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

[createthis]

Jesse here is where we went apart. A while back you learned How and measured each of your batteries Internal Resistance. I did that so you could understand the relationship of Voltage, Current, Power, and Resistance aka Ohm's Law the most basic fundamental lesson in electric 101. Literally the very first lesson any student of the trade learns. You even made a video doing it. You learned each cell has roughly 2.5 milli-ohms and when all for are connected in series with hardware have roughly 11 milli-ohms. Let's just 10 milli-ohms to keep it simple. You understand how to do the test, but you missed the point of the lesson.

So lets design a system, a 12 volt system with a 2000 watt Inverter. Any Inverter you buy is going to quit working when the voltage input drops to around 10.5 to 11 volts. Lets assume worse case 10.5 volts. Remember that 10.5 volts is a bad thing at the Inverter Input. Very first thing we have to look out for and control in the design is Voltage Sag and Drop.

So tell me what percentage are you comfortable with taking on the Battery? 1, 2, 3, 5, or 10%? Lets pick 5%. .05 x 12 volts = .6 volts.
How much for Cable? 2% sound good? OK .02 x 12 volt = .24 volts.
Total loss budget = 7% or .84 volts.

How much current are you running? Did you say 145 amps? Well at 145 amps on your battery the voltage sag is 145 amps x .01 Ohms = 1.45 volts. Your budget was 0.84 volts (7%) and your battery alone is at 1.45 volts or 12% loss and you have not even gone through the wiring for an additional .24 volt and now you have lost 1.7 volts or 14% power and voltage loss. That means when your battery is only discharged to 12.3 volts under load. your Inverter shuts off. Your batteries will still have significant capacity, they just cannot carry the load any longer.

Yup. Totally understood. I'm really not trying to get long run times out of this setup under full load. No matter how many times I say "toy system" that doesn't seem to sink in. I don't really use this system for anything other than learning and making videos. It has no other purpose.

[createthis]

Createthis - first, THANKS for doing the videos and sharing your experiences.

Secondly, thanks for using tools like Fluke(s) so that I can TRUST your readings.

You are definitely pushing the boundaries of the GBS cells, which I also use. But they have limitations as mentioned before, and your application is starting to look like a more suitable cell is in order, like Headway's.

For just safety and/or continued knowledge, it is good to get a second opinion from a related application, if nothing more than to come back here to get perspective, from a real engineer who has to eat his own dog-food. Huh?

ANYONE who needs additional insight, even if they don't use Headways (as opposed to large prismatics), or wants custom Powerlab 8 configurations for LFP charging, should read through some of the following from this UK site:

http://www.wheelchairdriver.com/board/viewforum.php?f=2&sid=5acb2e84be7e3fbeecdd967b0191d70d

Yes, bike-racer / engineer (Op: Burgerman) who basically has to LIVE on top of his LFP cells in an (awesome!) wheelchair. Non-commercial / no product engineering btw. See the "step by step lithium conversion" threads, and quite frankly any of the Pb based threads too.

While not exactly the same, your application and his are getting close to each other, and I think you'd profit from the additional information - if nothing more than to have a better understanding of the pros/cons of the GBS cells you (and I) use.

Sometimes it is good to get a second opinion / view of the LFP world.

Cool, thanks. I'll take a look. Sounds like an interesting application.

[createthis]

Nothing is contradictory, you are not understanding the information being given. That is why people are getting short with you. Over heating the batteries is not the issue. Those batteries are rated at 2C contentious. All that means with a lithium battery is it is thermally capable of being discharged at 2C. But that has nothing to do what I am talking about. You are off on a tangent.

So try this experiment. Repeat what you did, but at least collect some data with meaning.

1. Before you start measure the Open Circuit Voltage of the batteries directly on the battery term post.
2. Put your 1.8 KW load like you did in the video and let it run while you take some measurements.
3. Measure the voltage directly on the Battery Term Post again.
4. Measure the voltage directly and physically on the Inverter Input Term Post with the load cooking away.

Now tell me what you think is going on, and why you think it is safe and practical to run a 2000 watt Inverter on a 12 volt 100 AH battery.

You think the heat created by the resistance in the wiring plus the battery is a fire hazard. The 4/0 wires are certainly rated to handle it, but all that heat has to go somewhere. This isn't news to me. I'm the one who mentioned heat to you as a concern, Sunking, earlier in the thread. You're just proving me right in the same breath as you tell me I'm not listening.

[Sunking]

Jesse here is where we went apart. A while back you learned How and measured each of your batteries Internal Resistance. I did that so you could understand the relationship of Voltage, Current, Power, and Resistance aka Ohm's Law the most basic fundamental lesson in electric 101. Literally the very first lesson any student of the trade learns. You even made a video doing it. You learned each cell has roughly 2.5 milli-ohms and when all for are connected in series with hardware have roughly 11 milli-ohms. Let's just 10 milli-ohms to keep it simple. You understand how to do the test, but you missed the point of the lesson.

So lets design a system, a 12 volt system with a 2000 watt Inverter. Any Inverter you buy is going to quit working when the voltage input drops to around 10.5 to 11 volts. Lets assume worse case 10.5 volts. Remember that 10.5 volts is a bad thing at the Inverter Input. Very first thing we have to look out for and control in the design is Voltage Sag and Drop.

So tell me what percentage are you comfortable with taking on the Battery? 1, 2, 3, 5, or 10%? Lets pick 5%. .05 x 12 volts = .6 volts.
How much for Cable? 2% sound good? OK .02 x 12 volt = .24 volts.
Total loss budget = 7% or .84 volts.

