Yesss! This is what I was hoping to find last time I clicked on an HN headline "transformers from scratch", which turned out to be about machine learning: https://news.ycombinator.com/item?id=29280909
This is great. It gets into the flux density and iron loss calculations that affect the physical size of a transformer core, choosing the wire, and then exquisite detail of actually winding and finishing the thing.
I need to spend a bunch more time reading this site.
Or using the word "bandwidth" to refer to "capacity" or "data throughput" rather than "the width of the band that the signal occupies". Arrrrgh. Yes the two things are the same for certain naïve modulations, but the whole point of using a better modulation is that you get more throughput for the same bandwidth. Understanding this requires first unlearning the abuse of the term, and that's hard work for a lot of engineers who really need to understand this.
From what I've read, that's why physicists started giving things whimsical names like Quark, Charm, Strangeness, etc. The problem with using common words is that they always suggest an analogy, the analogy is never perfect, and often causes more confusion than understanding.
(Also, Murray Gell-Mann was a whimsical character to begin with).
I agree, but at the same time "Sequence-to-sequence model utilizing self-attention" doesn't roll off the tongue as well and would otherwise make the thing more difficult to talk about.
Ludens is absolutely legendary. This is part of his micro hydroelectric dam[1], which he uses to power his house, which he of course built himself.
Far different, but if you enjoyed this you may also enjoy another classic (which does not have explanation), Claude Paillard making a vacuum tube from glass and metal: https://www.youtube.com/watch?v=EzyXMEpq4qw
Incredible. I had a dream when I was a child of a house powered by small-scale hydroelectric, but learning the reality of water rights made me abandon it. It is truly inspiring to see someone live this dream.
> Transformer steel is not all born alike. Manufacturers will provide data sheets about their products (often on their web sites), where you can see what they offer. There are usually many grades, with vastly different loss characteristics. At a given flux density and frequency, a good material might have ten times less loss than a cheap material! So it pays to look, investigate, and decide intelligently what to buy. Thinner sheets normally have lower loss, and the rest of the secret lies in the exact alloy.
Okay this is what I come to HN for, thanks everybody!
I ran a high school science lab in Bolivia in 1968. It was cheaper to get a local guy to hand-wind forty centre-tap transformers, than to order them from Germany or the U.S.
There are interesting people on thebackshed.net who have been building whole house inverters, initially repurposing some Chinese inverter chip but more recently an arduino for the brains. Unfortunately a lot of the info is spread across many different build threads but a big part of it is about rewinding toroidal transformers.
Nearly all usecases for a power transformer are now better served by a switched mode power supply.
They tend to be much smaller, lighter, more efficient, cooler and cheaper. They also have features like adjustable output voltage, current limits, and overheat protection. Some can input and output AC or DC, at a configurable frequency and sometimes waveform. Some offer the same galvanic isolation that a transformer offers too.
The core of a switched mode supply usually is a transformer, or at least an inductor, but the key difference is that it operates at far higher frequencies than classic uses of transformers, which allows them to be far far smaller, and therefore cheaper for the same power output.
Those properties are all positive, but there is one glaring negative: rf radiation. I know some ham radio station builders that will not allow any switched mode power supply on their property, including wall warts and smartphone chargers.
That's a problem, especially with low-end power supplies.
I designed a switching power supply a few years ago for a specialist application - driving 1930s Teletype machines which need 120VDC 60mA.[1] A switching power supply is a spike generator. Here's the schematic.[2]
This is reasonably RF-quiet. The transformer of the switching power supply is a toroid in a metal can, so you don't get too much RF from the transformer itself. But that's not where it usually comes from. The important thing is to keep spikes out of both the input and output wiring. That's dealt with by using LTSpice to simulate the circuit, and adding small capacitors and inductors until the spikes have disappeared in both voltage and current. At the output end, note the snubber C7, R1, D10, and D11, to soak up any spikes from the inductive load, and L2, to soak up output side current spikes. There's L1 and C12, to soak up kickback from the switched input side of the power supply. Plus C10 at the power input, which is from a USB port. They're all tiny surface mount components. The inductors are ferrite beads in surface mount form.
