the same ones I have had installed in my off grid system for nearly three years.

I am not sure what part of my statement that Sunking disagrees with. I concede that if you leave a 16 cell 48 volt LFP battery floating at 54 volts (3.375volts/cell) for long enough that it will get to over 90%SOC. Is this what Sunking is getting upset about?

When I first got the battery I charged it to 27 volts (3.375 volts/cell) to hopefully increase its lifespan. After much research and anecdotal evidence I am now of the view that charging to 3.45 volts/cell and an SOC of around 95% will not make much if any difference to the lifespan of an LFP battery. I am happy to debate this point.

Simon

[danewguy]

I did some looking around and found a charger at Batteryspace. The CH-LF51215A.
It does not have a float charge just CCCV at 51.2v. It has a built in BMS connection but judging by the manual they only show how to interface with their own BMS system they sell. I emailed them and they could not direct me nor know if it would even be compatable with my BMS were I to try to hook it up to mine. - so in the end it might as well not have that I guess. But I'm finding it difficult to find the right lifepo4 charger. AND not spend a gazillion. Just so I can have a 'safety'. Depending in how long it will take to have my whole system set up.

[Sunking]

I did some looking around and found a charger at Batteryspace. The CH-LF51215A.It does not have a float charge just CCCV at 51.2v. .

CCCV is a Float Charger. However the voltage is to low at 51.2 volts.

You need a charger to supply at least a C/10 charge current, with a variable output voltage you can set. Unless you plan on using a BMS which is not necessary, you can use any charger with a CCCV output that has an adjustable voltage. Golf Cart charger will even work.

There are several ways to charge Lithium batteries. If you listen to manufactures and uninformed users would have you believe you must charge to 100% or close to 100% and use a BMS which is entirely false. It is too if you want to charge to 100% or close to it you should use a BMS and Lithium compatible charger, but that is a commercial application to suck more money out of your pockets. All commercial system made for consumer use, use that model. You do not want to flirt with a fully charged battery. You want to charge no higher than 90%, or go below 10%. Do that and you double the life cycle of the battery. This is the only way commercial EV manufactures can offer the warranties they offer. They will not allow the customer to ever reach 100% or even get close. Nissan, Chevy, and Tesla run 20/80 with Limp home down to 10% before you must call a tow truck.

Armed with this knowledge, knowing how battery chargers work, and Lithium charge characteristics you can mimic what commercial EV operators do. This works particularly good with solar applications and using standard Float aka CCCV chargers with variable output voltage . Starting with the manufactures BMS method to 100% is to charge at some C-Rate like C/10 and monitor battery cell voltages as the batteries charge. When the first cell reaches 3.6 to 3.65 volts, the BMS will tell the charger to reduce charge current to the value the Cell Bypass Boards can safely bypass around fully charged cells as not to over charge them. That value is 1 amp of less with 150 to 500 ma being the norm. When the last cell, reaches 3.6 to 3.65 volts, the BMS tells the charger to shut off. At that point every cell is 100%.

Another way to charge a Lithium cell to 100%, but only works for single cells is CCCV. Again you apply a charge current at some C-Rate like C/10 which is Constant Current mode. You set the voltage to 3.6 to 3.65 volts. You charge at C/10, when the voltage reaches set point of 3.65 volts you hold it at 3.6 volts until currents tapers off to C/20 to C/33 and them terminate the charge.

In either case when the cells are 100% SOC and allowed to rest the Open Circuit Voltage will relax to 3.375 volts. That would be 54 volts on a 16S 48 volt battery. This is very important to understand that 54 volt is a saturated charged.

Armed with that knowledge there is another way to get a single cell to 100% without any automation. That is by using a CCCV aka Float charger of roughly C/10, or really any charge rate you want up to 1C and set the voltage to 3.375 volts and walk away. When the cell is fully charged, current stops and holds 3.375 volts the saturated 100% SOC. You do not need to turn off the charger. If any load is applied the charger will supply the power assuming the load demand is within range of the charger. Once you grasp this concept you can now apply it. So how do you do that?

