What would happen to a small DC generator if it is spun at higher rpm?

[Quix270]

What would happen to a dc small generator if it is moved at more rpm that is it designed to? Does it will produce more, less or the same? I have this question since I while. Thank you

 

[anorlunda]

There are several types of DC generators, but do you mean something like this?

Open circuit and short circuit are load extremes. For intermediate cases, voltage and current depend on the load.

 

[Quix270]

Yes something like that. So for example if it’s produce 12 at 2,000 rpm at 4,000 rpm can produce more the same but not less? Right?

 

[anorlunda]

You don't say 12 what, but in general, yes. At least until something breaks.

Some quantities like power may peak at a max, then start going down as RPM increases more.

 

[berkeman]

What would happen to a dc small generator if it is moved at more rpm that is it designed to?

This question is likely about the 500W generator that you are building from scratch?

https://www.physicsforums.com/threa...gn-a-small-500w-synchronous-generator.974725/
In any case, at least in terms of failure mechanisms, a few come to mind:

• Depending on how well balanced the shaft and components are, you will start to over-stress the bearings and associated support structures as you increase past your design maximum RPM
• Since the voltage output will generally climb at higher RPM, you may run into some arcing or insulation failure issues with your wires and electrical connections
• If the increase in output voltage also results in an increase in output current, you will be heating your windings and electrical connections more than you probably designed for. The increased temperatures inside the motor housing can potentially add more stress to the bearing assemblies.

 

[Rive]

Every DC generator has AC somewhere inside. AC with metal core means losses. With high frequency (high RPM) this will increase => more heat, lower efficiency.
Up to a limit this will be handled by laminated cores: higher frequency requires thin plates. But if you run the device at significantly higher frequency than what it was designed for this won't really help.

 

[Quix270]

So if I increase rpm in a certain point it will decrease power output?

 

[anorlunda]

Yes.


I know you're trying to make a DIY hydro project. Why are you asking about higher than design RPM?

4000 RPM is likely to cause vibration problems. So electrical questions are not the only thing to worry about.

 

[Quix270]

So how car alternators don’t get ruined at different speeds?

 

[anorlunda]

So how car alternators don’t get ruined at different speeds?

They have a design max speed high enough to match top,engine RPM times the belt ratio. You asked about going higher than design speed.

In a car, the alternator begins working at about 2000 RPM engine speed. At higher speeds it can produce more, but its output is regulated by the voltage regulator. Smart voltage regulators match alternator output to the max charging current the battery can take.

Bottom line, you can't analyze the generator by itself. It is generator plus load that determines performance.

 

[Quix270]

So at the lower speed the car is moving the alternator, it produces enough current to charge the battery and then if the speed increase, that voltage is regulated?