How about 18650 Li-Ion battery pack over the Li-Po packs?

Power System
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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.

2 Likes
56

Thanks, confirms what I was thinking.

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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.

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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.

1 Like
59

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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Deleted…already been posted.

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Open ppg electric 84

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.

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62

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:

  1. Reprop for the lower voltage. Are props with double the pitch available? What sort of efficiency loss from the motors would result from spinning them at 1/2 design rpm? Change motors too?
  2. Electronically bump voltage up to 48. What sort of efficiency hit or extra weight might this add? Even doable at these amperages?
  3. Reconfigure the packs. How difficult might it be to get into these packs and rewire them. Essentially cut them in half and join the halves back in series instead of parallel.

Any thoughts?

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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.

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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. "

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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.

8 Likes
66

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 :slight_smile:

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I wired up this on the weekend - a little too big for our needs. 8S3P

image
image.jpg4231×2387 3 MB

Cheers

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LG HG2 Li-ion cells cost € 3,95 in the Netherlands. But are not the best Li-ion cells, are not cost-effective, has a short lifespan, like any INR cell.
Li-po lifespan is also a pain in the ass. And the specific energy is around 170Wh/kg for the best polymer “burner” bag.
Lithium-ion cells have very efficiency, especially NCA chemistry with a specific energy of 250Wh/kg, so you must use the battery pack with the best cells on the market. See Tesla choice!

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did you actually notice, that the OpenPPG requires up to 300A
with a 13S15 Setup, (195 individual cells) which already costs around 1.000 dollars, the HG2 from LG are on of the few options, as they have the highest discharge rate.

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I understand, but 300A peak can be reached also with Panasonic NCR20700B15A or NCR20700A30A cells, with NCA chemistry,colder due to aluminum oxide, and a longer lifespan.
LG HG2 can discharge the only 12A-13A before achieving 75 degrees and goes cut off. So 20A continuous discharge is a warming fantasy.
Sony VTC6 claim 30A continuous discharge rate, but achieve 80 degrees and cut off because become extremely hot. So work well on 15A-18A discharge rate. Heat for battery cells means also a short lifespan!

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Check this configuration: 13S13P Panasonic NCR20700B - 48V 55Ah 195A/300A 9360W. Cells cost around 950 euro. Battery pack weight: about 10 kg.

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VeConcepts is working on a lithium ion battery solution for us in 12s and 14s configuration. I guess there are 160kv motors available for the kits, this will allow higher voltage pack and reduce amperage. I’m planning to get this setup with 14s battery option from Chris at VeConcepts. Was going to build my own pack but I’d prefer to get an industrial grade battery that is made to handle the amps. Chris said the battery will have an on/off switch which would also eliminate the two red switches required now. Reducing some weight, wiring and complexity. Less failure points.

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I think 160kv will be too high for 14S. You may need to reduce prop size or limit throttle to prevent the amps from being too high. Paul has some 160kv on hand but I want to custom order some 150kv and convert to 14S from Chis. There would be a long lead time for the 150kv though.

50.4v * 180Kv = 9072 RPM
9072 RPM / 58.8v = 154Kv

I want to drop from 154 to 150 to be on the safe side which I think will draw just under 80 amps. My 12S setup draws up to 93 amps per motor now with full batteries and that’s more power than needed so I would rather be low than high on the Kv.

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Interesting. So if your saying that’s more power then you need, could I not limit the amount of power on the throttle either by changing the code or installing a spacer so the throttle can’t go to 100%? How long is long for the 150kv have you inquired?

I ordered amp meter you have so I can keep an eye on amp draw when I get this and test out chris’s Battery with this setup.