perestroika
@perestroika@slrpnk.net
- Comment on The Ultimate Guide to Affordable NVIS Comms (How to Build a Regional Off-Grid Radio Box) 5 days ago:
What makes me worry is the size of the “reflector”. I wonder what symbol rate it is possible to get if the “reflector” is literally everywhere above you - the time delay between start of reflection and end of reflection might be considerable.
I found a resource with practical advise about using NVIS, including using meteorological data (ionograms) to determine the best frequency, antenna diagrams and such.
- Comment on The Ultimate Guide to Affordable NVIS Comms (How to Build a Regional Off-Grid Radio Box) 5 days ago:
Thanks for dropping the abbreviation. :) For those who want text:
- Comment on A giant 'Air Battery' emerges in the Gobi Desert 1 week ago:
Given that…
The potential energy carried by Liquid Air/Nitrogen is just over 200 Wh/kg (watt hours per kilogram).
…this is on par with battery storage, but likely doesn’t need any scarce minerals.
- Comment on Lead acid battery reconditioning question 1 week ago:
Some tips: listen for bubbling. If a battery makes bubbling sound, that means it produces hydrogen. That’s not supposed to happen outside a short period at the very end of charging.
If it happens early, there could be one or several dead cells, causing other cells to experience overcharging. If it doesn’t hold a voltage of 2V per cell (6 cells = 12 volts), discontinue using, as a dead cell is then very likely present in the battery.
- Comment on How would I replace this possibly load bearing wall? 2 weeks ago:
Disclaimer: not an engineer, but I’ve built a house and squatted half a dozen.
Questions:
- how much load might it be supporting (what is the porch made of?)
- how high and long is the concrete beam and approximately how many decades old?
Ideas:
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don’t remove woodwork until you have investigated the cracked concrete, removing anything that comes loose without striking; determine for sure if the concrete is fully compromised or partly so
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if concrete is only partly compromised, one method would be cutting off the compromised layer and casting a filler, but you should re-calculate the load bearing ability of the beam as if the filler was nothing
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after this you have a concrete that can be effectively supported from below
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if you use a jack and a pillar, prefer a mechanical (not hydraulic bottle) jack, people sell and rent such instruments for temporary support, it’s a steel pillar made of 2 parts that you rotate against each other to extend
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your plan to offer support from the center and replace the framework from sides makes sense
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if water if a frequent visitor there, use treated wood
- Comment on The design behind the world's most efficient 27.81% silicon cell 1 month ago:
Pretty damn neat.
If it’s expensive, I would still think that people needing to charge cars, power up boats or supply electricity to high altitude pseudo-satellites (read: balloons that are permanently up there) or satellites will buy some.
If the price drops, solar power with far less surface is nice to have elsewhere too.
- Comment on Li-Ion fire safety, inert atmosphere 1 month ago:
Most likely, it could help slow the process (buy time for firefighters to arrive) in some percentage of cases.
Provided large amounts of nitrogen and an already empty battery (devoid of chemical energy), in a small percentage of cases, it might prevent a fire.
However, having seen a lithium polymer cell heat up from mechanical damage (a drone crash), I can confidently tell that very high temperatures can be achieved without oxygen.
- Comment on China lets fly world's largest kite in Inner Mongolia for electric power generation 1 month ago:
What puzzles me: what is the risk of wind lull at high altitude? I know that winds are terrifically fast there (100 km/h would be considered a slow day at 10 km altitude) and slow down approaching the surface, but do lulls exist at all?
- Comment on China lets fly world's largest kite in Inner Mongolia for electric power generation 1 month ago:
Yep.
5000 m2 is more or less “the size of a football field” (50 x 100 m).
5 km2 is 5000 x 1000 m, not a practical thing to get airborne with current technology.
- Comment on How to Remove Burn Mark from (acrylic ?) Sink 2 months ago:
I would likely try the methods of car headlight repair:
- fine sandpaper (e.g. 600)
- followed by ultra fine sandpaper (e.g. 900)
- followed by polishing sandpaper (e.g. 1200)
- followed by polishing paste (cerium oxide)
However, since I see that the sink has a glossy surface… I would be deterred by that. The method I mention may reach a layer which isn’t burnt, but may wear off glossy finish.
What paint to use - sorry, no idea.
- Comment on Charging the Future with Wood-Based Battery Breakthroughs 2 months ago:
This looks like it could credibly improve both safety, cost and ecological footprint. Nice. :)
(I was previously aware of peat-derived materials being used in batteries, but lignin seems to fit considerably better.)