So there are eight extra components, just to prevent unwanted RF generation.
The LTSpice simulation shows that they're all needed. The simulation was used to choose the values.
This is why good switching power supplies have more parts than bad ones. You see that in teardown videos.
Are you saying large Transformers 1 mva, 10 mva, 100 mva, 500 mva are obsolete and should be replaced by switched mode power supplies? What mva is the threshold?
For new installation, yes, for any size a switched mode supply will usually be better in all dimensions. For the largest sizes, you can't buy them off the shelf, and there design costs may dominate. But after the thing is designed, in component costs, switched mode will win. Everything scales linearly with kVA, so there is no economics crossover point for the fundamental materials.
Eventually it will be worth switching out old transformers - they contain a massive amount of valuable copper and quite valuable steel, and their lower efficiency means every year they remain in service they are wasting $$$'s of electricity.
Transformers in cities can often be replaced with much smaller switched mode units underground, allowing the building housing the old transformer to be rebuilt as luxury flats to make the project much more profitable too!
Winding your own transformer was one of those things which amazed me as a teenager: you do a simple math by calculating winding ratio and the voltage is changed at the secondary by magic...
Readit News
This is great. It gets into the flux density and iron loss calculations that affect the physical size of a transformer core, choosing the wire, and then exquisite detail of actually winding and finishing the thing.
I need to spend a bunch more time reading this site.
(Also, Murray Gell-Mann was a whimsical character to begin with).
Far different, but if you enjoyed this you may also enjoy another classic (which does not have explanation), Claude Paillard making a vacuum tube from glass and metal: https://www.youtube.com/watch?v=EzyXMEpq4qw
[1]: https://ludens.cl/paradise/turbine/turbine.html
Okay this is what I come to HN for, thanks everybody!
Here's a more modern video on winding toroids by hand.[1]
[1] https://youtu.be/sDIWNHOoNh8
They tend to be much smaller, lighter, more efficient, cooler and cheaper. They also have features like adjustable output voltage, current limits, and overheat protection. Some can input and output AC or DC, at a configurable frequency and sometimes waveform. Some offer the same galvanic isolation that a transformer offers too.
The core of a switched mode supply usually is a transformer, or at least an inductor, but the key difference is that it operates at far higher frequencies than classic uses of transformers, which allows them to be far far smaller, and therefore cheaper for the same power output.
I designed a switching power supply a few years ago for a specialist application - driving 1930s Teletype machines which need 120VDC 60mA.[1] A switching power supply is a spike generator. Here's the schematic.[2]
This is reasonably RF-quiet. The transformer of the switching power supply is a toroid in a metal can, so you don't get too much RF from the transformer itself. But that's not where it usually comes from. The important thing is to keep spikes out of both the input and output wiring. That's dealt with by using LTSpice to simulate the circuit, and adding small capacitors and inductors until the spikes have disappeared in both voltage and current. At the output end, note the snubber C7, R1, D10, and D11, to soak up any spikes from the inductive load, and L2, to soak up output side current spikes. There's L1 and C12, to soak up kickback from the switched input side of the power supply. Plus C10 at the power input, which is from a USB port. They're all tiny surface mount components. The inductors are ferrite beads in surface mount form.
So there are eight extra components, just to prevent unwanted RF generation. The LTSpice simulation shows that they're all needed. The simulation was used to choose the values.
This is why good switching power supplies have more parts than bad ones. You see that in teardown videos.
[1] https://github.com/John-Nagle/ttyloopdriver
[2] https://github.com/John-Nagle/ttyloopdriver/blob/master/boar...
Eventually it will be worth switching out old transformers - they contain a massive amount of valuable copper and quite valuable steel, and their lower efficiency means every year they remain in service they are wasting $$$'s of electricity.
Transformers in cities can often be replaced with much smaller switched mode units underground, allowing the building housing the old transformer to be rebuilt as luxury flats to make the project much more profitable too!