100W (or more) Vac dummy load

[M@X77]

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

[LabVIEWguru]

What about a 100 W incandescent lamp?

[forter]

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.

[M@X77]

What about a 100 W incandescent lamp?

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?

[kreutz]

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

[Checksum8]

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?

[forter]

@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

[flyback]

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

[bobcat1]

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  

[solutions]

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

[M@X77]

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.

---------

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.

[Sideshow Bob]

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

[Checksum8]

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.

[titi]

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
The video https://www.youtube.com/watch?v=YXUa-xOSNLE&t=

In attachemnt all the files of the project.

Best regards.

[M@X77]

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
The video 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