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 t
The current you are measuring has a phase angle relative to the mains voltage supplied, meaning this is not real power being consumed it is apparant power, ie not Watts but Volt-amps. You will need a
Author: "Dr. David Kirkby" <david.kirkby@onetel.net>
Date: Wed, 23 Apr 2008 10:08:24 +0100
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
Others have answered the question of phase angle, so I wont repeat that information again. To address the root of your question, all transformers have losses, due to 'copper' losses in the windings,
...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
Only if you get charged for kVA, rather than just kW... The 147 Watts you measured is 'real' power, the Watts part, so you will spin the meter by 147 Watts per hour, or 0.147 kWh at what ever your ra
David I don't think that's what Angel measured: I understood it was measured using a regular current meter, therefore the results are VA reactive not Watts. David G3UNA -- Email sent from www.virginm
Author: "Dr. David Kirkby" <david.kirkby@onetel.net>
Date: Thu, 24 Apr 2008 13:57:32 +0100
No, at least in the UK we are billed by power, and not by current. I know someone who managed to get free power by making use of the small voltage between earth and neutral. He knew of someone who cl
I must have missed that bit, or forgot. Yes, a current reading will give you VA if you don't have the phase angle information. But, that's not what the domestic electric meter will be measuring of co
Must be on an older 3 wire system then. Most new domestic supplies in the UK are two wire, with PME mains distribution systems. So, although you have a neutral and an earth connection marked up in th
I have also seen these microwave transformers draw a lot of primary current with no load connected to the secondary, a lot more, in the order of 3 to 5 amps..I know a ham who rewired the secondary fo
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 :
...that's right and that's what cosine is about. With real high power animals its not unusual to see reactance canceling capacitors across the primary theyre sometimes automatically adjusted too! Ale
I measured the temperature of my microwave oven transformer at over 180 degrees F. This was after over four hours of no load except the bleeder current. It came from a 1100 w oven. 73, Tom K6EU _____
Dear all, it seems that a little basic information about transformers could be good here. Yes, microwave oven transformers will indeed typically take more primary current at no load, than some other
Author: "Dr. David Kirkby" <david.kirkby@onetel.net>
Date: Sat, 26 Apr 2008 09:22:36 +0100
If I recall correctly, (and its a very long time since I did my EE degree), it can be shown that a transformer has maximum efficiency when the copper loss is equal to the iron loss. Hence if either o
I've been searching (without succss) for a post I remember where someone talked about the ratings on these transformers and how the primary current dropped if you reduced the line voltage a bit. I th
An interesting explanation of how a MOT compares with other transformers. Thanks Manfred! I guess that microwave oven transformers designers also try to use as little copper as possible, because of i
Hi Angel, Yes, of course they do! This approach generally leads to rather longish transformers (laminastion stack much taller than the with of the center leg). Also, such transformers are more suited
Here is another data point. This is for a transformer removed from a 1100W oven. Measurement made with one of those "Kill-A-Watt" meters. No load except for the bleeder. 67 watts, 170 volt/amps. Blee