Tagged Questions

3
votes
3answers
153 views

Building a power supply, want to stay alive

I am building a power supply for a very old laptop. The circuit uses a transformer (220 V primary to 15 V secondary, 33 VA) and that worries me a little. (Please note that I an enthusiast and so far I ...
2
votes
2answers
138 views

how do they make travel adapters so small?

How do they make cellphone adapters, especially "travel adapters", so small? I once peeked inside an old Nintendo adapter, and it had (among other circuitry) a rather-bulky step-down transformer to ...
4
votes
2answers
103 views

How to properly snub transient spikes from a transformer and prevent switch mode power supply burn out

I've received a failed switch-mode DC-DC step down converter (part# LTC3631 from Linear). This circuit was driven by a 24VAC transformer which is rectified on the circuit: simulate this ...
2
votes
1answer
165 views

advice on a transformer for power-supply

i know this type of question is common and yes i could just buy a known transformer for $10 on ebay or something. either way :) i am interested in building my own power supply, something variable ...
3
votes
2answers
220 views

Question about transformer design

I want to use a transformer to convert AC voltage. Input is 220V AC at 50 Hz and output is, for example, 5V 30mA AC. Many people told me, this transformer will be huge because the mains frequency is ...
-1
votes
2answers
53 views

subsituting one transformer for another [duplicate]

Possible Duplicate: Choosing power supply, how to get the voltage and current ratings? I have an eliptical machine that is no longer being manufactured. it appears that the AC to AC adaptor ...
4
votes
1answer
267 views

Is it possible to have a device with metal case and wireless charging?

Recently I encountered the following idea: that a mobile device manufacturer is not interested in including wireless charging in his devices because that prohibits him from using metal cases in the ...
1
vote
2answers
979 views

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

About the amp: This is from an old solid state audio amplifier with an AM/FM tuner. No digital parts or ICs were inside. It was all point to point. Unfortunately I threw out the amp and didn't write ...
1
vote
1answer
317 views

How to calculate the power requirements of a fan motor? [closed]

I bought a fan from the USA to use in Europe. The fan's specifications states the following: Requires a grounded electrical supply line of 120 volts AC, 60 Hz, 15 amp circuit. Here we use a ...
0
votes
3answers
333 views

Plugging a 65W computer power plug into a 45W step down transformer [closed]

Is it safe? Would it only charge slower, or could it damage anything? Here is the setup in more detail: I'm in Europe, where plugs are 230V. My computer was bought in the US, so it's a 110V ...
0
votes
2answers
1k views

Easiest / cheapest way to build a dc power supply in the 0 - 50V DC range?

I would like to build a small DC power supply (or find a cheap way) that allows me to get voltages in 0 - 50V DC range. I had a look on ebay and some electronic shops but most supplies dont get ...
2
votes
2answers
218 views

Does Transformer heating add noise to a circuit?

I have a circuit on PCB with a transformer that generates a lot of heat. It is actually an energy meter, and I'm getting increasing error as time goes on. I observe that the transformer heats up ...
0
votes
1answer
483 views

Powering a 30 watt peltier heatpump

I've got a Peltier element rated at 12V / 2.5A (30W), but I'd like some clarification on how I should power it. I'm familiar with building power supplies with LM78xx linear regulators, and I've had a ...
0
votes
2answers
536 views

Dual polarity power supply for project, possible choices?

For a variable power supply I require 15V to get ~0-12V, and +/-15V for an op amp as part of the project requirements, also negative rail in the future. Two plugpacks (isolated, 15/0/-15)to me seems ...
2
votes
1answer
415 views

How can I determine the maximum possible current in a transformer?

I am curious how far can I go if I'd like to rework a small 12V/0.1A DC power supply to give higher current without changing the transformer inside it. I understand that I have to upgrade the ...
2
votes
2answers
722 views

Is there any difference between “induction” and “resonant” wireless energy transfer?

This article compares two systems for wireless energy transfer - one is by WiTricity and another is Bombardier PRIMOVE. I've read their descriptions thoroughly - to me they both look like resonant ...
6
votes
4answers
557 views

How is inductive wireless charging of a moving vehicle on a public road possible in efficient way?

Looks like one of the major problems of wireless energy transfer is efficiency. For example, Magne Charge high power charging system seems to have about 86% efficiency which means that quite a lot of ...
3
votes
1answer
329 views

What's the need for higher frequency in inductive charging systems?

Consider an inductive charging system like Magne Charge - it has a rather huge "coupler" coil off the vehicle and a corresponding slot on the vehicle and the coils in the "coupler" and in the slot are ...
7
votes
1answer
278 views

Why does short distance wireless energy transfer have such low efficiency?

Wikipedia and numerous other sources cite the following statement about Magne Charge high-power inductive charging system: For example, the Magne Charge system employed high-frequency induction to ...
4
votes
2answers
248 views

Building a power supply for a Vic 20

I recently acquired an early model Vic 20 computer but don't have a power supply for it and thought I might be able to make one. The Vic 20 is the early model with the two pin AC connector - not the ...
3
votes
2answers
205 views

How to properly isolate multiple power supplies

Say you have a single 110V AC supply and need to use it for a number of devices, each requiring very different characterists. For me personally these are: a direct use of the 110V AC supply for a ...
6
votes
3answers
768 views

How to dimension a power supply transformer?

I always hesitate when dimensioning a transformer for a DC power supply, and I guess I sometimes overdimension them. My confusion stems from the difference in transformer and DC voltage. If I need 10V ...
3
votes
3answers
416 views

How to apply passive PFC on low side of transformer in power supply?

I have a low power power supply, built with a 60Hz 120v/12v 0.3A transformer. It will have an ordinary diode bridge and capacitor filter. What I want to achieve is reduction of current/magnetic field ...
6
votes
4answers
670 views

How does a wireless charger work without a magnetic core passing through both “coils”?

Every time I hear the description of a wireless charging system it goes like this: "remember a transformer? It's the same here - one coil is in the base and another is in the device and when you put ...
3
votes
4answers
371 views

Why don't we have wireless charger in every portable device yet?

Today I found Texas Instruments announced a circuit for wireless charging - all the materials emphasis how tiny, lightweight, portable, efficient and otherwise cool it is. While I of course like the ...
1
vote
2answers
272 views

Why would a power supply mess with my scope?

I recently bought a 0-35V 0-3A (105W) CC/CV linear power supply, made by Takasago in Japan, second hand. It's a nice unit, and inside of it is a massive power transformer along with three pass ...
3
votes
3answers
485 views

How do I build a cheap/efficient mains adapter for some LED lighting?

I've been considering building some LED lights to replace the mains-supplied lights in my house (as a more efficient alternative). For it to be worthwhile though I'd need to build an efficient UK ...
3
votes
6answers
2k views

Converting 24VAC to 5VDC - Need transformer demystification

I've got an automatic litterbox that 'needs' to be hacked for better control. As it ships, it comes with a 120VAC to 24VAC (300 mA) wall wart that drives the two motors in it. I'm trying not to change ...