How much current are you running? Did you say 145 amps? Well at 145 amps on your battery the voltage sag is 145 amps x .01 Ohms = 1.45 volts. Your budget was 0.84 volts (7%) and your battery alone is at 1.45 volts or 12% loss and you have not even gone through the wiring for an additional .24 volt and now you have lost 1.7 volts or 14% power and voltage loss. That means when your battery is only discharged to 12.3 volts under load. your Inverter shuts off. Your batteries will still have significant capacity, they just cannot carry the load any longer.

[PNjunction]

Createthis - first, THANKS for doing the videos and sharing your experiences.

Secondly, thanks for using tools like Fluke(s) so that I can TRUST your readings.

You are definitely pushing the boundaries of the GBS cells, which I also use. But they have limitations as mentioned before, and your application is starting to look like a more suitable cell is in order, like Headway's.

For just safety and/or continued knowledge, it is good to get a second opinion from a related application, if nothing more than to come back here to get perspective, from a real engineer who has to eat his own dog-food. Huh?

ANYONE who needs additional insight, even if they don't use Headways (as opposed to large prismatics), or wants custom Powerlab 8 configurations for LFP charging, should read through some of the following from this UK site:

http://www.wheelchairdriver.com/board/viewforum.php?f=2&sid=5acb2e84be7e3fbeecdd967b0191d70d

Yes, bike-racer / engineer (Op: Burgerman) who basically has to LIVE on top of his LFP cells in an (awesome!) wheelchair. Non-commercial / no product engineering btw. See the "step by step lithium conversion" threads, and quite frankly any of the Pb based threads too.

While not exactly the same, your application and his are getting close to each other, and I think you'd profit from the additional information - if nothing more than to have a better understanding of the pros/cons of the GBS cells you (and I) use.

Sometimes it is good to get a second opinion / view of the LFP world.

[Sunking]

Regarding I2R heating:



I love getting told I don't listen when I can quote contradictory material, btw. Keep it comin.

Nothing is contradictory, you are not understanding the information being given. That is why people are getting short with you. Over heating the batteries is not the issue. Those batteries are rated at 2C contentious. All that means with a lithium battery is it is thermally capable of being discharged at 2C. But that has nothing to do what I am talking about. You are off on a tangent.

So try this experiment. Repeat what you did, but at least collect some data with meaning.

1. Before you start measure the Open Circuit Voltage of the batteries directly on the battery term post.
2. Put your 1.8 KW load like you did in the video and let it run while you take some measurements.
3. Measure the voltage directly on the Battery Term Post again.
4. Measure the voltage directly and physically on the Inverter Input Term Post with the load cooking away.

Now tell me what you think is going on, and why you think it is safe and practical to run a 2000 watt Inverter on a 12 volt 100 AH battery.

[createthis]

Regarding I2R heating:

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

I love getting told I don't listen when I can quote contradictory material, btw. Keep it comin.

[jflorey2]

Where does this risk of fire come from?

I²R heating.

[createthis]

Jesse I have given up on you. You do not listen. Like your last thread you posted about hybrid Inverters, half a dozen different engineers and techinicans tried to help you, but all you want to do is fight the facts you cannot use a MSW Inverter with a hybrid. The Commercial AC port requires a 2-way utility connection, and generator with a real generator.

You have been told, now go learn the hard way. You are like Karrak, dangerous, You only know enough to be dangerous, and if you are not careful, will get yourself banned from the forum like Karrak did temporarily for unsafe practices.

I'm waiting to for you to tell me where the perceived fire risk is in my current system. I can't listen if you don't speak. I doubt I'll get banned for asking a question.

[Sunking]

Very clever. Teaching us all a lesson with that one.

Jesse I have given up on you. You do not listen. Like your last thread you posted about hybrid Inverters, half a dozen different engineers and techinicans tried to help you, but all you want to do is fight the facts you cannot use a MSW Inverter with a hybrid. The Commercial AC port requires a 2-way utility connection, and generator with a real generator.

You have been told, now go learn the hard way. You are like Karrak, dangerous, You only know enough to be dangerous, and if you are not careful, will get yourself banned from the forum like Karrak did temporarily for unsafe practices.

[createthis]

I rest my case. Keep repeating your test and you will find out.

Very clever. Teaching us all a lesson with that one.

[Sunking]

Where does this risk of fire come from?

I rest my case. Keep repeating your test and you will find out.

[createthis]

No assumptions made, you do not understand or else you would have understood the 20 amp current comment. When a person uses a battery operated device, he/she expects it to be safe, and all the battery capacity to be usable.Pulling 145 amps from a 100 AH battery will not allow you to use all the battery capacity and is quite dangerous. Sure you can make it work for a few minutes, but beyond that your Inverter is going to shut down from under voltage way before the battery capacity is depleted and running the risk of a fire.

Where does this risk of fire come from?

[Sunking]

More assumptions. I never said I didn't understand why the voltage dropped.

No assumptions made, you do not understand or else you would have understood the 20 amp current comment. When a person uses a battery operated device, he/she expects it to be safe, and all the battery capacity to be usable.Pulling 145 amps from a 100 AH battery will not allow you to use all the battery capacity and is quite dangerous. Sure you can make it work for a few minutes, but beyond that your Inverter is going to shut down from under voltage way before the battery capacity is depleted and running the risk of a fire.

How would you like it if you bought an EV and the manufacture claimed you get 100 mile range. You take it, go 50 miles and the EV comes to a stop from a dead battery. You return the vehicle, and the dealer ask how fast were you driving and you answer 60 mph, the dealer laughs and says you have to go 20 mph to get 100 mile range.

[createthis]

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.

More assumptions. I never said I didn't understand why the voltage dropped.