TV Flyback Transformers

[Smitty]

I have a flyback transformer I purchased surplus, It has 10 pins. I want to experiment with high voltage experiments using a DC input. How can I determine which pin produces which voltage and also how can I measure the voltage when my multimeter only goes as high as 1000 volts? Any help is appreciated.<p>Smitty

[Joseph]

One way to get an idea of the windings is to hook it up to a audio signal generator and probe the pins to find out what voltages are present between various ones. If you don't have a generator, you cam set up a simple 555 timer oscillator to feed into a stereo. Then you can take the stereo output through a resistor, say 10ohm.

[Chris Smith]

To check high voltages you need to make a voltage divider. Take a 10 meg [9 meg actual] resistor and one meg resistor and solder them together. Make these resistors a dead short across the voltage and tap across the one meg resistor[bridge] for a one tenth [apx] reading, or one equals ten. You can do this with 99 meg and one meg for 100 to 1 reading.

[MrAl]

Another idea is that the winding with the
highest resistance is probably the
high voltage winding due to many turns.
Also, since these things can put out over
20kv it can be a safety hazard.
I saw a high voltage probe built one time with
a string of series resistors. The values are
selected to drop a know amount of voltage
so as to provide a division ratio between
voltage at the probe tip and that actually
seen by the meter.

[HomeBrew]

There is only one high voltage winding on most flyback transformers. This is the output winding that goes to the doubler or tripler on modern TV's or monitors. The primary winding you want will be the one with the most resistance across it. TV receivers use the other windings to power other circuits in the set after they are changed to DC ,saving the expense of a seperate power supply. You can find many HV power supply designs using the flyback like you have on the net sometimes listed under TESLA power supplies or related subjects.

[Chris Smith]

Although the fly back transformer produces a high voltage, and although its not deadly to most healthy people, it is prudent to be aware of its danger and not come in contact with this power. After the fly back If or when using a double or tippler, this voltage becomes very unhealthy to even the healthy. The voltage divider that I mentioned can be made safer for voltages higher than 20 kv all the way to 50 kv by placing a series of resistor in a string, ten or twenty single 10 meg resistors and placing a single one meg resistor dead center between the series of resistors, or at the ground end of this string. The longer the series of resistors making up the divider, the less chance of jumping or arcing across a single resistor. Heat shrink the entire package with a single uncut tube and keep clean at all times. Body oil can cause arcing or tracing and so a alcohol wipe before applying the shrink is also prudent. A plastic tube full of non metallic liquid epoxy with the resistor string inserted is also suitable. Also when you test for voltage, complete hands off testing is prudent. At the one meg resistor, tipple insulate that resistor and its leads comming off buy using two or more layers of heat shrink, epoxy or other suitable material. If using voltages above 50k, sink all wires and currents into at least one half inch of epoxy resin, and cover the final unit with some sort of soft vinyl, heat shrink, or non conductive rubber. Never access these voltages to within a foot of your body from any exposed lead. For about two dollars you can build this tool and properly sink the whole thing into a clear or colored plastic tube with a handle safley away from all of the workings using a acrylic tube, ABS, or even PVC. The unit should be at least 18 inches long when you finish, with your hand being safely at least 8 or 9 inches away from the nearest sealed lead. Also use good high voltage leads [9mm] like the type used in HV ignition leads on a modern car.

[MrAl]

Hi again,<p>Does anyone know the max voltage that can
appear across a standard 1/4 or 1/2 watt
carbon resistor?
If we allow 250 volts max across a single
resistor, we need 80 resistors in series
to get up to a max measureable voltage of
20,000 volts. The string would have to be
carefully arranged mechanically to prevent
arc over between nodes.<p>--Al

[Chris Smith]

This is a guide line only but with experience and practice it should be a sound guide line to follow. There are many factors that affect the arcing over of a resistor. Humidity, body oils, contaminants, and others. Heat shrink and epoxy as well as high voltage putty will increase the allowable voltage going through a resistor to stop the arcing. The general rule I follow which is a comparison factor only is that it takes approximately 25kv to arc one inch through dry air. Using half this value I design my high voltage circuits. This is only applied to extremely low currents in the less than one milliamp range, usually in the ten thousandths of one amp range being normal. As you increase the amperage the barrier that stops the arcing is easily broken down and more distance and insulation is required. If your resistor is 1/4 of an inch in length it should easily hold 25/4 kv /2 = 3kv. These numbers are working experimental numbers with the leads exposed to air. As you insulate and increase the number of resistors, this number can go up three fold easily if it is done properly, clean, and neat.