7 ms·

> "A new battery module isolation loss alarm has been added." This is the worst fault possible in an EV 101 scenario right here (touch metal -> instant death),

> "A new battery module isolation loss alarm has been added." This is the worst fault possible in an EV 101 scenario right here (touch metal -> instant death), so I'm surprised that with all Tesla's experience, they didn't consider an isolation leak as a serious fault. And I'm surprised that they allow the battery monitoring system to be disabled during servicing, especially the IMD (insulation monitoring device).

londons_explore 5y ago
I am constantly surprised how many systems have no isolation when it would be easy and cheap to add. For example, typical solar inverter systems don't have isolation between the AC and DC sides. That means any chafed wire can be deadly. They do at least have leakage detection, but set at a 300mA level, which probably won't save your life. Considering solar inverters already uses high frequency switching inside the per-string MPPT boost converter, it would have cost mere cents to put two windings on that inductor rather than one and get isolation with no downside. The cynic in me says manufacturers don't add safety features not required by law, even if zero cost, because in the future laws might be updated to require that safety feature, preventing reuse of hardware already sold, which is good for business.
- baybal2 5y ago
  Aren't you are mistaking galvanic isolation with insulation?
  - aetherspawn 5y ago
    Galvanic isolation is useful because it means that you have to touch 2 specific points on the affected unit simultaneously to die, rather than 1 point. Galvanically isolated systems can detect leaks on both the positive and negative sides by using a dual channel IMD. Any insulation issue is bad, but this method of detection can usually detect it before it's able to instantly kill someone per-se. Electric vehicles are an example of a galvanically isolated system (from earth) with dual channel IMD, hence you can have massive leaks such as 8-20mA before it becomes a safety issue.
    - baybal2 5y ago
      Yes..., but what difference it makes to this fire? Are you working in EE?
      - aetherspawn 5y ago
        Galvanic isolation probably wouldn't have prevented this fire, it sounds like the cells just shorted together. They would have had to short over several cells, since a non-trivial voltage is required to break down coolant, so having maintenance contactors to break the pack up into 20V or so segments may have prevented this fire. Using a mineral oil type coolant that is not electrically conductive (such as used in Tesla vehicles) would have also helped to prevent this fire. The batteries should be galvanically isolated from the casing so that if liquid causes a current flow from any point in the pack, then the maintenance contactors can be opened and the opposite side current path for the leak is interrupted. We can only assume that they are already (galvanically isolated) since anything else would be bizarre.
  - deleted 5y ago
    [deleted]
- Filligree 5y ago
  > For example, typical solar inverter systems don't have isolation between the AC and DC sides. That means any chafed wire can be deadly. They do at least have leakage detection, but set at a 300mA level, which probably won't save your life. This is very yikes. I just installed such a system. Do you know any way to test if that's a problem? And is it possible to fix without opening the inverter?
  - londons_explore 5y ago
    It's normally set that high by design because the solar panels have substantial capacitance to ground (they are large flat conductors sat just a few cm off the ground after all). The capacitance to ground wouldn't be an issue if not for the fact the inverter is non-isolated. That means current can flow to/from the grid to charge and discharge that capacitor, which is indistinguishable from AC leakage. Some inverters will allow you to lower the leakage threshold (usually with settings in a service menu), but then you're limited to just attaching 3 or so panels or getting false isolation trips.
    - Filligree 5y ago
      In my case the panels are, in fact, mounted on wooden brackets a good 1.5 meters off the ground. On the other hand, there's 20 m^2 of them.
- Reason077 5y ago
  Huh? 300 mA should barely give you a tingle unless you're talking about some very high voltages. What am I missing here?
  - throwaway9870 5y ago
    A basic knowledge of electricity. 100-200mA will kill you. https://academic.oup.com/ptj/article-abstract/46/9/968/4637975?redirectedFrom=PDF https://academic.oup.com/ptj/article-abstract/46/9/968/46379... I have heard people say "that can't be right, because a car battery can source 100+ amps and touching those terminals doesn't kill me!" The reason is because you have a high enough impedance that 100mA doesn't flow from a 12V source through your body.
    - james400 5y ago
      "It's not the voltage that kills you, it's the amps!" Wouldn't power (W) (or joules) be a better way to phrase it? Because as you said, you can't have 100mA flowing through your heart unless you ALSO have stiff enough source to actually supply that current - which implies a high compliance voltage, can't escape ohms law.
      - kortex 5y ago
        No, it's not the power, either, as low resistant paths can be extremely dangerous (such as wet skin). Really, it's a 2 dimensional space that makes for a less catchy aphorism. "It's not the voltage that kills you, it's the combination of voltage and conductivity". Honestly I kinda hate that saying. It's like "it's not the fall that kills you, it's the sudden decelleration on impact." For most situations people encounter, it's high voltage sources with more than enough power which are dangerous.
        jfrunyon 5y ago
        "The combination of voltage and conductivity" is ... current, no?
      - 5y ago
- shadowpho 5y ago
  I spent a bit working on various power supplies and sadly isolation is non-trivial nor cheap. Adding isolation (transformer vs inductor) requires changing control signals, control mechanism, size. It costs far more then mere cents, and loses some efficiency.

