How do I limit the start output of a 300 amp Starter/Generator to 200 1

[crysta0728]

I want to limit the start output torque on a 300 amp generator to 200 amp, but I want the 300 amp generator to still be able to run as a 300amp gen. Are there some torque equations that I can use to create some parameters? Please help.

 

[nena0]

hello dear!

 

[WKTaylor]

This sounds like a question "best suited" for the electrical engineering forum.

Regards, Wil Taylor

 

[WoodrowJWeen]

Don't understand what limiting "output torque" on a generator would be. Generators take mechanical power (torque and speed) and put out electrical power (amps and volts). Do you mean limiting output current?

 

[MintJulep]

In very general terms there is a direct relationship between the torque generated by a motor and the current drawn by the motor, in that order.

That is to say the motor needs to be driving some load to bother trying to develop torque. No load, no torque (other than internal friction in the motor), very low current draw.

As torque demanded by the load goes up, the current draw goes up. If the torque demand exceeds the torque that can be generated by the motor the shaft stops turning, and the motor burns up.

So, the way to limit the current drawn by a motor is to limit the load.

 

[WoodrowJWeen]

The question concerned a generator not a motor.

 

[MintJulep]

WW,

The subject of the original post stated "starter/generator", which I assumed to be an electro-mechanical device that functions as a starter for an internal combustion engine that is not running, and then subesquently becomes a generator converting mechanical power from that same engine into electricity after it is running, such devices being known to exist.

Regardless, motors and generators are fundamentally the same machine.

 

[Sparweb]

Before getting too far down this garden path, let's ask Crysta0728 to please elaborate on what the problem is. It sounds like there's trouble with the battery/starter combination, and MintJ's answer is as far as we can get without more information.

Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[crysta0728]

The problem was for a starter/generator unit for a business jet size aircraft that I wanted to modify for a single engine helicopter..I wanted it to have the same generator capabilities but just limit the torque output at startup. I found the neccessary formulas and decided to go with decreasing the magnetic length versus increasing the resistance because adding another resistor would put more wieght on the aircraft and entail designing a new starter/generator. Changing the magnetic length allows me to just modify the unit currently in production. Thank you everyone for replying to my query it is much appreciated and I apologize for the unclearness of my question..I am an entry-level engineer, I just graduated college and this was my first real "engineering" project. Thanks again for all you help and input.

 

[Sparweb]

The "formula" that I'd start with would be P=T*w.
For a given power demand, Torque and RPM can be changed in inverse proportion to each other. Unfortunately, the torque required to turn the engine over is not the variable under your control. It still sounds like you have a mis-matched starter/generator, and you should use instead the starter/generators that are recommended by the engine manufacturer. To add electrical power durning operation, you can always add another generator to provide supplementary power to the main bus.


Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[thruthefence]

While I am not an engineer, I am an Aircraft mechanic with nearly 35 years experience. Lets see what happens when you tie a 40 amp hr nicad battery to a starter/generator. These are commonly series-wound motors. They will absorb whatever current is applied to them. That is, if your battery has 1000 amps available, it will absorb it & attempt to rotate whatever you have connected to it. There are current limiting devices installed on many aircraft to prevent shearing the starter quill shaft, but I would think that a 200 amp limit would prevent the powerplant from spooling up at any reasonable rate.