Absolutely awesome spreadsheet - nice work! I also like the idea of an 18650 based pack. I have access to a spot welder and actually a bunch of LG cells, so I’m going to give this a shot!
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Has anyone come up with a decent way of putting packs together? All the methods I’ve come across are either too heavy, too bulky or not enough amp output. Seems spot welding is the way to go so far.
Has anyone put any packs together that we can see?
Spot welding is the way to go. There are a bunch of DIY videos on YouTube on how make a spot welder, or you can buy one from alibaba.
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thought I’d post this here. Vruzend / Micah Toll has his 18650 diy Li-ion battery building kit upgraded to a version that supports higher current (due to nickel plated copper bus-bars).
See the kickstarter here: DIY Li-ion battery building kit | Make your own 18650 packs by Micah Toll — Kickstarter
I am seriously thinking to go ahead with this route.
Can anyone confirm that my calculations are correct, see below?
taking this cell LG HG2 18650 Battery, 3000mAh, 20A, 3.6V, Grade A Lithium-ion (LG18650HG2)
( https://voltaplex.com/lg-hg2-18650-battery-lg18650hg2 )
Since it has a discharge rate of 20A, and we need 300A, I need to put 15 in parallel (with 3000mAh per cell it will give me 45Ah capacity total)
Since we need 44V (or 48V) I’d go with 13 in Series
That’s 13S15P makes a total of 195 cells.
45A with 48V = 2.16 kW/h
Each cell weighs 48grams, 48g * 195 cells = 9360 grams = 9,36 kilograms (a little over 20lb) plus the caps, bus bars, cables, shrinkwrap and such…
And we need a proper Battery Management System, that is capable of supporting up to 13S and 300A,
this one should work: 300A BMS 2S 16S LiPo Lebensdauer der Batterie Management System TFT LCD Display Smart Lithium lifepo4 Li Ion Zellen chargery BMS16 V 2,0 neue|li-ion charger display|lifepo4 chargercharger lifepo4 - AliExpress
Again, is my thinking correct? Any comments ?
Thanks
Etienne
Check out this kickstarter kit for building packs without spot welding
That’s really cool but they recommend only 3.5A per cell, so does that mean we’ll need to build a 12s85p pack? 1000 cells seems a little excessive.
If you look at the link that I included (https://voltaplex.com/lg-hg2-18650-battery-lg18650hg2 ) you can see under the Specs that this specific cell has a constant discharge current of 20A (with a peak current of even 35A for max. 4 seconds).
So 13S15P (195 cells) give us 48Volts with 45Ah capacity and a 300A constant discharge current. The pack is going to weigh around 10kg
that’s basically the bottom line of my longer above text. 
Very cool, I can’t wait to get a kit to play around with.
Can someone please clarify the correct “S” number required we need using 18650’s…12S, 13S or 14S?
It’s all about cell chemistry, so there is no one answer, but assuming you’re using LiIon cells (which have a nominal of ~3.7V), the answer is 12S
12S Lipo pack has a nominal 44.4v
12S 18650 pack has a nominal 43.2v, 13S is 46.8v
I would rather make a 12S, but just want to make sure that’s ok before I build it. @Pdwhite could you confirm please?
@davek79 you’re right, it’s about the cell chemistry.
However the only reason why we’re all talking about 12s is because of the Bonka (or Multistar) Batteries are the preference of most of the future OpenPPG-Pilots. They are Li-ion Pouch cells with a 6s configuration per battery pouch - so two of them then make for the 12S / 44,4V configuration.
However:
Paul ( @Pdwhite ) stated in the above post, (Time until battery is out of charge? - #19 by Pdwhite ) that the OpenPPG is a 48Volt setup (which would be a sort of standard similar to Ebikes) - and that would be a 13S setup, if Li-ion cells (with nominal 3,7V) are used. That’s not possible with the Bonka or Multistar Pouch Batteries, but it is possible if you DIY your battery pack with the 18650 Li Ion cells.
Someone suggested the use of a wiki, since there’s so much information spread across so many posts in the forum - I would agree that a wiki would be very useful at this point
@OpenSky and @davek79 are you going the 18650 route as well ?
I did a quick calculation in regards to having a solution for putting and holding the cells together, and I’ve come to the solution that for larger packs it may already be more cost-effective to invest in a spot welder, instead of buying the pricier vruzend caps with integrated connectors.
this solution here: https://www.youtube.com/watch?v=CNmvx2JSCvA
costs around 100 euros plus a 12V car battery.
it can be purchased here: https://malectrics.eu/
@etienne Yes, I’m going 18650 route, and going to spot weld as no other “lego” type options will do the job.
Yes, I’m going to make my own spot welder. Was going to make one like this video, but with your find from malectics, will have a look at that solution now, good find, thanks!
Sometimes manufacturer’s list their nominal voltage as 3.6 instead of 3.7V. It can be confusing.
The 18650’s that are linked above still charge to 4.2V. Thus, a 12S pack should still be used.
Peak voltage will be 50.4V for any of these 12S systems. The ESCs may not be rated for anything more than that.
“nominal” voltage is a measurement of the average voltage of the cell over the discharge at a specific C rate. The IR will determine that number. The number the list is somewhat arbitrary, some are more honest and list 3.6V instead of 3.7…
We have to be careful about voltage conventions. For example, in automotive, “12V system” is charged and used at 14.4V, with something like 18V being a requirement for the modules.
Paul might call the openppg “48V”, but the ESCs will really determine the limit. I suspect they are listed as 12S maximum, meaning 50.4V peak.
So long as you are not using a lithium iron phosphate cell, 12S is right.
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Thanks, confirms what I was thinking.
Correct the nominal voltage is 48 volts with the max charge voltage being 50.4. The ESC are actually rated for 14s so there is wiggle room if you want to try something different.
One other thing to consider: In automotive and other industries, 50V is considered the limit after which the system is considered “High Voltage” meaning it can cause harm to human beings. For those industries, that entails different wiring, contactors, markings, etc…
We probably don’t care, but the thought crossed my mind if OpenPPG has to be certified by some regulatory body in certain countries. I have no idea if this would be an issue - just thinking out loud. Maybe those regulatory bodies have no idea and don’t care.
In anycase, just more reason to stick to 12S build.
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putting the batteries together and wiring them is not enough,
we will need to have at least some sort of enclosure.
I am thinking about sewing a sort of pouch with a zipper and some velcro straps to safely strap it to the OpenPPG frame.
a strong and durable material would be “Cordura protect” fabric in “1000 den”
Since we would never fly in rain, we could chose the uncoated version, which also would let some air flow to cool the battery a bit.
Any thoughts?
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