13 ms·

Given how popular (and damn near impossible to discern) unsafe and unprotected lithium-ion batteries are, the idea of making a homegrown power wall terrifies me

Given how popular (and damn near impossible to discern) unsafe and unprotected lithium-ion batteries are, the idea of making a homegrown power wall terrifies me in ways I can't even begin to contemplate. An 18650 battery, if combusted, can produce hydrofluoric acid with just water vapor in the air (or the water in your lungs) if they use lithium hexafluorophosphate as the electrolyte. Hydrofluoric acid can and will cause permanent damage to lung tissue if inhaled, and nasty, nasty chemical burns to exposed skin. 18650 batteries are supposed to have several failsafes to prevent thermal runaway, but counterfeit batteries can lack those failsafes. Not to mention, in some laptop battery packs, the protection was pack-wide, and not in individual cells. Not knowing the chemistry of the cells or the state of the protection circuitry of the battery would make me very nervous. Maybe someone else can provide more detail on how to test them safely.

gravypod 10y ago
I came here to say just that. This is a horrible idea and definitely not something you should do. Just use sealed AGM batteries, don't burn your house down or deal with spilling chemicals everywhere. Even just drawing in parallel from batteries like this is a fire hazard. Charging is an out of your mind goal.
- agumonkey 10y ago
  Wow, as someone uneducated about anything related to electricity and power, seeing the picture in the article really made me want to emulate the setup. Not anymore.
  - gravypod 10y ago
    You joke buy many many people don't know how volatile battery chemistry is and how different charging of Lithium cells works. I'd not have known how much of a bad idea this was had I not been a long time fan of EEVBlog. It's an entirely different world when touching Lithium cells. Even drawing in parallel from cells from the same batch can be a bad idea.
- userbinator 10y ago
  Even just drawing in parallel from batteries like this is a fire hazard. I think you've confused parallel with series; in parallel, the batteries will naturally balance themselves to the same voltage and discharge proportionally to their capacity. It's the series configurations that are riskier and need extra balancing circuitry. Also, I'm pretty sure the bulk of fires are from the much more fragile pouch "lipo" cells, not hard-cased 18650s like these. You may note the extremely large number of lipo fire videos on YouTube as evidence. On the other hand, 18650s tend to be quite a lot more robust and difficult to ignite: https://www.youtube.com/watch?v=vi5lGtm_ItQ https://www.youtube.com/watch?v=vi5lGtm_ItQ https://www.youtube.com/watch?v=uoFRrmhXoVw https://www.youtube.com/watch?v=uoFRrmhXoVw
  - qoobaa 10y ago
    I think @gravypod actually meant parallel connection, it might be quite dangerous in fact - you don't even need to draw anything from the battery to mess things up. If you connect a 100 cells in parallel and one cell dies creating a short in the circuit, the rest of cells will discharge through the shorted one. When you short a single 18650 cell, it outputs about 6-7 A of current on average. Multiplying by 100 gives you 600-700 A of current flowing through a single cell. That's why people use fuses to create parallel modules.
    - gravypod 10y ago
      Yes that was mentioned in one of the maaaany EEVBlog videos iv watch that these fail closed sometimes as well as the recommendation that "you should never buy lipo cells without a built-in controller" comeing from a guy far smarter then I about electronics design. If he is afraid of it, it's for a good reason.
      - throwaway7767 10y ago
        > Yes that was mentioned in one of the maaaany EEVBlog videos iv watch that these fail closed sometimes as well as the recommendation that "you should never buy lipo cells without a built-in controller" comeing from a guy far smarter then I about electronics design. If he is afraid of it, it's for a good reason. If you're building a large pack you don't want cells with a built-in protection. You connect all the cells to a pack-wide BMS that keeps things safe. The important thing is to never use unprotected cells without some protection circuit in the pack.
Reason077 10y ago
It's pretty safe so long as you use a battery controller with appropriate monitoring to prevent overcharging. Recycled 18650 cells that have worked fine in laptops for years are very unlikely to suddenly explode on you for no reason. I'd be more worried about the mystery Chinese ones you can get new on the web! Here's some Materials Science students at Oxford who built packs using recycled laptop cells. They used controller software that monitors the health of each individual cell: https://m.youtube.com/watch?v=RW1Xugey8j0 https://m.youtube.com/watch?v=RW1Xugey8j0 (It's towards the end of the vid)
- gravypod 10y ago
  It's still not the best idea unless you can control the draw from each cell individually. Hooking these up in parallel is a horrible idea.
  - deleted 10y ago
    [deleted]
- whamlastxmas 10y ago
  >very unlikely to suddenly explode on you for no reason It really depends on their condition. If you get some cells from a laptop and they've all fallen down to reading 1 volt, then yeah repeatedly charging them (especially at a high amperage) is going to be pretty dangerous.
asteli 10y ago
Building a pack from random cells like this is pretty much a cardinal sin with Li-Ion pack design. Cell resistance and state of health are carefully matched during pack manufacture to ensure cells charge and discharge evenly. Li-ion cells are pretty sensitive, so on top of that, large packs have battery management systems (BMS) to balance cell voltages and monitor for faults and damaged cells. Attempting to charge a pack like shown has a very real risk of causing one or more of the cells to overcharge and breach, or worse, violently catch fire.
- rektide 10y ago
