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Using DC electronic load for 50Hz AC Sinewave

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peter_mcc:
I want to use an electronic load to test outputs that are 50Hz sinewave waveforms coming from a transformer. All the AC Electronic Loads I can find are really expensive.

Can I run the output through a bridge rectifier and use a DC load in constand resistance mode? I realise there will be issues around the zero crossing point.

I'm looking at something like the Korad KEL103/Tenma 72-13200 or Siglent SDL1020X.

My only concern is how well the constant resistance mode can track the changing input voltage.

Kleinstein:
Some electronic load implement the resistance mode in software. So it may be slow in adjusting the current in reponse to a changing voltage. So the load would not be very much like a constant resistance.
One may be able to improve a little by using a parallel normal resistor to take over much of the current. So the electronic load with rectifier would only do part of the load.

Otherwise, just a set of resistors to combine in parallel or series may well be an alternative to an electronic load to simulate resistors.

Fungus:

--- Quote from: peter_mcc on November 07, 2022, 06:39:59 am ---Can I run the output through a bridge rectifier and use a DC load in constand resistance mode? I realise there will be issues around the zero crossing point.

--- End quote ---

I don't see why not. It may be exactly the type of load the transformer will be connected to anyway.

(unless you have a specific use case for these transformers that isn't that)


--- Quote from: peter_mcc on November 07, 2022, 06:39:59 am ---My only concern is how well the constant resistance mode can track the changing input voltage.

--- End quote ---

Most bridge rectifiers in the world have a big capacitor across the output to smooth it out.  :)

alm:
How important is the shape of the current to you? Does it need to be sinusoidal and in phase with the voltage (power factor = 1)? Or does it not matter as long as the average current is correct?

I don't see an issue with a full-bridge rectifier as long as the voltage is high enough that the drop in current around the +/- 1 V range doesn't matter. But I'm not convinced the load will be fast enough in constant resistance mode to track a 50 Hz signal, because many loads will implement the constant resistance control loop in software to save costs. I don't know these specific loads, and they don't seem to specify constant resistance bandwidth. I think you'll have to test it: feed a 50 Hz signal into a load through a bridge rectifier and a low value series resistor, and with a scope measure the voltage across the load and across the series resistor (careful how you connect the ground leads).

If you don't care about the shape of the current signal, then a cap in parallel with the load, as Fungus, would make the job easier on the load, but would make the current draw very non-sinusoidal.

gf:
Are the input terminals actually isolated/floating? Or is one of them earthed?

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