New answers tagged

1 vote

Why do some transformers trip circuit breaker. Eg a ups transformer. I need a soft start resistor details

It is all about the inrush current (1, 2). When the primary gets magnetised, the amount of current it needs to build up a magnetic field before collapsing and transferring the energy to the secondary ...
1 vote

Using an Ethernet gigabit PHY for only 100 and 10 Mbps speeds

First, I’ve used the RC Ethernet connection in a product (for an add-on WiFi adapter) so I can vouch for that. (I later made them do it properly with PCIe.) Second, there’s no issue with connecting 10/...
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3 votes

Using an Ethernet gigabit PHY for only 100 and 10 Mbps speeds

What you are proposing generally looks good. I can confirm that 100Mbps Ethernet uses pairs A+/A- (RJ45 pins 1/2) for transmit and B+/B- (RJ45 pins 3 and 6) for receive. Pairs C and D are unused. ...
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2 votes

Appropriate flyback transformer to boost 5V to 140 V

Flyback Converter I'm exploring this option but a couple of things are not clear. For one, I have not come across a transformer that has a 1:30 step up ratio. Does such a thing exists? This is a ...
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0 votes

Appropriate flyback transformer to boost 5V to 140 V

The “inductor boost” is not good at all – it makes very controversial requirements for switch element: high current and high voltage at the same time, so using transformer is the right way to go. It ...
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3 votes
Accepted

Recreating a transformer using gyrators

This screenshot from Wikipedia article of Gyrator tells what such item does: The full article is here: https://en.wikipedia.org/wiki/Gyrator Unfortunately our traditions have got distortions. One of ...
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1 vote

Can you calculate equivalent capacitance across a MOSFET if you know the rise/fall-times and voltage across it?

No, the rise time is a sum/product of many different parasitic elements in a mosfet. If you look below there are several elements (Cgd and Cgs being large contributors) as well as the inductance of ...
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0 votes

How do we use step-up transformers to get a very high voltage compared to the initial voltage?

To increase voltage we use more turns on the secondary than the primary, but that will make the transformer's size way to big and it won't be practical. No, that doesn't makes sense. The person who ...
6 votes
Accepted

Is there a simple method to estimate the copper loss of Litz wire?

You should further explain how the transformer is being used. I suggest you read the following answers given electronics.stackexchange on the subject of winding losses. If you have a university ...
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-1 votes

In a single-phase transformer output, which-wire would be phase, and which-one would be neutral?

I use a no-contact AC tester (12-600 VAC), even though the secondary is floating with no ground. There is a Hot lead and there is a Neutral lead.
0 votes

How do we use step-up transformers to get a very high voltage compared to the initial voltage?

High-voltage power supplies are a challenge to design. They stress the limits of materials and components, and so require some specialized knowledge. That said, a very common high-voltage supply in ...
  • 42.7k
-1 votes

Wiring a single-phase auto transformer

I use a no contact ac voltage tester. The tester flashes and beeps only when the tip is close to the hot lead. This is true on both the 220 and 120 connections. This is also the same, with the more ...
1 vote

How do we use step-up transformers to get a very high voltage compared to the initial voltage?

Increasing the frequency allows you to use smaller inductors or transformers, typically. The way I look at it is that the amount of magnetic energy that can be stored in an iron core depends on the ...
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0 votes

How can I find out which wires are the primary wires on this transformer?

Try "googling" the model number of that AM/FM reciever. If you have the case the transformer came from; look for a model number. The schematic might be available on line. Be safe, an ...
1 vote

Would this power supply modification work to double the voltage?

First, that doesn't make a voltage doubler. You would need to rearrange the diodes and capacitors to get a double, see here. Second, when specifying an AC voltage you don't say something like '+/- 18 ...
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1 vote
Accepted

Is there a relationship between capacitor ripple current and the transformer secondary current output rating?

