7 ms·

This seems like a great way to burn down your house and potentially injure firefighters coming to your rescue. Seriously this is quite a few leagues above norma

This seems like a great way to burn down your house and potentially injure firefighters coming to your rescue. Seriously this is quite a few leagues above normal DIY territory. Proceed with caution.

jpm_sd 9y ago
yep. incredibly dangerous. UL would not be impressed. [I have worked in lithium-ion battery design and testing for >10yr]
- ropeadopepope 9y ago
  Do you mind if I pick your brain about something? How feasible is it to homebrew a BMS for a Lithium-Cobalt battery pack that's relatively certain not to burn your house down? I know not going with a BMS at all is a huge nono. Lots of people in the e-bike community have found out the hard way how difficult it is to manage a battery pack without one.
  - jpm_sd 9y ago
    Cobalt cells always have an alarmingly non-zero chance of burning your house down, no matter how good your BMS is. Designing a BMS is a task for an experienced electrical & firmware engineer[ing team].
aaroninsf 9y ago
My thought exactly. Paging /r/osha
VectorLock 9y ago
Mixed batteries of unknown provenance/capacity without balancing isn't something I'd want in my basement personally.
- pmorici 9y ago
  If you watch the video it isn't quite what the headline suggests. The guy is collecting 18650 cells from old laptop batteries and using them with his own BMS to build a new battery. Not exactly mixing and matching rando used batteries.
  - jpm_sd 9y ago
    "collecting 18650 cells from old laptop batteries" is literally "mixing and matching rando used batteries". well, cells anyway.
    - pmorici 9y ago
      The dude in the video is using what appears to be the same type of cell.
      - ropeadopepope 9y ago
        It's still mixing and matching. Different cells that have been used in different ways have different resistances. That causes each cell to charge and discharge at slightly different rates. Over time, you'll wind up overcharging one of those cells in relation to the others and burn your house down. http://www.concordmonitor.com/electrical-bike-starts-fire-in-Boscawen-12134845 http://www.concordmonitor.com/electrical-bike-starts-fire-in...
        dlhavema 9y ago
        most of these I have seen have the charge protection tabs on the top. are the laptop batteries different? most of my experience is from buying fresh cells to use as caving headlamp batteries back in the day.
        dragontamer 9y ago
        > most of these I have seen have the charge protection tabs on the top. That depends on the cell. Some cells have charge protection. Others don't. The 18650 cell is standardized only in size-and-shape. The actual protection, chemicals, and other specifications are completely different from cell to cell. Heck, some 18650s have 3.2V nominal voltage, while others have 3.7V. IIRC, charge protection causes a voltage drop. So some applications prefer to use unprotected cells (with the overall device implementing charge protection elsewhere). For example, Laptops probably have ONE charge-protection circuit somewhere in their construction, rather than 6-charge protection circuits (each cell). This simple fix will cause 1/6th the voltage drop compared to 6x individual charge protection circuits.
nikodunk 9y ago
Caution, yes. But most things in hardware come with varying degrees of risk. If you make a chair it could collapse. Clothes? Toxins. Electric car? Explosive. Is the upside of "living in the future and building what's missing" not worth it though if you're cautious with the risk?
- matte_black 9y ago
  It is absolutely not worth it. There’s nothing futuristic about this DIY project.
- amluto 9y ago
  Unknown toxins in clothing is one thing. Building a device attached to your electrical wiring that likely violates the electrical code and puts firefighters as risk is something else entirely.
  - vvanders 9y ago
    Not just firefighters but linemen as well. If those things don't disconnect when the power goes out and have a physical lockout for switch over to battery power they can easily kill someone working on the line.
    - bluGill 9y ago
      Fortunately for linemen this risk isn't quite as high as it seems. If you are feeding power back power to the grid when it should be off your neighbors are likely to use enough power as to blow your local circuit breakers. Do not use the above as an excuse to not have proper backfeed prevention on your system. It is a last resort that might save a life, but there is always the possibility that the isolated section is small enough that you can supply your neighbors without blowing any breakers.
      - vvanders 9y ago
        That's assuming that your mains breaker is actually functioning, usually not too many of them get tested at 100-300A since the per-circuit ones trip first. Last time I read up on backfeeding one of the common refrains was that flipping the main breaker on many homes still left one leg hot back to the transformer. Totally out of spec but common enough to be called out. Hence why a transfer switch is legally required if you're going to run your house from a generator/etc.
ChuckMcM 9y ago
Exactly right. It will catch on fire, it will burn down the house. I expect the insurance would not cover it (just like it doesn't cover fires caused by storing gas or propane in your garage) I got a crash course on battery charging subtleties when building battle bots and there are many ways this can so south quickly, not the least of which is a battery in the middle of the pack developing dendrites and deciding its time to burn. The only way to prevent that is to have temperature sensors on every battery and a good enough model of the heat convection between the internal battery and the surface to recognize the temperature rise of a battery on its way to failing. Even with modern "battery monitor" chips like the ones Maxim and others sell there are corners in charge rate/temperature/battery that can get away from the algorithm before it recognizes a battery failure. The reasons this is "easy" with flooded lead/acid batteries is that, when they fail, the lead doesn't then turn into a torch at 500 - 600 degrees F. So you have a chance to fix failures and move on.
- fr0sty 9y ago
  > I expect the insurance would not cover it. I see this blanket assertion in lots of comment threads, but never with a citation. > (just like it doesn't cover fires caused by storing gas or propane in your garage)? This is an assertion I have never seen before. It is extremely common to keep gas cans in the garage around here (IL, USA), where else would you keep them that is safer?
  - Hello71 9y ago
    I googled "insurance fire caused by gasoline in garage" and found https://cpsc.gov/content/consumers-warned-against-storing-gasoline https://cpsc.gov/content/consumers-warned-against-storing-ga... as the third result. "CPSC also warns consumers that private storage of more than a limited amount of gasoline (usually five gallons or less) is illegal in many areas, and subsequent fire damage may not be covered by insurance policies." although IANAL, storing a large quantity of lithium ion batteries seems likely to be considered negligence, which is generally not covered under insurance.
  - ChuckMcM 9y ago
    I have discussed it at length with the USAA insurance people, I expect there are policy documents on their web site. The exact discussion was, "If the source of the fire is tracked back to a leaking gas can or a propane tank we won't cover the loss, we recommend you store flammables in a shed away from your house." My impression from them was they were very dubious about "off book" uses of things as well, which leads to my expectation that they would push back on covering a loss due to a "home made" battery wall. Could I sue them and get them to cover it? I don't know, perhaps. But, as with my propane tanks, I would keep this stuff out away from the house to limit my losses and avoid having to go there.
2474 9y ago
Yes, obviously do not try this unless you have tremendous electrical engineering knowledge. However, I do give kudos in finding a DIY solution to reuse what would likely just become waste in some landfill.
- blacksmith_tb 9y ago
  I would hope most of the lithium in old 18650s is recycled? But maybe that's me being overly optimistic.
simple00 9y ago
Don't even think about building something like that yourself in your home. If one of the cells gets damaged it can set of a chain reaction which will burn down everything around it. A fire like this is quite hard to extinguish, similar to the teslas that burn down sometimes ( https://www.youtube.com/watch?v=vYKTTCNUV3o https://www.youtube.com/watch?v=vYKTTCNUV3o ). Using lithium iron phosphate batteries might be a safer alternative.
PaulHoule 9y ago
If Tesla assumes liability for a PowerWall disaster than the $3500 price is a bargain.
JshWright 9y ago
As a firefighter, this is absolutely terrifying. We are not expecting this sort of hazard in a "routine" house fire.

