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Topband 3.2v 25Ah from BH - Testing and some questions.

meetyg

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So I saw these Topband at BatteryHookup.
Very popular in this forum.
IMG-20211219-WA0004.jpg
The deal was too good so I decided to get me a 4 pack to play with. I have no idea what I'm gonna do with them, but since ordering the 4 pack I ordered another 8.
I might build a 12v battery for my UPS, and a 24v for emergency storage... We will see.

Although shipping to the Middle East from the US was quite expensive (almost like the 4 pack itself, for the cheapest FedEx international). I did find them from from local seller, but for an outrageous price of around $90 per cell!

Now I have no idea how BH did this miracle, but the 4 pack arrived in 3 (yes three) days from ordering! Even you order something locally it takes longer.

The cells arrived nicely packed, each in a bubble-wrap envelope, and then in a cardboard box with alot of those Styrofoam pellets (or whatever they are called).

So first I checked for any damage to cells. All were looking pretty good.
Then I checked voltages, 3 of them were around 3.4v, one was a bit above 3.5v.
Kinda strange since they should have discharged them for shipping.

Anyways, I put them together in parallel for charging and testing. I used some antistatic foam I had laying around to separate them, and then some black tape for compression. Then connected in parallel for top-balance using some busbars.
Its ugly, but very temporary:
20211219_212754.jpg

I set my PSU to 3.64v and 8A (my PSU voltage is a bit higher when tested with DMM, so I didn't want to overcharge using 3.65v).

Here is where things got strange:
The PSU started at 5A CC and it took only about half an hour to get to 0.2A @3.64v
So either these cells were at very high SOC or something with my setup was not good.
I hand tightened the bus bars beforehand, and I think they were pretty snug. I also connected PSU leads at opposite ends of the parallel bank to avoid the first cell taking the most charge.

After disconnecting the PSU, I measured all 4 voltages, and they all were around 3.6v, with 10mv differences at most.
I disconnected the bus bars and let them sit for about 12 hours, then checked the voltages again.
3 were around 3.35-3.45v, while one was at 3.61v. I'm not sure if this is the cell that was initially high, since I forgot to label them. Now I labeled them...

So now I'm capacity testing each one separately at 0.2C (5A). I hope that I don't have one dud cell.
20211220_123403.jpg

As for my questions: Is it normal that there is such a deviation of voltage for the first 3 cells after sitting for 12 hours?
Second, what could be the cause that the parallel pack took less than 5A to charge up to 3.64v ?

Is this a true sign that there is a bad or very low capacity cell in the pack?

Third question: do you guys have any ideas how to put the "wasted" energy into good use while doing a capacity test on each cell?
It seems like alot of waste if energy to "burn" 25Ah for each cell. On the other hand, there isn't much usefull work I can do with 3.2v nominal volts.
 
View attachment 76483

As for my questions: Is it normal that there is such a deviation of voltage for the first 3 cells after sitting for 12 hours?
I'm not sure why one cell holds higher voltage than the others, but that's not a bad thing so I wouldn't worry about it quite yet. The capacity test will tell you more. It might affect how the pack performs as a whole, but based on my personal experience with those cells I don't think it will affect it all that much, ESPECIALLY for the price. Sometimes as soon as a load is applied, the voltage will immediately drop down to the 3.3-3.4 range. With lithium iron phosphate cells, the voltage is much less of an issue than the capacity itself. It's very hard to get any accurate information about state of charge or health of your cell based on voltage alone.

