Lifepo4 CATL 86Ah Cells - Very low Charging/Discharging Curent

[Honuz]

Hi all,

I've received cells, they are CATL 86Ah, i only tested 2 for the time being and they both show the same behavior :
- Using 3.65V and limiting my charger to 12A, charge current do not exceed 10A when cell is near empty (2.5V) and near 7.2A when cell is 3.2V.
- I used a capacity tester, parameter are : 100W discharge, cut voltage 2.5V : click on ... power is somethin like 40W..

My question is : appart from a bad conenction, would a defective cell (that would be 2 cells) or old cell would show this behavior ?

Tommorow i will clean contacts and try again but i'm pretty sure it's not a problem.

 

[Honuz]

I hink there are no problem trying at higher voltage for like 4 secondes. I wanted to know if it was a potential voltage difference that was the problem or my connection.
Cells i'm testing here is, let's say half charged.

Tommorow is sunny i will do a full charge/discharge again and check current / voltage

1 : Normal charge, Riden is at 3.65V, Cells are at 3.31V (do not mind the polarity -)
Cell do not accept more then 6.2A => 22.5W



2 : I increase the applied voltage to 3.8V
Cell do not accept more then 8.8A => 33.3W



3 : I increase the applied voltage to 4V
Cell accept more then 12A => 47.5W (12A is the limit of my charger)



What can we say about those cells ..?

 

[mikefitz]

You have volt drops in the cable and connections clearly shown by the voltmeter. When charging at mid SOC the cell volts will be 3.3 to 3.4 volts, this is normal.

Replace the cables and connectors you have with more suitable cable and connections, heavy gauge cable with crimped eye terminations.
Set the charge voltage to 3.65 as a maximum on the PSU with nothing connected. Do not adjust to a higher value

By increasing the charger voltage to compensate for cable/connection loss, its possible as the cells near full, the voltage will exceed the safe limit and damage the cells.

 

[Honuz]

You have volt drops in the cable and connections clearly shown by the voltmeter.

Replace the cables and connectors you have with more suitable cable and connections.
Set the charge voltage to 3.65 as a maximum on the PSU with nothing connected.

By increasing the charger voltage to compensate for cable/connection loss, its possible as the cells near full, the voltage will exceed the safe limit and damage the cells.

Allright, i double my cables and ... now it goes to 10A, but the voltage drop is the same : 3.55V at the charger output and 3.35V at the cell poles.
I mean... theorically this drop is just created by the wire/connections resistance .. right ?
3.55V (charger display 3.64 but my mulimeter say 3.55V at the charger output) => 3.35V is roughfly a 5% drop with one cable.

With one cable => 6.2A charging (3.55V => 3.31V)
With 2 cables in parrallel => 10.3A charging (3.55V => 3.35V)

=> The drop as not improved .. but charging has .. there is something i do not get here... does that mean that resistance as decreased ... and since U = R*I that mean I as increased accordingly, is that right ?
That would be coherent with the fact that by increasing voltage i get more Amp too... (I = U/R, R constant... U increase => I increase)

But then why when i started charging (empty cell at 2.00V), with one cable it was charing at 10A... does that mean that cells resistance increase and at a certain point make this cable resistance a "problem" while it's not when cells is at 2.00V ? Lol .. i'm sorry, i ned to clear my idead on how it physically work, i'm thinking on my feelings about how it works .. but obviously it's not right.

 

[mikefitz]

The cell is setting the values are seeing. The power supply is set for two condition, a maximum output of 3.65 volts and a maximum current of 10 amps.
Consider the battery in simple form as a resistance in series with an Internal voltage generator. The value of the voltage generator changes with SOC. Over most of the working range of the cell its internal voltage will be 3.0 to 3.4. To push current into the battery, the charge volts needs to be higher.
Initially, when the cell was discharged, there was a big difference between PSU volts and Internal cell volts, thus maximum current could be supplied even with the resistance of the interconnections.
As the internal cell volts increased with increasing SOC, the current fell to a lower value, due to a lower voltage difference.
It only takes a small increase is charge volts to increase the current Into the cell. By adding an extra cable you increased the voltage from 3.31 to 3.35 at the cell, this in turn allowed a higher current to flow.
You can not just use Ohms law since the PSU current limit operates at 10 amps. In theory ( much simplified) the current should have doubled to 12.4 amps, but cannot since the PSU limits the current.
Having 3.55 volts from the meter and 3.64 from the PSU displays is an issue for you. You need to decide which reading is correct, perhaps the meter.

