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We're Charging Our Cars Wrong

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Re: We're Charging Our Cars Wrong

#161

Post by adrian_b »

tlb wrote: post #54
loeg wrote: post #28

Earlier quoted context omitted.

> as it'll have to be able to break the fault if it happens Are you talking about the case where both of the ground wires fail while charging? If either is non-functional when charging starts, it disallows charging. If one fails during charging, charging disconnects.

When a fault occurs (say a battery fluid leak to the chassis) and is detected, a mechanical relay has to open to disconnect the power from the grid. That can take 200 ms or so, which is a long time to have 400v flowing through you.

One can have in series a very fast solid-state relay (which would disconnect in some tens of microseconds at most; e.g. with IGBTs) and a mechanical relay for permanent disconnection.

This would increase the cost, but by many times less than the insulated power converters used today.

Re: We're Charging Our Cars Wrong

#162

Post by adrian_b »

mschuster91 wrote: post #143
brabel wrote: post #112

Earlier quoted context omitted.

Imagine a catastrophic fault: a dude in another car drives into your car at the petrol pump. The petrol pump starts dropping huge amounts of petrol on the ground. Part of the car wreck falls back on the ground and ignites a fire, causing the whole station to blow up, killing everyone within 100 meters. Clearly, we cannot allow petrol stations to exist.

Modern petrol pumps have break-away detection, it can recognize when the nozzle/hose is broken along the chain - I _think_ it works via the nozzle being lower gauge, which means when the flow rate suddenly increases there must be a high volume leak in the hose. And even then, it's only a few liters a minute. That's enough for a nasty fire, yes, but you can usually extinguish it with a handheld extinguisher. Cars, at…

There is really no difference between the two cases, because any EV chargers will also have multiple levels of over-current, over-voltage and short-circuit protection, i.e. both at each charger and for the entire charging station.

So not even an exploding car would be able to prevent the disconnection of the chargers by some of the protection circuits.

Re: We're Charging Our Cars Wrong

#163

Post by rcxdude »

raldi wrote: post #91

Buried deep in the article, what the clickbait headline alludes to: Car chargers are too complicated and expensive. We can make them simpler and cheaper while keeping them safe, which would let us build many more charging stations.

I must say I'm a little confused by their proposal: yes, the later stages of the power conversion in the charger provide the galvanic isolation, but they also provide a more essential role of voltage conversion and current regulation. Connecting a battery directly to a grid-connected rectifier is likely to get melty and or explodey pretty quick, as huge amounts of current will flow in either direction to try to equalise the almost certainly quite-unequal voltages.

Fast chargers work because they can regulate the current flowing into the battery and convert the grid voltage to allow that to happen. Batteries are charged by feeding them with a constant current until you reach a certain voltage near 100% charge, then letting the current drop to get to a complete charge (which is part of why 20% to 80% charges are much faster than complete charges). This is 100% not what you get if you just cut out the charge circuit completely, you instead get a blown fuse at best or a fire at worst. There may be cheaper options for the charge circuit if you don't need them to provide the isolation, but they don't really discuss that, they just talk as if the cost would go to zero.

(For slow charging, this circuit still exists, it's just in the car instead. But it's quite hard to fit something that can handle the power involved in fast charging into a car, which is why it's in the charger side instead).

Re: We're Charging Our Cars Wrong

#164

Post by theshrike79 »

monero-xmr wrote: post #118
raldi wrote: post #91

Buried deep in the article, what the clickbait headline alludes to: Car chargers are too complicated and expensive. We can make them simpler and cheaper while keeping them safe, which would let us build many more charging stations.

Where I live the electricity is primarily generated by fossil fuels. The light is weak for many months of the year, and wind power is apparently way too expensive if they remove the subsidies (weird!). Wouldn’t gas cars just eliminate the middleman of fossil fuels -> power plant -> car? Like we did before EVs? I would love nuclear power but it doesn’t appear to be happening

Electric engines are 90-95 efficient in converting power to motion.

Even the very best experimental gasoline engines in Toyota's labs are around 30-35% efficient.

