# Tag Info

39

I have to start with some terminology -- sorry if it's esoteric, but this will bring things into line with how folks talk about this subject. When you turn a permanent-magnet DC machine*, the armature generates a voltage internally. This is called the "EMF"** of the armature, or the "back EMF" if the machine is running as a motor. This EMF is always ...

27

I would be surprised if a cheap DC toy motor contained a rectifier diode since it's designed to be a DC motor, not a DC generator A cheap DC motor of the type that has a permanent magnet stator uses brushes and a rotor commutator to continually reverse the current into the rotor coil thus the effect is like feeding AC into the coil: - If you didn't do ...

27

Buy power supplies. No, really. These things are produced in large quantities and sold into a competitive market. Leave the safety design and regulatory approvals to someone else. Anyone that has to ask here won't be able to design a "efficient and cost-effective" power supply compared to commercial offerings. Even if they could, it would cost way more ...

25

No, it's not for efficiency reasons. DC generators typically have commutators, i.e. contacts with brushes that reverse the polarity of the voltage at the generator clamps every half rotation. In essence, DC generators are just AC generators that have a "mechanical" rectifier. You can build generators without any electrical contacts between moving parts, ...

20

At relatively low frequencies you can simply divide down the voltage from an ordinary function generator. Very accurate, cheap and fairly low output impedance is easy. For example a 100K resistor and a 10 ohm will give you 10uV from 100mV function generator output with 10 ohm source impedance. You can use two stages to get even lower, but below 100nV or ...

19

Internally, a generator produces voltage proportional to its speed. However, that doesn't mean a constant voltage always comes out of a generator run at a fixed speed. The windings and other parts of the generator have some electrical resistance. To a first approximation, you can think of a generator as a voltage source proportional to speed, with a fixed ...

18

There is an upper limit to the amount of power each generator can supply. That upper limit is 90 kVA. At any given time, the amount of power needed to operate the aircraft systems will vary depending on which systems are active. For example, pumping fuel between tanks presumably uses electrical power and increases the load on the generators. The amount ...

18

Don't worry. Your PSU doesn't really work with AC. Most modern PSU fist change the AC to DC via a rectifier. The internal electronic then creates an own AC used to transform the voltage to the desired one. The internal AC has a much higher frequence to be more effecient. Most PSUs work with frequencies from 0 to over 60Hz. Even DC with down to 80V is ...

15

I believe your current requirements will be modest for electrophoresis. Consider a string of 9V batteries, which will be inexpensive (\$7 at the dollar store for Panasonic batteries) and relatively safe. If you can add a 100K resistor to the taps they will be even safer, but avoid contact with the batteries. It's possible to regulate the output of the ...

15

The alternator HAS to generate A LOT of amps at a very wide range of rotation speeds. Further the electrical load can and will change drastically from moment to moment. A fixed magnet dynamo would require an extremely beefy voltage regulation system to generate the required voltages and demands. A much simpler, and in my mind, more elegent solution is ...

13

Perhaps you're under the impression that generators don't put any load on the motor, so you can spin them for free. This is not true. Any current drawn from a generator will be converted into a mechanical load. A motor is a generator and a generator is a motor. The difference is in which direction the power's flowing.

12

It should have said safely provide. But also, there's often a confusion between drawing power and drawing current. For example, you can get the maximum power out of any voltage source if your load has exactly the resistance of the internal resistance of that source. You can of course also plug in a much, much lower (practically, a "short") resistance load....

11

The frequency of your square wave is the same as your sine, it's not half. The following solution focuses on getting the 45° phase difference between sine and pulse. Differentiate the sine to get a cosine. (Note that a simple RC differentiator won't give you the required 90° phase shift. The opamp differentiator will.) Pass both sine and cosine though a ...

11

A DC motor will generate a DC voltage if you spin it. That is to say, mostly a DC voltage. It will have skips and jumps in it due to the brushes and the gaps in the commutator. The commutator is the thing that makes the output DC, by the way. When you apply DC to the motor, it moves and rotates the commutator. The commutator changes which coils are ...