I have 48 of the same cells, I tested all of them with the same tester you did and EVERY SINGLE ONE of them tested over spec (they were like 81-86wh). They all settled close (enough) to the same voltage after a few hours. And when they were all put into a pack they functioned perfectly.
Second, what could be the cause that the parallel pack took less than 5A to charge up to 3.64v ?
Ditch the gator clips. They have high resistance, and can definitely have an effect on the readings. Add some ring terminals, I use these for everything. The yellow, 1/4 inch ones fot a 10awg wire (not sure of metric), and fit the 6mm terminal perfectly. Those clips suck, and I can guarantee that they are causing some sort of issue, whether it be a measurement, or real power, issue. I don't know if that's what's causing your problem, but it's definitely going to cause a problem somewhere at some point. The connectors are a great thing to have around your house anyway, I ended up using them for all types of projects. Eff a WAGO or wirenut, crimped heat shrink all day!

540 PCS Wirefy Heat Shrink Wire Connectors - Electrical Terminals Kit - Marine Automotive Crimp Connector Assortment - Ring Fork Hook Spade Butt Splices - 22-10 Gauge https://www.amazon.com/dp/B07124B886/ref=cm_sw_r_apan_glt_fabc_95AB1M851VQ3GSJ3Y2MD
Is this a true sign that there is a bad or very low capacity cell in the pack?

Third question: do you guys have any ideas how to put the "wasted" energy into good use while doing a capacity test on each cell?
It seems like alot of waste if energy to "burn" 25Ah for each cell. On the other hand, there isn't much usefull work I can do with 3.2v nominal volts.
I don't think that the capacity tester we have is able to do that. Someone on YouTube commented on one of my videos and said that the 2.1mm barrel Jack on the right side of the unit is to add an additional load to, but like you said, I don't know where I'd put power with that low of a voltage. Either way, those cells only hold 80 watt hours apiece, so it's not like you're dumping kilowatts of heat into your room.

Also, you need to make absolutely sure that the cells are all tested at the same temperature to get an accurate reading. When I was testing mine in the garage, a 10°f difference made up to a 5% capacity difference. It wasn't a huge deal with the smaller 25 amp hour cells, but when I got to testing some larger ones it made a big difference.

Worst case, Battery Hookup is normally pretty good at replacing faulty products.
 
Thanks for the heads up on the alligator clips.
I have ordered some larger ones, planning to connect them to some 10-12awg wire for my PSU.
But I will take your suggestion for round terminals too. I actually made a cable for my PSU with an XT60 connector on one side, and 6mm terminals on the other. My plan was to make several types of connectors with the XT60, so that I can easily swap just one side, and leave the other connected to the PSU. But then I noticed that I ran out of XT60 connectors, from a previous project I used them on.
Waiting for some more that I ordered to arrive.

It's good to hear that these Topband cells are working out for you in such a large setup.
That's one of reasons I got them, the many recommendations and various builds done with them here on the forum, and on YT.
I think that they are a nice balance between size, capacity, quality and price. Especially when you buy from BH, which in general have a good reputation, even more so compared to Aliexpress. I was surprised that they even ship to my region, as many US and European sellers (and Amy from Alibaba which I contacted) don't/cannot.
 
The results are in:
All 4 cells tested above 25Ah capacity!
I tested the first one using two pairs of alligator clips (before your replies here), and it tested out at 25.86Ah. But for the rest of the cells I used proper cables with terminal lugs as suggested for charging.
All 3 tested out at 26.6Ah !
Then I went back to the first cell, connected it with the new cables and was able to pull out some 460mAh out of it (without recharging in between). So in the end they all tested out above 26Ah, and this is with 2.6v voltage cutoff. Pretty amazing I must say!
If I were to know how nice these cells are, and at a deal of a price, I may have chosen these over some 40Ah cells I ordered from Aliexpress over a month ago (and counting... still not here).
The 40Ah are for a 8S 24v Lifepo4 pack I'm building for my dad's mobility scooter, to replace AGMs. He doesn't really need 40Ah, it will just give him some more range (motor rated at 25A max).

Well at least now I have a backup plan...
Here is my testing setup before and after:

Before:
20211220_123403.jpg

After:
20211221_004124.jpg

And an example of capacity test:
20211221_144252.jpg
 
I used some antistatic foam I had laying around to separate them, and then some black tape for compression.
How much compression should these have? Is the separation important?
 
