Hi Gyula

I do not know at which frequency pulsed dc was given at 250 volts.
I do not know much about terms so please forgive me if I make mistakes.
In India we get 220 volts and 50 Hz current from mains. Voltage fluctuates.
We connected the variac to mains. Output from variac was connected to a diode bridge rectifier which converts AC to sign wave pulsed DC if I understand correctly. Upto 220 volts from variac there is no change. But when we go above 240 volts the output voltage goes higher than input voltage and varia is limited to 250 volts and when we reach maximum the output voltage on load increased to 270 volts but when weremoved the diode bridge rectifier and gave AC this was not repeated and voltage decreased in the load.  The coil was wound with gaps ad in the gaps we put a lot of iron powder and paste

Hello All,

Rams,
I'm sorry... I didn't realize you were doing this in DC...I assumed you were just connecting to the AC mains...In the States we receive two wires of 120 and a neutral and each house is grounded in a single phase system... our main electrical appliances Air Conditioners, clothes dryers, stove tops and hot water heaters use 240 and everything else is 120 at 60 hertz ( sine waves )... I would imagine everybody else in the world is using 240 at 50 hertz ( cycles ) hence your DC cycles are 50 cycles ( hertz ) the unique thing about the circuit that Patrick used is that you can use any amount of DC current you want... for ex. I am using one 12 volt lawnmower battery... you could have endless current by adding in series batteries...

Gyula,
not to beat a dead horse... so what you're stating is everything is based on the input ( lenz law, flux, induction, gap potential and secondary  )...
X amount of energy from the source is going to produce Y amount of energy... no more... no Less...
is that correct...?

All the Best
Randy

Rams,

Electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied.

In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current (AC) circuit. Impedance extends the concept of resistance to AC circuits, and possesses both magnitude and phase, unlike resistance, which has only magnitude. When a circuit is driven with direct current (DC), there is no distinction between impedance and resistance; the latter can be thought of as impedance with zero phase angle

If for example you would need 160 turns of wire to hold a stable electromagnet at 50 volts AC, for pulsed DC you would need 640 turns of the same gauge wire wound on similar dia coils.

You could use a relay (s) to whatever amperage you wanted to make up the difference in turns... the problem in mains ( in the states ) the 120 AC comes in 20 amps and the 240 comes in 40 amps... but as I stated before any number of batteries in DC series could amp up any device ex. electric cars, trains and whatever...

All the Best
Randy

....
Gyula,
not to beat a dead horse... so what you're stating is everything is based on the input ( lenz law, flux, induction, gap potential and secondary  )...
X amount of energy from the source is going to produce Y amount of energy... no more... no Less...
is that correct...?
...

Hi RandyFL,

I do not know if there is a dead horse or there isn't.  What I wrote earlier to you was meant specifically for your question, and please interpret it in that connotation,  and NRamaswari also explained to you in Reply #2175.

Gyula

Gyula:

Your Questions:

when diode bridge is not present in the circuit and the Variac is cranked up to give the 250V AC output for the load, does the 220V voltage  at the Variac input also go down when the 250V goes down across the load?   How low does it go down? from 250V to how many volts?

Answer: The Input from the mains to the Variac does not go down. The diode Bridge consumes as I estimated approximately about 20 to 22 watts. It is a 35 Amps 1000 Volts Diode Bridge Rectifier. At the load the voltage went down to 220 if my memory serves me right. This was an experiment done in probably April 2013. We Considered the device to be failure as it did not get magnetized. We tried to make an electromagnet by connecting the device to the variac (2 amps maximum and it fumed and so we immediately stopped) and connected to the load.

Stable Electromagnet: A stable electromagnet is one where the coils can receive the input and work as an electromagnet. At higher voltages We need a lot of turns and length of wire to hold the magnet or otherwise either the fuze blows out or the office circuit breaker which I believe is rated at 35 Amps blows out. If the fuze does not blow out and the electromagnet can remain available to perform its intended function it is a stable electromagnet.

I have my own questions..

What is Pulsed DC? The Analog voltmeter which can show both DC and AC voltage readings showed 270 volts. But the digital multimeter showed 220 volt AC and 90 Volt DC. Now Patrick has taught me that pulsed DC is nothing but AC without the negative or bottom wave while Randy says it is DC. I'm very confused on this. My understanding is that it is a kind of interrupted DC and it goes in one way only with positive sign wave only when we used the diode bridge. That way it differs from AC but with the sign wave it differs from DC which has a square wave.

I do not have the variac in working condition. I think it is gone. You may wind a coil with space of one wire each between each turn and complete about 1000+ turns. And check this yourself. Please put plastic iron sheet and plastic between each layer when you wind because that is how that device was wound.

