meetyg
Solar Addict
- Joined
- Jun 4, 2021
- Messages
- 1,101
So I saw these Topband at BatteryHookup.
Very popular in this forum.
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:
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.
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.
Very popular in this forum.
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:
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.
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.