Self accelerating reed switch magnet spinner.

[TinselKoala]

Stable running at 1285 RPM, total input power around 1.3 Watts using inline DMM for current. This is for comparison with what we get using the MH comparator-computerator once I get it built.

[MileHigh]

TK:

I'm flattered that you want to build the analog computer for computing power draw in real time.  Good luck and no rush, do things at your own pace.

That was so cool in your clip where you see the rotor rocking back and forth with increasing amplitude until it breaks through and takes off.  I don't think I have ever seen anything like that before.  You get the sense of "active power" wanting to be unleashed.  It makes me think of all of those clips of alleged over unity motor generators.  A month or so ago there was one that was supposed to have a COP of 18 or something like that.  I posted that when you play with an alleged over unity machine like that you should get a sense that the bloody thing is almost _alive_ and itching to jump into a positive feedback loop and keep increasing in speed.  Even in a clip you should be able to sense that and of course there is no sense of that happening at all.  Your little "active rotor" being triggered by the op-amp gives you a small version of that feeling - but of course there is a non-hidden power source...

MileHigh

[MileHigh]

I assume that a lot of pulse motor builders are watching this thread and are learning as we go along.  So much the better and I hope that some people are being inspired.

I wanted to discuss how to get more speed in somewhat abstract terms.  To get speed you need a low friction rotor and good timing with full control, and power.  The low friction rotor is a mechanical issue that each builder deals with on their own terms within their own budget and available materials, etc.  Good timing with full control has been taken care of with the MileHigh op-amp circuit.

So what about power?  Let's assume that we have a typical 12-volt battery source and a standard drive coil with a core.  What can we do to get stronger magnetic field pulses produced by the coil?  Let's assume that the physical size of the coil remains about the same.  In other words we need to think of some way to push more power through the coil to create stronger magnetic field pulses without changing the physical dimensions of the coil.

Note also that the average pulse motor builder does not know if they have saturated the core in their drive coil.  It's an issue that's never even discussed as far as I am aware.  That is something that ultimately may come into play and there are ways of checking for that but we are just going to put that issue aside for the moment.  Let's just focus on this issue of getting more bang out of the coil for a faster spinning rotor.

Notice again, that this is almost uncharted territory.  Builders make a drive coil with or without a core (I believe most use a core) and then it's more or less a given - they work within it's constraints and worry about other things.

Okay, that was the setup, so let me start a fresh posting to look at this issue - How can you supercharge your drive coil?

MileHigh

[MileHigh]

How can you supercharge your drive coil?

I thought about this for 15 minutes and I have an idea.  We are just going to use a quasi-abstract example to make it simple and understandable for most people.

For starters, we know the core is there, but we are not going to discuss it.  We can safely put it aside for now and the discussion will be perfectly valid.

Here is you quasi-abstract drive coil configuration:  It has 100 turns, and one ampere of current flows through it when you connect it to your 12-volt battery.  Forget about details like calculating the wire resistance, we don't need that data.  We are going to also use an abstraction for the energizing time constant and say that it takes one unit of time.

So we can say that when this coil is energized, after five time constants, there is one ampere flowing through the coil.  Therefore, the strength of the magnetic field generated by the coil is 100 ampere-turns.

What can we do to improve this?

Let's split the coil into two separate 50-turn coils.  Two 50-turn coils will fit on exactly the same spool as a 100-turn coil.

So let's look at each 50-turn coil.

We know that the energizing time constant for the 100-turn coil is L/R.   We know that L is proportional to the square of the number of turns.  Therefore the L becomes (L/4) for the 50-turn coil.   The R becomes (R/2) for the 50-turn coil.  So the time constant for the 50-turn coil is ((L/4)/(R/2)) = L/2R.

So, we know that for the 50-turn coil, the energizing time constant is one-half the time constant of the 100-turn coil.  That means that the current rise in the 50-turn coil is faster, and a faster current rise time means faster appearance of the magnetic field.  This will become more important as the rotor speed increases.

We know that the maximum current in the 50-turn coil is two amps, simply because the resistance of the wire is one-half the resistance of the 100-turn coil.

So how many ampere-turns of magnetic field generation do we get with the 50-turn coil?  It's 50 turns x two amperes = 100 ampere turns.  Holy crap, that's the same amount of magnetic field generation as the 100-turn coil!

Surprising isn't it?  A 50-turn coil gives you the same amount of magnetic field production as a 100-turn coil and it does it faster!

MileHigh

[MileHigh]

So now that we know that a 50-turn drive coil for your pulse motor is just as good if not better than a 100-turn drive coil, how do we take advantage of that?

I am assuming this part is something that will come naturally to most builders, it's very easy, especially if you are using the op-amp timing circuit.

So you take your 100-turn drive coil and you split it into two 50-turn coils.  You use TWO MOSFETS, and there is nothing stopping you at all from using TWO separate batteries sharing a common ground if you are worried about the increased load on a single battery.  Or perhaps you have a big beefy bench power supply and supplying the increased current is not an issue.  (Note you don't necessarily need to use two MOSFETs either.  This is where you start looking at spec sheets.  It all depends on how much total current you are dealing with. In the real world you rarely see "over design" because that increases costs.  However, having separate MOSFETs is "sexier" and more fun!)

There is a very decent chance that the active pull-up and pull down of the op-amp output will be able to drive the two gate capacitances of the two MOSFETs.  This is where you check with your scope.  If yo have to, nothing is stopping you from adding a MOSFET driver chip if you want.  My feeling is you won't need one but I am not sure.  I looked at the schematic for the TL082 and I think it's output impedance for sourcing or sinking current is 50 ohms.

So there is your supercharged drive coil:  You double the magnetic field strength of the drive coil if you split the coil into two halves and you decrease the energizing time constant by one half.  Nothing is stopping you from splitting it into three or even four if you want to.

Of course it goes without saying that when you do this you pay a price for this:  You double the current consumption and you double the power consumption of the drive coil also.

Finally, you have a "real" bifilar or trifilar or quadfilar application for a coil that really does something - it supercharges your drive coil.  It might require more batteries and more MOSFETs, but that should be cool and a fun thing to build.

A coil like this might be so powerful that it will saturate your core.  That has the potential to create "current runaway" so you should monitor your drive coil to make sure it does not get too hot.

You want to dump the current pulses into a charging battery?  No problem at all, just give each coil its own separate diode and it will work perfectly.

You can wind a bifilar yourself, or just buy a spool of speaker wire.  Or, you can fill up the front half of the spool with one integral coil and the back half of the spool with another integral coil - it won't make a damn difference in the world - the only thing that counts is ampere-turns.

MileHigh