  Yeah, very much. Some basic dilligence with a somewhat even set of cells will probably be harmless. I would not be afraid of that kind of homebuilt power-store, if some decent practices are followed. (But you should do your dilligence & check to make sure all the cells remain ok, as you start using this pack!) This... this is an hellish unbelievable nightmare, is asking for something to go wrong. It is certianly possible to invest the time & effort to balance the hell out of such a chaos-pack, but for one's own sanity, using normalized cells will save a lot of sanity & rework, and drastically decrease risks of catastrophic f-up. Don't do like this person! Do build weird electric systems though, unlike OP's way too broadscale doomsaying fear-mongering.
- keenerd 10y ago
  Charging the "pack" shown is impossible. There are no wires connecting any of the batteries. He made a case that can hold a bunch of cells. Not a battery pack.
  - gravypod 10y ago
    That's ever beginning of a larger project I assume.
jrockway 10y ago
You have to realize that 1kWh is a lot of energy. Imagine being hit (in a world without an atmosphere) by a 60 pound suitcase falling out of an airliner flying at 45,000 feet. Same amount of energy as that battery pack. (Alternatively: the most powerful air conditioner you can buy running full blast for 30 minutes. Incidentally, that battery pack has as much energy as 100mL of gasoline, which is why gasoline-powered cars are so popular.) When you put a lot of energy in a small space and release at all at once, it's called a bomb. Li ion batteries are small bombs that can be used to power electrical devices. Some chemistries are safer than others, like A123 cells. The market did not care about safety and they went bankrupt. Energy density is king.
- walrus01 10y ago
  > (Alternatively: the most powerful air conditioner you can buy running full blast for 30 minutes. I can easily buy a 16 ton (1 ton = 12000 BTU/h) air conditioner, it uses a great deal more than 1kWh in 30 minutes. http://www.ebay.com/itm/Carrier-16TON-R-410A-Puron-Air-Conditioning-Unit-Heat-Pump-40RUQA16A2A6A0A0A0-/180981368202 http://www.ebay.com/itm/Carrier-16TON-R-410A-Puron-Air-Condi...
  - jrockway 10y ago
    I mean to say, "plug in to your 120V 18A circuit".
    - StavrosK 10y ago
      I wonder why we have a tendency to nitpick rough estimates and go "YOU DIDN'T ACCOUNT FOR X EDGE CASE!", when even we get the gist.
      - viewer5 10y ago
        If I had to guess, it's someone who's like "I wonder how big that AC unit is" because the idea tickled their imagination, googles it, then finds that it doesn't quite match with the scenario given.
cmdrfred 10y ago
Maybe throw the whole mess into an out building with a fire suppression system of some sort? It says more details are to come, my curiosity is peaked.
userbinator 10y ago
I think your concerns are somewhat alarmist and tend to be a bit scaremongering. You may want to read an actual study about just how much HF is present in the fumes of burning cells. In this one, near the end they burned a whole laptop pack and analysed the gases that were emitted: http://www.brandforsk.se/MediaBinaryLoader.axd?MediaArchive_FileID=8605faf9-52ed-4d4e-89d6-0147c894f91f&FileName=BF_402_111_Rapport.pdf&MediaArchive_ForceDownload=true http://www.brandforsk.se/MediaBinaryLoader.axd?MediaArchive_... The relevant datapoint is on page 61: "As seen the yields of HF is much lower for the lap top cells, in fact the HF detected online was below the determined detection limit." The graphs on page 101 also show HF concentrations below 4ppm --- and keep in mind this is basically all of the gases collected from the burning pack. Looking at the safety data for HF, the permissible exposure limit is only slightly lower at 3ppm and it's immediately dangerous at 30ppm. In other words, it would be a bad idea to deliberately concentrate and inhale the fumes of a burning cell, but the HF probably isn't going to kill you. Some good ventilation of the area should be sufficient.
- spdustin 10y ago
  The PF6 ions in the electrolyte of some Li-ion batteries (not all use the same chemistry) will readily combine with hydrogen in the air to form HF if the battery is combusting. Cylindrical Li-ion cells, like those part of an 18650 battery, literally hold their chemistry under pressure, and a thermal runaway will normally cause the vents in the cell to release the pressure. If that's happening due to a short (which can and does happen when a cell is charged improperly, or even put under resistive load after the cell is discharged below a safe limit -- copper or other ions, depending again on battery chemistry, can literally bridge across the electrolyte to short the cathode and anode) the result of the release of pressure combined with the reactive nature of now exposed lithium is a small rocket that shoots a plume of gasses like sulfur dioxide or hydrofluoric acid. Again, this depends largely on battery chemistry, and without an MSDS on these particular cells, there's no way to know. But there's a reason why any chemist you care to phone up will say, if you tell them you're in possession of a cylinder of a compressed compound that contains fluorine (it won't matter what kind, fluorine really really likes to bond promiscuously and with reckless abandon), they'll tell you that you're braver they are. Tell them you're intend to string up a few hundred of them and pass an electric current into them, and they'll call a hazmat team for you. A casual stroll through forums frequented by flashlight fans (yeah, it's a thing) and you'll see plenty of demonstrations of what happens when a Li-ion cell begins a thermal runaway. And plenty of memorials to those who gave up their passion because they're on ventilators after experiencing profound damage to their lung tissues. Hell, ask the firefighters that respond to a fire at a battery recycling plant; granted, that's a bigger scale than one cell, but even one cell in a small room can, depending on its chemistry and how violently it's outgassing, emit enough HF to cause lung damage. Read an MSDS yourself: http://www.uscg.mil/hq/cg4/cg432/docs/msds/MSDS_LiIon.pdf http://www.uscg.mil/hq/cg4/cg432/docs/msds/MSDS_LiIon.pdf LiPo "pouches" mentioned elsewhere in this thread are much less likely to explode spectacularly before bursting, and much less likely to exhaust a plume of corrosive, toxic chemicals in their wake.
Confusion 10y ago
For those wondering about how nasty HF is: http://blogs.sciencemag.org/pipeline/archives/2004/03/03/things_i_wont_touch_1 http://blogs.sciencemag.org/pipeline/archives/2004/03/03/thi...

