LifePO4 GBS Amp Hour Testing 2.5v to 3.6v per cell

[karrak]

A unique characteristic of lithium batteries is there Internal Resistance vc SOC curve. It is reverse of all other batteries. As it charges up, its internal resistance goes UP.

Can you please give some references to back up your argument about Internal Resistance vs SOC. I found this graph for LFP batteries from file.scirp.org/Html/11-6201413_25079.htm

Very desirable but gives us a challenge when charging. Unlike eall other batteries can tolerate excessive over charging. In fact we use that ability. With a Lead Acid battery when one gets fully charged up its resistance is at it lowest and passes current down to lower level batteries thus EQUALIZING them.

Not Lithium, current stops when a Lithium cell is Saturated and fully charged up. Its resistance shoots up to stop current flow. If you force it with higher voltage is converted directly as heat. More heat, more current. Thermal Run-Away.

The reason that lead acid batteries will pass current through them if you raise the voltage high enough is that you start breaking down the water in the electrolyte to hydrogen and oxygen. This is a side reaction within the battery.

It is the cell voltage that goes up when the LFP battery is full. The battery will only get hot if you are charging it at high charge rates. If you charge it at a very low charge rate when the battery is full the voltage will rise but it will not get hotter until you reach a voltage of around 4.5V at which point you will start breaking down the electrolyte, this will generate heat. Rather like the water being broken down in the lead acid battery.

Simon

[karrak]

Not to worry, all of it is manageable. Only thing that cannot be managed today is economics. Today Pb batteries are king of economics and performance. Until lithium battery prices fall to equal or less than PB, then Pb will dominate. The only huge advantage lithium has, energy density, is not required or can be justified for most off-grid systems. One exception I can think of is RV or Boat where weight and space come at premiums.

I can think of a few other advantages of LFP over Pb, how about

1. Higher charge acceptance right up to 100%SOC. Means you can charge at 0.5C with a very small absorb time.
2. Very high efficiency, around 95% power efficiency
3. Very flexible charge parameters, basically from 0A to 0.5C. None of this having to charge at around 0.1C
4. No voltage sag on high discharge current over a period of time, peukert coefficient close to 1
5. Zero maintenance if BMS if fully automated
6. Ability to utilise 80%-90% of the battery capacity on a regular basis
7. Ability to accurately calculate to within a few percent the amount of power left in your battery.
8. Ability to leave battery partially full for an extended period of time with no detriment to the battery

You are wrong about cost, LFP batteries come out around the same if not better if you compare them on a cost per kWh cycled through the battery.

Simon

[Sunking]

Having lead acid batteries is one of the main reasons for not having an inverter with a high current draw as they don't cope with high currents for any length of time. The classic Lead acid battery voltage sag.Simon

Wrong again Simon, and you cannot keep your story straight. One minute Voltage sag is not a problem, and the next it is real. Make up your mind. Simple physics.

You are speaking of Specific Power which i know you have no clue what that means because if you did, you would know you just stuck your foot in your mouth and proved you do not know much.

Specific Power or gravimetric power density, indicates loading capability expressed in W/Kg. Picture says it all. Cheap Chi-Coms run the low on the graph. However that does not tell the whole story because that is weight for weight comparison, not capacity to capacity. If we take a 100 AH Chi Com @ 12 volts we have a 12 Kg battery and a Pb of equal capacity and voltage would weigh in 50 Kg. The LFP would have to have 4 times the Specific Power to equal a Pb battery. So when it comes right down to it Ah per AH, Pb is equal to Specific Power. No gain.

Its all about application and find the right battery for the job. You are a 1-trick pony who really does not know much.



Give you a Clue Simon. Specific Power is Directly related to Internal Resistance. Another Clue many AGM batteries are deigned to be discharged in 15 minutes. and Forklift and Golf Cart batteries are made for 10C. Its the application one trick pony. Just about any AGM battery is equal to or better than any Chi-Com with respect to Specific Power. Any decent AGM, Telecom AGM/FLA, or Traction AGM/FLA is superior and any Traction FLA/AGM will last longer than Chi-Com LFP and less expensive.

[Sunking]

Can you please give some references to back up your argument about Internal Resistance vs SOC. I found this graph for LFP batteries from file.scirp.org/Html/11-6201413_25079.htm




The reason that lead acid batteries will pass current through them if you raise the voltage high enough is that you start breaking down the water in the electrolyte to hydrogen and oxygen. This is a side reaction within the battery.

