Think I destroyed my batterys

[Greenan_Energy]

So I but 8* 3.2V 202ah batterys in series. I discharged the batteries to 24V and all cells had the same voltage. I then charged them without the BMS using a Victron charger which had a voltage limit of 28.4. Now when I put my batteries back in my solar system I have the mppt at 26.4V but as soon as I put a charge on them it drops to 26V and stays around there and then seems to go down as normal. I haven't done a capacity test yet but I'm worried that this is a sign I've destroyed my batteries. Just on face value, what do people think of that as shouldn't its stay at 26.4 even under load

 

[jasonhc73]

They can go higher and lower.

But don't.

Brand new, they are designed to go 0% to 100% to 0%. So I think you are fine.

I am assuming you are using LiFePO4 cells based on your voltage.

I made a chart and graph you might want to reconsider your max and min usage with.

Lithium Iron Phosphave Charge Range

Sheet5 Lithium Iron Phosphate Charge Voltage Range (LiFePO4) What to charge your cells/batteries/packs to. (SOC),Never More than,3.650,Shown is the "FLAT CURVE" of LiFePO4 cells/batteries/packs. What to not discharge past. (DOC),Nominal,3.200,The steap parts on the left and the right are the "Le...

docs.google.com

 

[Sgt Raven]

So I but 8* 3.2V 202ah batterys in series. I discharged the batteries to 24V and all cells had the same voltage. I then charged them without the BMS using a Victron charger which had a voltage limit of 28.4. Now when I put my batteries back in my solar system I have the mppt at 26.4V but as soon as I put a charge on them it drops to 26V and stays around there and then seems to go down as normal. I haven't done a capacity test yet but I'm worried that this is a sign I've destroyed my batteries. Just on face value, what do people think of that as shouldn't its stay at 26.4 even under load

Do you have a DMM? Are the batteries in a position you can use your DMM and read individual cells?
You don't have to tear the packs apart to check the cells.

 

[Greenan_Energy]

I understand the SOC levels and that's why I'm worried that it's going so low so fast. Yes I have a DMM, that's how I read the voltages

 

[jasonhc73]

I understand the SOC levels and that's why I'm worried that it's going so low so fast. Yes I have a DMM, that's how I read the voltages

Get an ISDT Battgo and measure the voltage of each cell. One could be kaput.

Robot Check

and wires

Amazon.com

 

[Greenan_Energy]

All the voltages are the exact same. What I'm saying is that there is a voltage drop on each cell. So when a load is put on the battery the it drops from 26.4V to 26.0V

 

[Sgt Raven]

I understand the SOC levels and that's why I'm worried that it's going so low so fast. Yes I have a DMM, that's how I read the voltages

Hey Dude, don't get your back up. Since we're not watching you test them, we have to ask some basic questions to set a baseline.

So you're starting with 3.3V per cell and dropping to 3.25V per cell. Is that under a load, when the pack drops to 26.0V? If so, do they rebound to 26.4V when you remove the load? I don't have the answer, but I'm trying to get some information, so when someone who knows more about it, will have more info to work with. To help them get ahead of the game, so to say.

ETA: I feel your pain. Sometimes the questions make you say, hey I'm not stupid. But just asking them is not to infer that you are.

 

[Greenan_Energy]

Sorry if it came a cross that way, just trying to be clear. I do appreciate you trying to help. Yeah it rebounds but ever so slowly. Like about 10 minutes. The load itself I put on it is around 100w

 

[Sgt Raven]

Hey no problem. I could read/feel the frustration in your POST, and I understand where it is coming from. IMO, the more of these simple questions we have the answer to, the faster someone with more knowledge can come up with more technical questions. Because we've got the simple stuff out of the way.

