Electrical Faux Pas

[BEP]

@Wattsup

I'm sure there is a better way (usually burning the insulation off with a soldering iron and solder flux) but my favorite when I have a lot of little connections:

Take one busted (missing the drill bit part) small hole saw.
Insert it in the chuck of a small battery drill or screwdriver.
stuff the hole saw full of fine steel wool.
Stick the wire end in the center of the steel wool and pull the trigger.

It takes a bit of practice but it works. After you get the hang of it you'll stop breaking wires 

[gyulasun]

@all

Since z_p_e is no longer around, thought I'd put this here.

One thing that has bugged me for a long time now was how to skin magnet wire. When you have 20 of these to do using sand paper, it starts getting messy, your fingers ache and it takes forever.

So, I just found this video attached below.

If anyone has a better idea, I'm all ears, uh eyes, uh fingers, uh whatever. lol

Hi Wattsup,

I used to use alcohol or spirit burner to burn the enamel (nowadays a gas-filled lighter is ok just like in your video) and when the wire end is red-hot you suddenly immerse/dip it into spirit (denaturated alcohol) to cool it down.
Usually you get a nice/clean copper surface ready to solder. Be careful not to light the spirit with the lighter (spirit was poured into a small bowl or cap in advance).
Basically this method was preferred to clean Litz wire ends but obviously should work for single wires too.  If you happen to have contact spray (Tuner 600, or the like that has no oil/lubricative additive) at hand, you may use it a little after you take the wire ends out from the spirit. Then you are ready to solder the surfaces.

rgds
Gyula

[wattsup]

Hi Guys;

I have been mulling over an idea for a few weeks now and thought to resurrect this thread instead of starting another one for what may be a few questions.

The topic is Microwave Ovens. lol. No this is not a cooking question. Well maybe.

I know that some of the devices by Otto, Roberto and especially @GK can produce some pretty nasty waves that may be harmful.

I also know that my EE prowess is in the gutter, but my continuous quest for pulsing things (all sorts of coils, etc.) is never ending.

So what I am wondering is can I use a microwave oven. Remove the magnatron that has two wires connected to is. Put a plug connector on those two wires and run this into the cooking chamber where I can connect all sorts of coils. I can also run the coil output out from the same hole to measure output power.

What I am thinking is the oven already has all the electronics, you can choose time, power level and some other parameters. Then when I drive a coil, the coil would be inside the cooking chamber that is already designed to protect from microwaves so it should be good to protect against other types of waves. Plus if this could work, it would be easy to measure power input as 120vac or whatever and then check the amperage, then compare this with the output.

Microwaves are super cheap to buy these days. Used ones are even cheaper. Plus, if you really get to know what is coming out of the control panel circuit, you can make changes to the cap value and even the microwave transformer.

Maybe one last thing. I know many will say do not touch it if you don't know what you are doing, but that never stopped me before. I know how to be careful. I think this may have some merit and provide a secure way to test devices, even if it's just for the cooking chamber itself.

So, anyone have any ideas about this.

[armagdn03]

Below are two errors that seem to occur on a regular basis, yet I have seen no one yet correct them.

These are fundamental faux pas and should not be propagated any further. They are:

1) Square waves contain all frequencies.

2) Transformers do not faithfully pass square waves. A 50% duty-cycle square wave applied to the primary of a transformer, will only yield a "short pulse" on its secondary. This is because most of the square wave time is spent on a steady voltage, either +V, or 0V... i.e. the wave form is hardly ever "changing" over time.

Both notions are absolutely false!

1) True square waves contain only odd order (integer) harmonics. A sawtooth wave form does contain all integer harmonics (one example).



