Test Sample Chinese Lifepo4's arrived

[JIMMY]

Before biting the bullet on a large bank of batteries I ordered a test sample of some 200ah cheapies air freight from China to try out and have a play with and really get my head around how LiFePo4 perform.








They have the specs mostly scratched off.

2/4 are marked 3.22V - 663wh
1/4 all marks are scratched off
1/4 marked 3.22v - 659wh

The totally demarked one has a red T on it.
I can only assume they are resold / second hand / factory seconds?

Having dealt with Chinese manufacturers a few times before I am looking forward to hearing the sellers rationale for this. ?

Now to hook up the Daly 60amp BMS and test them out.

Shout out to Will for the inspiration to have a play with these things. ?

Jimmy
Down Under

 

[gnubie]

Definitely let us know how your tests go.

 

[Newenough]

Who was the seller and what was the site? Thanks.

 

[JIMMY]

I ended up speaking to the manufacturer.
They confirmed they were grade b cells.
They have still tested to over 200ah but they do go out of balance towards the top end of the charge cycle.
Still amazing value for the $.

Jimmy

 

[msdmaddog]

what does this mean jimmy (do go out of balance towards the top end of the charge cycle ) does this mean, they cannot be used in a power bank ?

 

[Picasso]

Just that he need's to use them with a balancing BMS, OR he can lower his upper voltage for his charge to keep them in balance.

Did you weigh the cells? Wonder if the internal resistance verys on the cells?

 

[JIMMY]

It just means one of the four cells hit 3.65v charging cut off before the others did.

Ie one cell hit @100% charge while the others were at ~95%.

It effectively means I am losing a small % of potential capacity out of the other batteries.

No real issue for this small bank. But a bit more of an issue for the 40kwh bank I am about to build.

Jimmy

 

[msdmaddog]

how many of these cells would you set in parallel max. without any "big" issues ?

 

[JIMMY]

how many of these cells would you set in parallel max. without any "big" issues ?

Its more about having reduced capacity than any hard limit I think.

A bank is limited by the weakest cell. If you have to adjust your charge window to account for that cell you reduce your capacity of the rest of the cells.

The larger the bank the bigger the effect / loss of capacity.

IE in a 2.5kwh bank of batteries you might lose 120wh of storage from the one weak cell.

In a 40kwh bank you might lose 2kw from the same single weak cell.

Active balancing can offset this to a degree.

But better to have then better matched to begin with.

Jimmy

 

[msdmaddog]

thx for your perfect explanation. its clear now.

 

[DThames]

Its more about having reduced capacity than any hard limit I think.

A bank is limited by the weakest cell. If you have to adjust your charge window to account for that cell you reduce your capacity of the rest of the cells.

The larger the bank the bigger the effect / loss of capacity.

IE in a 2.5kwh bank of batteries you might lose 120wh of storage from the one weak cell.

In a 40kwh bank you might lose 2kw from the same single weak cell.

Active balancing can offset this to a degree.

But better to have then better matched to begin with.

Jimmy

When using "what you can afford", either cheap or used cells, it might be that you have some cells of lower capacity. I have two used 24v batteries and I am trying to decide if I need to parallel the cells or not, which would help even things out if I were lucky to not have two lesser cells in the same series position. But what I have been considering is that if i find a weak cell that I might augment it with some small cell(s) in parallel with that cell. I have some 6500 Ah cells that could beef up a week 200 Ah cell, so to be able to take the entire battery down to normal lower discharge voltage.

It is not uncommon that when someone builds a large battery from used 18650 cells that they might have a large number of mixed capacity cells in parallel and then series those packs up to build their battery. In that case it is not the number of cells in parallel that you worry about but the capacity of all the cells in parallel. So you might have 50 on one "cell", 48 on another, and 51 on the third and have a nearly perfect balanced capacity. So with that thinking I might tune up a used battery by piggybacking smaller cells. I know this might not be best for higher C loads but for low C loads, I think it is worth experimenting with.

 

[Dzl]

Jimmy, what seller did you buy these cells through? and at what price?

 

[JIMMY]

Xinglongding (XLD)
$60USD / Cell

 

[JIMMY]

What was the response from SHENZHEN XINLONGDING TECHNOLOGY CO.,LTD ?
If I was given that price I would assume they were Grade B cells.

Their response was that the manufacturer just does that with the codes. ?

That being said those cells have been cycled hard for a year now and I have learnt alot about Lifepo4 so all in all not a bad outcome.

Jimmy