- Comment on Creating microbial fuel cells using bacteria in your garden 2 months ago:
it doesn’t really say how much power you can get out of it, but it sounds interesting!
Not much. The manual says you can run one LED off 5 mud cells. That would imply about 3 volts and maybe 10 milliamps. Enough to show that there’s a gradient of potential, not enough to accomplish much of anything. :)
- Comment on Acquired a sliding mitre saw 4 months ago:
I cut aluminum with mine, but I will second the “be careful” part.
Aluminum can snag your saw blade with dangerous results (saw jumping upward and losing teeth in the procecess).
Ensure the work piece is clamped down very well. Ensure that the saw is either on a large level surface or better yet - bolted or clamped down. Ensure that the saw jumping cannot hurt you in any way.
When cutting aluminum, push very gently.
- Comment on Engineering Breakthrough Opens Door to Cheap Hydrogen Power 5 months ago:
Most of it, yes.
But there is no requirement to do it that way.
- Comment on Engineering Breakthrough Opens Door to Cheap Hydrogen Power 5 months ago:
Anything that brings operating temperatures down by a half while maintaining efficiency is good news. :)
- Comment on Finland warms up the world’s largest sand battery, and the economics look appealing 6 months ago:
As much as I’ve understood, yes - heat pumps have difficulty with reaching high temperatures.
- Comment on Finland warms up the world’s largest sand battery, and the economics look appealing 6 months ago:
They use resistive heating, so they can only charge it dirt cheap when there is surplus solar or wind.
- Comment on Finland warms up the world’s largest sand battery, and the economics look appealing 6 months ago:
It’s a pretty neat system:
- can be set up anywhere
- can supply high grade heat (process heat, not space heating heat)
However, heat stores are subject to scaling laws which don’t favour sand on the large scale. Large thermal stores benefit from storing heat in water, and placing the water deep underground so the boiling point rises.
For comparison Helsinki (.fi) has a 10 GWh underground thermal store. Where I live, Tallinn (.ee) will soon get a 1 GWh thermal store. And Vantaa (.fi) will soon complete a whopping 90 GWh thermal store that’s located 100 m underground, so their water will boil at 140 C instead of the usual 100 C.
- Comment on New fuel cell could enable electric aviation | MIT News 7 months ago:
With this technology, it’s just the combination of fuel and exhaust that makes it unlikely to reach peaceful applications sooner. A user of this technology must be willing to tolerate (and cause) considerable inconvenience just to increase the range of their electric aircraft.
Fuel distribution would be an annoying but surmountable problem. Not the easiest, but doable. Sodium needs to be stored either in mineral oil or inert gas. Otherwise it will spontaneously oxidize quite fast. Airports would need sodium warehouses with specialized equipment (either oil baths to submerge it or an unbreathable atmosphere). Trucks with the same kind of equipment would be needed to deliver the stuff.
Fuel production efficiency would be a problem. I don’t know the efficiency of sodium production, but intuitively this is likely to be around 80% (plus road transport). Charging a battery from the grid is more efficient, so the user of this technology must either have cheap electrical energy (this might be true in future with lots of renewables) or be willing to ignore the cost of energy (military users will do that already now).
Finally, the debate over a caustic exhaust stream is likely to be non-trivial. I predict that people will be quite worried about the direct effects of NaO and NaOH air pollution - it’s one of those things which is clearly health negative, even if climate positive. Unsurprisingly, military users are pretty unconcerned about being health negative.
- Comment on New fuel cell could enable electric aviation | MIT News 7 months ago:
Thanks for the tip, both the popular and scientific article are interesting.
Short summary of the pros an cons:
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energy density: 3 x better than lithium ion
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power density: really poor (if they raise their power density by 10 times, it will suffice for cruising, takeoff will require supplementary high-current batteries)
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exhaust: sodium oxide, converted by moisture in air to sodium hydroxide (caustic), converted by CO2 into sodium bicarbonate (harmless) --> this is a tech for cruising up high, not for takeoff or flight above settlements
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operating temperature: reasonable (about 100 C)
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mass production of sodium: doable, but somewhat messy (electrolysis of seawater?)
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fire safety: sodium burns just as bright as lithium, nothing cheerful here
My personal conclusion: currently, this is a potential military technology (“electric cruise missiles with 500 km range”), but likely won’t reach passenger or cargo aviation soon.
