# Loading a transformer for testing



## greco (Jul 15, 2007)

I have a power transformer with tapped secondaries that was given to me by a friend.

When I want to test the voltages on the secondaries, what value (in ohms) of resistors should I use as loads so that the secondaries will not be "open". 

Do the resistors have to be rated for a certain power level (e.g. 5 watts or so) to be sure that the transformer will not be damaged?

Is this the typical and correct way to approach this type of testing....if not, please advise me as to the correct procedure.

Many thanks 

Dave


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## Wild Bill (May 3, 2006)

greco said:


> I have a power transformer with tapped secondaries that was given to me by a friend.
> 
> When I want to test the voltages on the secondaries, what value (in ohms) of resistors should I use as loads so that the secondaries will not be "open".
> 
> ...


No need for all that trouble, Dave! You don't need any resistors at all.

Just put voltage into the primary wires and read the secondaries. I use cheap 'gator leads to keep wire ends from shorting against each other.

Once you've got your voltages scrawled on a piece of paper you can apply the old Radio Experimenter's Rule of Thumb for Power Transformers: "An unloaded power transformer will read about 10% high on its windings!"

Close enough for rock and roll! I've never bothered with resistors in my life.:smile:

:food-smiley-004:


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## greco (Jul 15, 2007)

Thanks Wild Bill !

It is always nice to be able to keep things simple.:food-smiley-004:

Hope you are feeling much better as time moves forward. 

All the best.

Dave


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## SinCron (Mar 2, 2006)

Resistors are futile.


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## greco (Jul 15, 2007)

SinCron said:


> Resistors are futile.


Could you please explain this to a newbie like me.

Are you just saying that they aren't needed?........as Wild Bill said

Thanks

Dave


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## bagpipe (Sep 19, 2006)

greco said:


> Could you please explain this to a newbie like me.
> 
> Are you just saying that they aren't needed?........as Wild Bill said
> 
> ...


I think SinCron was making a clever pun by using the phrase "resistance (resistors) is futile".

http://en.wikipedia.org/wiki/Resistance_is_futile


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## greco (Jul 15, 2007)

bagpipe said:


> I think SinCron was making a clever pun by using the phrase "resistance (resistors) is futile".
> 
> http://en.wikipedia.org/wiki/Resistance_is_futile


AHHHHHHH....Got it now.....a bit slow here. 
Now Paul's comment (re: attenuated") makes much more sense.

I sometimes suffer from a _direct short _when it comes to puns.

Thanks Bagpipe

Dave


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## greco (Jul 15, 2007)

Paul said:


> I've tried nine other times to make you laugh with jokes like that, but alas, no pun in ten did.
> 
> <me ducking the thrown items>


What can I say...too serious....thick as a brick, at times, OK , often.....I'll try harder naxt time.

Cheers

Dave


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