Electric motors/generators

[NiteWulf]

I read howstuffworks.com for how electric motors work, but I have some questions. I don't have any electronics instruction and this is really just for a project or two that I've been looking at.

1. How would you increase/decrease the amount of torque in an electric motor without changing the power source (110/120 VAC @60Hz or a 9-volt battery, for ex.)? Do you increase the number of magnets or wire coils? Feel free to use whatever size and shape of motor you want here, nothing has been built yet.

2. Why aren't coils insulated? I would think that you want electricity flowing along the wire path to get the most magnetic influence.

3. If I built a basic generator (one magnet spinning in a coil), how would I regulate the power generated when rotational speed varies? Thinking about a homemade windmill. I have a lot to learn yet.

 

[CrispyFried]

Cants answer all of it but I race electric 1/10 scale radio control cars, and this is how you mess with the motors for added rpm or torque.

With DC motors, to increase torque you decrease the timeing (and get a lower rpm), to make more rpm, you increase it (at the expense of torque). You can do this by cutting the brushes or rotating the end of the motor that has the brushes.

Also more powerful DC motors seem to have less turns in the coils.

The coils are insulated, its usually some kind of coating. Just looks bare.

 

[Mday]

Originally posted by: NiteWulf
I read howstuffworks.com for how electric motors work, but I have some questions. I don't have any electronics instruction and this is really just for a project or two that I've been looking at.

1. How would you increase/decrease the amount of torque in an electric motor without changing the power source (110/120 VAC @60Hz or a 9-volt battery, for ex.)? Do you increase the number of magnets or wire coils? Feel free to use whatever size and shape of motor you want here, nothing has been built yet.

2. Why aren't coils insulated? I would think that you want electricity flowing along the wire path to get the most magnetic influence.

3. If I built a basic generator (one magnet spinning in a coil), how would I regulate the power generated when rotational speed varies? Thinking about a homemade windmill. I have a lot to learn yet.

1. that's not going to really work, I mean, how would you change the coils without changing the motor. You can use a resistor (variable) to decrease the effective power by putting it in series or parallel with the motor. Depends on what you want to do. There are motors that allow you to adjust things internally or externally, but they are designed like that. It's not like you can take a generic motor, and poof, mod it to effectively have configurable windings.

torque is another issue. if you want to spin it with more power, you would have to allow an increase in the current. consider torque here being used as a means to prevent the RPMs from decreasing when you dont want it to, i.e. more force required to stop it from spinning. if you don't apply a clutch here, you can wind up stripping some gears.

Torque and rpm are like current and voltage. Given a fixed power, they have an inverse relationship.

2. the coils are insulated, as mentioned before. they are coated in a transparent enamel. The enamels can typically take higher temperatures before their insulating ability goes to hell, i.e. melts.

3. it's hard to regulate power from a windmill, you would need another circuit attached.

The problem with windmills is that the power generated is not always consistent. They are attached to huge batteries. The system to maintain the battery (charge it) is really what regulates the power. You set up a system that is meant to put out X amount of power. When the wind conditions do not let you have X, stored power from batteries is injected (forgive the term) to boost it back to X. Of course, the magnitude of X will have to be much less than the average power the windmill can generate.

 

[Mark R]

1. With a permanent magnet (brushed) DC motor - one way of changing the torque is to change the magnets. Stronger magnets will give a lower speed, but higher torque. Weaker magnets can increase speed, but reduce torque. Reduce the strength too far, and the motor won't have enough torque to get up to full speed and will burn out.

With an AC motors (brushless) you need to change the windings. In these the mains frequency governs speed - e.g. a 3600 rpm motor is '2 pole' which means that the winding is arranged so that one pole of the electromagnet is at the top, and one at the bottom. One AC cycle (1/60 of a second) will cause the magnetic field to go one way then reverse and go back in the original direction. A magnet (or induction coil) on the rotor will follow this to perform 1 revolution in 1/60th second. You can increase torque by adding a 2nd winding at 90 degrees. In this case you can arrange the magnetic field to rotate only 180 degrees in 1/60th sec - so you get 1800 rpm. But because you've now got 2 windings pushing on the rotor, you get double torque.

Increasing power (torque x rpm) is difficult because it involves pushing more power through the windings (causing more heat), and more power through the magent cores (in AC motors) - usually, it's far easier to build/buy a bigger motor in the first place.

3. You need some for of regulation circuit. The easiest way is just to use a huge battery which is capable of absorbing any energy from the generator. However, the battery will have to be very big, and this is not a very efficient solution.
A very slightly more complicated approach is to use a more sensibly sized battery with a safety circuit* - if the safety circuit sees the voltage rise too far (battery overcharge) it just dumps any excess power into a heater or lamp (anything which can waste the power). Both these methods can be used with a simple permanent magnet generator (e.g. car alternator modded by putting bar magnets on the rotor), and the battery can store energy when the wind doesn't blow.

* the circuit can be pretty simple - at minimum a couple of resistors and a transistor - but the transistor needs to be a high power version capable of handling the full output of the generator and it will need a huge heatsink.

An alternative approach is what is used on car alternators and involves using an electromagnet in the generator - adjust the strength of the electromagnet by varying the current and you can vary the amount of power generated (as long as the wind is strong enough to keep up) - the main disadvantage of this approach is you have to have a battery to start up the generator and some sort of control circuit to control the power to the electromagnet.

If you want maximum complexity (and performance) then you can use a computer controlled DC-DC converter to match load/battery charging/discharging to the speed/performance/torque-power curve of your generator - if you are serious about wind power and have a big turbine, a sophisticated inverter/controller is a sensible investment, but they aren't cheap.

 

[Calin]

Originally posted by: CrispyFried
Cants answer all of it but I race electric 1/10 scale radio control cars, and this is how you mess with the motors for added rpm or torque.

With DC motors, to increase torque you decrease the timeing (and get a lower rpm), to make more rpm, you increase it (at the expense of torque). You can do this by cutting the brushes or rotating the end of the motor that has the brushes.

Also more powerful DC motors seem to have less turns in the coils.

The coils are insulated, its usually some kind of coating. Just looks bare.

There is some kind of enamel on the outside of the wires. It is not a very good insulator, however, it is not needed considering the coils have very little voltage difference from one to the next. Usually different levels of wires are insulated in other ways (lacquer, oiled paper strips and so on)