10

Short Answer: Synchronizers Basically, feedback is used to keep the generator and grid in sync. There are many ways to do this. A nice overview is here. Virtually all modern power generation systems use some form of digital controller for the task. My grid-tied solar panel inverter has a PIC18F class microcontroller managing some solid-state relays (SSR) ...

9

~ People are making vibration coupling backpack type units that produce in the few Watts range. ~ A typical Chinese squeeze light when operated frenetically will give about 1 Watt. After 5 minutes of use at that level your hand drops off or feels like it has. ~ A properly build hand squeeze power unit could make more like 5 Watts at the same level of ...

9

I think you may have found a good example of something that I've been looking for which came up in my answer to this question. Namely, the difference between a sinusoidally wound motor and a trapezoidally wound motor. The way in which a motor is wound controls the distribution of the magnetic flux density throughout the motor. Which in turn controls the ...

9

Yes, if the reverse EMF of the motor and its DC resistance are specified. Good datasheets do provide these figures. At first approximation, a generator looks like a voltage source proportional to speed in series with the DC resistance of the windings. Put another way, you can usefully model a motor as a Thevenin source. Good datasheets tell you the ...

9

Any DC motor with permanent magnets can easily be a generator. It doesn't matter whether it is brushed or not; brushless motors make great generators but you will need to add a rectifier to get a DC output. If the motor has a separate field winding instead of a permanent magnet, you will need to energise that winding from an external DC source, e.g. a ...

9

The answer is not infinity, even 'theoretically'. There are at least 3 defined currents for any point on the supply, and that point can be anywhere from the terminals of a nuclear power station, down through transformers and transmission lines, right to the socket on your wall. 1) Rated current This is the maximum current it's designed to deliver, 24/7, ...

9

This depends on the type of motor. Not all motors work like generators without any electrical power applied. For example, if this is a AC induction motor, then it is only due to accidental residual magnetism that you are getting anything at all.

8

Does increasing the number of turns by $\frac{2000}{700}$ do the trick? Almost. That should change the back-emf by a factor of K = 20/7, to compensate for the change in speed. The problem is that even if you manage to rewind the motor effectively, the electric machine's resistance and inductance will increase by a factor of K2 = 8.16 -- the I2R losses ...

8

I don't design automobile alternators, so I can't say exactly what goes into the engineering decisions. However, here are some reasonable speculations. Alternator efficiency is simply not a big deal in a car. The power the engine has to put out to move the car dwarfs what the alternator requires. If this tiny fraction of overall motor power were 1/3 less ...

8

Quick Summary: Check your reactive droop control setpoints on all three machines and make sure they match. Forgive me; I don't know how much you've worked with this, so I'm going to write this for the uninitiated. When machines are in parallel, they have to share load. If their controllers are set to maintain one, specific voltage, they don't share very ...

8

The law of Conservation of Energy states: Energy can be neither created nor destroyed, but can change form, for instance chemical energy can be converted to kinetic energy in the explosion of a stick of dynamite. You put X amount of energy in, and you have to get X amount out in whatever form. In your example, you put in X amount of electrical energy. ...

8

Do you own a car? It's a very easy experiment, just turn everything electric on and you can "feel" the engine working harder. The reason for this is the magnetic field every current creates. Under no load you have the spinning magnetic field from the rotor, which creates a voltage in the stator. If there is a load a current starts to flow which creates a ...

8

If you look at the 555 internal diagram you can see that the output you use is not symmetrical: the top side is a darlington, so it has (at least) two Vbe drops. The low side is a common emitter, so it can be saturated. In short: the output low will be closer to ground than the output high will be to Vcc. One way to compensate would be a low-valued ...

8

The rotor of AC asynchronous motors is simply a lump of aluminium and iron. As there isn't any magnetically hard material involved, there is little to no residual magnetism stored and so, the motor, as it comes from the shelf, has no field. When connected to AC power, the AC in the stator first has to induce a field inside the rotor. Then the rotor starts ...

7

Rewinding as single phase makes no sense. If you have a 3-phase system it is almost always preferable to single-phase: the ripple current caused by 3-phase rectifiers is much smaller the power flow is smooth (vs. single phase which has very high 120Hz power ripple) use of copper is more efficient Not to mention that I have no idea how you would manage to ...

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