It is the cell voltage that goes up when the LFP battery is full. The battery will only get hot if you are charging it at high charge rates. If you charge it at a very low charge rate when the battery is full the voltage will rise but it will not get hotter until you reach a voltage of around 4.5V at which point you will start breaking down the electrolyte, this will generate heat. Rather like the water being broken down in the lead acid battery.

Simon

You just proved you are as clueless and dangerous as DAX. You have no clue what Ohm';s Law is

It all has to do with Internal Resistance. If you really knew your stuff, you would know if you look at any charge/discharge curves every manufacture publishes gives the Ri in graphical form The Ri Curve is identical charge/discharge voltage curve. It is simple Ohm's Law and you can calculate Ri from any discharge curve. They are hiding in the math you cannot see or understand. Those Knees of the curve are direct result of the Ri changes. Voltage and Resistance controls current flow, not SOC. Any student of the trade can tell you that.

[J.P.M.]

You cannot have heat without current and voltage

I don't always agree with him, but, in this application, in the final analysis, unless you manage to violate the applicable laws dealing with entropy, I think SK has a point there.

[Sunking]

You are wrong about cost, LFP batteries come out around the same if not better if you compare them on a cost per kWh cycled through the battery.

All wrong again Simon. Maybe in your country LFP make sence, but that is because you do not have access to quality made batteries at reasonable price points. Your stupid government energy policies and taxes prevents you from access. You get Chi-Coms, the stuff you sell to suckers. Quit denying it or I will post your full name, email address and your company web site. You are easy to find, and wreckless on the web.

In the USA top of the line 5 to 10 year Pb battery cost 20-cents per watt hour. 1 to 2 year Chi-Coms like you own, sell , and advocate cost 40 to 50-cents per watt hour. There is no comparison. Even with the smaller LFP requirement of 3/5 of Pb at end of lifetime still cost 200 to 400% more than Pb.

When it comes to cost justification, EV's are on eof the few that can justify the cost of Lithium Batteries. None use Chi-Com or LFP batteries. The public has no access to quality Lithium batteries other than Salvage operations from a wrecked EV which is where I got mine.

[jflorey2]

Peak recorded current from my battery is 245A. Normal heavy load is ~150A and normal load ~5A. Has not burnt the house down yet.

That's great, but "I have not burnt my house down yet" is not a good argument that what you are doing is desirable or safe.

I've made a lot of mistakes over the years without burning my house down. They were still mistakes.

[Sunking]

That's great, but "I have not burnt my house down yet" is not a good argument that what you are doing is desirable or safe.

I've made a lot of mistakes over the years without burning my house down. They were still mistakes.

Well said sir. Karrak is a fool just like Dax. Has no clue how dangerous high current is Every time they open their mouths exposes their ignorance and poses a clear and present danger to the public.

Dax I have figured out. He is a uneducated installer working at a RV shop pretending to be a designer. Simon was easy to find and figure out. He is just a re-seller/importer of cheap Chi-Com electronics. He peddles telephones, monitors, cameras, batteries, fake MPPT controllers, and other Chi-Com copy cat junk. Simon exposed his ignorance trying to defend Dax which is defenseless.

[Sunking]

I don't always agree with him, but, in this application, in the final analysis, unless you manage to violate the applicable laws dealing with entropy, I think SK has a point there.

Yeah Ohm's Law in particular.

Watts = Power = Heat

Watts = Voltage x Current

You cannot have electrical heat without Voltage applied and Current flowing through a Resistance. Impossible otherwise except on planet Dax and Karrak

[karrak]

I don't always agree with him, but, in this application, in the final analysis, unless you manage to violate the applicable laws dealing with entropy, I think SK has a point there.

How about a fire, or a little off topic but a thermonuclear chain reaction. Heat is not from current in these and many other cases.

Unfortunately Sunking as usual has edited the original message so I can't get the context for your statement.

If it was in regards to overcharging LFP batteries you have to provide the energy from an external source to heat the battery up to the point that the battery gets so hot that the temperature alone will cause the rates of the breakdown chemical reactions to become self sustaining. At this point the battery will continue to decompose without any current flow in the external circuit. If you stop injecting energy into the battery before the point that the reactions become self sustaining they will subside and the battery will cool down.

Simon

[karrak]

That's great, but "I have not burnt my house down yet" is not a good argument that what you are doing is desirable or safe.

