and another supplier http://www.pingbattery.com/
The only issue with LiFePO4 packs is they tend to have a lower wh/kg rating. They’re great for bikes since they won’t cause a lipo crotch fire (I use a 20Ah 72v pack on my ebike as well), but they’re too heavy for use in a PPG.
Ok I understand! What about the Tesla batteries?
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F123061970360
I asked the guy who’s selling them and apparently they weigh 22kg. Would it be worth putting these into the spreadsheet?
Maybe we would just have to source them ourselves from Ebay etc?
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I was about to post about the same batteries. The voltage on a module is 24V so you would need two. However, I think you could modify the connections and make this a 48V module. I did the numbers for a 5.3 kWh module out of an 85 kWh car.
Cost: $1372.50 shipped
Cells: 12 (reconfigured)
mah: 116,500 (reconfigured)
weight: 25 kg
C rating: 4C
Results:
Flight Time: 55 min 55 s
wh/kg: 207 (2nd Best)
Wh/$: 3.77 (3rd Best)
The spreadsheet has a subjective score which basically prioritizes cost of the minimum battery needed. I know its subjective but I personally would add quite a bit of value to the total flight time. This pack has the best specs if you want longer flight time. This is just my opinion.
Personally I’m more interested in getting longer air time aswell! You mention that the battery would have to be reconfigured. Is that easy to do? I don’t mind the weight of it actually 25kg for just the battery is reasonable considering the longer flight time. Is there anyone out there that could show us how to reconfigure the batteries? And then comes the charging how would you charge these batteries? And finally a question for paul, is there any chance we could include this into the spreadsheet please?
I actually didn’t set up that spreadsheet I think @DanielArnett did?
I don’t know how difficult it would be but you would basically have to cut the large plates that group the cells together in half. You would separate the 6 sections in half and then wire it in the desired configuration. I have never had a module in person but would definitely like to give it a try. I will look into the tear down of these modules. I have seen at least one person tear them apart to get the individual cells out. This wouldn’t be as involved.
Here is what I meant. The red section is a single plate connecting the negative of one group (74 cells) to the positive of another group of cells. The blue line separates the groups. You would have to make a cut where the yellow line is to split the group into 37 cells. The pack is configured as 6S74P. By doing this to all groups, you would make it 12S37P. I am not saying this exact cut would be optimal. I would need a module to figure out the sequence of groups and the best way to re-wire it. Hope this is clear enough.
So there’s another thread about making batteries out of cells which I think makes more sense than this Tesla battery since it has better density and price, and uses similar cells. The bms in this Tesla battery was designed for it’s current configuration and not for this modified 12S configuration.
I want to be clear about this one point to everyone reading: if you have not been trained in the safe design of batteries and are actually planning to build or modify your own battery packs, then flying just isn’t for you.
We’re taking enough risks as it is by flying. Modifying real batteries that trained engineers have designed without us knowing the associated long term risks is foolish and can get you killed. I’m okay with people asking “what if we use X battery”, but when we get into conversations about chopping up batteries or making our own packs, we’re asking for trouble. Not only is this conversation leading toward us taking dangerous actions, it’s signalling to lurkers reading in that modifying battery packs and flying with them is okay.
Use real batteries. Use batteries at the right voltage. Use batteries sized appropriately for the application.
Forgive me if I’m overreacting, the Tesla battery does look cool but this is not the right thread, nor the right forum, or even the right hobby for modifying batteries.
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I understand and respect where you are coming from and this is your project, but I disagree with several points. People are going to take risks with a product like this. By creating and sharing information, we can develop best practices. If we ignore it, then someone will try it without the proper knowledge and create a safety issue. Burying your head in the sand about people building battery packs is not the solution.
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BMS: Almost all of the batteries you are recommending will likely not have any BMS at all. Many people bypass the Tesla BMS and use their own BMS anyway. I am relatively new to this but what is the recommended BMS solution on this PPG? I just haven’t seen much talk of it. From what I can tell, its set up like a RC airplane with only a LVC at the pack level. I may be incorrect but wanted to ask. Without a cell level BMS, the risk of a single lipo cell discharging below the limit is much too likely and could cause a fire.
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Modification: Yes this could be dangerous and this should not be attempted by someone who has no idea what they are doing. The modification is not reconstructing and entire pack. It is simply making a few cuts in the bus bars and running some new ones. Compared to other options that people WILL try, this is a much safer one.
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Alternatives: You mention that there is an alternative cells with better density and price…I do not see one. The biggest benefit of using a module like this is because it has every other option beat. In order to get the same flight time out of another pack, it would cost substantially more.
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Open Source Community: By creating a community like this, you attract people that are going to build their own packs. You have created this environment by selling the units without one. If you only allowed a proprietary system that was vetted by your design team, it would make it unlikely people would design their own.
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Safety: I agree re-configuring the pack adds some risk. I do not agree that it is more risky than some of the alternatives. People will likely be using other cells and soldering them. This can introduce heat and damage the cells. Tesla modules are ultrasonically welded and therefore much safer. The Tesla module is also much more robust in design. It has the ability for thermal management unlike almost every other option listed.
Summary: I respect what you are saying and agree that there is risk. I just don’t think you can expect people to find their own battery solution while expecting them to ignore the most appealing options. People will take risks based on their personal preference. Hiding knowledge from them will not help the situation. If I have said anything that is inaccurate, please correct me. I really do appreciate what you guys have done for electric flight and hope this is a constructive conversation.
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Hi guys I’m asking that ping lifep04 battery supplier some questions.and he’s asking me what is the maximum charge current going to be?
Can some one help me on this? I’ve told him I want a 140,000mah battery!