I don't think these cells will bulge much, as they are fairly small, so I'm not sure compression is actually needed.

But, I would always put some separation material, and then pack them tightly just to protect the cells and the terminals, just in case there is some movement of the cells.
 
What is the function of the separation? Isn't using foam counter to the objective of providing compression?
 
The foam will present some compression, if the cells are taped together.
Probably enough for these cells.
Again, this was only a temporary setup just for testing.

On another Lifepo4 build I'm recently working on (with 40Ah cells), I used a thick double sided tape to bind the cells together, but also to apply compression. The thick tape is around 3mm thick. I put the tape in 3 strips vertically, to allow for heat to escape.
Then I tightly packed these cells in the yellow fiberglass type material, to make a tight pack.

These 40Ah cell are also fairly small, so I don't think massive compression is needed, just a bit to prevent stress on the cells.

20220103_233804.jpg20220103_235819.jpg20220104_000232.jpg
 
Thanks, meetyg. I just bought some of these myself, which is why I'm interested. What I don't understand is how this is better than putting the cells right against each other.
 
What I don't understand is how this is better than putting the cells right against each other.
The cell casing is bonded to one of the poles, and the PVC wrap can get worn down because of vibration. If that happens, you get a short circuit and a fire.
 
OK, so I will try to break this down:
There are two things to consider: 1 - Compression, 2 - Separation.

Compression:
Most prismatic type cells have a fairly thin aluminum casing. As these cells are charge and discharged, this can cause movement of the casing, decreasing the longevity of the cells. This is mainly a problem in larger cells such as the ~200Ah and above cells used by most of the people here.
When the cells are fully charged, the casing expands, and can cause bulging. As they are discharged, this bulging goes down a bit.
In order to increase the number of cycles and lifespan of these prismatics, most manufacturers recommend compression of the cells. How much? well that depends on the type of cells, their size, and the manufacturers recommendations.
Whether to compress or not has been discussed here on the forum many times. It also depends on the C rates you are going to charge/discharge the cells, as I understand. Higher C rates may cause more excessive "movement" of the cell enclosure.

One more thing to consider, is stress on the terminals: If you use solid bus-bars, the movement of the cells may cause stress on the terminals (which we don't want either, because it will also reduce the lifespan of the cell and may even break it).
Some small movement of the cell enclosure is OK, from what I understand here on the forum. Most DIYers here use some form foam between the cells, that will aid in compression, but also "give" a little. Some also use flexible bus-bars, in order not to stress the terminals, while this little movement happens.

Separation:
As mentioned, the cell's casing is usually either negative or positive bonded. Having no separation, can cause the thin plastic wrap to wear out and create a short. This is true not only for mobile applications (RV/Boat), but also true for static applications (off-grid storage), because of the "movement" issue mentioned earlier. For separation you could use any non-conductive (and preferably also heat resistant) material.

For these Topband cells:
I didn't see any manufacturer recommendations, but for safety, I would use some form of separation. As for compression, because these cells are fairly small, compression may not be such a big issue as they are in the larger Lifepo4 prismatics. Again, for added safety and to prolong their lifespan, I would recommend to do some form of compression, but not something massive.

If you do both compression and separation, I think that using solid bus-bars would be OK. Its also hard/impossible to find ready-made flexible bus-bars for this size.
 
Reading more this morning, I realize you're re-answering some rather basic questions for me, that have already been covered elsewhere on the forum. I appreciate your taking the time to do that.
As mentioned, the cell's casing is usually either negative or positive bonded.
It seems that the casing is isolated in these Topband cells, correct?
 
Reading more this morning, I realize you're re-answering some rather basic questions for me, that have already been covered elsewhere on the forum. I appreciate your taking the time to do that.

It seems that the casing is isolated in these Topband cells, correct?
When I tested them they were isolated, yes.
 
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