Very cool. Over a year and a half ago I installed a towing brake controller in my Tesla Model Y. Found the location of the plug, how to access and the pinout online (confirmed via a voltmeter..) so the car's side felt straight forward. But then I needed to find a brake controller that can work with the higher voltage (14.4v vs the normal 12v). Then built a cable from the brake controller to the connector that plugs into the car that I found on eBay. I velcro'd the controller under the dashboard. It works pretty well. I towed my small camper several times with it last year with no issues. Yay! However my little project is nothing compared to this post. Love people hacking away. So cool.
>then I needed to find a brake controller that can work with the higher voltage (14.4v vs the normal 12v)
Put a voltmeter on the battery terminals of a regular car at 2000rpm and note the voltage. You'd be surpised (the alternator can produce as high as 15V on some cars).
Automotive transients can be wild. I did a bringup with a board that had specified 100+v range specified for transients and finicky quality requirements on the output. The power supplies took up most of the (very large) board.
14v is not a transient, if your voltage was 12v with the car running, there's something wrong with the charging system (DC-to-DC in an EV, alternator/generator in an ICE)
13-14v is normal in all 12v automotive systems as the charging voltage
If I recall correctly, a fully charged lead acid battery has an open circuit voltage of 13.6V.
So the alternator has to put out at least something higher than if it’s planning on recharging the battery after 500 to 700 amps have been pulled from it for a few seconds to start the engine.
Yeah, max CV charging voltage is ~14V, max charging C rate is ~0.2C, open circuit voltage at 100% is that 13.x range. And lead acids like to stay at 100% unlike Li-ion which likes 50% +/-30%, so "12V" ICE cars just use a bus voltage of 13-14V and wire the battery there. At any given moment, the car's "12V" bus voltage MUST be above 13.x and below 14.4(absolute max).
It's a bit perplexing that those lead acid systems are referred to as "12V" systems when that figure is effectively the 0% voltage, whereas 3.7V for single Li-ion cell is the 50% voltage.
e: also, ICE transients can be in kV range, coming from ignition mechanisms. I've heard that you can literally measure engine RPM by selecting 1/dt on an oscilloscope and dividing that by cylinder count.
The nominal range for automotive systems is 10-16v. If you are designing anything for automotive use that doesn’t work reliably in that range, you are manufacturing problems for people.
This. Most cars nowadays come with the so-called "smart" alternators that vary voltage wildly depending on the current driving conditions.
One minute you might be accelerating and the onboard voltage drops as the battery supplies most of electricity. Then, as you reach the crest of a hill and start engine-braking, the car frantically tries to convert all the available kinetic energy to electricity, raising the onboard voltage to quickly charge the battery.
>This. Most cars nowadays come with the so-called "smart" alternators that vary voltage wildly depending on the current driving conditions.
Which in practice means that they do a very miserly job charging the battery and are a ton more sensitive to a battery being in less than tip top shape so you can expect your battery lifetime to go down.
But it's a "win" because they pushed the serp belt change outside of whatever interval the reviewers who calculate TCO care about and they saved .000003mph in the process.
nit: Some vehicles can use a two stage charging system where if the ECU is not trying to charge the battery and the power draw is otherwise low, the voltage sits in a lower range rather than constantly float charging the battery. This can surprise you if you're trying to diagnose a battery issue!
Yeah, this is normal. When the battery suddenly disconnects (for example of the lugs pop off) the alternator's momentum will send a massive, long-standing transient on the bus up to 100V. This is called a load dump.
Saw up to 800A on units like the FSD for the short time until the caps were full. Slow starting a SoC is a software problem, slow starting the Cs and keeping the impedance low at the same time a non-trivial hardware problem.
I typically fault anything above 15.6V as “that’s a bit high, your alternator might be on its way out” when working on automotive / caravan / camper van appliances and accessories.
you're correct. a '12v ICE' alternator generates up to 14.8-15.2v. Most automotive stuff can operate between 9ish-16ish-v , of course totally depending on the product.
of course this is just a modern interpretation. older stuff runs at 6v and some weirdo offbeat cars have a 24v/48v rail sitting around somewhere. Cop cars often had alternators that put out weird voltage ranges for certain equipment, or dual 12v for high amperage output.
Even just a "12v" automotive battery itself is mostly dead if if actually reads 12.0V. Fully charged is around 12.6 or 12.7. If a car had an electrical system that actually ran at 12 volts, the battery would always be dead.
"12v" in reference to anything automotive is very much a nominal reference.
> Whilst cranking, an ICE car will drop to around 6 volts (then maximum power is extracted according to thevenim's theorem).
> That means all computers etc will work at 6v.
Not necessarily all of them. Plenty of stuff will drop out while cranking; hopefully not the computers that run the fuel injection and ignition, though.
Not a car engineer, but those motors can be pretty high A, so this could also just be a feature that helps the starter get as much power as it can while cranking.
The specs say no less than 6volts. In the real world when the temperature drops down to -70F or colder and batteries get old the voltage goes well below that: deal with it.
You are probably right. Surprisingly the first controller I tried didn't work. I assumed the voltage was too high since it worked in my other (much older) car. I found a reference online of people that tried a particular brand/model and that's what I went for. Thankfully my car isn't the model with the internal 18v battery.
