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Compairing VA to A

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  • Member since
    January 2006
  • From: Manitou, Okla
  • 1,630 posts
Compairing VA to A
Posted by mikesmowers on Wednesday, December 19, 2007 2:32 PM
  Some power packs are rated in VA (Volt Amp?) and some are rated in A (Amp) what is the difference. I don't think that a 7 VA power pack is the same as .7 Amp . could someone explain this to me?          Thanks.               Mike
Modeling Trains Is Not A Matter Of Life Or Death, It Is Much More Important Than That!!
  • Member since
    November 2003
  • From: Central Texas Cow Pasture
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Posted by jawnt on Wednesday, December 19, 2007 3:04 PM

Mike, just did a google on Volt-amp to amp  ----- in DC VA = watts, but not so in AC. The example given was for an Uninteruptable Power Supply, that the VA rating was approximately 60% higher than the wattage --- all due to inductance and capacatance in AC circuits.

There is more info than you ever want to know on google.

Hope this is a start for you ------------  John T.

  • Member since
    January 2006
  • From: Portsmouth, VA
  • 372 posts
Posted by jfallon on Wednesday, December 19, 2007 3:10 PM
    To figure amps, divide VA by the rated output voltage (maximum DC output for the power pack).

If everybody is thinking alike, then nobody is really thinking.

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  • Member since
    January 2006
  • From: Manitou, Okla
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Posted by mikesmowers on Wednesday, December 19, 2007 3:31 PM

  The power pack I am refering to at the time is rated at 16 volt and 7 Volt Amp. Divide the VA (7) by the total output (16) and I get .4375 amp. is this correct?

  That is the rating on the power pack I took off the layout and installed the new one. If this is the case, the new power pack has over twice as much power as the old one. 

   BTW for those that have been following my thread about the power problem on my layout,  The trains ran near perfectly last night for over 3 hours. I started out at about 75 % throttle and around .67 amps. after about an hour I was down to about 67% throttle and around the .45 amp range. I did some extensive checking on the voltage and amps at the rails and there was little if any voltage or amp loss at the spot in question.

   Thank you all that helped me on this problem.                    Mike 

Modeling Trains Is Not A Matter Of Life Or Death, It Is Much More Important Than That!!
  • Member since
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  • From: Weymouth, Ma.
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Posted by bogp40 on Wednesday, December 19, 2007 4:16 PM
 mikesmowers wrote:

  The power pack I am refering to at the time is rated at 16 volt and 7 Volt Amp. Divide the VA (7) by the total output (16) and I get .4375 amp. is this correct?

  That is the rating on the power pack I took off the layout and installed the new one. If this is the case, the new power pack has over twice as much power as the old one. 

   BTW for those that have been following my thread about the power problem on my layout,  The trains ran near perfectly last night for over 3 hours. I started out at about 75 % throttle and around .67 amps. after about an hour I was down to about 67% throttle and around the .45 amp range. I did some extensive checking on the voltage and amps at the rails and there was little if any voltage or amp loss at the spot in question.

   Thank you all that helped me on this problem.                    Mike 

Mike check those spots again. This time wiggle the wires and push down on the rails. You just are trying to make sure that there is a solid electrical connection. Sitting static w/o a train may not show an intermittant bad connection. Just good to check before assuming there's no problem there.

Modeling B&O- Chessie  Bob K.  www.ssmrc.org

  • Member since
    January 2006
  • From: Manitou, Okla
  • 1,630 posts
Posted by mikesmowers on Wednesday, December 19, 2007 4:24 PM
   I checked the voltage and amps while the train was running. I took my testor probes and touched the outsides of the rails and checked it directly under the moving loco at the spot in question. I checked it in several places on the track while the train was in motion and found there to be very little difference if any at all.   Thanks for the help.             Mike
Modeling Trains Is Not A Matter Of Life Or Death, It Is Much More Important Than That!!

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