Mike

 

[Bud Martin]

Allright, i double my cables and ... now it goes to 10A, but the voltage drop is the same : 3.55V at the charger output and 3.35V at the cell poles.
I mean... theorically this drop is just created by the wire/connections resistance .. right ?
3.55V (charger display 3.64 but my mulimeter say 3.55V at the charger output) => 3.35V is roughfly a 5% drop with one cable.

With one cable => 6.2A charging (3.55V => 3.31V)
With 2 cables in parrallel => 10.3A charging (3.55V => 3.35V)

=> The drop as not improved .. but charging has .. there is something i do not get here... does that mean that resistance as decreased ... and since U = R*I that mean I as increased accordingly, is that right ?
That would be coherent with the fact that by increasing voltage i get more Amp too... (I = U/R, R constant... U increase => I increase)

But then why when i started charging (empty cell at 2.00V), with one cable it was charing at 10A... does that mean that cells resistance increase and at a certain point make this cable resistance a "problem" while it's not when cells is at 2.00V ? Lol .. i'm sorry, i ned to clear my idead on how it physically work, i'm thinking on my feelings about how it works .. but obviously it's not right.

'3.55V (charger display 3.64 but my mulimeter say 3.55V at the charger output) => 3.35V'
That means one of the meters is not correct.
You can easily measure the Voltage drops on the wire by measuring the Voltage between the ends of the wire.

 

[Honuz]

'3.55V (charger display 3.64 but my mulimeter say 3.55V at the charger output) => 3.35V'
That means one of the meters is not correct.
You can easily measure the Voltage drops on the wire by measuring the Voltage between the ends of the wire.

The meter is a cheap one, the power supply is certainly the right one. Not that important here cause i only take the voltage delta.
Yea i've taken the voltage drop, RED side got more drop then the black one.... cable itself or connections .. i dunno, i moved them around .. it do not improve so i would think .. cable.

 

[HRTKD]

If you want to check the accuracy of your multimeter, get a voltage reference device from Voltage Standard. I have their base model and found my cheap multimeter was more accurate than I thought.

 

[Honuz]

If you want to check the accuracy of your multimeter, get a voltage reference device from Voltage Standard. I have their base model and found my cheap multimeter was more accurate than I thought.

I think i could use my power supply as a reference cause it seems rpetty good :

Problem is that my cheap meter can't be calibrated, i only use it to have a rough idea on what's going on.

 

[HRTKD]

I think i could use my power supply as a reference cause it seems rpetty good :

Problem is that my cheap meter can't be calibrated, i only use it to have a rough idea on what's going on.

That'll work! Wish I had a setup like that.

 

[Honuz]

That'll work! Wish I had a setup like that.

Wowowo .. i only got the Riden 6018 ...
I'm a computer guy not an electronic guy ..

 

[HRTKD]

I'm a computer guy not an electronic guy ..

Same here. Data Warehouse consultant.

Almost everything I know about DC and PV came from here on the forum or Will's videos.

 

[Honuz]

Same here. Data Warehouse consultant.

Almost everything I know about DC and PV came from here on the forum or Will's videos.

Hooo i used to be DBA in an edition company and they made me use Business Object to generate some reports .. what a mess it was ... was not a fan of it. I was more fond of Sql Server to make those reports cause .. i know what really in it, with BO, many things became abstract and some results were pretty hard to explain.
Was 15 years ago, i retired at 42 yeasr old, just living in a degrowth economy since then, life cost me near nothing now, no electricity or water bills, no pressure and since we are vegetarians, and produce like 30% of our food, even that do not cost a lot.
Like you, i learned a lot in DIYSolarForum, before that just got some base at school .. : U=R*I ...

 

[HRTKD]

I'm the database architect (aka DBA) and write all the ETL to populate the warehouse. We do use BO but they don't let me write reports (which is a good thing!). I work with the report developers to refine the BO Universe. If the Universe is bad then writing reports is hell. I do a lot of work in the database and ETL to make reporting and Universe development easier. But it can still get complicated. For a university, we have some very large tables (in the billions of rows) that make it possible to write reports that can't be written off of the OLTP system.

 

[Honuz]

I'm the database architect (aka DBA) and write all the ETL to populate the warehouse. We do use BO but they don't let me write reports (which is a good thing!). I work with the report developers to refine the BO Universe. If the Universe is bad then writing reports is hell. I do a lot of work in the database and ETL to make reporting and Universe development easier. But it can still get complicated. For a university, we have some very large tables (in the billions of rows) that make it possible to write reports that can't be written off of the OLTP system.

I got you, i was doing a very similar job. Lucky you you do not have to touch this BO which is... sometimes illogical for sane people like us.... i had to work with a (my vision) dumb designed universe, with crossed tables that should have never been (cause it was illogical) and giving incoherent results which people were using as a base to take business decisions .. what a mess.
I worked for Shell (Petrol) for years and created a prevision tool to optimise oils movement between ports to satisfy demand. Most stats were done with views and stored procedures (SQL Server) and a web backoffice for user input. They are still using it. I'm not in that anymore, i just grow my trees and build my house...