Voltage isn't the whole story, controllers also need to survive current spikes and power transients, and Tesla's rails may not look like generic 12V gear.
A while back I wanted more menu options with Firefox so I made an extension [1]. Basically when you highlight a word or a sentence on a page a menu popups up with some options like to copy, search, or lookup on Google maps. Or whatever option you want. I use it often and find it useful.
Yeah the Google Maps was my primary goal. But I was also thinking a person can add other options. For example different search engines. Or maybe your favorite AI agent search.
There's a neat way to do this that is super simple... The electricity company publishes an equation that determines the price based on the AC frequency. Ie. price_per_kwh = tan(min(max((-60 + system_frequency) * 1000, -pi/2), pi/2)).
Now every device in your home knows the price. For this to work, everyone must get the same price across the whole grid, and there must be sufficient grid capacity for energy to flow freely which isn't always the case. It will also cause issues with some very old (ie. 60+ year old) clocks with mechanical timers.
All of these issues can be fixed by updating the formula:
The published_offset would be unique to each district and adjusted from time to time to keep old clocks working properly, and sometimes to deal with limited transfer properties of the grid...
But the neat thing is that even if you don't take into account the published_offset, you still make nearly optimal economic decisions.
Great explanation about the grid being a giant machine that couple smaller machines with each other. About your last point, the buffer, I think batteries (chemical and also physical) seems to be the main key going forward.
I wonder how does it compare to hoisting a concrete (or something heavy) block up a pulley system as an energy store? When you need the energy you let it slide down pulling some steel cable that turns a generator, or multiple cables into multiple generators. Or even a cascade of concrete blocks at different heights as a space saver.
Good point. I was thinking more about areas without much water and a large field of poles each hoisting several blocks. Sort of wind turbines but without the blades.
...and even dangling heavy objects in the air and dropping them. (The creativity devoted to LDES is impressive.) But geologic constraints, economic viability, efficiency, and scalability have hindered the commercialization of these strategies.
I like your idea. We can now generate substantial amount of power from floating wind turbines. Coupled with floating batteries (ie on cargo ships) we perhaps build floating charging stations along major shipping routes. There is no need for nuclear or to only charge at ports. Would it work?
Clusters of floating wind turbines each with their own battery storage might be useful here. I imagine along strategic (ie major) shipping channels. Would it pencil out? I have no idea.
Actually thinking about it some more why not park a couple of dozen older cargo ships along major shipping route. Equip them with wind turbines and batteries in shipping containers. Now the actual cargo ships passing by can stop for a few hours, plug in and charge. Use sodium ion batteries that can support thousands of cycles. Even use regular fuel as a backup in the charging ships. You can build and maintain anywhere and then haul them to the right location.
It depends on the appreciation and in turn the property taxes. I own my house outright. Completely paid off. But the increases in property taxes is forcing us to sell and move, likely in the next 5 years. Too bad, love the neighborhood and the area.
I don't understand. The increase in property tax is forcing you to sell? How much percent is the property tax? Alternatively won't you make a windfall in the sale (I assume property tax only go up when the value goes up)
In most places in the US (california being a notable exception) taxes are reassessed regularly based on market conditions. In some areas this can result in the property taxes rising to an appreciable fraction of the mortgage rate - or in the GPs case, what the mortgage would have been, if they hadnt paid it off already.
Yeah. Unfortunately the real market value grew so fast that when the assessed value catches up over the next few years the property tax is going to take a nice chunk of my net income.
Honestly, this is not a hardship but a nice problem to have. I grew up chronically poor and I feel fortunate and grateful that we have a comfortable home that is ours with equity while a lot of people have housing insecurity.
I agree on the windfall part but selling to get that money is not that simple in the current real estate market and political climate. ie you got to live somewhere... and everywhere you desire is expensive.
If you own the house outright then how can the increased value force you to sell? You don't have a mortgage, and your property tax can't be that much more than a normal rent in the area. Can it?
Because of the rising tax rate relative to income. Ours is projected to increase to about 20% of our net income. That's why.
So yeah nice on paper that the house is worth a lot more than we bought it... but that value matters if we sell and move. There is a lot more to that decision than just the property tax, however it sort of putting a time limit to it.
For my EV, which I charge about once a week on average, with 4,000 cycles that means about 77 years!! That's a huge deal. CATL quoted 10k cycle battery too. Wow. Very cool. Yeah energy density and operating profile and all that. But color me impressed.
It’s not only about longevity in time but also in terms of miles.
For heavy users and given a standard range of 250+ miles, we are talking about a longevity of 1 000 000 miles. I never had a car with more than 200.000km (120 000 miles).
In the US you see a lot of cars with many miles on them because distances are bigger there, especially on the west coast.
Also, there's just smog you need to pass which is significantly less than in many other developed countries. Some have yearly required checks that would check all safety features like brakes, tires etcetera. That's where a lot of cars fail that would just keep driving in the US
If you look through second-hand car listings in Europe, >400,000km is not that usual to see. In places where cars are relatively expensive, folks keep them running forever...
That said, a million miles is probably enough for anyone :D
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