[GreenKeys] Rectifier AC amp draw question...

[Peter Gottlieb]

Transformers will draw more VA than watts. 

A transformer with 3 amps in the 120 primary may only be drawing 100 watts, for example. 

A very lightly loaded transformer has a terrible power factor. 

Peter

> On Sep 11, 2019, at 3:54 PM, Ralph Mowery <rmowery28146 at earthlink.net> wrote:
> 
> Transformers are around 80% efficient or more as my number is very conservative for this example .  So with out anything on the secondary circuit they will draw a small amount of current.  For a loop of say 150 volts AC (which will give you around 200 volts dc and the nominal 60 ma of current , you are looking at about 9 watts.  Just call it 10 watts .  So on the primary side you will draw about 12 watts, around .1 amp.  Almost nothing so to speak.  The transformer just sitting across the 120 volt lime may draw that much with nothing on it.  You will not draw 3 amps unless you have a load of close to 300 watts on the output side.  
> 
> In other words, it only draws about 120 % ( that number is probably high, it may be closer to 105% more than the actual load on the secondary.
> 
> 
> 
> 
> -----Original Message-----
> From: greenkeys-bounces at mailman.qth.net [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of E.
> Sent: Wednesday, September 11, 2019 2:31 PM
> To: Robert Downs via GreenKeys
> Subject: [GreenKeys] Rectifier AC amp draw question...
> 
> 
> This is probably a silly question by my audio engineer wife was also having trouble answering it ;o …
> 
> …anywho - question:
> 
> Let’s say I have a rectifier that draws 3 amps on the AC side and 1 amp on the DC side… according to the plate.  If I put a big honkin’ resistor on the DC side - for a loop current.  Will that limit the DC draw to below 3 amps on the AC side, or will the AC side remain at 3 amps???
> 
> 
> 
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