Short circuit current for an HVAC 24 v transformer?

Yoyizit

"On paper" it's about 25 A.
Anybody measured this?

hvaclover

Clearify, Yowzie.

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beenthere

Hope that was suppose to be 2.5 amp.

Yoyizit

For 40 VA @ 24 vac the current is 1.7 A. The rated 24.0 v only applies when the transformer is loaded to its rated value of 40 VA.

If the open circuit voltage for one of these is, say, 26 vac then the internal impedance of the secondary is (26-24)/1.7 = 1.2 ohms.
26/1.2 = 22 A of short circuit current.

If it's 27 V o-c then it's 1.8 ohms and 15 A short circuit current.

I've never tested one of these HVAC transformers.

And this arith. doesn't apply to bell transformers because they shut down if they're shorted.

beenthere

Go to radio shack. And get yourself some resistors. And test a 40 VA transformer.

It will burn up before you reach 25 amps.

beenthere

While a dead short amp draw, will be higher then a load increase burn up.

Your applying a DC formula. It is used on A/C transformers, as many DC formulas are applied to A/C.
There is always a difference is actual outcome though.

If you are supplying 120 volts to the primary, as measured by a standard meter/or true RMS meter. The transformer primary is actually subjected to 170 VOLTS at peak and bottom sine.

yuri

I've never tested one of these HVAC transformers.


You have one in your furnace. Let us know how it turns out, Yoyzie.

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Yoyizit

You try it first.
Can you imagine how mad my frau would be if I were somehow remotely responsible for our AC to suddenly stop working after I went into the basement?
She's already asking questions about the catapult that I'm testing in the backyard [powered by garage door springs] and is openly wondering where the puppy went.
http://www.youtube.com/watch?v=F5Y_4d9UhEA
Now, really, how would I know where the puppy went?

I e-mailed an HVAC manuf. whose name kind of rhymes with. . .dunno'. . .warrior/carrion/Vikky Carr/sumpin' . . .with my question.

Scuba_Dave

No trebuchet ?

hvaclover

That makes the second time Yowzie has been busted applying DC rules of electricty to AC practical application.

You gotta use Impedance and Reactance for Alternatin Current Yowzie.
But that is an interesting topic for discussion. We all have TRANSFORMER FROM HELL horror stories we could share I'm sure.

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Yoyizit

It's kind of the same.

There's a YouTube video of a young girl setting one of these off. I'm sorry to say the makers of that video have no idea what they are messing with and the danger she is in.

hvaclover

Dude don't get him started! The next thing we'll see is Da Vinci style drawings and lonf drawn out equations!

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hvaclover

You wouldn't say that if she landed in your lap....

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Yoyizit

Look to your east - I'm sending you a cinder block at Mach 1. Allow 40 minutes for the flight time.

hvaclover

My wife said it would not match our existing stone work----better make it a hard baked red brick instead.

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