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Author Topic: Silly question about voltage and current  (Read 37412 times)

Offline MarkE

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Re: Silly question about voltage and current
« Reply #60 on: February 28, 2014, 11:59:49 PM »
Why is this important, because we can use the pos energy to pulse a coil, now the diode works bidirectional it passes the pos bemf from the negatively pulsed coil into another coil, pulsing this coil with pos energy its bemf will be neg and will pass through the same diode, now your coils can ring back and forth.
Even if you fix the MOSFET orientation you are in trouble.  That is a good way to ruin a perfectly good MOSFET.

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Re: Silly question about voltage and current
« Reply #60 on: February 28, 2014, 11:59:49 PM »

Dave45

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Re: Silly question about voltage and current
« Reply #61 on: March 01, 2014, 12:13:15 AM »
Even if you fix the MOSFET orientation you are in trouble.  That is a good way to ruin a perfectly good MOSFET.
Ok fix the mosfet orientation - the mosfet is not what we are discussing here. This is how a discussion turns into miles of senseless posts.

We are talking about the bemf of a negatively pulsed coil and its polarity not the mosfet orientation, so its wrong, I told you I took it from a schematic that was handy.

Offline MarkE

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Re: Silly question about voltage and current
« Reply #62 on: March 01, 2014, 12:39:41 AM »
Ok fix the mosfet orientation - the mosfet is not what we are discussing here. This is how a discussion turns into miles of senseless posts.

We are talking about the bemf of a negatively pulsed coil and its polarity not the mosfet orientation, so its wrong, I told you I took it from a schematic that was handy.
Dave, all coils have real resistance.  All diodes have resistance and forward voltage drop.  Therefore, anything that you do to connect a coil through a diode dissipates energy that you put into the coil to build up its magnetic field. 

Forty years ago when transistors were expensive so called bi-level circuits were popular for things like solenoids and stepper motor drives.  A drive voltage would be applied to a coil for a certain period of time to build up the current, and then a lower sustaining voltage would be applied that would ideally match the I*R drop of the coil in order to hold the current.  The power drawn from that second, lower voltage supply is the ongoing loss in the magnetics.  Since the mid 1980's we have had wonderful switching drivers that deliver the same effect by periodically connecting the coil to a power supply and then allowing the current to recirculate either through the coil or back through the power supply.  These devices are carefully designed to minimize losses.  And there are always losses.  The bottom line is that any combination of coils and switches you can think of, it is almost certain that someone else has already used in some form or another.  Resistance, eddy current losses, and hysteresis losses aren't going away.  They eat at the energy stored in any non-superconducting magnetics ever built.

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Re: Silly question about voltage and current
« Reply #62 on: March 01, 2014, 12:39:41 AM »
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Offline MileHigh

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Re: Silly question about voltage and current
« Reply #63 on: March 01, 2014, 01:35:19 AM »
Dave:

My request is that if you are going to put up a diagram, then make it complete.  Assuming that it is being driven by an external voltage source, what are the polarities of that voltage source?  You put arrows up for current, are you talking about electron current or conventional current?  You say "positive this" or "negative that" with reference to something in your simplified schematic, but you put no polarity indications on the components you are talking about.   It would take you five more minutes to mark up your schematic segment, so why not do it?  Why should the readers of the thread have to do mental gymnastics trying to figure out what you really mean?

Just take the example of a "positively pulsed coil."  You can just as easily call that a "negatively pulsed coil."  If you don't define which of the two terminals of the coil is your voltage reference, then your statements about the polarity of the pulsing of the coil are meaningless.

Quote
Why is this important, because we can use the pos energy to pulse a coil, now the diode works bidirectional it passes the pos bemf from the negatively pulsed coil into another coil, pulsing this coil with pos energy its bemf will be neg and will pass through the same diode, now your coils can ring back and forth.

Yeah, sure, that's really clear.  I can do mental gymnastics trying to figure out what you are saying, or you can do a proper diagram or sequence of diagrams to effectively communicate what you are trying to get across.  About the only thing that I can say is that relative to schematic snippets I have seen, there will be no coils ringing back and forth.  Why don't you draw out a timing diagram along with a properly done schematic diagram to explain what you are trying to get across.