 

[Greenan_Energy]

The issue I'm having is finding where I could have went wrong. I did everything by the book except for one occasion which was described up above. Also when I reinstalled them I set the value to 24V on the mppt but when I returned a week later I notice the batterys weren't charging. The victron mppt changed the voltage back to 12V automatically. I have no idea why it did this as its a 24V battery. but the mppt did save the battery I think by stopping charging and there was also a warning saying its stopped charging "Voltage too High" I guess cause it new it was a 24V battery . I don't know if I'm being parinoid but I think on the first day it did charge @12V and the warning only came on in the second day to stop charging. Is that possible or am I being parinoid

 

[nosys70]

when you put a load on battery , the voltage drops, that is normal.
the battery recover, (even slowly) that is normal too.
the absolute minimum low for a 8s battery is about 17V and the maximum high is about 32V.
but the standard "real life range" is between 20 and 28V.
so you never go really low and high, and your batteries "should" be ok.
an explanation would be that
-your batteries have not been properly charged (you have to test the battery after the charge to check they are really a 28.4 and wait 1 hour after charge to measure)
- your batteries are worn, so they do not show bad signs (like low cell) but cannot provide the expected Amps, no reach the max voltage..
- your load is too high for the batteries, so the voltage drop immediately.

202Ah under 24V is about 4500W at 1C, but LFP are usually not made to run at 1C or more especially if they are on the cheap side.
(and who needs only 1 hours of capacity anyway ?)

and since you said you have a solar system, is the solar system not able to support the battery charging ?
Why do you need to put the battery on the victron for charging ?

 

[Greenan_Energy]

Yeah I understand all those concepts and thanks for writing. But I feel the issue is as though the capacity underload seems to be affected. So if 26.4 —26.1 represents 90%-40% does it mean by my batteries dropping from 26.4- 26.0 immediately that my batterys are destroyed

 

[Greenan_Energy]

when you put a load on battery , the voltage drops, that is normal.
the battery recover, (even slowly) that is normal too.
the absolute minimum low for a 8s battery is about 17V and the maximum high is about 32V.
but the standard "real life range" is between 20 and 28V.
so you never go really low and high, and your batteries "should" be ok.
an explanation would be that
-your batteries have not been properly charged (you have to test the battery after the charge to check they are really a 28.4 and wait 1 hour after charge to measure)
- your batteries are worn, so they do not show bad signs (like low cell) but cannot provide the expected Amps, no reach the max voltage..
- your load is too high for the batteries, so the voltage drop immediately.

202Ah under 24V is about 4500W at 1C, but LFP are usually not made to run at 1C or more especially if they are on the cheap side.
(and who needs only 1 hours of capacity anyway ?)

and since you said you have a solar system, is the solar system not able to support the battery charging ?
Why do you need to put the battery on the victron for charging ?

There was very little sun and I wanted to top my batteries up after bottom balancing them. Which is why I used the Victron charger. The load is quit small at 100W. I

 

[Stupid Monkey]

So if 26.4 —26.1 represents 90%-40% does it mean by my batteries dropping from 26.4- 26.0 immediately that my batterys are destroyed

No - and this is why you'll keep seeing written "voltage is not a good indicator of SOC for LiFePO4" use a shunt to measure SOC ...what you need to do is charge them fully with BMS, and allow some top balancing time to be sure, then do a capacity test.

Then you'll have your capacity, see if it matches expectations. It hopefully will, and that will give you a baseline for future comparisons too.

 

[Sgt Raven]

Yeah I understand all those concepts and thanks for writing. But I feel the issue is as though the capacity underload seems to be affected. So if 26.4 —26.1 represents 90%-40% does it mean by my batteries dropping from 26.4- 26.0 immediately that my batterys are destroyed

I wouldn't jump to that conclusion this fast. They maybe a little weak or not. I have a pretty good handle on Li-Ion batteries from using them in Vaping. I have some knowledge of batteries from working on cars, trucks, and big rigs. I'm still learning about LFP batteries.

We have some pretty smart people on here and they're willing to help, so try and chill. I know it's easy for me to say, it's not my batteries. But I bet over the next couple of days, you will have lots of help, here. But as they say, hope for the best, prepare for the worse.

