[Amps] current in primary of microwave oven transformer

[Alex]

...that's right and that's what cosine Φ is about. With real high power animals it’s not unusual to see reactance canceling capacitors across the primary – they’re sometimes automatically adjusted too!

Alex   4Z5KS

 

-----Original Message-----
From: Angel Vilaseca [mailto:avilaseca at bluewin.ch] 
Sent: Thursday, April 24, 2008 9:54 AM
To: Alex; dave.g0dja at tiscali.co.uk; david.kirkby at onetel.net; d.cutter at ntlworld.com; amps at contesting.com
Subject: Re: [Amps] current in primary of microwave oven transformer

 

Good mews then! My MOTs are OK.

 

Bad news: although no real power is delivered to my house, the power 

company will bill me for it! :-)

 

Thanks for your help, guys!

 

Angel Vilaseca HB9SLV

 

 

Alex a écrit :

> ...guys this is normal behavior for all transformers!

> It is the result of the existence of a magnetizing inductance, usually

> depicted as a parallel inductance across the primary and every transformer

> has it. Don't worry about it: it's something physical and cannot be avoided!

> There are higher power transformers  in which this current can reach in the

> amperes range, but it's reactive current, except for a few watts loss in the

> ohmic component: that the reason it doesn't show up as heat. These

> transformers are usually good for about 750 watts continuous, 1000 watts

> ICAS.

> Alex 4Z5KS

> 

> -----Original Message-----

> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On

> Behalf Of Dr. David Kirkby

> Sent: Wednesday, April 23, 2008 12:08 PM

> To: Angel Vilaseca; 'AMPS'

> Subject: Re: [Amps] current in primary of microwave oven transformer

> 

> Angel Vilaseca wrote:

>   

>> Hi,

>> 

>> I have a microwave oven transformer that I plan to use for my next HV 

>> power supply.

>> 

>> With the secondary unloaded and 220 V into the primary, I measured  670 

>> mA through it.

>> 

>> This is a 220 V unit so that means 147 Watts, with no load on the 

>> secondary. Magnetic shunts were taken off.

>> 

>> I have another two MOTs. Made the same measurement. They all behave the 

>> same.

>> 

>> On the other hand, the transformers do not hum, not smoke, not even get 

>> hot, so I was wondering if this primary current could be "wattless" 

>> current, that is a current that is out of phase with voltage.

>> 

>> 

>> Should I worry about this amount of "idle current"?

>> 

>> Is this behavior particular to microwave oven transformers?

>> 

>> Is there a way to know what is happening here without using a double 

>> trace oscilloscope?

>> 

>> 

>> Vy 73

>> 

>> Angel Vilaseca HB9SLV

>> 

>>   

>>     

> The power dissipated is V*I*Cos(phi) where phi is the phase angle 

> between the voltage and current. (Assuming they are pure sine waves of 

> course, which is not necessary so.)

> 

> There are ICs around which measure phase, but a scope is the easiest way.

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>