as mentioned here: How about 18650 Li-Ion battery pack over the Li-Po packs? - #60 by SimLoop , I was thinking to build a battery pack out of 18650 cells.
Since we need 48 Volts and the maximum discharge current is around 300A, I needed batteries that support this rather high discharge current. I found the LG 18650 HG2 cell that can handle 20A constant discharge per cell. To reach 300A I need to put 15 of them in parallel (15P).
To have 48Volts, I need to put 13 of them in series, that makes it a 13S15P Pack, a total of 195 cells with a capacity of 45Ah (3000 mAh per cell) total.
I am going to add plastic cell holders and a battery management system for charging and discharging. I will be spot welding the batteries with pure nickel strips.
The arduino basically controls the pulses to do the spot welding. with the knob you can set the desired pulse length.
I purchased the board, a (3D printed) case and the welding cables/probes.
It took me about 20 minutes to put everything together.
I still need to buy the 18650 cells, however I am waiting for some quotes first (I need 195, but I will be buying 200, to have 5 as a spare).
The charger that I am planning to buy is the Cycle Satiator. It is quite versatile, so it will be able to charge the 12V car battery as well as the 48V OpenPPG battery (once it is fully assembled).
I will post more pics once I receive all the material and can start building.
EDIT: Nevermind! I see you have a charger in mind that will work!
How do you plan to charge 13S? Are you going to have connectors that split the pack into 6S + 7S components to charge with conventional RC chargers?
Be careful with using “dual” chargers to do that. In most of those the two channels are not isolated from one another. Connecting both sections of a larger pack to each channel, while the whole pack is still in series can short through the charger. I learned this the hard way a while back on a large automotive lithium battery.
I was cautious about welding 18650’s only because i have never seen it done. Would you mind making a quick video of the actual welding once you have your pack set up and ready to weld?
Thx
paul
Plus i think the Satiator is a good choice. I have one of Justins CA3’s on my bike and it is very good.
Hi Paul, I am not sure if I really do want to go the video route…
however there are tons of videos on youtube about spot welding battery packs. this is a video of the manufacturer of the arduino based spot welder, that I purchased:
Hi… you might consider copper strips instead of nickel. I’ve heard (but not used) that this is much better for high current situations. Makes sense…
@pofries yes, copper strips would be better (lower resistance), however you can’t weld copper with the copper electrodes of the spot welder. another option would be nickel plated copper strips, or simply weld two or three pure nickel strips on top of each other, which is what I am going to do.
However I think I remember that @Pdwhite said somewhere here in this forum, that with 8 of the multistar 16000 mAh Batteries (2 in series, 4 in parallel, total capacity 4x16000 = 64000 mAh) we would have a flight time of around 40 minutes (see quote below).
My battery will have 45Ah with a little more voltage (48V nominal instead of 44V nominal, so a bit more RPM for the motors) - you do the math.
Look on the last row. This is my best guess for the values.
From those numbers, it looks very competitive at 0.83 $/s. It may also be less likely to explode on your back (these are more stable?) and longer lasting than Lipos.
Okay, I added it, but I added more weight than you were estimating. I’m expecting that people will use a battery kit when using these cells, like the Vruzend kit, which will weigh around 5kg to hold all of your cells. Feel free to correct me, I just would rather overestimate weight of harnessing and everything until someone can give me a definitive answer on how much the batteries + harness will weigh.
By now, I received the cells, nickel strips, plastic holder/spacer as well as the BMS.
as soon as I start putting everything together, I will post more pics!
Hi Lukas,
I completed the spot welding of the first layer of Nickel strips yesterday. I will have to add more layers for the serial connections, to support the high current of 300A max, but I need to wait for more nickel strips to arrive.
It was the first time for me to use my newly purchased arduino/car battery spot welder. It was quite easy, no hassle. However it took some welding to figure out that the pressure of the electrodes being applied also makes a different in the welding quality, just like the amount of milliseconds (duration of current applied) makes a difference.
It took about 90 minutes to spot weld all 195 cells. I had to pause every few minutes for a few minutes, as the electrodes got quite hot in my hands.
Overall I think I am quite happy. Will post more pictures later.
I wondered how this would fit in the current frame. I assumed these were about 70mm tall with the plastic connectors, and 19mm between the centers. A 13S15P pack looks like it fits nicely, assuming the motors aren’t too squat:
For fun I also did a 13S20P which might extend the flight time from about 24 minutes to 32 minutes:
This would also add an estimated 4kg in weight, from 12 to 16kg. I’m not including the BMS or cables in these size or weight estimates.