According to the spreadsheet, the system draws 300 amps. This is a C rating of about 2.15 for a 140,000 mah pack.
I would be concerned that this pack would be too heavy. One LiFe example in the spreadsheet has a max pack size of 90,000 mah. This is due to the 173 Wh/kg energy density. Assuming a similar energy density, this pack would weigh 80lbs, making the motor weight over 100lbs. That exceeds the recommended maximum of ~75 lbs.
Another thing to consider is that a LiFe pack would need to be 14S instead of 12S due to the lower voltage. LiFe cells are ~3.6V max vs ~4.2V for LiPO cells.
@DanielArnett Do you agree that there is an error in the spreadsheet for the Evlithium batteries? It should be 14S. Nominal voltage for the LiFe chemistry is 3.3V instead of 3.7V. May want to add a column for chemistry.
Edit: I believe the voltage discrepancy also reduces the energy density to 155 Wh/kg. This would increase the weight of the battery by over 10%.
Hello @Jonerickson as @DanielArnett has pointed out, there is another thread (started by my) that talks about building a custom Battery Pack with 18650 cells.
They are widely available, and building such a pack from scratch with new cells is indeed much safer than tearing a Tesla pack apart.
Just check it out:
I’m still trying to get a handle on how much of a danger this is (if lipos are charged and maintained properly), and how the danger of using lipos compares to other options such as 18650.
There was a thread about this topic which zjwhitehead actually delisted from the forum: Battery/motor quick release - #46 by zjwhitehead (an action which is not helping to build trust in the management of the forum and safety concerns related to the project).
I think it was delisted because it was off-topic (a battery/motor release system) and the install questioner question was answered and he agreed it was not feasible of a good solution to drop things from the PPG.
As far as your question about battery safety your correct that a properly maintained lipo/lion its what make batteries safe or unsafe. Think about how may DJI drones there are out there and in operation and used every day and there is essentially no incidences. Its all about taking care and chargeing cortly and it will be perfectly safe.
Thank you Paul, as always, I appreciate all the time you’ve taken to answer questions.
I really have no idea about those numbers. That’s exactly the sort of statistical information which would be helpful for someone like me (and I’m sure other potential customers with no background in RC and these power systems). I suppose having watched nonstop videos of Lipo fires for several weeks, while first learning about lipo maintenance, didn’t help much to build my confidence, or my understanding about the probability of fire 
The answers on the other thread were really helpful in comforting many of my concerns. When I read the following, it was just another red flag (I don’t know how to put the likelihood of this statement into probable context):
What exactly is ‘too likely’?
This thread is about battery comparisons, so my real question here is about the differences in safety between li-po and li-ion (or any other viable option). How much safer is li-ion, or is it truly not something that I should worry about enough to consider li-ion?
When it comes to delisting the other topic, the OP actually changed the title of his original post to clarify the intent of the post (that the conversation was not off topic), and several other members voiced concerns about the removal of what might be considered a critically important conversation. As others have clarified, I’m grateful and entirely supportive of all the work you’ve done on this project. Like everyone involved in the community, and everyone testing the first units with their own lives, I want nothing more than to see this project become successful. I don’t want to see any trust in the community damaged by a lack of willingness to discuss safety. It seems to me that any discussion about batteries (this thread included), will see that topic brought up. It would be nice to have a mature thread available for newcomers to read, so that any previous conversations don’t need to be rehashed. With that in mind, I hope future topics won’t be delisted.
I’m 100% behind you and this project, and eagerly looking forward to testing the units.
Hey Nick,
My 2 cents about some of your questions: Concerning a single cell overdischarging; so long as the battery is quality (roughly the same IR) and they are balanced, an undervoltage event of a single cell won’t happen.
I imagine the flight controller is going to have pack level voltage measurement or other means to measure SoC. As such, it will just be part of the pilots responsibilities to not over discharge the pack as a whole. Alternatively, the ESCs can be programmed with low voltage cutoffs.
Concerning your question about lithium ion vs polymer: the main difference is in the electrolyte. Polymer, as the name implies, is not a liquid, but rather a gel type electrolyte.
In practice, the two names are often used interchangeably. I would caution against any person that claims that either is somehow safer than the other. Both have the same failure modes (thermal runaway) if mistreated.
Best,
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I think you nailed it in saying this here
You can find or support anything you want to on the internet and the media like to highly exaggerate the risk of lipos. Also, its fun to try to make a lipo smoke (its really hard and I have tried many times)
Actually, it’s the exact opposite and a fire cases because of going below the low threshold of 3v per cell is not what happens. What happens is you will damage your cells and lose capacity. Where there is a risk of fire the vast majority of the time is with improper charging/overcharging or just driving a nail through the cells. That’s what you are seeing in those lipo fire videos.
It’s hard to stop the spread of misinformation or fear-mongering, and there are a lot of people that claim to be experts (just the nature of the internet). I don’t have to time to go through and correct or police false info, what I’m trying saying it just don’t believe everything you see or hear on this forum do the research yourself. Lipos are not a new technology by any means nor are we the first ones to use them, so no need to reinvent the wheel of discovery. They used every day in loads of applications every day and the topic on dropping batteries out of a moving aircraft is not constructive. When basic battery chemistry is being discuses incorrectly it’s just fear mongering and no new info is being brought to the table therefore it’s not helping anyone or the project.
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Thank you fellas, my concerns have been totally satisfied (aided by an additional private conversation with Paul).
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At the risk of going a little off topic if you want an amusing demonstration of how quickly people will believe pseudo science may I suggest you search Wikipedia for the story of Dihydrogen Monoxide.
All the best, Paul in Australia