Short Circuit Current For An HVAC 24 V Transformer? - HVAC - DIY Chatroom Home Improvement Forum

 DIY Chatroom Home Improvement Forum > HVAC Short circuit current for an HVAC 24 v transformer?
 Register Blogs Articles Rewards Search Today's Posts Mark Forums Read

07-17-2010, 08:08 PM   #1
Member

Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,990
Rewards Points: 2,000

## Short circuit current for an HVAC 24 v transformer?

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

07-18-2010, 03:38 AM   #2
Member

Join Date: Oct 2008
Location: Suburbs of Detroit Mi
Posts: 3,704
Rewards Points: 2,000

Quote:
 Originally Posted by Yoyizit "On paper" it's about 25 A. Anybody measured this?
Clearify, Yowzie.

 07-18-2010, 07:34 AM #3 An old Tradesmen   Join Date: Oct 2008 Location: Somewhere Posts: 34,627 Rewards Points: 8,240 Hope that was suppose to be 2.5 amp.

 07-18-2010, 10:38 AM #4 Member   Join Date: Jul 2008 Location: NW of D.C. Posts: 5,990 Rewards Points: 2,000 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.
 07-18-2010, 11:06 AM #5 An old Tradesmen   Join Date: Oct 2008 Location: Somewhere Posts: 34,627 Rewards Points: 8,240 Go to radio shack. And get yourself some resistors. And test a 40 VA transformer. It will burn up before you reach 25 amps.
 07-18-2010, 11:18 AM #6 An old Tradesmen   Join Date: Oct 2008 Location: Somewhere Posts: 34,627 Rewards Points: 8,240 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.
 07-18-2010, 12:38 PM #7 Hvac Pro     Join Date: Nov 2008 Location: Winnipeg, Canada Posts: 16,130 Rewards Points: 398 I've never tested one of these HVAC transformers. You have one in your furnace. Let us know how it turns out, Yoyzie. __________________ "Cut it twice and it is still too short".
07-18-2010, 02:32 PM   #8
Member

Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,990
Rewards Points: 2,000

Quote:
 Originally Posted by yuri I've never tested one of these HVAC transformers. You have one in your furnace. Let us know how it turns out, Yoyzie.
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?

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.

Last edited by Yoyizit; 07-18-2010 at 02:55 PM.

07-18-2010, 04:49 PM   #9
Member

Join Date: Jan 2009
Location: South of Boston, MA
Posts: 17,248
Rewards Points: 2,000

Quote:
 Originally Posted by Yoyizit 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. Now, really, how would I know where the puppy went?
No trebuchet ?

07-18-2010, 04:50 PM   #10
Member

Join Date: Oct 2008
Location: Suburbs of Detroit Mi
Posts: 3,704
Rewards Points: 2,000

Quote:
 Originally Posted by beenthere While a dead short amp draw, will be higher then a load increase burn up. Your applying a DC formula.
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.

07-18-2010, 04:52 PM   #11
Member

Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,990
Rewards Points: 2,000

Quote:
 Originally Posted by Scuba_Dave No trebuchet ?
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.

07-18-2010, 04:53 PM   #12
Member

Join Date: Oct 2008
Location: Suburbs of Detroit Mi
Posts: 3,704
Rewards Points: 2,000

Quote:
 Originally Posted by Scuba_Dave No trebuchet ?

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

07-18-2010, 04:55 PM   #13
Member

Join Date: Oct 2008
Location: Suburbs of Detroit Mi
Posts: 3,704
Rewards Points: 2,000

Quote:
 Originally Posted by 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.
You wouldn't say that if she landed in your lap....

07-18-2010, 05:02 PM   #14
Member

Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,990
Rewards Points: 2,000

Quote:
 Originally Posted by hvaclover You wouldn't say that if she landed in your lap....
Look to your east - I'm sending you a cinder block at Mach 1. Allow 40 minutes for the flight time.

Last edited by Yoyizit; 07-18-2010 at 05:13 PM.

07-19-2010, 02:17 AM   #15
Member

Join Date: Oct 2008
Location: Suburbs of Detroit Mi
Posts: 3,704
Rewards Points: 2,000

Quote:
 Originally Posted by Yoyizit Look to your east - I'm sending you a cinder block at Mach 1. Allow 40 minutes for the flight time.
My wife said it would not match our existing stone work----better make it a hard baked red brick instead.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are Off Refbacks are Off Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post jlmran Electrical 7 02-08-2010 12:04 PM RST Electrical 15 07-21-2009 07:38 PM hellothere123 Electrical 22 07-21-2009 06:07 PM Redparis HVAC 2 02-26-2008 10:21 PM lapsis9 HVAC 4 12-20-2006 08:09 PM

Top of Page | View New Posts