Even if all gasoline and diesel was used in massive generator units to produce electricity, EVs would still be better for the environment and the total gasoline/diesel usage would go down.

Re: We're Charging Our Cars Wrong

#165

Post by stavros »

Dylan16807 wrote: post #157
stavros wrote: post #156

Earlier quoted context omitted.

Ahh, I didn't realize "outlet" referred to just the socket, thanks. In that case, isn't the GP describing pretty much a level 2 AC charger? Those don't come with cables (at least here).

Pretty much. They're saying put in really cheap and reliable power sources with a cheap and reliable funding mechanism. And put them everywhere. Only go to level 2 if it's just as easy and reliable as level 1, prioritize ubiquity over speed.

That makes sense, thanks.

Re: We're Charging Our Cars Wrong

#166

Post by theshrike79 »

monero-xmr wrote: post #127
MostlyStable wrote: post #123

Earlier quoted context omitted.

I guess it depends on your driving habits and homecharging situation, but after a year with my EV, I wouldn't go back if God came down and personally told me that every EV resulted in a baby seal being clubbed. Among the many advantages, never having to go to a gas station is so much better.

Why is going to a gas station difficult? I’m far more concerned about needing to charge in a pinch than needing to find a gas station

There are no gas stations on my route. I'd need to specifically drive to one.

And the one closest to my commute has a massive queue _every_ time.

I just rather drive home, plug in and the battery will be at 80-100% next morning, depending on how much I drove that day.

Re: We're Charging Our Cars Wrong

#167

Post by theshrike79 »

Elixir6419 wrote: post #10

It would be nice if instead of the fast charging problem the focus would be shifted to standardized battery packs, that can be field replaced. I don't really want to own 50-100kwh battery. I just want to use the charge in it and happy to pay for that.

Now think about a field you know. Maybe laptops or phones.

Would a standardised battery block in laptops work? The same battery would work in a Frame.work, System76, MacBook air, MacBook pro, a Lenovo Thinkbook and whatever gaming monster there is from Asus.

Sounds stupid, right? It's just as stupid for cars.

And if laptops had battery swapping, would you swap your brand new battery, but empty, to a random one at a swapping station? Would you trust the people and systems that the battery hasn't been tampered with and is in good working order?

Re: We're Charging Our Cars Wrong

#169

Post by ZeroGravitas »

robertlagrant wrote: post #142
IneffablePigeon wrote: post #120

Earlier quoted context omitted.

EVs emit less carbon even when powered by a fossil fuel dominated grid. The power plant is more efficient than your car, and often uses LNG rather than petrol or diesel, and there are still some renewables in almost any grid. In addition, air pollution close to where you live will be lower. In addition, the grid can be decarbonised over time and your car will become greener as it does.

While a power plant is more efficient than my car, transmission reduces that efficiency sigificantly (I think here in the UK transmission accounts for 40%-50% of usage, although I may be misremembering). Does that affect the calculation at all? EDIT: I was totally wrong - it's more like 7%. Still interested whether that affects the calculation, although it's much less likely to!

You might be recalling that 40-60% of the fossil fuel is wasted as heat when generating the electricity, before transmission.

Since cars are more like 80% waste heat, it still works out better to generate the electricity and feed it to EVs.

Re: We're Charging Our Cars Wrong

#170

Post by theshrike79 »

ZeroGravitas wrote: post #169
robertlagrant wrote: post #142

Earlier quoted context omitted.

While a power plant is more efficient than my car, transmission reduces that efficiency sigificantly (I think here in the UK transmission accounts for 40%-50% of usage, although I may be misremembering). Does that affect the calculation at all? EDIT: I was totally wrong - it's more like 7%. Still interested whether that affects the calculation, although it's much less likely to!

You might be recalling that 40-60% of the fossil fuel is wasted as heat when generating the electricity, before transmission. Since cars are more like 80% waste heat, it still works out better to generate the electricity and feed it to EVs.

And when burned in bigger plants the waste heat can be used to heat up homes: https://en.wikipedia.org/wiki/District_heating
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