Electronics > Beginners
DC bias in transformer
johansen:
--- Quote from: Simon on September 06, 2013, 12:52:49 pm ---no it won't be a problem, you don't need a perfect balance. you can infact send DC pulses to a transformer and you will get AC out the other side although I guess it is not the best method
--- End quote ---
you do need a perfect balance or the dc current will flow according to the dc content of the signal, saturating the transformer, and you won't get much ac out the other side at all.
one part in a thousand is enough to notice. that's only half a volt on a 500 volt inverter, enough to cause major issues.
lower voltages don't help.. 30 milliohm mosfets and a 10 milliohm transformer running from 12 volts will have .17 amps flowing.. probably not enough to notice, because most people don't use ferrite emi beads as transformers.. but sometimes they are handy.. you must have a dc blocking capacitor most of the time.
Electrocow:
I'm sorry to wake up an old thread, but this thread was the top proposal when searching the topic on Google, and I have to leave a comment.
As DC bias in mains is usually extremely low, unbalanced loads in a big network (such as in your neighborhood) may cause a substantial bias. As mentioned earlier in this thread, this DC bias will go straight through any transformer primary winding only limited by the winding resistance. Depending on the DC current, this can partially or fully saturate the transformer core. Aside from the heating caused by the DC current, this can also manifest itself as humming in the transformer. As the bias is dependent on the network load, this humming can come and go during the day (such as when your metal-head neighbor turns on their 10 kW stereo).
This is not something mortal people encounter during our day-to-day activities, but this issue is highly prevalent among audio-engineering aficionados. A common solution is to put two huge electrolytic capacitors in series with the mains in the power supply for example an audio amplifier.
Kleinstein:
A known source for some DC bias on the mains grid are some cheap hair dryers on the low power setting. Some use a diode to draw only half the current, which is not really nice to the grid. Normally even such an current in the 8 A range does not cause too much DC voltage.
BravoV:
--- Quote from: Kleinstein on October 11, 2019, 03:29:33 pm ---A known source for some DC bias on the mains grid are some cheap hair dryers on the low power setting. Some use a diode to draw only half the current, which is not really nice to the grid. Normally even such an current in the 8 A range does not cause too much DC voltage.
--- End quote ---
Yep, I did a test using a hairdryer and measure the generated DC across the mains line (220VAC), details with video -> HERE
Simon:
--- Quote from: Electrocow on October 11, 2019, 02:06:37 pm ---I'm sorry to wake up an old thread, but this thread was the top proposal when searching the topic on Google, and I have to leave a comment.
As DC bias in mains is usually extremely low, unbalanced loads in a big network (such as in your neighborhood) may cause a substantial bias. As mentioned earlier in this thread, this DC bias will go straight through any transformer primary winding only limited by the winding resistance. Depending on the DC current, this can partially or fully saturate the transformer core. Aside from the heating caused by the DC current, this can also manifest itself as humming in the transformer. As the bias is dependent on the network load, this humming can come and go during the day (such as when your metal-head neighbor turns on their 10 kW stereo).
This is not something mortal people encounter during our day-to-day activities, but this issue is highly prevalent among audio-engineering aficionados. A common solution is to put two huge electrolytic capacitors in series with the mains in the power supply for example an audio amplifier.
--- End quote ---
So you felt the need to resurect a 6 year old thread.... :palm:
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