Today the price is 20% higher than the OP, $8 is now $10- at least with shipping to Canada anyways.
Nobody tried the $16 DIY spot welder on these? (note this needs a small resister mod and possible isolating the logic chips) https://www.aliexpress.com/item/.html
I saw a video showing the cells can heat up to 125 C even with a quick solder job of 3 seconds or less. Typical was 60 C. Since the life of LFP is reduced significantly over 40 C that may be something to consider. How about freezering the batteries before soldering? Maybe the case will heat up and leave the contents frozen while we solder.
Making a 30amp Ebike 52V 16s battery pack with BBSHD Bafang motor, daly 40a bms.
Also will be testing with a shottky diode sbr60a60ct when using 2 packs at the same time in parallel and different SOC.
EDIT: There are nice brackets available for these now. 30 for $5.
Received the cells and they are all identical and the date says 11/21 so these were stickered within 2 weeks or less of my ordering them. All at 3.23 volts give or take 0.01v. So they match very very well from their 1st appearance, the shipping took 6 weeks from my order date and the shipping address is from Ontario, Canada despite my ordering from aliexpress.
There are 2 notable things:
1. The copper terminals now have been laser welded with a sharp little square piece of nickel. So I should be able to spot weld them with a $20 spot welder when it arrives in the mail!
2. The internal resistance is advertised at under 8 m.ohm. The cells all measure exactly 16.12 m.ohms.
Is that still small enough resistance to not be concerned? More resistance = more self discharge I just read on this site, is that true? I know that more resistance = more heat loss when discharging. 8 miliohms sounds like a small amount to worry about but it is DOUBLE what is advertised. How do your cells measure?
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Internal resistance will not affect self discharge. It only affects losses when you draw a lot of current & similarly if charging at high amperage. So, at 20amps, 0.016ohms will drop 0.32volts and cost 6.4watts (so you will lose 6.4 of your nominal 3.2x20=64watts. This will manifest as heat.
Also, I would question how you are measuring this? Have you welded or soldered on contacts because if not, your measurements might not be accurate. It does not take much of za poor contact to add a few milliohms. Also, are you measuring DC resistance or using an AC impedance technique?
The fact that the cells all measure the same is good. However they are shipped with about 20% SOC for longevity and I would therefore expect them to be extremely similar because 20% is on the flat part of the LFP discharge curve.So, do not read a lot into the same voltage. On capacity, mine were all 15-16AH as advertised.
That's interesting about the nickel. That should make things easier!
It is a battery operated digital multimeter so that should be a DC measure, I don't have any fancy equip for AC resistance.
Those are some great tips, thanks doggy. When I touch the probes together they zero out so the wire resistance should be adjusted for already.
I will be discharging with an ebike with a 52V @ 30amp controller. Your calculation states a 10% power loss to heat, just in the battery pack. Is there a decimal out of place? I guess 90% efficiency is decent for batteries but then the motor has another 10% too. 6.4 watts of heat loss x 16 cells is 102.4 watts. Then I should be able to ride in the average Canadian winter days (-20C average) assuming the battery started at room temp.
How much resistance do your cells give?
I put the multimeter probe into to 10A connector and measured current. I got a peak of 30amps. That is only 2C. I have no idea is that is the peak current the battery can give, I guess I would have to find a better load.
5C discharge and only 0.33C for charging.
Input Charging Current5A
Continuous Discharging Current75AMax Current Discharge5C
My trusty old 20 year old digital multimeter said 16.12 miliohms, it was a decent quality meter from it's day with diode and current testing. I have a new $35 multimeter coming in the mail but that is a month away at best. I just got the 2nd one so I can calibrate my new bench power supply a little more accurately.
I don't have any reason to distrust the meter until now, I hope those cells can perform as good as yours 0.006 ohms is great. What kind of meter are you using, anything special?
I don't know how else I could measure mOhms. I got a precharge resistor, I will try adding it in series and see if that makes a difference when I sum the battery plus the resistor then subtract the resistor ohms from the total.
Regarding: " I got a peak of 30amps. That is only 2C. I have no idea is that is the peak current the battery can give, I guess I would have to find a better load."