It is easy. First we decide we do not want to flirt with 100% SOC. We elect to stay safe and prolong battery life and eliminate thermal runaway by choosing to charge no higher than to 80 to 90%. At 90% OCV on lithium is 3.3 volts or 52.8 volts on a 16S battery. So if you use a Float Charger, set the voltage 52 to 52.8 volts, just walk away and let it run forever and Float. Once the cells reach saturation, all charge current stops. Only thing you need to do is monitor cell voltages to make sure no cell goes above 3.375 volts.

That method can be used very effectively with most solar charge controllers that allow you to set Bulk, Absorb, and Float to 52 to 53 volts. If the cells reach set point by noon, from non to sunset any power demands come from the panels, not the batteries. If you went to 100% you would have to shut off the Controller for the day and use Battery Power, instead of Solar Power. You want save the batteries for night. That is what Karrak and others cannot wrap their brains around.

Last note Lithium batteries perform best at PSOC partial state of charge. Taking then near or to 100% stresses them. This is exact opposite of lead acid where they must remain at 100%, and fully recharged after any use. The thing with solar and Pb batteries is you can really never ever reach 100% in a working system, at least not for any amount of significant time. Lithium operate best at PSOC and never need or require 100%, so no need to try to even get close.

[karrak]

I did some looking around and found a charger at Batteryspace. The CH-LF51215A.
It does not have a float charge just CCCV at 51.2v. It has a built in BMS connection but judging by the manual they only show how to interface with their own BMS system they sell. I emailed them and they could not direct me nor know if it would even be compatable with my BMS were I to try to hook it up to mine. - so in the end it might as well not have that I guess. But I'm finding it difficult to find the right lifepo4 charger. AND not spend a gazillion. Just so I can have a 'safety'. Depending in how long it will take to have my whole system set up.

This charger could be connected to the BMS that you currently have in your battery system, you would have to make up the cable to hook the two units together.

I still can't see the need for you to get a charger at this stage, your battery is around 50% full. It has been sitting for months with no problems and I would think will continue to sit for months without any problems. If you are concerned, do as Raj has said and check the battery voltages one a week or more often if you want. If you do buy this charger you will probably only use it once as you will be charging the battery from your solar charging system when you get that installed.

What are your plans if you don't have enough solar power and your battery is empty?

Simon

[karrak]

CCCV is a Float Charger. However the voltage is to low at 51.2 volts.

You did not read the specifications correctly, that is the nominal voltage of the battery pack, the charger will charge to 56.8 volts

There are several ways to charge Lithium batteries. If you listen to manufactures and uninformed users would have you believe you must charge to 100% or close to 100% and use a BMS which is entirely false.

Sure you don't have to charge to nearly 100%, but by not doing so you waste expensive battery storage capacity. The operating range that you used to recommend was 80% https://www.solarpaneltalk.com/forum...516#post246516 to 20% which in Danewguys case means not utilising over $4,000 of battery capacity. At least with your new 90% to 10% range which I don't think you can safely operate within without a BMS you are at least using 80% of the battery capacity. From the evidence I have seen I think you can charge to whithin a few percent of 100% as long as you keep the charge voltage and current low without affecting battery live to any great extent. Charge voltages of 3.45-3.5 volts and charge current < C/2

This is the only way commercial EV manufactures can offer the warranties they offer. They will not allow the customer to ever reach 100% or even get close. Nissan, Chevy, and Tesla run 20/80 with Limp home down to 10% before you must call a tow truck.

Even is this statement is correct, none of these cars use LiFePO4 batteries so you can't use them as examples.

You do not want to flirt with a fully charged battery. You want to charge no higher than 90%, or go below 10%. Do that and you double the life cycle of the battery.

You keep saying this or was it 80% to 20% but have never given any reasons for making that statement. Evidence please.

That method can be used very effectively with most solar charge controllers that allow you to set Bulk, Absorb, and Float to 52 to 53 volts. If the cells reach set point by noon, from non to sunset any power demands come from the panels, not the batteries. If you went to 100% you would have to shut off the Controller for the day and use Battery Power, instead of Solar Power. You want save the batteries for night. That is what Karrak and others cannot wrap their brains around.