gravypod 10y ago

I came here to say just that. This is a horrible idea and definitely not something you should do. Just use sealed AGM batteries, don't burn your house down or deal with spilling chemicals everywhere. Even just drawing in parallel from batteries like this is a fire hazard. Charging is an out of your mind goal.

agumonkey 10y ago
Wow, as someone uneducated about anything related to electricity and power, seeing the picture in the article really made me want to emulate the setup. Not anymore.
- gravypod 10y ago
  You joke buy many many people don't know how volatile battery chemistry is and how different charging of Lithium cells works. I'd not have known how much of a bad idea this was had I not been a long time fan of EEVBlog. It's an entirely different world when touching Lithium cells. Even drawing in parallel from cells from the same batch can be a bad idea.
userbinator 10y ago
Even just drawing in parallel from batteries like this is a fire hazard. I think you've confused parallel with series; in parallel, the batteries will naturally balance themselves to the same voltage and discharge proportionally to their capacity. It's the series configurations that are riskier and need extra balancing circuitry. Also, I'm pretty sure the bulk of fires are from the much more fragile pouch "lipo" cells, not hard-cased 18650s like these. You may note the extremely large number of lipo fire videos on YouTube as evidence. On the other hand, 18650s tend to be quite a lot more robust and difficult to ignite: https://www.youtube.com/watch?v=vi5lGtm_ItQ https://www.youtube.com/watch?v=vi5lGtm_ItQ https://www.youtube.com/watch?v=uoFRrmhXoVw https://www.youtube.com/watch?v=uoFRrmhXoVw
- qoobaa 10y ago
  I think @gravypod actually meant parallel connection, it might be quite dangerous in fact - you don't even need to draw anything from the battery to mess things up. If you connect a 100 cells in parallel and one cell dies creating a short in the circuit, the rest of cells will discharge through the shorted one. When you short a single 18650 cell, it outputs about 6-7 A of current on average. Multiplying by 100 gives you 600-700 A of current flowing through a single cell. That's why people use fuses to create parallel modules.
  - gravypod 10y ago
    Yes that was mentioned in one of the maaaany EEVBlog videos iv watch that these fail closed sometimes as well as the recommendation that "you should never buy lipo cells without a built-in controller" comeing from a guy far smarter then I about electronics design. If he is afraid of it, it's for a good reason.
    - throwaway7767 10y ago
      > Yes that was mentioned in one of the maaaany EEVBlog videos iv watch that these fail closed sometimes as well as the recommendation that "you should never buy lipo cells without a built-in controller" comeing from a guy far smarter then I about electronics design. If he is afraid of it, it's for a good reason. If you're building a large pack you don't want cells with a built-in protection. You connect all the cells to a pack-wide BMS that keeps things safe. The important thing is to never use unprotected cells without some protection circuit in the pack.