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- Comment on Questions on how to connect a PC to a washing machine (USB→TTL serial) 8 months ago:
Note: another really common baud rate is 9600, 8, 1.
- Comment on Questions on how to connect a PC to a washing machine (USB→TTL serial) 8 months ago:
You don’t need to connect the 5V pins. Otherwise it seems sound.
- Comment on Wind/solar motorcycle [with 50 km solar/wind range] looks like an April Fools' joke ... but it's legit 9 months ago:
I would think the drag is considerable.
I would also worry about stability in a strong side wind.
As a result, I would not like to ride the 2-wheeled version in strong side wind. The 3-wheeled version looks OK, but also suffers from drag.
Besides, to generate power from wind while parking, you would have to choose your parking direction. But you can’t always choose the parking direction - location dictates it often. That kind of a wind generator on a vehicle looks severely half-assed. They should have though two steps ahead.
- Comment on Flow Battery Research Collective: Building an Open-Source Battery for Stationary Storage (FOSDEM 2025) 11 months ago:
Nice project, I hope they arrive at good recipes. :)
- Comment on This is the first silent home wind turbine that destroys solar panels - 1500 kWh of free electricity 11 months ago:
The article triggers my hype meter, which is a bad thing if the product actualy delivers what it claims.
The design is new and looks neat, so I searched for an article with more information, and found this:
They do firmly claim a very high energy extraction rate:
Today the company officially introduced its Liam F1 Urban Wind Turbine, which is said to have an energy yield that is “80 percent of the maximum that is theoretically feasible.” That’s quite the assertion, given that most conventional wind turbines average around 25 to 50 percent.
The downside is a rotor with great surface area, and thus mass. It doesn’t weigh 20 kilograms like a bladed 1.5 meter turbine might be expected to weigh, it weighs 75 kilos.
The 75-kg (165-lb) 1.5-meter (5-ft)-wide Liam obviously doesn’t look much like a typical turbine. It draws on the form of the nautilus shell, and the screw pump invented by ancient Greek mathematician Archimedes of Syracuse.
For now, sadly, the cost is ridiculous. But I guess they need to recover their development cost somehow, and the manufacturing cost is considerably higher than with bladed turbines.
Although no price was given in today’s announcement, a previous posting on the company website puts it at €3,999 (about US$5,450).
- Comment on Will solar panels overrun farmland? The two are more likely to coexist. 11 months ago:
Indeed, vertical solar panels are fully compatible with farming. :) And it’s also smart to position them north-south, to get on the market on morning and evening hours - because midday is already “crowded” by conventional solar parks.
Also, vertical panels are more resistant to hail.
- Comment on First sodium battery urban e-bike offers 45-mile range and operates in cold weather without capacity loss 11 months ago:
A big advantage of its sodium cells is also the fact that they can retain more than 92% of their capacity even when operating at -20°C (-4 Fahrenheit) and discharging at those freezing temps.
That is very promising to hear. My current vehicle, which uses first-generation lithium batteries (made on 2011), loses almost half of its range at that temperature, and that is before heating.
- Comment on Homebrew battery 11 months ago:
Nice to know. :)
The comment from the reader John Beech (an old radio amateur) at the bottom is probably of greater practical value: he describes how he developed DIY cells to the point of running a 2 W radio.
Another way to build DIY batteries is using the iron-air chemical combination. A decent collection of recipes can be found here, using filter cartridges of activated carbon as cathodes and rebar wrapped in steel wool as anodes.
- Comment on Trump Says He Wants No Wind Turbines Built During Administration 1 year ago:
Some gusses:
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Vanity and spite. After all, he’s not emotionally mature.
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With some probability, he’s seeking attention from his supporters and needs to satisfy lobbyists who bought and propagandized his way to power. He has to deliver them goods. This is how he shows that he intends to deliver the goods… that he actually cannot deliver without changing the constitutional order very much.
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Maybe he wants to test the mettle of the terrible Renewable Industries Complex - an industry very prone to organizing coups and hiring assassins. If I were him, I’d consider twice, all the people in the solar business that I know have been extremely menacing. ;P ;P ;P
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- Comment on Dark Doldrums Overshadow Europe’s Energy Markets | Periods of low sun and wind, a weather pattern known as a Dunkelflaute, can increase electricity prices and stoke political tensions. 1 year ago:
It seems that weather patterns lasting longer is part of the new climate pattern.