2

What would be the best way to limit mains (240V @ 50Hz) current? I want at least 1A of current. The output should be AC 240V at any frequency greater than or equal to 50Hz. It should be able to endure short circuit like conditions. I have tried dimmers (which instantly explode when connected) and fluorescent tube electronic ballast (too low current). I would be using this to power a hand wound toroidal transformer.

JYelton
  • 32,302
  • 33
  • 134
  • 249
AvZ
  • 317
  • 1
  • 5
  • 17
  • True current limiting is quite a complex issue when it comes to AC, but if you just want a trip-point blow out, which I think is more than enough for "playing" with hand-made transformers, get a 1A electronic Fuse (normal DIN rail type costs somewhere near €15 on Farnell) or a PTC resettable fuse rated for your current and voltage, though to my knowledge the mainstream resettables are all below 80VDC. (Your rated voltage would be 370V or higher) – Asmyldof Oct 04 '14 at 14:07
  • 1
    Is this the toroid ferrite you asked about yesterday? Do you have a data sheet for it? There is significant danger in what you are doing and I must advise you against this - if you do not know the core material you cannot hope to know it's ability to "isolate" should one on the primary winding's insulation break down to the core - if this happens you could be in for a serious shock. – Andy aka Oct 04 '14 at 14:58

2 Answers2

3

The simplest thing to do for this sort of testing is to put an ordinary incandescent light bulb in series with your transformer primary as a "ballast" resistor. But for 1A, you'll need a 250W bulb, or maybe four 60W bulbs in parallel.

A better solution is to use a Variac (variable autotransformer) to bring up the voltage on your homemade transformer gradually. Use an ammeter to monitor the current.

Dave Tweed
  • 168,369
  • 17
  • 228
  • 393
3

You can implement a transformer with magnetic shunt. You can select the output voltage, but only at line frequency. It is a popular method for battery chargers where the battery may require a large current spike when it is flat. Obviously, it is not necessary to implement the rectifier for the application you require.

The saturation level of the core (magnetic flux density) depends on the current. When incorporating the magnetic shunt transformer, saturation occurs at a lower current than could be obtained without magnetic shunt.

The magnetic shunt also applies to transformers for welding machines. Normally, in a welding machine with magnetic shunt, there is a mechanical device that regulates the action of the magnetic shunt, and therefore, the output current of the welding machine.

Martin Petrei
  • 3,034
  • 12
  • 20