MileHigh

Offline Farmhand

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Re: Silly question about voltage and current
« Reply #64 on: March 01, 2014, 01:35:19 AM »
Dave, if you don't draw things correctly then it is going to throw the conversation off.

Well this is all a bit odd, I have evidence to show that when a coil is snubbed by a freewheel diode the current in the coil stops immediately as compared to when the coil is allowed to discharge into a higher voltage.

Dave you are trying to use electron movement "current" for the coil charging then applying conventional current to the coil collapse. The coil is charged with positive potential and discharges current in the same direction of current flow when the coil is switched off, very simple the discharge of a coil is not Back emf is is forward emf. Understand that and you'll get somewhere.

Here these scope shots show the voltage and current through the coils when the coil is allowed to discharge through a higher voltage load and also what happens when the coil is snubbed by a free wheeling diode. As we can see the snubbed coil's current ceases immediately with no extra current ( the energy is wasted) likely burned off in the diode and coil, where the coil discharging to a higher voltage takes time to discharge.

Not talking in absolutes but to me the theory that the current recirculates in the snubbed coil falls flat on it's face in reality.

The top two shots are from a snubbed coil with a free wheeling diode (current stops immediately on switch off), and the bottom two the coil discharges into a load at double the supply voltage and current continues after switch off. Yellow are current traces across a CSR and blue are drain voltage traces.

The bottom of the "on" times looks angled because the scope grounds were connected to the positive rail at a discharge capacitor, I can assure you the switching was sharp as anyone would want. I grounded the scope there for ease of connection so I could measure the current and voltage together and keep the grounds in the same place.



..

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Re: Silly question about voltage and current
« Reply #64 on: March 01, 2014, 01:35:19 AM »
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Offline MileHigh

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Re: Silly question about voltage and current
« Reply #65 on: March 01, 2014, 01:48:54 AM »
Farmhand:

When a coil is snubbed by a freewheel diode then by definition the current decay will take much longer as compared to when a coil discharges into a high voltage EMF source or it discharges into a high resistance which causes the coil to generate a high voltage.

Unfortunately you are in the same territory as Dave.  You put up a scope screen grab and you aren't saying what trace is what and what case is what.  You have no related schematic showing where the scope probes are connected to the schematic, signal and ground connections.

So it's back to doing mental gymnastics to try to figure out what you are saying.  All that I can state is that your comments about the discharge time for the coil are wrong and I can perhaps make some inferences about what your traces mean.  But I am not going to spend five, ten, or 15 minutes trying to figure out the pieces to the puzzle.

MileHigh

P.S.:  I can see how you were still editing your posting when I commented and added more information.  It's an improvement but I will remain a stick in the mud and would prefer an accompanying schematic snipped with probe positions and all that jazz so that I can try to understand your points without the mental gymnastics.  This is just an editorial comment, I am not literally asking you to do this.

Offline Farmhand

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Re: Silly question about voltage and current
« Reply #66 on: March 01, 2014, 01:56:34 AM »
Farmhand:

When a coil is snubbed by a freewheel diode then by definition the current decay will take much longer as compared to when a coil discharges into a high voltage EMF source or it discharges into a high resistance which causes the coil to generate a high voltage.

Unfortunately you are in the same territory as Dave.  You put up a scope screen grab and you aren't saying what trace is what and what case is what.  You have no related schematic showing where the scope probes are connected to the schematic, signal and ground connections.

So it's back to doing mental gymnastics to try to figure out what you are saying.  All that I can state is that your comments about the discharge time for the coil are wrong and I can perhaps make some inferences about what your traces mean.  But I am not going to spend five, ten, or 15 minutes trying to figure out the pieces to the puzzle.

MileHigh

I do have a related schematic and you have seen it before, but you must have forgotten. The top shots show a coil pulsed and the discharge clamped by a freewheeling diode, the bottom shots show a coil pulsed and the discharge directed to a higher voltage load. I can find the schematic or draw another. There should be no need.

I don't see any discharge of current continuing after the snubbed coil is switched off do you ?

