39 votes
Accepted

Why is it harder to turn a motor/generator with shorted terminals?

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 ...
TimWescott's user avatar
  • 46.2k
29 votes
Accepted

Does a generator produce voltage or current?

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 ...
Olin Lathrop's user avatar
27 votes
Accepted

Does a DC toy motor emit AC when you spin it?

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 ...
Andy aka's user avatar
  • 457k
27 votes

How can I generate voltage for a science project?

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 ...
Olin Lathrop's user avatar
26 votes
Accepted

Advantage of using AC generators in cars instead of DC generators

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 ...
Marcus Müller's user avatar
26 votes
Accepted

Can we tell which way AC power is going through a cable without cutting the cable?

A cable consists of two conductors, with a finite space between them. Let's assume they're insulated. Use capacitive sensing to determine the polarity of the instaneous voltage between them as a ...
Neil_UK's user avatar
  • 166k
21 votes

Is it safe to touch 200 volts DC?

No, most electrical regs class low voltage “safe” as below 50V DC It is not the max current but where it travels through the body and, also, when in the heart cycle it hits... So, don’t play.
Solar Mike's user avatar
  • 6,539
20 votes
Accepted

Is it safe to touch 200 volts DC?

The content maker simply declared that 200/300 volts DC is safe to touch. He didn't say this anywhere in the video, and he didn't imply it either. In the first few seconds he says: I want to kick ...
Gabriel Luci's user avatar
18 votes

Laptop failure due to constant fluctuation of AC frequency and voltage

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 ...
rundekugel's user avatar
15 votes

How can I generate voltage for a science project?

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 ...
Spehro Pefhany's user avatar
15 votes

Advantage of using AC generators in cars instead of DC generators

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 ...
Trevor_G's user avatar
  • 46.7k
14 votes

How to connect two wildly different power sources?

There are some single-chip solutions for this exact situation, called OR-ing controllers. While most of them are designed for use at low voltages (e.g. the TPS211xA, limited to 5.5 V) there are some ...
Hearth's user avatar
  • 32.6k
13 votes

Generator burnout

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 ...
Marcus Müller's user avatar
12 votes
Accepted

Does the electrical load on a generator affect its mechanical resistance?

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 ...
Christian's user avatar
  • 1,283
12 votes
Accepted

Source of initial magnetic field in an alternator

The initial field excitation, in an automotive alternator, is provided by the battery. In an automotive alternator, AC output from the star-connected 3-phase winding is rectified by a 3-phase full-...
vu2nan's user avatar
  • 18.3k
12 votes

Can we tell which way AC power is going through a cable without cutting the cable?

Since you can measure the electric field (red arrows) between both lines of the cable and the magnetic field (green arrows) around each line of the cable without cutting it, you can determine the ...
Curd's user avatar
  • 16.3k
11 votes
Accepted

Converting a DC motor to a generator

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 ...
William Brodie-Tyrrell's user avatar
11 votes

Does a DC toy motor emit AC when you spin it?

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 ...
JRE's user avatar
  • 71.4k
9 votes

Does the electrical load on a generator affect its mechanical resistance?

Yes. All the electrical output of the generator has to be provided as mechanical input, plus a bit more for losses. One horse power is roughly 750 watts. However, car alternators are relatively ...
Neil_UK's user avatar
  • 166k
9 votes
Accepted

555-timer circuit supposed to give 50% duty cycle square wave doesn't

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 ...
Wouter van Ooijen's user avatar
9 votes
Accepted

What is the maximum possible current that can mains supply can deliver?

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 ...
Neil_UK's user avatar
  • 166k
9 votes

Fruit juicer motor generates very low voltage

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 ...
Olin Lathrop's user avatar
9 votes

Why are Marx generators built like that?

You could use a parallel arrangement of resistors, but you would need very high voltage resistors, and clearances round them. The main point of a Marx is to get a very high output voltage with ...
Neil_UK's user avatar
  • 166k
9 votes
Accepted

How/where does a generator + motor dissipate heat?

The motor uses most of the input power to cause motion, not to generate heat. A 1kW motor that made 1kW of heat from 1kW of electrical power would be a very poor motor - it would more commonly be ...
JRE's user avatar
  • 71.4k
9 votes
Accepted

Is the overvoltage protection used in this circuit a normal way of doing it?

Is the overvoltage protection used in this circuit a normal way of doing it? I've seen it done this way. It's basically equivalent to a programmable zener diode i.e. nothing is shorted out; if the ...
Andy aka's user avatar
  • 457k
9 votes
Accepted

Does speeding up a diesel generator result in a better load response?

Higher RPM will proportionally raise the peak power a diesel engine can deliver - up to a point, of course. But 62Hz is just 3% more than 60Hz, so it's not very relevant. You can get similar variation ...
Kuba hasn't forgotten Monica's user avatar
8 votes

Does the electrical load on a generator affect its mechanical resistance?

This is the basic principle of generator. The energy is converted from mechanical power into electrical power, it is the opposite of motor mode where electrical power is converted into mechanical. ...
Marko Buršič's user avatar
8 votes
Accepted

Fruit juicer motor generates very low voltage

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, ...
Janka's user avatar
  • 14.3k

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