This seems like a great way to burn down your house and potentially injure firefighters coming to your rescue. Seriously this is quite a few leagues above normal DIY territory. Proceed with caution.

jpm_sd 9y ago

yep. incredibly dangerous. UL would not be impressed. [I have worked in lithium-ion battery design and testing for >10yr]

ropeadopepope 9y ago
Do you mind if I pick your brain about something? How feasible is it to homebrew a BMS for a Lithium-Cobalt battery pack that's relatively certain not to burn your house down? I know not going with a BMS at all is a huge nono. Lots of people in the e-bike community have found out the hard way how difficult it is to manage a battery pack without one.
- jpm_sd 9y ago
  Cobalt cells always have an alarmingly non-zero chance of burning your house down, no matter how good your BMS is. Designing a BMS is a task for an experienced electrical & firmware engineer[ing team].

aaroninsf 9y ago

My thought exactly. Paging /r/osha

VectorLock 9y ago

Mixed batteries of unknown provenance/capacity without balancing isn't something I'd want in my basement personally.

pmorici 9y ago
If you watch the video it isn't quite what the headline suggests. The guy is collecting 18650 cells from old laptop batteries and using them with his own BMS to build a new battery. Not exactly mixing and matching rando used batteries.
- jpm_sd 9y ago
  "collecting 18650 cells from old laptop batteries" is literally "mixing and matching rando used batteries". well, cells anyway.
  - pmorici 9y ago
    The dude in the video is using what appears to be the same type of cell.
    - ropeadopepope 9y ago
      It's still mixing and matching. Different cells that have been used in different ways have different resistances. That causes each cell to charge and discharge at slightly different rates. Over time, you'll wind up overcharging one of those cells in relation to the others and burn your house down. http://www.concordmonitor.com/electrical-bike-starts-fire-in-Boscawen-12134845 http://www.concordmonitor.com/electrical-bike-starts-fire-in...
      - dlhavema 9y ago
        most of these I have seen have the charge protection tabs on the top. are the laptop batteries different? most of my experience is from buying fresh cells to use as caving headlamp batteries back in the day.
        dragontamer 9y ago
        > most of these I have seen have the charge protection tabs on the top. That depends on the cell. Some cells have charge protection. Others don't. The 18650 cell is standardized only in size-and-shape. The actual protection, chemicals, and other specifications are completely different from cell to cell. Heck, some 18650s have 3.2V nominal voltage, while others have 3.7V. IIRC, charge protection causes a voltage drop. So some applications prefer to use unprotected cells (with the overall device implementing charge protection elsewhere). For example, Laptops probably have ONE charge-protection circuit somewhere in their construction, rather than 6-charge protection circuits (each cell). This simple fix will cause 1/6th the voltage drop compared to 6x individual charge protection circuits.