In India we have a problem of spurious components. The fuse that was rated at 1 amp did not blow out even at 7 amp input the otherday. The variac was made only for 2.25 amps input limit I think. It is a 500 watts Variac. So the fuse must have allowed more current to flow through and it should have caused the variac to short at some place. I think it can be repaired but there is no use for it now.

One of the forum members is replicating the device described by me. Let him complete and verify if the results are replicatable. He lives in a rich country and has heating equipment that can be heated by the device output and can measure what is the input and what is the output on load. He also has the facilities for testing.  So I would request others who want to replicate to hold until he finishes.

I think if the secondary is a thicker wire or as thick as the primary wire, then at a certain length and turns of the secondary and at a certain voltage level we are able to reach COP>1 level. But this can never ever be achieved if we use the transformer design where the Lenz law effect is predominant. But after crossing this voltage level it the COP level suddenly shoots up. I have checked for a 4 sq mm wire ( which is not used normally for wiring) up to 300 volts and it did not cross COP=1 level itself. But when the voltage has gone to 620 it was COP>8. I think all our equipment are rated to fail below this voltage level and are designed for this purpose.

Similarly I have seen that a very thick insulation plays a very important part for the output. I do not even understand why but you can check it for yourself with a three core or four core cable which has a very thick insulation and use it to make an electromagnet and use ordinary wires and alternate the cable and wire for the primary and secondary and you can see the difference. I'm not able to really explain but thicker insulation and thicker wires provides better performance. I think if we use 10 sq mm wire the COP>1 results may come even at 300 volt levels but we never ever would that wire for normal wiring purposes.

When I read transformers I asked why the secondary should not be wound with a lot of thick wire and a lot of turns and length? I felt that both votlage and amperage should go up.  What will happen if it is wound like that and did not find the answer any where and so I did this arrangement. Unfortunately the higher gauge copper wires are so expensive I could not check them for the secondary performance. Similarly I do not know why thicker secondary wires are not used in Tesla coils. It will be bulky and uneconomical perhaps but a thicker wire in the secondary of a Tesla coil must provide for higher amperage and if the turns are the same as the smaller wire the voltage cannot go down either. Why no material which can stand high frequency is put inside the Tesla coil?  May be I do not have the brains to understand that this will not work but I do not hesitate to ask questions and investigate. This is how I tried.

Randy:

Thanks for the explanation. Please keep in mind that I'm not trained and may use phrases that are not used normally. Like the stable electromagnet above for which I had to explain to Gyula.

It appears that there are some misconceptions forming in this topic.

First, a fullwave diode bridge does not "slice out the negative" of the incoming AC waveform --- see the graphic below. Rather, it takes that negative portion and flips it over to become a positive portion in the output waveform. If the input is "50Hz" then the output will have 100Hz peaks.

Second, the "220VAC" that the wall plug provides is 220 V RMS. This means that the _peak_ voltages are quite a bit higher: about + and - 310 V.
When this is run through an unflitered Full Wave diode bridge, the DC Peaks as shown in the waveform below will be at +310V, minus a little bit for the fed voltage drop of the bridge. An averaging meter will then knock off some more from this value -- 270 volts DC might well be an indicated "average" from this kind of waveform. Once this DC output from the bridge is filtered by capacitors, the voltage will be steady and near the _peak_ value of the AC input... not the RMS value. So it is not surprising that a bridge rectifier can put out DC voltage measurements that are much higher than the "nameplate" voltage input (which will usually be an RMS value.) I think this fully explains the Variac results reported by NRamaswami: nothing unusual happening, just some misunderstandings about FWB action, RMS vs. Peak values, and the averaging functions of meters.

Third... DC pulses most certainly do interact with the inductances of coils. One common form of inductance meter stimulates the coil-under-test with square wave pulses at a given frequency, then looks at the ringdown frequency of the coil's response and computes the inductance from that. If the coil didn't respond to the DC impulses in the first place, this couldn't happen. As long as there is a _change_ in voltage, for example at the leading and trailing edges of a DC pulse, the inductance "feels" this change.

Fourth... what is AC, what is DC? You will find that even trained engineers will argue about this distinction. In my opinion AC requires that the direction of current flow changes, so an oscillating signal must go below the zero baseline level for at least part of a cycle. Others will say that simply oscillating voltage magnitude is enough to call it "AC" even though the current _direction_ may always be going in the same direction, while only the magnitude fluctuates. For example a 5v peak-to-peak sine wave with a 7 volt positive offset would still be called "AC" by this camp. I don't happen to agree with this view myself since the direction of current in such a signal does not change direction.

(EDITED to remove the "wrong" FWB diode diagram! I got that image from the internets and didn't notice it had the diodes mixed up until just now. Sorry about any confusion that might have caused...        )

Heh... you should be even more confused... since that silly drawing I got from the Internet doesn't even have the FWB schematic correct! I just noticed this myself...

The waveforms are correct but the diode configuration isn't.

Here's what it should look like: