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Comment by ActorNightly | Hacker News Reader

If there is anything that requires consumer protection its the batteries in these cars. The interface should not be proprietary. There should be no reason why you couldn't buy $7000 worth of batteries, put them together with BMS systems, and replace them yourself.

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I think in many cases you can. If you replace with compatible cells, you can keep the BMS. For some batteries there are reverse-engineered or alternative BMSes.

However, cells need careful soldering, and the BMS must be working properly to prevent overcharging and overheating. Mistakes can cause nasty and expensive fires, so it's not a DIY job for anybody.

Batteries need spot welding, not soldering.

It is stupidly easy to use a spot welder to put together a pack without damaging the cells compared to soldering without damaging.

The only thing I can think of is the high voltage. I don't mind working with 220v but anything higher I tend to shy away with. I think some of the voltage systems in the battery packs can peak at 800v with most of them between 400v and 600v.

The EV is also DC, significantly more dangerous than the AC at the same voltage.

Well, no, AC is more lethal, also it contracts the muscles more easily.

The high voltage ranges are different between AC and DC, with AC being lower than DC range due to the higher risk.

Even in college, I was taught AC passes on your skin away from your heart and is therefore safer at the same voltage. Is this a myth?

It's complicated and likely not at all relevant at 50 or 60 Hz frequencies. You want the sqrt(2p/ωμ) formula if you're curious.

https://en.wikipedia.org/wiki/Skin_effect

My understanding is that DC currents are more dangerous as the effect is continuous. Whereas there is some electrician humour that at least with AC you have 50 chances per second to pull away (Americans get 60 chances per second)

It's not so straightforward. Volts, amps, and frequency (in the case of AC) all play a factor in lethality of electricity.

keep in mind that peak voltage of AC is 1.4 of nominal. So keeping hat in mind, range is about same.

I've been shocked by 300V DC @ 500mA and I'll take the equivalent AC any day. Obviously both can kill you, but the DC was far more painful and instantly gave me 3rd degree burns. Also made me ululate some kind of tone I didn't even know the human throat could emit.

The consensus I've heard from a few family members who work in airport maintenance is that HVDC will make you wish you were dead, while HVAC will make you dead dead.

The voltages are not going to be high enough to cause things like arcing through air. Basic precaution is necessary.

The idea is not even that you yourself are going to replace it, its more for shops with equipment and skills to order individual cells, put together battery packs, and then just replace them in cars without worrying about compatibility.

You generally can. The problem is that the batteries are generally so specific to the car, you can't just swap them out with any random battery and expect the same performance. Additionally, given the immense power most battery packs put out, replacing individual cells (or banks) of batteries can cause an imbalance that will damage or degrade the pack over time. The best solution most of the time is to replace the entire pack at once if there's damage to a bank, and have the installer take the rest of your battery as a core rebate.

But, but... we want structural batteries. I heard.

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