londons_explore 5y ago

I am constantly surprised how many systems have no isolation when it would be easy and cheap to add. For example, typical solar inverter systems don't have isolation between the AC and DC sides. That means any chafed wire can be deadly. They do at least have leakage detection, but set at a 300mA level, which probably won't save your life. Considering solar inverters already uses high frequency switching inside the per-string MPPT boost converter, it would have cost mere cents to put two windings on that inductor rather than one and get isolation with no downside. The cynic in me says manufacturers don't add safety features not required by law, even if zero cost, because in the future laws might be updated to require that safety feature, preventing reuse of hardware already sold, which is good for business.

baybal2 5y ago
Aren't you are mistaking galvanic isolation with insulation?
- aetherspawn 5y ago
  Galvanic isolation is useful because it means that you have to touch 2 specific points on the affected unit simultaneously to die, rather than 1 point. Galvanically isolated systems can detect leaks on both the positive and negative sides by using a dual channel IMD. Any insulation issue is bad, but this method of detection can usually detect it before it's able to instantly kill someone per-se. Electric vehicles are an example of a galvanically isolated system (from earth) with dual channel IMD, hence you can have massive leaks such as 8-20mA before it becomes a safety issue.
  - baybal2 5y ago
    Yes..., but what difference it makes to this fire? Are you working in EE?
    - aetherspawn 5y ago
      Galvanic isolation probably wouldn't have prevented this fire, it sounds like the cells just shorted together. They would have had to short over several cells, since a non-trivial voltage is required to break down coolant, so having maintenance contactors to break the pack up into 20V or so segments may have prevented this fire. Using a mineral oil type coolant that is not electrically conductive (such as used in Tesla vehicles) would have also helped to prevent this fire. The batteries should be galvanically isolated from the casing so that if liquid causes a current flow from any point in the pack, then the maintenance contactors can be opened and the opposite side current path for the leak is interrupted. We can only assume that they are already (galvanically isolated) since anything else would be bizarre.
- deleted 5y ago
  [deleted]
Filligree 5y ago
> For example, typical solar inverter systems don't have isolation between the AC and DC sides. That means any chafed wire can be deadly. They do at least have leakage detection, but set at a 300mA level, which probably won't save your life. This is very yikes. I just installed such a system. Do you know any way to test if that's a problem? And is it possible to fix without opening the inverter?
- londons_explore 5y ago
  It's normally set that high by design because the solar panels have substantial capacitance to ground (they are large flat conductors sat just a few cm off the ground after all). The capacitance to ground wouldn't be an issue if not for the fact the inverter is non-isolated. That means current can flow to/from the grid to charge and discharge that capacitor, which is indistinguishable from AC leakage. Some inverters will allow you to lower the leakage threshold (usually with settings in a service menu), but then you're limited to just attaching 3 or so panels or getting false isolation trips.
  - Filligree 5y ago
    In my case the panels are, in fact, mounted on wooden brackets a good 1.5 meters off the ground. On the other hand, there's 20 m^2 of them.
Reason077 5y ago
Huh? 300 mA should barely give you a tingle unless you're talking about some very high voltages. What am I missing here?
- throwaway9870 5y ago
  A basic knowledge of electricity. 100-200mA will kill you. https://academic.oup.com/ptj/article-abstract/46/9/968/4637975?redirectedFrom=PDF https://academic.oup.com/ptj/article-abstract/46/9/968/46379... I have heard people say "that can't be right, because a car battery can source 100+ amps and touching those terminals doesn't kill me!" The reason is because you have a high enough impedance that 100mA doesn't flow from a 12V source through your body.
  - james400 5y ago
    "It's not the voltage that kills you, it's the amps!" Wouldn't power (W) (or joules) be a better way to phrase it? Because as you said, you can't have 100mA flowing through your heart unless you ALSO have stiff enough source to actually supply that current - which implies a high compliance voltage, can't escape ohms law.
    - kortex 5y ago
      No, it's not the power, either, as low resistant paths can be extremely dangerous (such as wet skin). Really, it's a 2 dimensional space that makes for a less catchy aphorism. "It's not the voltage that kills you, it's the combination of voltage and conductivity". Honestly I kinda hate that saying. It's like "it's not the fall that kills you, it's the sudden decelleration on impact." For most situations people encounter, it's high voltage sources with more than enough power which are dangerous.
      - jfrunyon 5y ago
        "The combination of voltage and conductivity" is ... current, no?
    - 5y ago
shadowpho 5y ago
I spent a bit working on various power supplies and sadly isolation is non-trivial nor cheap. Adding isolation (transformer vs inductor) requires changing control signals, control mechanism, size. It costs far more then mere cents, and loses some efficiency.