@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.
This raises an interesting question- Assuming that two packs are only 140mm tall, and that they are not too heavy when stacked, I wonder if we can arrange the electronics so that a second pack could be added for some flights? I do this for my FPV planes and lipos by just putting them in parallel. I don’t know if the BMSs fight with each other with these packs, however.
One pack is about $1200, so this gets expensive, except when you consider that a Carbon Scout is about $9k plus all the maintenance, drama with airlines and fuel, and noise. I’m not saying I’d turn down a Carbon Scout if I could afford one, but it does put things into perspective.
@tombusey thanks for checking whether this fits, or not. However I am thinking to place the battery rather lower, between the legs. In either case this is probably going to be a trial and error process, and see what works best, when the whole setup is on my back.
Here’s the battery with the first layer of nickel strips:
The serial connections will definitely need a second and third layer of nickel strips welded on top, to support the high current flow, I also still need to add the BMS and the cables to connect the whole thing to the openppg.
This was a helpful series for me to watch. He suggests keeping weight higher and as close to the body as possible. But I agree that eventually you just have to try different positions once you have the motors and harness in place. Our setup is different in that our motors are much lighter and we don’t have a fuel tank that is lower.