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December 09, 2019, 01:41:46 01:41


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Author Topic: 100W (or more) Vac dummy load  (Read 2935 times)
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[email protected]
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« on: November 27, 2019, 11:03:31 11:03 »

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
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« Reply #1 on: November 27, 2019, 07:25:24 19:25 »




What about a 100 W incandescent lamp?




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forter
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« Reply #2 on: November 28, 2019, 12:12:03 00:12 »


Hi, [email protected]!
 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.
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[email protected]
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« Reply #3 on: November 28, 2019, 10:16:41 10:16 »



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?


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kreutz
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« Reply #4 on: November 28, 2019, 10:34:20 10:34 »

I have used a water filled bucket and water heater heating elements in the past.
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Checksum8
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« Reply #5 on: November 28, 2019, 10:41:07 10:41 »

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?
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forter
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« Reply #6 on: November 29, 2019, 12:42:15 00:42 »

@[email protected] 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
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flyback
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« Reply #7 on: November 30, 2019, 05:26:04 05:26 »

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
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bobcat1
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« Reply #8 on: December 01, 2019, 01:57:29 01:57 »

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  

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solutions
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« Reply #9 on: December 01, 2019, 08:14:53 08:14 »

What exactly are you testing on these transformers...and why?
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[email protected]
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« Reply #10 on: December 02, 2019, 04:06:24 04:06 »


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.
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Sideshow Bob
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« Reply #11 on: December 02, 2019, 06:49:55 06:49 »

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
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I have come here to chew bubblegum and kick ass... and I'm all out of bubblegum
Checksum8
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« Reply #12 on: December 02, 2019, 11:28:55 11:28 »

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.
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titi
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« Reply #13 on: December 02, 2019, 11:59:05 11:59 »

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.
« Last Edit: December 02, 2019, 12:01:16 12:01 by titi » Logged
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