Battery pickup testing-due diligence

[Bluedog225]

Good evening

I’m thinking of driving to Houston and picking up 32 (or 34) lifepo4 280ah cells (280k). It would be a pay and done deal. They are represented as grade A, fully matched and top balanced the voltage and IR.

Two questions:

1. I’m being offered the opportunity to test prior to paying. What tests can I realistically perform in an hour or two?

2. I ask for a certificate of testing and the seller didn’t know what I was asking for. Is there another name for the testing report I think I’ve seen mentioned here?

Any tips on how to perform due diligence would be appreciated.

Ps-what does the “k” stand for?

Thanks

 

[sunshine_eggo]

If this is a craigslist deal, don't bother unless you're willing to throw all the money away on the risk of getting a good deal.

If this is that one seller that's stocking in TX, then it's probably fine.

1. Voltage and IR (YR-1035). Most cells are shipped at a reduced state of charge, 30-50%, around 3.29X. I would be hesitant to accept anything outside that range, especially if any are outliers.

2. Either the seller just doesn't know, or these aren't grade A cells. A group of matched cells should list serial number, capacity and 3 voltage and IR readings.

Suggest you go with a reputable seller.

 

[Steve_S]

K is the series, the previous version was the N series.
Fully Matched & Batched means they have been run through test cycles of being charged & discharged with IR Readings at the various set point. It is a long, tedious & costly process.

Voltage & IR Matching at a static storage voltage is of little use. This has little value because matched cells will have identical IR at 2.50, 2.75, 3.0, 3.25 etc...

HERE is one company in US and this is what they want for Matching & Batching (and not a great description either)

Custom Job for matching cells

8818

www.batteryspace.com

 

[Bluedog225]

It is the warehouse and one of our known sellers. I’ll try again regarding the serial number, capacity and 3 voltage and IR readings.

I can pick them up in one day but I guess no way to do any meaningful testing at pickup.

No buyer protection if I pay cash it check.

Interesting to trade same day pickup with the ability to bring home and test.

Thanks for the quick responses.

 

[Steve_S]

Thing to your advantage, if this is a regular vendor, then should something be amiss, a swap is a heck of a lot simpler with less futsing. Definitely do a review on it, I'm sure many would be very interested.

 

[Bluedog225]

TL:DR-I going to give this some more thought. I suspect they are bulk cells that failed some test. They may still be fine for my purpose but I’m not sure the are “Grade A, fully matched and top balanced,

Detail:

The claim is that the cells are fully matched and top balanced re voltage and IR. Grade A with laser welded studs.

With regard to the certificate, they state they only receive “bulk” certificates, not for individual cells. The individual cell certificates may be available but from the China warehouse only, not the Texas warehouse. And for an extra fee.

The email did offer a 3 year warranty, however, this is the disclaimer attached to the last email I received this morning.

DIY battery pack must get the cells balanced (same voltage ) before assembly. Later if there happens don't know how to assembled or wrong assembly is not accepted refund. Professionals will detected voltage/resistance/appearance and other issues before every shipment, we can only ensure that the single battery is good, when arrival you can test the cells within 15 days, after that means batteries have no problem, does not provide return nor refund. If you found problems you can contact us for return or refund. Battery can only be unused (the electrode intact, no welding, no wear, the appearance good) to provide return. Any return behavior buyers need to be responsible for shipping fee.
1).Warranty period:3 years(from the date of successful delivery),if the single battery capacity less than 80% initial capacity, take the test pictures or video to us,we will replace it or give satisfied solution.
2).If any miss or damaged for the shipping. Please contact us firstly, then send us the picture or video to check. In case of loss of cargo or the battery is damaged and can not be used or there is a greater risk of use, we will communicate with buyer if resend it or replace it or refund the product cost.If buyer send back the cells to seller,buyer should pay for the shipping cost

 

[Bvillebob]

All I can add is I've bought 48 cells from the same vendor in the last few months, in 3 separate orders, and all have been essentially perfect. They arrived in great condition, and after being assembled into batteries the voltages stay within 3-5 millivolts of each other across the charge band. The vendor seems to be working hard to develop a reputation for honesty and good service, which has been my experience in dealing with them, I'm sure you'll be happy and if not I'll bet they take care of you.

BTW, there's plenty of vendors that are happy to supply you with all the certifications you ask for, but of course they're completely fabricated or for a different batch of cells. Performance counts more than paperwork.

 

[Bluedog225]

Thanks. You make an excellent point. Their reputation is very good.

 

[S Davis]

I have purchased 28 LF280N cells from Jenny at the Huston warehouse in two separate transactions and all have been great so far, all top balanced well and stay within .006 voltage difference. I have two 12 volt 280ah batteries built and am starting top balancing on the third of seven.

 

[Bluedog225]

Good looking build. Is that a special tape for short prevention?

 

[Horsefly]

Good looking build. Is that a special tape for short prevention?

Looks like Kapton tape, and yes it prevents shorting.

 

[RCinFLA]

The best test is a moderate load for 3 minutes.

With batteries at least 40% state of charge, about 3.28-3.33 vdc preferred rested open circuit voltage, load a cell with 50-100 amp load. After 3 minutes of load record terminal voltage with load still connected (directly on battery terminal edge so not to be impacted by high current load connection).

The closer they match in delta volt slump with same amount of load current the better cells are matched. A drop of more than 100 mV from initial open circuit voltage after 3 minutes of load indicates a used cell. Really used cells may drop more than 300 mV. A new 280 AH cell should drop about 70 mV from unloaded voltage after 3 mins of 100 amp load, about 50 mV drop for 50 amp 3 minute load. For these voltage slumps to be representative the battery should not be cooler than 60 degs F.

The voltage slump has an exponential decay which flattens out after about 2-3 minutes. If in a pinch for time you can likely do with 1 minute load to tell state of cell quality. Battery open circuit voltage for load test should not start out greater than 3.400v because a higher voltage indicates a surface charge voltage from full charging that will give a false starting unloaded cell equilibrium voltage.

It would be worth having two DL24P load testers you can run in parallel to get the 50 amp load.

 

[S Davis]

Good looking build. Is that a special tape for short prevention?

Thanks, it is tight working in the back of the truck and I want a little protection from dropping anything on top of the batteries. I think I will eventually use a piece of poly sheet to cover the top, I haven’t yet as I am having problems with the DALY BMS and the design will probably change when go to a different BMS.

 

[Bluedog225]

That is a great response RC. Thanks!

What a cool piece of kit.

 

[RCinFLA]

That is an older model. Newer one have four wire connections with separate load current and voltage sense circuit connects. Voltage sense is pair of smaller gauge wires brought directly to battery terminals to avoid voltage drop on the high current load wires.

I use #8 for load current lines and #16 for voltage sense lines.