ETA: see here comes the Cavalry, as in the post before this one. You will get through this and some good people here will help you.....

 

[Greenan_Energy]

No - and this is why you'll keep seeing written "voltage is not a good indicator of SOC for LiFePO4" use a shunt to measure SOC ...what you need to do is charge them fully with BMS, and allow some top balancing time to be sure, then do a capacity test.

Then you'll have your capacity, see if it matches expectations. It hopefully will, and that will give you a baseline for future comparisons too.

Thanks for the message. The system has a BMS and what a parameters should I set the mppt to fully charge them. How do you use a shunt to check the SOC. Sorry if I sound like I've crayons in my hand here I'm just finding it hard to get a final answer on things. I don't really know which direction to go. Thanks again

 

[Greenan_Energy]

I wouldn't jump to that conclusion this fast. They maybe a little weak or not. I have a pretty good handle on Li-Ion batteries from using them in Vaping. I have some knowledge of batteries from working on cars, trucks, and big rigs. I'm still learning about LFP batteries.

We have some pretty smart people on here and they're willing to help, so try and chill. I know it's easy for me to say, it's not my batteries. But I bet over the next couple of days, you will have lots of help, here. But as they say, hope for the best, prepare for the worse.

Ah sound man I do appreciate your help. You read me like a book too. I'm under serious stress. I'm an electrical engineering student in my final year and spent my last penny on those batterys. Housing prices are nuts in Dublin so I'm living off grid

 

[Stupid Monkey]

While I know those answers, there are better people to explain them - especially Will's video's - so I'll leave it to them. But basically 28.8v is considered a good voltage to charge too / top balance at - with individual cells at no more than 3.65 and cut off when one cell hits 2.5v at the bottom end.

Log the voltages to see if all cells discharge together or if 1 stops your capacity test early while others are still at higher volatges.

 

[Sgt Raven]

Ah sound man I do appreciate your help. You read me like a book too. I'm under serious stress. I'm an electrical engineering student in my final year and spent my last penny on those batterys. Housing prices are nuts in Dublin so I'm living off grid

I know it's just platitudes. But it really is darkest, before the break of day.

If you really want to talk about darkness, I can tell you about the first year + after my wife of 28 years died from Cancer. That was 8.5 years ago. I went to some really dark places the first year or 2.

Recently I had some pretty bad pain caused by a pinched nerve in my neck. Lots of people talk bad about the VA healthcare system, I've had some good Docs, Nurses, and such that are getting me through it.

There is a couple of other forums I'm on and people on them helped me a lot. The thing about forums like this, there are people on them 24/7. No matter the time of day or night, someone is on them. So don't be afraid to lean on them when you need help or are feeling down. There are more good people, than bad, out there.

 

[Greenan_Energy]

I know it's just platitudes. But it really is darkest, before the break of day.

If you really want to talk about darkness, I can tell you about the first year + after my wife of 28 years died from Cancer. That was 8.5 years ago. I went to some really dark places the first year or 2.

Recently I had some pretty bad pain caused by a pinched nerve in my neck. Lots of people talk bad about the VA healthcare system, I've had some good Docs, Nurses, and such that are getting me through it.

There is a couple of other forums I'm on and people on them helped me a lot. The thing about forums like this, there are people on them 24/7. No matter the time of day or night, someone is on them. So don't be afraid to lean on them when you need help or are feeling down. There are more good people, than bad, out there.

Jesus christ, I'm so sorry to hear about that man. It sounds like you've been through some really though times. I can't imagine what that is like to loose someone. My heart goes out to you and I hope you are starting to find yourself again We have the pinched nerve in common though. I was in a car crash 3 years ago and spent a year and a half in constant pain with a ruptured disc in my lower spine. Got surgery, did constant physio and now fitter than I've ever been. So Dawn has broke for me and I wear it with pride that I've been able to get through it. Yeah I guess you are American, I'm Irish so I guess sour Healthcare is drastically different