nikodunk 9y ago

Caution, yes. But most things in hardware come with varying degrees of risk. If you make a chair it could collapse. Clothes? Toxins. Electric car? Explosive. Is the upside of "living in the future and building what's missing" not worth it though if you're cautious with the risk?

matte_black 9y ago
It is absolutely not worth it. There’s nothing futuristic about this DIY project.
amluto 9y ago
Unknown toxins in clothing is one thing. Building a device attached to your electrical wiring that likely violates the electrical code and puts firefighters as risk is something else entirely.
- vvanders 9y ago
  Not just firefighters but linemen as well. If those things don't disconnect when the power goes out and have a physical lockout for switch over to battery power they can easily kill someone working on the line.
  - bluGill 9y ago
    Fortunately for linemen this risk isn't quite as high as it seems. If you are feeding power back power to the grid when it should be off your neighbors are likely to use enough power as to blow your local circuit breakers. Do not use the above as an excuse to not have proper backfeed prevention on your system. It is a last resort that might save a life, but there is always the possibility that the isolated section is small enough that you can supply your neighbors without blowing any breakers.
    - vvanders 9y ago
      That's assuming that your mains breaker is actually functioning, usually not too many of them get tested at 100-300A since the per-circuit ones trip first. Last time I read up on backfeeding one of the common refrains was that flipping the main breaker on many homes still left one leg hot back to the transformer. Totally out of spec but common enough to be called out. Hence why a transfer switch is legally required if you're going to run your house from a generator/etc.

ChuckMcM 9y ago

Exactly right. It will catch on fire, it will burn down the house. I expect the insurance would not cover it (just like it doesn't cover fires caused by storing gas or propane in your garage) I got a crash course on battery charging subtleties when building battle bots and there are many ways this can so south quickly, not the least of which is a battery in the middle of the pack developing dendrites and deciding its time to burn. The only way to prevent that is to have temperature sensors on every battery and a good enough model of the heat convection between the internal battery and the surface to recognize the temperature rise of a battery on its way to failing. Even with modern "battery monitor" chips like the ones Maxim and others sell there are corners in charge rate/temperature/battery that can get away from the algorithm before it recognizes a battery failure. The reasons this is "easy" with flooded lead/acid batteries is that, when they fail, the lead doesn't then turn into a torch at 500 - 600 degrees F. So you have a chance to fix failures and move on.

fr0sty 9y ago
> I expect the insurance would not cover it. I see this blanket assertion in lots of comment threads, but never with a citation. > (just like it doesn't cover fires caused by storing gas or propane in your garage)? This is an assertion I have never seen before. It is extremely common to keep gas cans in the garage around here (IL, USA), where else would you keep them that is safer?
- Hello71 9y ago
  I googled "insurance fire caused by gasoline in garage" and found https://cpsc.gov/content/consumers-warned-against-storing-gasoline https://cpsc.gov/content/consumers-warned-against-storing-ga... as the third result. "CPSC also warns consumers that private storage of more than a limited amount of gasoline (usually five gallons or less) is illegal in many areas, and subsequent fire damage may not be covered by insurance policies." although IANAL, storing a large quantity of lithium ion batteries seems likely to be considered negligence, which is generally not covered under insurance.
- ChuckMcM 9y ago
  I have discussed it at length with the USAA insurance people, I expect there are policy documents on their web site. The exact discussion was, "If the source of the fire is tracked back to a leaking gas can or a propane tank we won't cover the loss, we recommend you store flammables in a shed away from your house." My impression from them was they were very dubious about "off book" uses of things as well, which leads to my expectation that they would push back on covering a loss due to a "home made" battery wall. Could I sue them and get them to cover it? I don't know, perhaps. But, as with my propane tanks, I would keep this stuff out away from the house to limit my losses and avoid having to go there.

2474 9y ago

Yes, obviously do not try this unless you have tremendous electrical engineering knowledge. However, I do give kudos in finding a DIY solution to reuse what would likely just become waste in some landfill.

blacksmith_tb 9y ago
I would hope most of the lithium in old 18650s is recycled? But maybe that's me being overly optimistic.

simple00 9y ago

Don't even think about building something like that yourself in your home. If one of the cells gets damaged it can set of a chain reaction which will burn down everything around it. A fire like this is quite hard to extinguish, similar to the teslas that burn down sometimes ( https://www.youtube.com/watch?v=vYKTTCNUV3o https://www.youtube.com/watch?v=vYKTTCNUV3o ). Using lithium iron phosphate batteries might be a safer alternative.

PaulHoule 9y ago

If Tesla assumes liability for a PowerWall disaster than the $3500 price is a bargain.

JshWright 9y ago

As a firefighter, this is absolutely terrifying. We are not expecting this sort of hazard in a "routine" house fire.