I've made a lot of mistakes over the years without burning my house down. They were still mistakes.

I was being sarcastic.

There are many devices in everyones house that would capable of burning them down. This doesn't happen because the vast majority of these devices have been designed, manufactured and installed properly. This is the case with my inverter. I am temping providence here

As you know engineering decisions are rarely made on one factor alone. Sure I have to run a higher current at 24V, the reasons for running 24V was that when I designed my system solar panels cost $8.00 per watt. I was going to run a 24V fridge, the lighting is all 24V and I have have a 24V circuit to run all the electronics. This means I could run the inverter on standby for the bulk of the time which saves around 0.5kWh per day. If I were to design the system today I would use 48V. 48V is not without its dangers, more problems with voltage arcing and then open circuit voltage of two 24V panels in series is around 90V which is starting to get dangerous.

Simon

[Sunking]

How about a fire, or a little off topic but a thermonuclear chain reaction. Heat is not from current in these and many other cases.

Now you are really showing how ignorant you are. I will let the other engineers bury you once and for good like Dax. You really showed your ignorance with that statement. If you had any understanding of Ohm's Law and Lithium Battery electrical characteristics you would be laughing with me. The dang Discharge Curves proves even lithium batteries have to comply with physics. If you understood the resistance of a lithium battery goes up and spikes when a Lithium battery is fully charged is responsible to the sharp upward curve or spike in voltage. If it behaved like say a Pb battery which goes down as SOC rises, you would know current would easily would flow with very little voltage increase. being passed down to lower energy state cells.

You just hung yourself with your own rope. You do not understand a very simple equation Amps = Volts / Resistance. You cannot change that no matter what you say or do.

[karrak]

You are speaking of Specific Power which i know you have no clue what that means because if you did, you would know you just stuck your foot in your mouth and proved you do not know much.

I am not talking about Specific Power, I am talking about voltage sag over a period of time and charge loss characterised by the peukert law.


If the relative sag in the voltage over time with different load currents does not charge the different discharge curves stay parallel to each other as per the LFP curves. If the relative voltage sag gets larger the longer we discharge the battery the curves diverge as we can see with the Pb-acid curves. This is showing that the Ri of the Pb-acid battery is getting substantially larger the longer we discharge the battery.

On top of this we see for Pb-acid batteries that higher current drawn from the battery substantially decreases the charge (Ah)we get out of it. This effect is not nearly as noticeable with LFP batteries.

We have probably all come across the effects of this when we try to start our car. It is more noticeable when the battery is old and the temperature is cold. When we first turn the ignition key the engine will crank over at a reasonable speed. If it doesn't start the starter motor will slow down. If we turn the ignition off, wait for a while and try again the engine will crank over at a reasonable speed although less that the first time we tried.

Simon

[karrak]

Quit denying it or I will post your full name, email address and your company web site. You are easy to find, and wreckless on the web.

Please do, I am interested to know who you think I am.

In the USA top of the line 5 to 10 year Pb battery cost 20-cents per watt hour. 1 to 2 year Chi-Coms like you own, sell , and advocate cost 40 to 50-cents per watt hour. There is no comparison. Even with the smaller LFP requirement of 3/5 of Pb at end of lifetime still cost 200 to 400% more than Pb.

I am not talking about the cost of the battery divided by its rated capacity, I am talking about the cost per kWh cycled through the battery over its lifetime.

[karrak]

It all has to do with Internal Resistance. If you really knew your stuff, you would know if you look at any charge/discharge curves every manufacture publishes gives the Ri in graphical form The Ri Curve is identical charge/discharge voltage curve. It is simple Ohm's Law and you can calculate Ri from any discharge curve. They are hiding in the math you cannot see or understand. Those Knees of the curve are direct result of the Ri changes. Voltage and Resistance controls current flow, not SOC. Any student of the trade can tell you that.

Good luck trying to calculate the Ri from the discharge curves. It is a constantly moving target especially with lead acid batteries.

I haven't said anything about the battery Ri when you are charging an LFP cell and it runs out of accessible lithium ions in the cathode, this is outside the normal operating window of the cell. You stated "A unique characteristic of lithium batteries is there Internal Resistance vc SOC curve. It is reverse of all other batteries. As it charges up, its internal resistance goes UP." I gave you a Resistance vs SOC curve for LFP batteries. Not surprisingly I couldn't find any curves that go outside the normal operating range of the batteries.

Simon