 

[HRTKD]

I got you, i was doing a very similar job. Lucky you you do not have to touch this BO which is... sometimes illogical for sane people like us.... i had to work with a (my vision) dumb designed universe, with crossed tables that should have never been (cause it was illogical) and giving incoherent results which people were using as a base to take business decisions .. what a mess.
I worked for Shell (Petrol) for years and created a prevision tool to optimise oils movement between ports to satisfy demand. Most stats were done with views and stored procedures (SQL Server) and a web backoffice for user input. They are still using it. I'm not in that anymore, i just grow my trees and build my house...

My wife retired from Shell (US) three years ago. It was a great company when she started. Years ago I worked for Conoco in IT supporting the downstream area. We were both in Houston.

 

[Honuz]

My wife retired from Shell (US) three years ago. It was a great company when she started. Years ago I worked for Conoco in IT supporting the downstream area. We were both in Houston.

I was working in Paris, but now living in south west of France. Shell was a nice company yes, nice food, big building (approximatively 1000 people were working in there). But my spirit is now too far from cities and big business ... .
Conoco is not known here in France (i needed to check what it is) but i guess there are so many petrol companies in the US.
Houston make me think of the old serie "Dallas" ... JR and Bobby Ewing, and .. Pamela .. Wooooo ..

Are you still working in the Petrol business ?

 

[HRTKD]

I was working in Paris, but now living in south west of France. Shell was a nice company yes, nice food, big building (approximatively 1000 people were working in there). But my spirit is now too far from cities and big business ... .
Conoco is not known here in France (i needed to check what it is) but i guess there are so many petrol companies in the US.
Houston make me think of the old serie "Dallas" ... JR and Bobby Ewing, and .. Pamela .. Wooooo ..

Are you still working in the Petrol business ?

Nope. I'm working as a consultant at a university.

 

[Honuz]

Hello All,

Wanted to post some news about my case, after asking for a partial refund du to the lack of capacity (74Ah vs 90Ah description), Aliexpress as accepted a 120€ refund.
I needed to post 6 vidéos of 6 cells, take me some days to do the test but i did not want this lier seller to go away with it.. so i did those test and posted those 6 videos.

I used Time lapse videos, then end up with those capacities : (higher to lower capacity)
75.4Ah
74.8Ah
74.4Ah
73.8Ah
72.4Ah
71.7Ah


Plus one cell is swelled :

Swelled :


Normal :


So i asked for a linear reduction, 18% less capacity => 18% less price, that was 105€ rebate, then they added 15€ for others reasons : Lie on capacity (sticker on cell say 86Ah vs 90Ah => obvious lie) and the swelled cell.



I'm happy how Aliexpress handled the case, i was worried. I got to say i got more then 400 orders on Ali and i do apply for refund only for good reasons, i never abuse it like soem others do.
My pack is noticeably smaller capacity then anticipated (71Ah vs 90Ah) but the price is now fair, let's build it.

 

[Urgi]

Hi is this same store I just purchased from here 8pc £236

just wondering what to expect...

 

[Honuz]

Well you got an answer just a post above ..
My post was not that clear, i payed 590€ and was refunded 120€ => Final price : 470€ for 3.3kWh
Now ... i do not know if this pack will still be ok in a year ..

 

[Urgi]

MY store are called "Liitokala battery flagship" most likely is same ?...
I can see you had 16 was all approx 70ah? Did you try full charge few times?
Did they looks new? Depends on your measumerment looks like B used cell ...

 

[Honuz]

MY store are called "Liitokala battery flagship" most likely is same ?...
I can see you had 16 was all approx 70ah? Did you try full charge few times?
Did they looks new? Depends on your measumerment looks like B used cell ...

Tried full charge few times : no
All 16 cells are distributed between 71Ah and 82Ah.
They seems new but not in the same serial series, i got 2 different "series".

I will cycle this pack in the next month, i had a lot of things to do since i bought those cells and no time to include it in my actual pool of batteries.
I'm swapping my chinese inverter for victron devices ... will add this pack at the same time.

 

[Urgi]

Thx for info I will keep you informed when my arrived

 

[augiedoggy]

I bought these same cells just about a year ago from the same globalpower... I did not test the capacity of the cells but I suspec they are likely the same around 74 as other reviews stated such. I had them in a golf cart and now they are in my riding mower with no issues. when I purchased mine the seller advertised them as high output 3c rated cells which was false. they since changed the marketing.