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

[Sunking]

I'm really not sure where you got that 20 amp figure from, unless you're assuming a certain runtime.

I know you do not understand and that is the problem. You don't understand and then make videos about how things work. For one you do not understand why your battery voltage dropped from 13.6 to 12.4, and why that is a huge problem.

[createthis]

No heat is not going to be an issue for you. You will not be able to pull 200 amps from your batteries for any meaningful amount of time for them to get hot enough to worry about. Using 1% rule on battery voltage sag, your batteries are only good for 20 amps (C/5) or 1/10th what you want.

Good luck, time for me to go play

It pulls about 145 amps just fine:

Jump to 7:36 for the 145 amp draw. Tried to jump there from the link, but it wouldn't let me.

I'm really not sure where you got that 20 amp figure from, unless you're assuming a certain runtime.

I did decide to derate the whole system with a 150 amp DC breaker.

[karrak]

The discussion has been about voltage sag with time, I will amend the original post to make it clearer

[Sunking]

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

It is easy peasy, a fith grader can do it. If you understood math and Ohm's Law you would know better. I can look at any discharge graph and tell you the Ri within 5 seconds at any point. It looks exactly like the Charge Discharge cures.

Even Jesse aka Creathis knows how, I taught him how to do it, He made a video how to do it. Watch it and learn from him who knows more than you do now. because he listened. I learned how 40 years ago from the battery manufactures. That is why they publish Charge and Discharge curves. Very simple find Delta Voltage and Current which screams out at you when you look at the graphs. If you really knew anything about batteries, you would know that. Jesse is a beginner and he knows it. How many years did it take you to get so ignorant?

[Sunking]

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.

So am I, Pb is much more cost effective. I have proved it many times, get over it one trick pony.

[Sunking]

I am not talking about Specific Power, I am talking about voltage sag and charge loss characterised by the peukert law.

Voltage Sag is Specific Power period. You have no clue what you are talking about. Peukert Law has nothing to do with Specific Power or Voltage Sag. You are really making a fool of yourself. Here is your education from MIT

Specific Power (W/kg) – The maximum available power per unit mass. Specific power is a characteristic of the battery chemistry and packaging. It determines the battery weight required to achieve a given performance target.

Peukert Law expresses approximately the change in capacity of rechargeable batteries at different rates of discharge.

[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

[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]

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

[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]

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

[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

[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

[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.

[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.