Reason077 10y ago

It's pretty safe so long as you use a battery controller with appropriate monitoring to prevent overcharging. Recycled 18650 cells that have worked fine in laptops for years are very unlikely to suddenly explode on you for no reason. I'd be more worried about the mystery Chinese ones you can get new on the web! Here's some Materials Science students at Oxford who built packs using recycled laptop cells. They used controller software that monitors the health of each individual cell: https://m.youtube.com/watch?v=RW1Xugey8j0 https://m.youtube.com/watch?v=RW1Xugey8j0 (It's towards the end of the vid)

gravypod 10y ago
It's still not the best idea unless you can control the draw from each cell individually. Hooking these up in parallel is a horrible idea.
- deleted 10y ago
  [deleted]
whamlastxmas 10y ago
>very unlikely to suddenly explode on you for no reason It really depends on their condition. If you get some cells from a laptop and they've all fallen down to reading 1 volt, then yeah repeatedly charging them (especially at a high amperage) is going to be pretty dangerous.

asteli 10y ago

Building a pack from random cells like this is pretty much a cardinal sin with Li-Ion pack design. Cell resistance and state of health are carefully matched during pack manufacture to ensure cells charge and discharge evenly. Li-ion cells are pretty sensitive, so on top of that, large packs have battery management systems (BMS) to balance cell voltages and monitor for faults and damaged cells. Attempting to charge a pack like shown has a very real risk of causing one or more of the cells to overcharge and breach, or worse, violently catch fire.

rektide 10y ago
Yeah, very much. Some basic dilligence with a somewhat even set of cells will probably be harmless. I would not be afraid of that kind of homebuilt power-store, if some decent practices are followed. (But you should do your dilligence & check to make sure all the cells remain ok, as you start using this pack!) This... this is an hellish unbelievable nightmare, is asking for something to go wrong. It is certianly possible to invest the time & effort to balance the hell out of such a chaos-pack, but for one's own sanity, using normalized cells will save a lot of sanity & rework, and drastically decrease risks of catastrophic f-up. Don't do like this person! Do build weird electric systems though, unlike OP's way too broadscale doomsaying fear-mongering.
keenerd 10y ago
Charging the "pack" shown is impossible. There are no wires connecting any of the batteries. He made a case that can hold a bunch of cells. Not a battery pack.
- gravypod 10y ago
  That's ever beginning of a larger project I assume.

jrockway 10y ago

You have to realize that 1kWh is a lot of energy. Imagine being hit (in a world without an atmosphere) by a 60 pound suitcase falling out of an airliner flying at 45,000 feet. Same amount of energy as that battery pack. (Alternatively: the most powerful air conditioner you can buy running full blast for 30 minutes. Incidentally, that battery pack has as much energy as 100mL of gasoline, which is why gasoline-powered cars are so popular.) When you put a lot of energy in a small space and release at all at once, it's called a bomb. Li ion batteries are small bombs that can be used to power electrical devices. Some chemistries are safer than others, like A123 cells. The market did not care about safety and they went bankrupt. Energy density is king.