I doubt that you were being restricted by the cell/s. Given the good and consistent reports about the Liitokala original store and this product, I would guess that the cells really can deliver 75 amps. If you got only 30amps, that signified that your load plus internal resistance was 107 milliohms.
I suspect your project is going to be okay. Also, I cannot imagine your bicycle would be pulling 1.5kw very much. That's two horsepower which would presumably make a bike into a mini-rocket (but I have no experience of electric bikes). So presumably your average power is going to be a couple of hundred watts?
At full speed the motor will take W from a 52V 16S battery pack. That would be around 35mph. That is constant when riding at top speed on pavement. For off road then the speed varies a lot.
I have been trying to measure the internal resistance with what I could rig together. I got a new model coulometer that I got a discount on (I posted the discount for others in another thread) and I was excited to hook it up but at 3.2V with a tiny load was all I could rig together. This meter tells me the internal resistance of the battery automatically. Need to wait for spot welder to arrive, in the meantime I will also order some alligator clips so I can at least get up to 12v so I can find a compatible automotive load. I had no idea that is how you measured the internal resistance, I thought you just check the ohms between + / -
I am excited that these seem to be new cells. I was thinking ALL the cells on aliexpress were heavily used and had downgraded capacity.
I also ordered some 14 ah rectangular cells. from a seller with a similar name but ppl are reporting only 12ah capacity (used?) and the same price with much slower shipping. The definitely seem the be the better choice and there are nice modular battery brackets.
Sorry to put you out, doggy, you have shown your thorough knowledge about these cells, may I ask you a direct Q? I wasn't able to find any 52V fuse for the 52V 30amp ebike system. So I went with a 12V automotive fuse I see ppl using for RV solar builds. I ordered a 12V 40amp for the job, and I have a 60amp version onhand already. Do you think these will be able to stop the 52V arcing over the broken fuse conductor? I have a cheap hardware Daly BMS that will be installed but I would like to use the fuse as on ON/OFF battery switch. Also, since FETS on the BMS fail in a closed state, this will protect the battery from a short circuit caused by some crazy vibration water bike trail situation.
Did you or do you top balance your cells? Some alligator clips would work but I dont have 64 of them available, not even 32 or even 2.
I noticed the terminals extend past the cell cases, so I am thinking about laying out a strip of aluminum foil and standing them up vertically in parallel on top of the foil strip. Then I would make a strip for the top as well and lay it across the top of the cells, maybe putting a coin on to each cell to weight down the top aluminum stip. Maybe a strip of cheap kitchen foil can only carry 1,2, or maybe 5 amps but I think this should be enough to balance these new cells when they are charged to 3.65V?
Jumper wires are an easy way to top balance these before they are spot welded, but no bolt on terminals means we don't get to switch from parallel to series and back for a top balance. Going to have to trust the BMS.
$8 for 15AH far too expensive. translates to 150 bucks for 280ah, what's the point of using such small cells?
I have built and deployed three 19.2V UPS batteries each in 6s config. Perfect size for my applications as they will run for more than three times the AGMs they replace, which are similar volume. Also excellent rated cycles. Price is good for this size cell. I will save money compared with the replaced AGMs. Cheaper than deploying s.
I also have 460AH and 180AH cells for other applications. Of course they are cheaper per AH.
I'd like to know where you think you can get 15AH cells for 15/280 times the cost of a 280AH cell.
In volume, you can get these cells quite a bit cheaper. It's important to get good ones which is how this thread started. I'm happy to not pay a bargain basement price if I can be sure of quality.
Old thread, but I've got a bajillion of these things and have been building 24V modules in ammo cans, assembling everything via Weller D650. It works great.
I'm so glad I found your post on this old thread. I just ordered some of these for a project and have been scouring the web looking for a non laser solution. What type of flux and solder has worked for you on these s? I wonder if a lower melting solder would be a solution to mitigate some of the damaging heat in the cells during the solder process.
I also had a crazy idea to design and 3d print a battery case with copper tabs inside that would just press fit against the battery like a AA or AAA in a toy or remote control.
Have you discovered anything new on soldering these cells since your posting here?