Sonsivri

Hi to everyone, I need to test some transformers, I would like to avoid to use a rheostat, but a dummy Vac load.
Someone did had the same question? Found a solution? I tried to search but I didn't get any results.
In google I found the attached schematic, but it don't convince myself.
It seems strange where the potentiometer get ref (r3 on load input), I think it need a voltage reference if I want costant current load.

thanks
Massimo

What about a 100 W incandescent lamp?

Hi, M@X77!
 If done as shown in the diagram, it turns out that the conductivity will depend on the input voltage.
And this means non-linearity of resistance.

I would like a costant current load to do AC transfonformer experiance

@forter: it's my own thought, if so, just use a reference voltage, no?

I have used a water filled bucket and water heater heating elements in the past.

Years ago, I did transformer testing using a dc constant current load with a 25 amp bridge rectifier between the two. I don't remember the details, like if a  electrolytic capacitor was needed on the load side?

@M@X77 I think the idea of Checksum8 of ​​using a bridge rectifier is a very interesting solution. Only, of course, without any capacitor and of course R3 must be connect to a constant reference voltage

I found this link. Seems that's more or less what you sought (an AC constant current load).

https://electronics.stackexchange.com/questions/218976/ac-constant-current-source-design/219747

Hi

Both circuit are simple to simulate in LTSpice or Pspice just to know whether they work or not - you don't have to use same components just choose close parameters.

All the best

Bobi  

What exactly are you testing on these transformers...and why?

I need to test nominal current and check temperature, the problem was the current is different and I need flexibility.

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I think to use a classic DC mosfet dummy load and put a Graetz Bridge without capacitor, the current tha flow in the circuit is equal, the mosfet "sees" DC pulse current but this I think is not a problem.

By the way. You are aware that regarding current ratings. They are in AC. If you load your transformer with a typical setting with a rectifier and filter (inductor/capacitor) The DC current you should allow for. In some cases should be much lower than the transformer AC current rating.
Just in case this something new for you I leave this Google link for you
https://www.google.com/search?q=Design+Guide+for+Rectifier+Use  (https://www.google.com/search?q=Design+Guide+for+Rectifier+Use)

I would use a clamp on AC current meter or current transformer to get actual readings from the transformer. Don't rely on some pulsed DC on the load side.

Hi,

In Elektor Labs there is an article about an Electronic load for DC and AC.
May be it can helps.

They use an DC Electronic Load behind a bridge rectifier for AC mode.

https://www.elektormagazine.fr/labs/electronic-load-for-dc-and-ac  (https://www.elektormagazine.fr/labs/electronic-load-for-dc-and-ac)
The video https://www.youtube.com/watch?v=YXUa-xOSNLE&t= (https://www.youtube.com/watch?v=YXUa-xOSNLE&t=)

In attachemnt all the files of the project.

Best regards.

Very interesting! thanks
I trying to do