walrus01 10y ago
> (Alternatively: the most powerful air conditioner you can buy running full blast for 30 minutes. I can easily buy a 16 ton (1 ton = 12000 BTU/h) air conditioner, it uses a great deal more than 1kWh in 30 minutes. http://www.ebay.com/itm/Carrier-16TON-R-410A-Puron-Air-Conditioning-Unit-Heat-Pump-40RUQA16A2A6A0A0A0-/180981368202 http://www.ebay.com/itm/Carrier-16TON-R-410A-Puron-Air-Condi...
- jrockway 10y ago
  I mean to say, "plug in to your 120V 18A circuit".
  - StavrosK 10y ago
    I wonder why we have a tendency to nitpick rough estimates and go "YOU DIDN'T ACCOUNT FOR X EDGE CASE!", when even we get the gist.
    - viewer5 10y ago
      If I had to guess, it's someone who's like "I wonder how big that AC unit is" because the idea tickled their imagination, googles it, then finds that it doesn't quite match with the scenario given.

cmdrfred 10y ago

Maybe throw the whole mess into an out building with a fire suppression system of some sort? It says more details are to come, my curiosity is peaked.

userbinator 10y ago

I think your concerns are somewhat alarmist and tend to be a bit scaremongering. You may want to read an actual study about just how much HF is present in the fumes of burning cells. In this one, near the end they burned a whole laptop pack and analysed the gases that were emitted: http://www.brandforsk.se/MediaBinaryLoader.axd?MediaArchive_FileID=8605faf9-52ed-4d4e-89d6-0147c894f91f&FileName=BF_402_111_Rapport.pdf&MediaArchive_ForceDownload=true http://www.brandforsk.se/MediaBinaryLoader.axd?MediaArchive_... The relevant datapoint is on page 61: "As seen the yields of HF is much lower for the lap top cells, in fact the HF detected online was below the determined detection limit." The graphs on page 101 also show HF concentrations below 4ppm --- and keep in mind this is basically all of the gases collected from the burning pack. Looking at the safety data for HF, the permissible exposure limit is only slightly lower at 3ppm and it's immediately dangerous at 30ppm. In other words, it would be a bad idea to deliberately concentrate and inhale the fumes of a burning cell, but the HF probably isn't going to kill you. Some good ventilation of the area should be sufficient.

spdustin 10y ago
The PF6 ions in the electrolyte of some Li-ion batteries (not all use the same chemistry) will readily combine with hydrogen in the air to form HF if the battery is combusting. Cylindrical Li-ion cells, like those part of an 18650 battery, literally hold their chemistry under pressure, and a thermal runaway will normally cause the vents in the cell to release the pressure. If that's happening due to a short (which can and does happen when a cell is charged improperly, or even put under resistive load after the cell is discharged below a safe limit -- copper or other ions, depending again on battery chemistry, can literally bridge across the electrolyte to short the cathode and anode) the result of the release of pressure combined with the reactive nature of now exposed lithium is a small rocket that shoots a plume of gasses like sulfur dioxide or hydrofluoric acid. Again, this depends largely on battery chemistry, and without an MSDS on these particular cells, there's no way to know. But there's a reason why any chemist you care to phone up will say, if you tell them you're in possession of a cylinder of a compressed compound that contains fluorine (it won't matter what kind, fluorine really really likes to bond promiscuously and with reckless abandon), they'll tell you that you're braver they are. Tell them you're intend to string up a few hundred of them and pass an electric current into them, and they'll call a hazmat team for you. A casual stroll through forums frequented by flashlight fans (yeah, it's a thing) and you'll see plenty of demonstrations of what happens when a Li-ion cell begins a thermal runaway. And plenty of memorials to those who gave up their passion because they're on ventilators after experiencing profound damage to their lung tissues. Hell, ask the firefighters that respond to a fire at a battery recycling plant; granted, that's a bigger scale than one cell, but even one cell in a small room can, depending on its chemistry and how violently it's outgassing, emit enough HF to cause lung damage. Read an MSDS yourself: http://www.uscg.mil/hq/cg4/cg432/docs/msds/MSDS_LiIon.pdf http://www.uscg.mil/hq/cg4/cg432/docs/msds/MSDS_LiIon.pdf LiPo "pouches" mentioned elsewhere in this thread are much less likely to explode spectacularly before bursting, and much less likely to exhaust a plume of corrosive, toxic chemicals in their wake.

Confusion 10y ago

For those wondering about how nasty HF is: http://blogs.sciencemag.org/pipeline/archives/2004/03/03/things_i_wont_touch_1 http://blogs.sciencemag.org/pipeline/archives/2004/03/03/thi...