Rewinding A Car Alternator For 240 Volt

February 3, 2026 by Maya Posch 22 Comments

Two phases installed on the stator. (Credit: FarmCraft101, YouTube)

As part of his quest to find the best affordable generator for his DIY hydroelectric power system, [FarmCraft101] is trying out a range of off-the-shelf and DIY solutions, with in his most recent video trying his hands at the very relaxing activity of rewiring the stator of an alternator.

Normally car alternators output 12VDC after internal rectification, but due to the hundreds of meters from the turbine to the shed, he’d like a higher voltage to curb transmission losses. The easiest way to get a higher voltage out of a car alternator is to change up the wiring on the stator, which is definitely one of those highly educational tasks.

Disassembling an alternator is easy enough, but removing the copper windings from the stator is quite an ordeal, as they were not designed to ever move even a fraction of a millimeter after assembly.

With that arduous task finished, the rewinding was done using 22 AWG copper enamel wire, compared to the original 16 AWG wire, and increasing the loops per coil from 8 to 30. This rewinding isn’t too complicated if you know what you’re doing, with each coil on each of the three windings placed in an alternating fashion, matching the alternating South/North poles on the rotor.

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Bosch Starter Motor Freed From Mercedes Prison

January 24, 2025 by Bryan Cockfield 79 Comments

Vehicle alternators are interesting beasts. Produced on a massive scale, these electric machines are available for a minimum of cost and contain all kinds of great parts: some power electronics and a belt-driven generator are generally standard fare. This generator can also be used as a motor with only minor changes to the machine as a whole, so thanks to economies of scale it’s possible to get readily-available, powerful, compact, and cheap motors for all kinds of projects using alternators as a starting point. [LeoDJ] noticed that this starter motor in a modern Mercedes had some interesting benefits beyond all of these perks, but it took a bit more work to get up and running than a typical alternator would have.

The motor, built by Bosch, can be found in the Mercedes E200 EQ Boost. This is a hybrid car, but different than something like a Prius in that it doesn’t have an electric motor capable of powering the car on its own. Instead it uses a combination starter motor/alternator/generator to provide extra power to the engine during acceleration, increasing efficiency and performance. It can also charge the small battery bank when the car slows down. Vehicles that use this system need much beefier alternators than a standard car, but liberating it from the car means that it has much more power available than a typical alternator would.

There were a number of issues to solve, though. Being that the motor/alternator has to do all of this extra work (and that it came out of a car whose brand is known for being tedious to work on in the first place) it is much more complicated than an off-the-shelf alternator. [LeoDJ] has been able to get his to spin by communicating with it over the CAN bus, but there’s still some work to be done before it goes into something like an impressively fast electric bicycle.

Thanks to [RoganDawes] for the tip!

Restarting The Grid When The Grid Is Off The Grid

December 6, 2022 by Ryan Flowers 33 Comments

If you watch YouTube long enough, it seems like going “off the grid” is all the rage these days. But what if the thing that goes off the grid is the grid itself? In the video below the break, [Grady] with Practical Engineering explores the question: How do you restart an entire power grid after it’s gone offline? It’s a brilliantly simple deep dive into what it takes to restore power to large amounts of customers without causing major damage to not just the grid, but the power generators themselves.

What’s A Power Grid Operators Favorite Band?

The hackers among us who’ve dealt with automotive alternators know it must be excited in order to generate electricity. What does that even mean, and how does it affect the grid? Simply put, it takes power to make power. For example, old heavy equipment had what they called pony motors — a small easy to start engine that’s sole purpose was to start a much larger engine. Aircraft have auxiliary power units (APUs) for the same purpose. What do power grids have? You’ll have to watch the video to find out.

Once at least two power generators are online, grid operators can just flip the switch and start feeding power to customers, right? Not quite. [Grady] once again uses a clever test jig and an oscilloscope to show the damage that can occur if things aren’t done just right. It’s a fascinating video well worth watching.

Learn how grid operators use a Power Grid Emulator called LEGOS to help them with keeping the electrons flowing in the right direction.

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How Far Can You Push A £500 Small Electric Car; Four Years Of The Hacky Racer

June 22, 2022 by Jenny List 31 Comments

Four years ago when the idea of a pandemic was something which only worried a few epidemiologists, a group of British hardware hackers and robotic combat enthusiasts came up with an idea. They would take inspiration from the American Power Racing Series to create their own small electric racing formula. Hacky Racers became a rougher version of its transatlantic cousin racing on mixed surfaces rather than tarmac, and as an inaugural meeting that first group of racers convened on a cider farm in Somerset to give it a try. Last weekend they were back at the same farm after four years of Hacky Racer development with racing having been interrupted by the pandemic, and Hackaday came along once more to see how the cars had evolved. Continue reading “How Far Can You Push A £500 Small Electric Car; Four Years Of The Hacky Racer” →

Motorcycle Regulator By Popular Demand

May 23, 2022 by Bryan Cockfield 23 Comments

A few weeks ago we posted a build of an avid motorcycle enthusiast named [fvfilippetti] who created a voltage regulator essentially from the ground up. While this was a popular build, the regulator only works for a small subset of motorcycles. This had a large number of readers clamoring for a more common three-phase regulator as well. Normally we wouldn’t expect someone to drop everything they’re doing and start working on a brand new project based on the comments here, but that’s exactly what he’s done.

