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

[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]

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.

[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.

[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]

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.

[Sunking]

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.

You are making videos and acting like an expert for people to follow your lead. I really do not care what you do, or if you destroy something.

[PNjunction]

I haven't seen the schematic for your project, but just a tip - hope there is a "CLASS T" fuse somewhere inline within a foot or so of the battery terminals as your first line of defense to protect the wiring.

Like all batteries, and especially the LFP's, it has the potential to arc-weld a permanent short, say inside your inverter making the inverter's overload breaker a moot point. Use a class-t not only to protect the wiring, but the class-t under a catastrophe tends to fail gracefully, rather than explosively like a stereo-fuse under these conditions. Kind of like a Fluke, but I digress ...

And, as a last resort with such a large battery, I'd keep some insulated cable-cutters around the garage.

[Mike90250]

And often, it's the inverter that catches fire, because of poor practice in it's construction.
Wrong fuses, batteries, bad crimps and idiots who have been warned repeatedly, cause fires.

But the real crime is that you are posting "How to burn your house down" videos on youtube where any fool is considered an expert.
In the future DO NOT LINK to any more of your homemade battery bomb videos, or you will be banned from this board.

[createthis]

And often, it's the inverter that catches fire, because of poor practice in it's construction.
Wrong fuses, batteries, bad crimps and idiots who have been warned repeatedly, cause fires.

But the real crime is that you are posting "How to burn your house down" videos on youtube where any fool is considered an expert.
In the future DO NOT LINK to any more of your homemade battery bomb videos, or you will be banned from this board.

I'm not sure where the line is between one of my videos getting stickied for being useful and one of my videos being a battery bomb. I don't think I have enough information to comply with that statement, so I'll just stop posting videos here. Sorry for the trouble.

[createthis]

I haven't seen the schematic for your project, but just a tip - hope there is a "CLASS T" fuse somewhere inline within a foot or so of the battery terminals as your first line of defense to protect the wiring.

Like all batteries, and especially the LFP's, it has the potential to arc-weld a permanent short, say inside your inverter making the inverter's overload breaker a moot point. Use a class-t not only to protect the wiring, but the class-t under a catastrophe tends to fail gracefully, rather than explosively like a stereo-fuse under these conditions. Kind of like a Fluke, but I digress ...

And, as a last resort with such a large battery, I'd keep some insulated cable-cutters around the garage.

There's a Blue Sea Systems thermal breaker on top. Lots of them, actually. I decided to use those instead of the large Class-T fuse I originally bought. Is that a problem?

[createthis]

You are making videos and acting like an expert for people to follow your lead. I really do not care what you do, or if you destroy something.

That's an assumption on your part. I don't think I have to be an expert to make videos. I'm muddling through things and sharing as I go. As I share I learn from the feedback. It's a control loop.

[Sunking]

Yes an assumption shared by most of the stupid public. You do not have to be an expert to make a video, you just cannot post them anyplace you want, and like it or not are LIABLE for the content if needed to be used against you. Some idiot may copy you. I warned you are on shaky ground trying to defend unsafe practices and promoting them.

[SunEagle]

That's an assumption on your part. I don't think I have to be an expert to make videos. I'm muddling through things and sharing as I go. As I share I learn from the feedback. It's a control loop.

How making a major disclaimer up front about not doing this at home due to the potential of risk of life and limb. You have to take some responsibility when you show a video to the world that can result in someone with little knowledge getting hurt.

How many idiots smoke while pumping their own gas into their vehicle. Unfortunately still some.

[createthis]

How making a major disclaimer up front about not doing this at home due to the potential of risk of life and limb. You have to take some responsibility when you show a video to the world that can result in someone with little knowledge getting hurt.

How many idiots smoke while pumping their own gas into their vehicle. Unfortunately still some.

Did you see a disclaimer not to try this at home on the recent iphone 7 headphone jack drilling video? I think those disclaimers are for network television, not youtube. The default assumption is different on youtube, I think.

That said, I'm considering it because of the response in this thread.

[SunEagle]

Did you see a disclaimer not to try this at home on the recent iphone 7 headphone jack drilling video? I think those disclaimers are for network television, not youtube. The default assumption is different on youtube, I think.

That said, I'm considering it because of the response in this thread.

Look. We are just trying to help you and others not do something that could get someone hurt. Putting up a warning is easy and may head off a disaster before it happens.

[createthis]

Look. We are just trying to help you and others not do something that could get someone hurt. Putting up a warning is easy and may head off a disaster before it happens.

I appreciate that. I respect it. What I don't appreciate is the way you're all going about it. Threatening and making assumptions is counter productive. You all could have taken an entirely different tone with the conversation by asking questions and pointing out risks and recommending ways to mitigate those risks.

Stop making statements and assumptions. Start asking questions.

If you really think I'm not listening you're crazy. All I've done since I've joined this forum is listen, ask questions, and attempt to understand. Once I feel like I've reached an understanding, I try to make a video. I'm not going to stop doing that, but I'll definitely stop posting them here since they aren't received in the spirit I make them.