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> chainsaws, cars, and many other types of motorized or heavy equipment

You know what a bunch of those have in common? A ton of effing safety measures.

Chainsaw chaps, ROPS, etc all exist exactly because those things are so dangerous. The power density of an e-bike is at least one if not more orders of magnitude less than a 40kWh bank of batteries.

He also has the potential to not only burn down his house but kill a lineman working on the line if the power ever goes out.

All the table saws I've ever used have been super dangerous. Car crashes are a leading cause of death for young people. I could go on, these sorts of things can't be made safe while still being useful. Beyond a point, it's up to the user to understand the danger, learn behavior that minimizes risk, and pay attention when using the tool.

With all of those things, like batteries, it's not good to assume the general public can use them, so they shouldn't be as common as elevators, shopping carts, and other ubiquitous tools/machines. But it's very dis-empowering to claim only elites can use these tools.

Your final comment regarding lineman safety is completely decoupled from DIY battery pack with re-used cells. That would be a failure of the inverter in a grid-tied system. You could have an unsafe grid-tied inverter with a 100% functional battery pack with every certification in the universe and backfeed the utility lines, or I could connect a faulty battery to a proper grid-tied inverter and it would not cause the utility lines to be energized by my house when the utility shuts off the power upstream.

Additionally, you can use a home storage battery without a grid-tie inverter at all.

Your tablesaw example doesn't really disprove anything, that's why they now have riving knives[1], push sticks and lifting guards that make them a heck of a lot safer.

It's not that they can't be made perfectly safe, but that you take reasonable safety measures and mitigate risks appropriately. If he had this off in a shed ~40ft from the house that's a lot different than inside the garage.

The article didn't mention how he's connecting it to the grid so there's a very real possibility that he could have an inverter directly connected which is why we have building codes and inspections to catch things that have the possibility to kill people or do significant property damage.

[1] https://en.wikipedia.org/wiki/Riving_knife

But the dangerous tables saws were still used to build things by lots of people before 2009 when riving knifes were mandated.

I don't see why it's a crime to build a battery pack if you aren't working for Tesla.

I still don't get how you can bring up mis-wired inverter as anything related to a DIY battery pack. Without using any batteries, I can go take a wire strippers and 2 extension cords, make a male-male 120VAC cable, plug it into the gas generator in my shed and plug it into an outlet in my house when the powers out and shock a lineman.

In the country I live in we have building codes that describe how the work must be done. An owner without a license is allowed to perform that work and have it inspected and permitted. Screwdrivers aren't like lightsabers that can only work if you're a jedi (or have a college degree or certification).

I disagree with lumping every form of DIY together. Incompetent DIY projects are dangerous therefore all DIY projects are dangerous?

> Without using any batteries, I can go take a wire strippers and 2 extension cords, make a male-male 120VAC cable, plug it into the gas generator in my shed and plug it into an outlet in my house when the powers out and shock a lineman.

Yup, and that's highly illegal because it can kill someone. If you want to do that you're required by code + law to have a mains transfer switch.

I don't think anyone is saying you can't play with battery packs, it's just that this guy is a freaking idiot for doing it in his house where any miscalculation can cause a chain reaction that may kill him and his family.

It's about orders of magnitude and safety mitigations.

Look at blackpowder/low power explosive regulations. You can keep a small quantity in your house to reload/etc. However if you want to store more you need a separate shed + BATF is allowed to show up at your house and inspect it any time. Back when I was involved with amateur rocketry all of the our vendors went through this process. It's a standard thing when you're involved with elements that have a high potential energy and can go wrong if not treated with the right respect.

> Yup, and that's highly illegal

Which part? Powering your house w/out transfer switch (when disconnected to the utility), or actually back-feeding power to the utility? I would be surprised if the former was uniformly illegal across the US, but the latter certainly is.

NEC requires a proper transfer switch: https://diy.stackexchange.com/questions/22154/are-generator-...

Table saws are dangerous, yes. It is important to be careful with them.

But it's a whole different kind of stupid to recommend building your own table saw with salvaged parts and zero safety features.

"In contrast to what all the expert statisticians here have to say, I watched a guy on Youtube play Russian roulette and he was fine. I've played these kinds of "dangerous" games myself and it's always been fine. Ignore the experts, what could go wrong?"

There are all kinds of dangerous things in the world, and many can injure or kill you if you don't treat them carefully. I don't understand the callous disregard for safety concerns, nor the attacks on people with expertise and credentials in these areas, all in favor of some random guy you saw on Youtube who happened to survive and your own limited experience.

If that's your interpretation then we fundamentally disagree.

"Random guy on Youtube" happened to be an intelligent and capable human being who learned all the relevant techniques and principles from available information without paying for "credentials".

Go watch the technique used for testing, evaluating, sorting, and re-using batteries used and tell me specifically what is unsafe rather than trying to spread fear because there's no college degree/certification/other form of economic gate keeping.

I'm not attacking people with credentials, only the type of people who vaguely threaten people not to twist 120VAC wires together in a wirenut unless they understand Maxwell's Equations.

People, in general, are terrible at effectively evaluating risks.

It's my impression that those that DO understand Maxwell's equations (or any other similar field-specific factors) often overlook just how fundamentally bad others are at factoring risks. The stupidity of those assuming "it won't happen to me" is likely nearly as great as the field experts expectations that "it most definitely WILL happen to YOU".

Hmmmm, wonder if there's a maxim or law for that?

Hopefully at least some of those dabbling at the fringes will at least become better educated about the risks when reading a wider range of perspectives on it.

Anyway, quite often the idiots double-down on their beliefs and the experts fail to realize they're beating a dead horse. Welcome to human discourse.

I think the main issues it that it's always "on" and sourced with an unknown usage history. And it seems like it's placed in a location where if things were to go wrong, without proper mitigation, it could cause serious harm.

The chance of injury is probably higher with Chainsaws and cars as you say, but they are not in constant use, and usually have safeguards in place by a regulatory board.

This is the important point. A whole lot of things are dangerous when you're using them. But when you're not they're largely safe. Various saws, tools, cans of gasoline, propane, butane, etc. They're all unlikely to be used on a 'set and forget' kind of basis.

Whereas a battery bank is VERY likely to be used that way. Set it up and get on with other activities, likely including leaving the building entirely. Meanwhile the unsupervised device has an exponentially greater risk of become unstable and causing tremendous damage.

It seems like a clever idea but how much risk it poses is debatable. One would hope anyone attempting to do this is going to be dissuaded from pursuing it on a grand scale because of the various problems they're going to have along the way. But some 'mad scientist' types are never going to be dissuaded. With luck the rest of us will at least get an entertaining video clip of their disaster. Hopefully without anyone else suffering from the ignorance.