Car Alternators Make Great Electric Motors; Here’s How

The humble automotive alternator hides an interesting secret. Known as the part that converts power from internal combustion into the electricity needed to run everything else, they can also themselves be used as an electric motor.

The schematic of a simple automotive alternator, from US patent 3329841A filed in 1963 for Robert Bosch GmbH .
The schematic of a simple automotive alternator, from US patent 3329841A filed in 1963 for Robert Bosch GmbH.

These devices almost always take the form of a 3-phase alternator with the magnetic component supplied by an electromagnet on the rotor, and come with a rectifier and regulator pack to convert the higher AC voltage to 12V for the car electrical systems. Internally they have three connections to the stator coils which appear to be universally wired in a delta configuration, and a pair of connections to a set of brushes supplying the rotor coils through a set of slip rings. They have a surprisingly high capacity, and estimates put their capabilities as motors in the several horsepower. Best of all they are readily available second-hand and also surprisingly cheap, the Ford Focus unit shown here came from an eBay car breaker and cost only £15 (about $20).

We already hear you shouting “Why?!” at your magical internet device as you read this. Let’s jump into that.

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Turn By Turn Driving Directions From A Turntable

Many of us now carry a phone that can give us detailed directions from where we are to a destination of our choosing. This luxury became commonplace over the last decade plus, replacing the pen-and-paper solution of consulting a map to plan a trip and writing down steps along the way. During the trip we would have to manually keep track of which step we’re on, but wouldn’t it have been nice to have the car do that automatically? [Ars Technica] showed us that innovators were marketing solutions for automatic step by step driving directions in a car over a 100 years ago.

Systems like the Jones Live-Map obviously predated GPS satellites, so they used vehicle odometry. Given a starting point and a mechanical link to the drivetrain, these machines can calculate miles traversed and scroll to the corresponding place in the list of instructions. This is a concept that has been used in many different contexts since, including the “Next Bus in 7 Minutes” type of display at bus stops. Because a bus runs a fixed route, it is possible to determine location of a bus given its odometer reading transmitted over radio. This was useful before the days of cheap GPS receiver and cellular modems. But the odometry systems would go awry if a bus rerouted due to accidents or weather, and obviously the same would apply to those old school systems as well. Taking a detour or, as the article stated, even erratic driving would accumulate errors by the end of the trip.

The other shortcoming is that these systems predated text-to-speech, so reading the fine print on those wheels became a predecessor to today’s distracted driving problem. One of the patent diagrams explained the solution is to hand the device to a passenger to read. But if there’s a copilot available for reading, they can just as easily track the manual list of directions or use a map directly. The limited utility relative to complexity and cost is probably why those systems faded away. But the desire to solve the problem never faded, so every time new technology became available, someone would try again. Just as they did with a tape casette system in the 1970s and the computerized Etak in the 1980s.

[Photo by Seal Cove Auto Museum]

A Behind The Scenes Look At Small Scale Production

Back in 2013, [Karl Lautman] successfully got his kinetic sculpture Primer funded on Kickstarter. As the name implies, you press the big red button on the front of the device, and the mechanical counter at the top will click over to a new prime number for your viewing pleasure. Not exactly a practical gadget, but it does look pretty slick.

These days you can still by your very own Primer from [Karl], but he tells us that the sales aren’t exactly putting food on the table. At this point, he considers it more of a self-financing hobby. To illustrate just what goes into the creation of one of these beauties, he’s put together a time-lapse video of how one gets built from start to finish, which you can see after the break.

Even if you’re not interested in adding a mathematics appliance to your home, we think you’ll agree that the video is a fascinating look at the effort that goes into manufacturing a product that’s only slightly north of a one-off creation.

The biggest takeaway is that you really need to be a jack of all trades to pull something like this off. From milling and polishing the metal components to hand-placing the SMD parts and reflowing the board, [Karl] demonstrates the sort of multi-disciplinary mastery you need to have when there’s only one person on the assembly line.

Small scale manufacturing isn’t cheap, and is rarely easy. But stories like this one prove it’s certainly possible if you’re willing to put in the effort.

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