How Do Transformers Work?

So, transformers are these really cool robots that turn into cars, trucks, jets and the like. They usually end up breaking a major city, there’s some explosions, and a lot of screaming going on. It’s all because of this big war of the robots going on..



You really thought I was gonna talk about robots when we have Electrical Transformers to talk about? No, no, no. These things are just too cool to pass up. We use them EVERYWHERE. Seriously, if you live in 21st Century USA and use electronics, you have at least one transformer, but more likely, probably dozens to hundreds of them. You need them in your washer, drier, computers, cell phone chargers, TVs, and so much more. It’s amazing.


The Problem

Everything in the world runs on electricity, but the details about that electricity are different for nearly every device. Your home most likely receives AC Power from your local provider. In the US, that’s 120 VAC at 60 Hertz. What’s a little weird is that we transmit AC power everywhere, near every device in your home is run with DC Power. That’s alternating current versus direct current.

So, we’re sending the wrong kind of power to your home or business, which can’t directly power your devices. It gets worse.

The voltages are all different too. The processor in your computer needs multiple voltages. Generally at most, 1.35 Volts, plus some others. Your cell phone probably charges at 2 volts or so. Your HVAC system may have parts running up to 220 and 440 volts. We have all these competing needs for modern life. It’s not feasible to have a power plant churn out all these voltages. Only a few voltages will actually transmit well from a power station to your home or office. All the others either wouldn’t make it, or they’d launch you across the room when you plug something in. We need a way to manipulate the power to fit our needs.



Transformers alter the voltage of current. If you have 220 but you need 110, you’d use a transformer. If you have 9 volts but you need 5, you’d use a transformer or one of it’s cousins. We’re going to look at two ways of changing electrical current: an old fashioned coil transformer and a switched mode power supply.



These are probably the oldest known way of changing voltages. We have two coils of copper, that never touch each other, yet if you put power into one coil, it comes out the other. That might sound spooky or magical, but it’s not. It’s science.

When you put an electrical charge on a wire, it has the secondary effect of creating a small electro-magnetic field. Some of the energy you put in that wire goes out into this field. This is how a stud-detector also detects if there’s a live wire under it: reading that field. These electrical field is made of energy. With another wire, we can convert that field back into electricity.

We can “wirelessly” send power from one place to another. That’s cool, Mr. Tesla, but it does still beg the question, how do I put in 9 and get out 5?

The coils are different sizes. By having a big coil create an electrical current in a smaller coil, we can take all the energy of the big coil and cram it into a tighter space, raising the voltage. With a sufficiently large difference, your coil could shoot out lightning, a Tesla Coil. In day to day use, this allows us to convert up and down in currents as our hearts desire, but we do have to accept a trade off.

This is incredibly, incredibly, incredibly inefficient. You technically won’t get as much energy out of the transformer as you had to start. The problem is that we’re putting power into this coil, which is being eaten up by the coil itself. We’re losing power to the resistance of the coil. We’re losing power to the magnetic field we’re making, because the whole field cannot be converted back into usable power.

This approach does work for handling enormous amounts of power. To an extent, it’s perhaps the only way to do high voltage conversions without getting into advanced, expensive, and complicated equipment. Coils are cheap and capable of handling tiny and enormous amounts of power, but you’re making a sacrifice to save those pennies.


DC Power Switching

This second methodology only works on DC Power and only steps down voltage, but it can hit around 90% efficiency. These are the way of the future, at least for powering your computers, cellphones, and tablets. They’re compact, efficient, and reliable.

In the realm of Direct Current, it turns out you can lower the voltage by turning the power on and off. We can do this with things like relays, mosfets, transistors, and so many other little switching devices. If the power is only actually flowing for half the time, that becomes half the voltage. You can somewhat visualize it like this:


DC Power Before Conversion: ————————————————————————

DC Power After Conversion: —-   —-   —-   —–   —–   —-   —-   —–   —-   —-   —-
So, we have what looks like a five year old gone wild with a light switch or a telegraph operator who can only send one letter. We need to clean this up a bit. We need a buffer. Where the Coil transformers are always operating, and therefore, always filling the wire, we need something to capture the power we send out and make it more even. For this, we use capacitors.


DC Power After Conversion: —-   —-   —-   —–   —–   —-   —-   —–   —-   —-   —-

With Capacitor 1: ———   ———   ———   ———   ———   ———   ———

With Capacitor 2: —————————–     ——————————    ————————–

With Capacitor 3: ————————————————————————————————-


We use the capacitor to filter out the rises and dips, providing clean, constant power. Boom. We’re back where we started, steady DC power, BUT at a new, lower voltage. We didn’t need to induce any currents or do anything wild, so in large part our losses are near the same as what it was to just put the power through the wire in the first place. We have some losses from the capacitors and resistance of the equipment, but that’s about it.


Repairs and Replacement

All things fail eventually. Most transformers don’t fail until they’ve either been run to the ragged edge of performance, abused in a misconfiguration, or have had a very long working life. In both the DC Switched Mode approach the AC Coil approach, there isn’t much to go wrong.

The AC Coils are made of insulated wires that never actually touch. If any of the wires touch, the coil would short out. These wires can short out if their coating is work away or damaged, either by use over time or excessive heat causing the wires and coatings to melt. In most cases, you would replace the transformer or the entire board it’s mounted to. That’s an applicant-dependent thing. Refurbishing the transformer honestly costs more time than the replacement costs, as you have to undo all the windings, find the short, and redo them. No thanks.

Switching Power Supplies however, are a little less robust. Arguably, their Achilles heel is the capacitors. While a transistor can last seemingly forever, every capacitor fails eventually. They are, like the battery in  your car or cell phone, living on borrowed time. They tend to fail over time, leaking their oils onto the motherboard or possibly rupturing explosively. Repairs can be either a whole new board or just desoldering and replacing the failed capacitors. It depends on the skills your repair technician and how much damage the capacitors did to the board when they failed.

These sort of repairs are probably best left to your contractor or building maintenance crew. With electrical work, things get to be very, very scary. Things can look fine and perfect until you brush against the case for an air conditioner. The next thing you know, your heart’s stopped, your hair’s on fire, and Uncle Jimmy is trying to give you CPR. Don’t mess with electrical things unless you know what you’re doing and can take the appropriate precautions. This is especially a point to bring up with transformers. Replacing a low voltage component like an interface board is pretty safe because all you’ll get is a good little tingle. A 440 volt transformer is like a date with Zeus on a bad day.

The Wrap Up

As always, we welcome your feedback and input on future posts to the blog. Let us know if we’ve got something wrong or if you want to see something covered, in the comments below.


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