There is no puzzle, have Conrad do the experiment for you. It's very simple.

The top shots show a coil pulsed with a diode clamping the discharge to the supply rail, where is the current after switch off.

P.S. you reacted too quickly and didn't give me time to edit the post. re read it now. Slow down champ.
..

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Re: Silly question about voltage and current
« Reply #66 on: March 01, 2014, 01:56:34 AM »
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Offline MileHigh

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Re: Silly question about voltage and current
« Reply #67 on: March 01, 2014, 02:02:26 AM »
Farmhand:

You can't expect people to look at a scope screen capture from you and then pull the correct schematic from a "mental memory file of previous Farmhand postings" and then visualize that in their mind while looking at your scope capture.   That doesn't make any sense.  When you make presentations you have to come out of your own personal bubble and pretend that you are an outside observer with no preloaded preconceptions.

Anyway, my points have been made.  When presented with incomplete data like this I normally simply tune out.

MileHigh

Offline MileHigh

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Re: Silly question about voltage and current
« Reply #68 on: March 01, 2014, 02:10:25 AM »
Farmhand:

I don't know why your tests are giving you contrarian results.  However, the coils doesn't lie.  The higher the resistance the coil discharges into, the higher the output voltage and the faster it discharges.  An ideal coil discharging into a zero ohm resistance will never discharge and have an output voltage of zero, and the current will flow forever.  When a coil discharges across a diode, that's akin to a very low resistance, hence a larger discharge time.

MileHigh

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Re: Silly question about voltage and current
« Reply #68 on: March 01, 2014, 02:10:25 AM »
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Offline Farmhand

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Re: Silly question about voltage and current
« Reply #69 on: March 01, 2014, 02:11:18 AM »
Actually I "may" be wrong in where I placed the current sense resistors, so you are probably right, I will need to do that experiment again to get a better result. No problem.

Point taken. Will provide revised shots as soon as I can with a setup made just for the experiment. And the schematic.

Offline MileHigh

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Re: Silly question about voltage and current
« Reply #70 on: March 01, 2014, 02:12:39 AM »
Cheers.

Free Energy | searching for free energy and discussing free energy

Re: Silly question about voltage and current
« Reply #70 on: March 01, 2014, 02:12:39 AM »
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Offline Farmhand

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Re: Silly question about voltage and current
« Reply #71 on: March 01, 2014, 02:21:01 AM »
So in the mean time can it be established that the discharge from a coil is forward emf ? Not Back emf ? That would be a big step.

Cheers

Offline MarkE

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Re: Silly question about voltage and current
« Reply #72 on: March 01, 2014, 02:34:26 AM »
This is how coils behave when connected to switching circuits.

Offline TinselKoala

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Re: Silly question about voltage and current
« Reply #73 on: March 01, 2014, 02:34:54 AM »
Yes please. If we use the term "current" can we agree to stick to the established convention of the direction of "travel"? And if we are talking about charges, then let's call them charges and accept that they go the other way around the circuit. But if we are analyzing circuit behaviour from the standpoint of electromagnetism, power dissipation, and all that, we should stick with the established convention, even though we know it is "wrong".  Drive on the left side of the road if you are in Britain or Japan, please, and if you are on Earth.... current (consider "conventional" as always implied) goes from positive  to negative.

Offline TinselKoala

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Re: Silly question about voltage and current
« Reply #74 on: March 01, 2014, 02:40:37 AM »
Ok fix the mosfet orientation - the mosfet is not what we are discussing here. This is how a discussion turns into miles of senseless posts.

We are talking about the bemf of a negatively pulsed coil and its polarity not the mosfet orientation, so its wrong, I told you I took it from a schematic that was handy.

Indeed. If we get the _basics_ wrong, it is difficult to make any progress at all. Posting wrong schematics and then trying to discuss them as if they were right, or that the wrong parts don't matter, makes it very difficult for us poor hidebound folks that build and experiment. And it can really_really_ lead people to stray very far from reality if it's not nipped in the bud, so to speak.

Would you like to see some good examples of this? Just go over to
http://www.energy-shiftingparadigms.com/index.php and read the "papers" that are posted there.

 

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