It’s important to note that the solutions he has developed are currently only in the simulation phase, but they show promise in SPICE models. There are actually two schematics available for those who would like to continue his open-source project. Compared to shunt-type regulators, these have some advantages. Besides being open-source, they do not load the engine when the battery is fully charged, which improves efficiency. The only downside is that they have have added complexity as they can’t open this circuit except under specific situations, which requires a specific type of switch.

All in all, this is an excellent step on the way to a true prototype and eventual replacement of the often lackluster regulators found on motorcycles from Aprilia to Zero. We hope to see it further developed for all of the motorcycle riders out there who have been sidelined by this seemingly simple part. And if you missed it the first time around, here is the working regulator for his Bajaj NS200.

Motorcycle Voltage Regulator Uses MOSFETs

April 29, 2022 by Bryan Cockfield 34 Comments

For how common motorcycles are, the designs and parts used in them tend to vary much more wildly than in cars and trucks. Sometimes this is to the rider’s advantage, like Honda experimenting with airbags or automatic transmissions. Sometimes it’s a little more questionable, like certain American brands holding on to pushrod engine designs from the ’40s. And sometimes it’s just annoying, like the use of cheap voltage regulators that fail often and perform poorly. [fvfilippetti] was tired of dealing with this on his motorcycle, so he built a custom voltage regulator using MOSFETs instead.

Unlike a modern car alternator, which can generate usable voltage even at idle, smaller or older motorcycle alternators often can’t. Instead they rely on a simpler but less reliable regulator that is typically no more than a series of diodes, but which can only deliver energy to the electrical system while the motor is running at higher speeds. Hoping to improve on this design, [fvfilippetti] designed a switched regulator from scratch out of MOSFETs with some interesting design considerations. It is capable of taking an input voltage between 20V and 250V, and improves the ability of the motorcycle to use modern, higher-power lights and to charge devices like phones as well.

In the video below, an LED was added in the circuit to give a visual indication that the regulator is operating properly. It’s certainly a welcome build for anyone who has ever dealt with rectifier- or diode-style regulators on older bikes before. Vehicle alternators are interesting beasts in their own right, too, and they can be used for much more than running your motorcycle’s electrical system.

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Modified Car Alternator Powers Speedy DIY E-Bike

October 25, 2021 by Tom Nardi 40 Comments

Your garden variety automotive alternator is ripe for repurposing as is, but with a little modification, it can actually be used as a surprisingly powerful brushless motor. Looking to demonstrate the capabilities of one of these rebuilt alternators, [DIY King] bolted one to the back of a old bicycle and got some impressive, and frankly a bit terrifying, results.

We should say up front that the required modifications to the alternator are quite extensive, so before you get too excited about building your own budget e-bike, you should check out the previous guide [DIY King] put together. The short version is that you’ll need to machine a new rotor and fill it with the neodymium magnets salvaged from hoverboard motors.

A custom built alternator rotor is the key to the project.

Once you’ve got your modified alternator, the rest is relatively easy. The trickiest part of this build looks like it was cutting off the bike’s rear wheel mount and replacing it with a plate that holds the alternator and a pair of reduction gears pulled from a 125cc motorbike. Beyond that, it’s largely electronics.

Naturally, you’ll also need a pretty beefy speed controller. In this case [DIY King] is using a 200 amp water-cooled model intended for large RC boats, though interestingly enough, it doesn’t seem he’s actually running any water through the thing. He’s also put together a custom 1,500 watt-hour battery pack that lives in a MDF box mounted under the seat.

To test out his handiwork, [DIY King] took to the streets and was able to get the bike up to 70 km/h (43 MPH) before his courage ran out. He thinks the motor should be able to push it up to 85 km/h, but he says the bike started wobbling around too much for him to really open it up. In terms of range, he calculated that while cruising around at a more palatable 30 km/h (18 MPH), he should be able to get 100 kilometers (62 miles) off of a single charge.

If you like repurposed motors and suicidal bike speeds, you’ll love this build that uses a washing machine motor to push a rider to a claimed 110 km/h. If you’re not worried about speed or range, then this supercapacitor e-bike is certainly worth a look as well.

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