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.
quick update:
I received the missing nickel strip, that I still needed, also the 8AWG Silicone wire. Still waiting for the RC Pro Plus bullet connectors.
I’ll be coming to the States for the duration of one week, I hope to be able to continue my build by the time I come back to Germany.
Also waiting for @Pdwhite to starting to accept orders again for batch 3, as I haven’t ordered the openppg kit yet.
Thanks @tombusey for the hint with keeping the weight higher. Logically you are right. and yes, the video series from Miroslav/Scout is indeed awesome for some background information.
Can this battery be made in two 13S8P configurations? With all of the discussions around the failures of the Batch2-included switch, it seems like a good idea to split the current into two switches, each of which would support two motors. If these were diagonal from each other, and spinning in opposite directions, this would provide some redundancy in the event of a prop or esc failure (which IMHO are far more likely than a motor failure). In the event of an ESC failure, you could just turn off one circuit and land using the other. The amount of current going through any one set of wires is also half. Presumably one set of motors wouldn’t have torque or other spin issues.
Maybe a downside is the need for two BMS? There is also the need to link the grounds (maybe not a problem?), and there is additional complexity in monitoring both packs.
2 BMS is a bit of a PITA - as would be 2x the switches and 2x the current monitoring, etc.
What would be ideal (not sure we can find the parts however) would be going to a higher voltage configuration - like 24S. We’d halve the current everywhere, which would open up a ton more options.
Now, we start getting into HV potential concerns, and the safety associated with that… but I think our issue might be finding the parts, and of course the motors would need to be re-wound to an ~90kV configuration (assuming the insulation could handle the voltage)
I’ve seen such things… haven’t found readily available, reasonable priced sources for any of them, however. They mostly seem to be the subject of obscure YouTube videos
@etienne , I am happy to say that I got in on batch 3. I hope that you got in also.
Do you have any updates on your battery build? I have ordered a spot welder like yours and have begun collecting the other parts too. Malectrics appears to have designed a good welder…one of the best that I have seen on the web. I believe that your 13S15P 18650 pack is a great choice for a battery, and I do plan to follow your progress.