One huge problem with this is that it will take forever to get the battery to anything like full and you only have so many hours of sun in a day.https://www.solarpaneltalk.com/forum...orb#post301695

Simon

[Sunking]

Even is this statement is correct, none of these cars use LiFePO4 batteries so you can't use them as examples.

Hogwash, they are all Lithium, same rules apply to all lithium batteries. Only the voltages are different. FWIW the Chevy Volt uses LiFePo4.

[karrak]

Hogwash, they are all Lithium, same rules apply to all lithium batteries. Only the voltages are different.

This statement is as bad as saying you should treat all types of Lead Acid batteries the same!

Maybe it explains your insistence that an LiFePO4 battery will last twice as long if it only charged to 80% or is it 90% rather than 100%. This statement is a fair approximation for Li-ion batteries charged to 4.2 volts, see http://batteryuniversity.com/learn/a...ased_batteries for more details. This article says that for every 0.1 volts drop in voltage that a Li-Ion battery is charged to you get a doubling in battery life. Following this logic, charging LiFePO4 batteries to only 3.5 volts should mean that they last 128 times longer than an Li-ion battery charged to 4.2 volts. I doubt this is the case, but it implies to me that the voltage within reason and SOC that an LiFePO4 is charged to is less of an issue than with Li-ion batteries charged to 4.2 volts.

FWIW the Chevy Volt uses LiFePo4.

Are you so sure? http://www.edn.com/design/automotive...tronic-secrets

Simon

[Sunking]

This statement is as bad as saying you should treat all types of Lead Acid batteries the same!

Exactly. Just like Lithium, only the SOC voltage and charge rates change from one type to another. Gel charges slower to a lower voltage, FLA charges faster than Gel to the highest voltage, and AGM charges the fastest with a voltage higher than Gel and less than FLA. But al of them must be charged to 100% SOC after any use and held there until ready to be used again. Yep you treat all Pb batteries the exact same.

Maybe it explains your insistence that an LiFePO4 battery will last twice as long if it only charged to 80% or is it 90% rather than 100%. This statement is a fair approximation for Li-ion batteries charged to 4.2 volts, see http://batteryuniversity.com/learn/a...ased_batteries for more details. This article says that for every 0.1 volts drop in voltage that a Li-Ion battery is charged to you get a doubling in battery life. Following this logic, charging LiFePO4 batteries to only 3.5 volts should mean that they last 128 times longer than an Li-ion battery charged to 4.2 volts. I doubt this is the case, but it implies to me that the voltage and SOC that an LiFePO4 is charged to is less of an issue than with Li-ion batteries carged to 4.2 volts.

Again proves you do not know what you are talking about. Please oh please charge your batteries to 4.2 volts.

And if you want to use GM as you model please do and listen to them when they say:

[QOUTE] The Volt’s lithium-ion battery is controlled so that it operates
within a state-of-charge window at any given time. Controlling
the battery in this way avoids fully charging or discharging the
battery which can shorten the life of the battery.[/QUOTE]

Here that it is called a SOC Window? Prevents the customer from fully charging or discharging the battery. If you listen to what the professionals do you might learn something. That window GM uses is 20/90 as does Tesla, Nissan, and Toyota use. Only the clueless charge large format cells to 100%. Charging cell phone batteries that Cadex (Battery University) refers to is no big deal to a $20 cell phone battery or power tool. They fully intend for you to replace them every year or two by design. Only the informed know if they stay away from full charge, they will double the life cycle. In fact you can download an App for any cell phone that allows you to do exactly that, turn down the voltage so your battery last longer.

Battery manufactures want you to use a BMS and fully charge your batteries. Many require it. Why? So you have to replace them more frequently. Users are too ignorant to know otherwise. So we know you are Ignorant and fall for marketing. Works for me.

[Mike90250]

....... In fact you can download an App for any cell phone that allows you to do exactly that, turn down the voltage so your battery last longer.....

Please, where is that app ? I've seen ones that just tell you the state, not able to control the charger setpoints