Here are simulations for a 24 VAC 4 A transformer having 260 mOhm secondary with 10,000 uF capacitor and 8 ohm load. I ran it at other values as well. Your transformer would have less internal ...
  • 2,123
3 votes
Accepted

High-reliability transformer selection

The power you are talking about is 380V 3-phase. It is generally supplied in "Wye" configuration. If you make a connection phase to phase, you get 380V. If you make a connection phase to ...
1 vote

Transformer selection for a power inverter

It sounds like you are either using the H bridge to produce a sinewave input to the transformer in a linear fashion or, you are using PWM to create an equivalent sinewave. Either way will be fraught ...
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3 votes

Wiring a single-phase auto transformer

You would need to check the resistance between the terminals on the 220 V terminal block and the 110 V one. The terminals between which the resistance is the lowest would be the neutral terminals.
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2 votes

Wiring a single-phase auto transformer

If it's a 220 volt in and 110 volt out auto transformer then there are only 3 effective connections and there should be symmetry like this: - simulate this circuit – Schematic created using ...
  • 396k
7 votes
Accepted

Wiring a single-phase auto transformer

You should be able to determine which terminals are neutral (or rather common between input and output) by measuring resistance between each of the 220V terminals and each of the 110V terminals. All ...
1 vote

Centre-tapped-secondary transformer's primary leakage

The measurement of the inductances in question can be more accurate when measuring secondaries with primary SC or OC respectively. In regards to the the current imbalance in the HB LLC. The main ...
1 vote

How to safely switch a high voltage transformer?

This is probably some sort of flyback converter that may be driven by an oscillator and transistor, or even an electromechanical buzzer. Thus, it probably has considerable delay between applying input ...
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0 votes

Why isn't a transformer a short circuit?

Any current that changes with time creates a self-opposing electric field. Inductors and transformers are just highly concentrated forms of this phenomenon. We concentrate, then magnify, this effect ...
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1 vote
Accepted

Impedance of transformer

To calculate the value of R you would need the value of the transformer losses (from the data sheet or test report). Unfortunately, the value of losses is not an information that is required by ...
1 vote

Why isn't a transformer a short circuit?

The answer is reactance, which is a form of impedance, and is measured in ohms, which is also the unit of measurement for resistance. It is directly related to inductance and frequency: 2·π·f·L (f=...
1 vote

How do transformers comply with Ohm's law and KVL?

Transformers driven by an ideal AC voltage source just convert the voltage as per the turns ratio, and the currents will change to match the circuit. First you fix a scenario where secondary output is ...
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3 votes
Accepted

How do transformers comply with Ohm's law and KVL?

You're assuming that the currents are determined by the transformer, but they're not, the voltage ratio is determined by the transformer, and the currents are then determined by the load impedance. So,...
  • 6,601
6 votes

Why is the magnetizing current in a transformer always constant irrespective of the load?

Why is the magnetizing current in a transformer always constant irrespective of the load? Ignoring core loss current (a step too far), there are two different currents taken by the primary winding: - ...
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5 votes
Accepted

Why is the magnetizing current in a transformer always constant irrespective of the load?

The magnetising current is, by definition, that current required to set up the flux in the core. Whether the secondary is supplying a load current or not, the core flux is generating a voltage in both ...
  • 145k
4 votes

Why is the magnetizing current in a transformer always constant irrespective of the load?

Yes, exactly -- all that you're missing is a formula to express how the currents and fluxes vary with load. Your doubt concerns whether, and how, the magnetization nearly cancels out. Maybe they go ...
  • 6,506
3 votes

Why is the magnetizing current in a transformer always constant irrespective of the load?

By definition, the magnetizing current is the current required to set up the flux with an open secondary. Yes, when the secondary is delivering current to a load, the primary must draw more current, ...
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1 vote

How to safely switch a high voltage transformer?

Presumably this will be a problem if I try to switch it using a normal transistor-based solid-state system? I'm sure you could and that they used to, but relays can weld. Thyristors, among the most ...
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0 votes
Accepted

How is primary defined for FL2015-3L?

I assume this means each half has an inductance of 19uH/4=4.75uH. Do you read this the same way? I read it the same way. Each half primary has an inductance that is a quarter of the full primary. ...
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5 votes

DC saturation current of a power transformer of a given VA rating

Calculate it backwards instead. Say we have a transformer with Ae = 200 mm2, le = 240 mm, μr = 10k, and Bsat = 1.2 T. First, solve for turns: $$ N = \frac{ V_\textrm{rms} }{ 4.44 B_\textrm{sat} F A_e ...
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6 votes
Accepted

DC saturation current of a power transformer of a given VA rating

So the peak current used to find \$B\$ is \$I=I_{RMS}\cdot \sqrt2\$. No, that is not the case. The load current passing into the transformer primary and exiting on the secondary has nothing to do ...
  • 396k
1 vote

Quick reset technique of pulse transformer core

Replace the SPICE switch with a transistor switch. Probably move it to the low (GND) side as well. Effectively a duplicate of: Zener Diode Selection for Relay but the different applications (relay / ...
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