Car Alternator as BLDC and Controller Compatibility?

Other Hardware Motors, Mechanics, Power and CNC
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I have seen different videos on YouTube where people convert car alternators into BLDC motors and run them using cheap Chinese 36V/48V BLDC controllers, whose current capabilities are far below those of a typical car alternator. For example, can a cheap 48V 30A BLDC controller safely drive a 12V 120A car alternator (modified to run as a motor)? Specifically, will the controller be able to manage the high current during heavy loads or stalls, given the alternator's low internal resistance? More specifically, are dangerously high current spikes possible during the high state of the PWM, and is the PWM signal sufficient by itself to limit the current and prevent damage in such a setup?

Thanks in advance

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Do any of the videos show the alternator running with a significant load?

For example, can a cheap 48V 30A BLDC controller safely drive ...

The question can't be answered on the forum without technical details of the controller. Try it and let us know.

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If the controller has a current limiter, you should be safe.
Of course you will not be able to run the alternator at its designed spec of 120Ax12V=1440W. The alternator will not deliver the max. torque as the current limiter will kick in at low RPM.
The motor is an inductor. So short spikes will see high resistance. When current limiter kicks in, pwm will send shorter pulses. So pwm control should work.
No guarantees!

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What was the motor use for? Did they keep the flat belt pulley and run a new flat belt to power something? Finally, what will you use the motor for?

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The first video I looked at the guy said I won't show you how to do the conversion just how to connect the ESC. So obviously bogus

In the second video I looked at he use a 1.5V AA battery to energize the rotor, so that uses brushes. Actually NOT a BLDC

In the third video the guy basically had a machine shop. He machined the rotor to accept magnets. So that was a true BLDC.

So, will you be machining your rotor and inserting magnets?

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Sorry, I didn't formulate the question correctly. In most cases, they control them as BLDC motors but use a separate power supply to energize the rotor's field windings. And yes, it's not technically correct to call this a true BLDC motor.

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I want to build test equipment to measure the electrical characteristics of different alternators at various RPMs, but I need a way to spin them. My idea is to use a larger alternator as an electric motor for this purpose, but I need to find a way to utilize its full potential as a motor. Of course, since the main idea of this project is to use cheap components, I don't want to buy an expensive controller. I can find second-hand car alternators for about $20.

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Have you developed a solution for the different types of belts used to drive the alternators?

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If you do a Google of "alternator test bench" you will find these benches normally use a variable speed DC Motor to turn the alternator. Most are belt driven with the needed fixturing. You will never get the required torque to drive an alternator while using an alternator as a motor. Once you have a mating motor drive system you will need a load bank to load your UUT (Unit Under Test). Once at test speed you want to be able to switch loads in and out to the UUT.

Anyway you will never get the horsepower you need using an alternator as a motor to drive another alternator. Do the math just to drive a 100 amp alternator and see how much drive force is needed. You will need a large motor. This is one reason that a good alternator test bench runs about $8,000 USD and up.

Ron

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