2) All transformers have a finite bandwidth. Any wave form can be disassembled into its constituent sine wave components, a la Fourier. A square wave can be reasonably constructed using the first 5 sine waves, i.e 1, 3, 5, 7, and the 9th harmonics. The more harmonics applied, the more exact the resulting square wave shape will be. It comes down to transformer bandwidth, and what square wave frequency is applied to it. Too high an applied frequency, and the corners will start to become more rounded. In addition, the flat portions will begin to show "ripple" until finally, only the fundamental sine wave will appear. Too low a square wave frequency, and the flat portions will begin to tilt. At no time however between these two extremes, does the secondary exhibit a "short pulse-like" output. The transformer does not arbitrarily convert the square wave duty cycle to something other than what it is at the primary. Transformers therefore can pass square waves, and in fact any wave form faithfully, as long as the input frequency lies reasonably within the bandwidth of the transformer. If this were not the case, Audiophile tube amplifiers would not be possible.

Sorry to butt in, and I only read this one post, so this might have already been corrected but....

Square waves can only excite harmonics that are of the same wave length or longer than the rise / fall time of the "square" pulse. first off, there is no such thing as a  square wave, they are all trapezoidal, it takes time from "on" to the steady state, and it takes time to turn off too, its not instantaneous as a square wave would imply. So lets say that a square wave has a rise time of 1us, this means that it takes .001 second for it to rise, this is known as its period, and we also know that frequency is the inverse of period, meaning that 1/.001 = 1000 hz, and this would be the fastest frequency it could excite. this same principle holds true for physical vibration as in spring mass systems, and also for other wave forms, including saw tooth.

[armagdn03]

Sorry to butt in as well, but I think I can offer a realistic word of warning.

The voltage from the microwave transformer is a LOT higher then you would
normally want in a TPU type of coil.  (Assumption on my part...)  I can't give
any form of exact figures without measuring, but I would assume always
greater than 1Kv unloaded.  (I think around 4Kv is average, but again, I have
not measured it personally.)  If anyone has done a measurement and I am
wrong, please say so, but trying to measure this high of a voltage with a normal
DVM will cause the end of the DVM.  (Most are rated to 600V....)

Armagdn03:

Little oppps.  I think you meant 1mS rise time, not 1 uS.  1uS rise time would be 1Mhz.
Also, you are in what I call a "Gray" area, because the "Output" Frequency is going to
be as much related to what you drive as the square signal.  Example:  Send the wave
you describe to a tank ckt and the output will be whatever the tank is tuned to.  Freq.
multiplication is common in digital logic and the output freq of a simple ckt can be
higher than the rise time would suggest. 

Now, to ensure that I'm branded the idiot, what you state is exactly correct for a resistive
load, and being that this is a "Faux Pas" thread, That is the best way to look at it.  As far
as driving a coil, the Freq that you are going to get will depend on WHERE you measure
or get the signal from, as anyone could guess.  The Coil ring is one.  The Actual Current
input to the Coil is the Square wave on input (Mostly.....)  The inductive output from the
coil should match the ring but may have components from both of the above.  To go any
further, you would have to talk to people well versed in RF, which I am not.  (Just basics..)

The biggest killer is, modern switching times for Square waves are Soooo fast for common
parts (50nS is easy today.) that the freq people are trying to use is usually much slower
than what the square wave puts out.  I bet that causes the most trouble.  Most people
don't realize how fast that is.  (20 Mhz)  For someone trying to work in the Khz, this is
way beyond where they are working and, for me, clouds the issue of basic signals.  20Mhz
is plenty high enough to be RF, and will transmit all over the place.  All it means is, unwanted
effects can appear from the RF that comes off a normal logic gate or transistor when using
square waves.  This is also where I lose drive to MOSFETS.  The instant current value for fast
switching gets crazy on fast risetimes, which is what a good 555 can put out.  I'll shut up
now and leave the theory to people that know far more than I.  (Try using 100pS Switching...)

Yes, I agree with everythig you wrote, I should have been more specific, the 1Mhz (thanks for the correction) would be the fastest it could excite, if you impart this pulse on a circuit containing both inductance and capacitance (which all systems I am aware of do) it will excite its natural frequencies.