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.
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.
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?
Paracell is using 20 Amp 18650 LG IIG2 Cells…
This pack in 72 Ah would be around 5000 $ from Paracell.
336 Cells 18650 LG IIG2 a 6.50$ = 2184 $ for the Cells only for a 72 Ah pack.
Lipo in 76 Ah (4 x 22000mAh + 4 x 16000mAh) should be around 1800 + 250 Charger
Thought lifespan should be better with Li-ion 18650 cells.
The Tesla packs seem to be just about perfect weight/energydensity/capacity/cost/availability/reliability/etc.
If they were 48V instead of 24.
Three solutions:
Any thoughts?
Option 3 seems to be the best. However I havent actually taken apart the packs. Wiring in series is what we are doing now with the LiPo batteries.
I have a relative who is knowledgable about Tesla batteries. I asked him about using Tesla tech, and here is what he said:
"For batteries on these devices, I would look to the drone guys as leaders. They have done a bunch of good work modifying batteries for their applications. In general, they have been using lithium iron phosphate (LiFePo or LFP) as their chemistry of choice. This chemistry works well because it has a high power density, is fairly safe to use and is less expensive. The chemistry used in Tesla and other EVs has a higher energy density, but it is not as intrinsically safe as the the LFP. They have to be handled really carefully. I would strongly recommend against using Tesla batteries for this application. The LFP is much more forgiving. "
This is actually untrue. The chemistry of choice for drone use is not, and never has been LiFePo.
Most of the safety concerns we have with the cells used for ePPG is not the cell chemistry. Rather, it is the safety you nay or may not build into the power delivery system.
Most fires in battery powered machines do not originate from the cell. They are nearly always due to ancillary equipment failure , poor/insufficient current carrying capabilities of wiring and interconnects , shorting to to mechanical failure of insulation etc.
All of the cell types are absolutely capable of supplying currents far exceeding that required to initiate ignition of other materials in case of a short etc.
The current capabilities, and its ability to start fires external to the cell is magnitudes more of a concern that the safety of the cell itself.
Also, those weldless/solderless pack building systems should be ABSOLUTELY AVOIDED. Do NOT consider using them in your PPG project. The contact resistance alone (as they are using what appears to be standard zincated screws as contacts, will be relatively very high. Not to mention thermal issues that will arise from these parts moving all over the place when at higher temps. Just dont do it.
The Tesla packs/cells are perfectly suitable if reconfigured to meet the electrical requirements. However, buying them used is not such a great idea. They are not in service for a reason. The cells are likely at about 60% or less usable life, and a significant reduction in usable capacity.
I have discussed with @Pdwhite in the past about some pack options. I am working on an LTO option, as well as a 26650 cell based option.
I currently work in the automotive industry as a EE. I served 15+ years in the EV industry as a mechanical/manufacturing/electrical engineer with focus being power delivery and traction motors/inverters. I have built motors for Tesla, and have worked closely with cell/battery manufacturers in the development and integration of the packs in to EV’s. I have deep connections in the lithium chemistry cell industry and often get absolutely amazing deals on cells from various manufacturers.
I currently have plethora of various cell types and chemistries I will be testing once the PPG is built. The first two will be Altair Nano LTO cell based, and a MoliCel 26650 based pack.
Also, the first link explaining Li-Ion vs Li-Po is grossly incorrect (as most sources are). Do not use it as a source of valid scientific information in deciding what cell chemistry to use.
I cant stress enough. Dont harp on the cell chemistry much for other than power/energy density concerns. 90% of your focus on safety should be applied to your wiring and interconnects. That is where your primary mode of failure is going to occur.
Li-Ion seems to be used also in other commercial eppg projects - see E-GLIDER. They use either 30Ah or 50Ah Sony Li-Ion packs (two different ppg models, one for short cruises and thermals, another for cruising). As a side note - I like their folding propeller design, but torque-wise the openppg design is great