# Tag Info

## Hot answers tagged mains

18

An unloaded power transformer is a pure inductance. As you increase the load, the power factor improves. So, take a Variac, plug an incandescent light into it, and you should be able to dial up any power factor you like.

8

The cheaper LED lamps - the ones that use a capacitive dropper rather than a switch-mode power supply - can have a very poor power factor. The power factor could be as low as 0.2. Buy a bunch of them, and wire them in parallel to get a significant current draw.

5

I don't see any connections to the case. There should not be any connections to the case. Assuming there isn't, you should run the ground wire to the case and to the output receptacle. You can drill a hole in the case and attach both to the a screw with a lockwasher and nut. Measurements made with a multimeter on a voltage range are not reliable since the ...

4

Up to this day, I don't know the answer to the following question: Why the plastic tube connecting the metallic needles burned right in the middle? I assume the plastic tube had zero conductivity. I'm guessing that it had a cable through the middle of it for strength, and the plastic tube on the outside protected the knitting from the cable. Additionally, ...

4

simulate this circuit – Schematic created using CircuitLab Figure 1. On a split-phase supply L1 and L2 are 180° out of phase. L1 - N = 110 V. L2 - N = 110 V. L1 - L2 = 220 V. You saw something other than what you thought you saw.

4

IS this design safe? If this variac has only a two prong plug, and there is a connection between one of the prongs and the chassis, then the chassis is at neutral, not at ground. IMHO, this is NOT safe. Hopefully you have ground fault circuit breakers or their equivalent in whichever country you are in. If the neutral wire should become disconnected, while ...

3

You can buy inductors with a wide range of current and inductance ratings. An unloaded induction motor has a low power factor. If you use a single-phase motor, you can probably disconnect the capacitor if it has one. Unloaded, it should start with a little manual twist of the shaft. You may have difficulty with the distorted magnetizing current waveform if ...

3

The only way to do this is to use a time standard independent of the mains frequency. This is usually done with a crystal oscillator which has been used in watches for years since they don't connect to mains power. These oscillators are more stable than the mains frequency over short periods but will eventually drift significantly over long periods (months ...

2

As is often the case, it depends on context. If the entire waveform is present, but you you want to point out a particular half-cycle, you should say "positive half cycle" or negative half-cycle. If you have a zero-crossing switch that lets through a half cycle out of every 5 cycles then you have a series of "sinusoidal pulses" or a ...

2

You have a ground fault and thus no ground which is defined by 0 V. Neutral should be earth grounded outside at your distribution transformer and your voltage drop permitted is 10% of line on neutral if drawing maximum current in your location. (e.g. 100 or 200A) Check at breaker box and move towards the problem (inside or out) to get it fixed otherwise if ...

2

Poor power factor in practice is usually inductance-based. On the other hand, inductors for testing purposes look rather bulky and expensive. If you are OK with capacitive load, the capacitors for asynchronous motors come in various capacitances and are rated above mains voltage. They are also rather cheap. You can combine them with incandescent lamps, space ...

2

No it is not suited. Raspberry Zero power specs recommend at least 1.2A supply for the Zero itself, plus whatever the relays and other circuitry uses. Besides that model is supposed to be soldered on PCB. It would not be very safe or professional to connect it in any other way than soldering it on a PCB.

1

"Off the shelf" requests for specific devices make for shopping questions, which are forbidden, but it's ok to ask what the name of such a device is. In this case, "Power Factor Load Bank", "Resistive/Reactive Load Bank" or separate resistive and reactive banks will work for you. They look expensive. A large inductor has a ...

1

You have to know the maximum Vrms that the MOV is subject to. Go to digikey.com pick a MOV that has VAC larger by 20% than Vrms. When filtering the results in digikey.com, be informed that VAC is the RMS voltage. See here for example: https://www.littelfuse.com/~/media/electronics/datasheets/varistors/littelfuse_varistor_ciii_datasheet.pdf.pdf Take a look ...

1

I need to be able to know how much energy/ voltage and the where bouts of the circuit operates in a surge , fast transient and ESD situation and How do you calculate/simulate or choose the correct MOV model/value for the above application to pass the test conditions mentioned above ? You need to model the way in which the surges, bursts and ESD are ...

1

So, you need about 8..12 V DC on the input of 7833 (to have some room for line voltage variation). When rectified, AC voltage is multiplied by a factor of 1.4. A single rectification diode will give about 1 V voltage drop. So, the required AC voltage would be (8…12)/1.4+1 (V) = 7…10 (V), not 15 V AC. Since line isolation is not required (at this point), AC ...

1

simulate this circuit – Schematic created using CircuitLab Instead looking for the transformer you can use components already pre-made, like isolated RS485 transceiver module, MCU module, lastly your custom metering module with isolated DC/DC converter and signal isolator IC, like ADUMxxxx ISO RS485 examples: The black bricks on photos are isolated DC/...

1

A possibility is that your power strip is a "smart" power strip where the presence or absence of current draw on one outlet causes the power to turn on and off on the other outlets.

1

Essentially what is happening is that when you turn on the fan, as it uses an electric motor, it draws a fairly large current surge as the motor comes up to speed. This is evidently enough to cause your elliptical machine to respond, perhaps it sees the AC voltage drop enough that it resets or perhaps there is some other form of interference. The power ...

1

If your clocks could be controlled by computer somehow, NTP (Network Time Protocol) provides a traceable standard time reference. If you're feeling ambitious, and your clocks are on their own feed, here's a pointer to some accurate 50Hz inverter solutions: https://bestengineeringprojects.com/crystal-controlled-inverter-verified-inverter-circuit/ Combine this ...

1

There's a time signal broadcast from Rugby, UK, and you should be able to find "motor" modules which pick this up. It may be possible to retrofit these to your clocks but I suspect that mounting and fitting hands will be problematic - unless there are some standard sizes that I'm not aware of. The signal, also known as the MSF signal (and formerly ...

1

Perhaps you could use a UPS which is connected to the mains normally but produces its own sine wave output (i.e. does NOT pass the mains AC through during normal operation). This isolates any variances in frequency in the grid from the clocks incoming AC power. However this could be quite expensive if all you're using it for is to keep clocks accurate. It ...

Only top voted, non community-wiki answers of a minimum length are eligible