starter motor

3 Articles

Bosch Starter Motor Freed From Mercedes Prison

January 24, 2025 by 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!

Fail Of The Week: Car Starter Motors Aren’t The Best Fit For EBikes

April 14, 2023 by 40 Comments

A lot of what real engineering is all about is designing to the limits of your materials, with a healthy margin for error. On the other hand, seat-of-the-pants engineering often takes the opposite tack — working with the materials you have and finding their limits after the fact. While the former is more rigorous and better suited to anything where life and limb are on the line, there’s something to be said for the flexibility that informal engineering offers.

[Austin Blake]’s latest eBike is a case study in informal engineering. [Austin] started out wondering if a starter motor from a car engine would make a decent electric bike motor. Our first instinct before watching the video below was to answer that question with a resounding “No!” Yes, starter motors seem like a natural for the job, delivering high torque in a compact package. But starting a car engine is the very definition of a low-duty-cycle application, since it should only take a second or two of cranking to get an engine started. Pressing a motor designed for such a task into continuous duty seems like, well, a non-starter.

And to be fair, [Austin] fully acknowledges this from the start. He even retrofits the motor, wisely replacing the shaft bushings with proper bearings in an attempt to get a better duty cycle. And it works, at least for a while — with the motor, a homebrew battery, and an ESC mounted to a bike frame, the bike was actually pretty peppy. But bearings aren’t the only thing limiting a starter motor to intermittent duty operation. The short drive really heated up the motor, and even with a few ventilation holes knocked in the motor housing, it eventually released the Magic Smoke. The video has all the gory details.

As always, we like to stress that “Fail of the Week” is not necessarily a badge of shame. We appreciate it whenever someone shows us the way not to go, as [Austin] did here. And let’s keep in mind that he’s had success with this approach before, albeit with a much, much bigger starter motor.

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Heavy-Duty Starter Motor Powers An Awesome Drift Trike

December 15, 2021 by 11 Comments

Starter motors aren’t typically a great choice for motorized projects, as they’re designed to give engines a big strong kick for a few seconds. Driving them continuously can often quickly overheat them and burn them out. However, [Austin Blake] demonstrates that by choosing parts carefully, you can indeed have some fun with a starter motor-powered ride.

[Austin] decided to equip his drift trike with a 42MT-equivalent starter motor typically used in heavy construction machinery. The motor was first stripped of its solenoid mechanism, which is used to disengage the starter from an engine after it has started. The housing was then machined down to make the motor smaller, and a mount designed to hold the starter on the drift trike’s frame.

A 36V battery pack was whipped up using some cells [Austin] had lying around, and fitted with a BMS for safe charging. The 12V starter can draw up to 1650 amps when cranking an engine, though the battery pack can only safely deliver 120 amps continuously. A Kelly controller for brushed DC motors was used, set up with a current limit to protect the battery from excessive current draw.

The hefty motor weighs around 50 pounds, and is by no way the lightest or most efficient drive solution out there. However, [Austin] reports that it has held up just fine in 20 minutes of near-continuous testing, despite being overvolted well beyond its design specification. The fact it’s operating at a tenth of its rated current may also have something to do with its longevity. It also bears noting that many YouTube EVs die shortly after they’re posted. Your mileage may vary.

For a more modern solution, you might consider converting an alternator into a brushless electric motor. Video after the break.

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