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transformer help?

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spitso

Member
hi all

Im just enquiry about miniature audio transformers,
why are they rated in ohms?
how can i use these values to find what i need?
average voltage they can handle on primary side?

specs

i am trying to build a taser from my own schematics so i need to get as high as possible voltage on secondary.
going to be using voltage multipliers so secondary output doesnt need to be in the KV's.
running primary from 9v

thanks

MikeMl

Well-Known Member
You dont need an audio transformer. You need a transformer with a high step-up turns ratio. To get 500V from 9V would be a turns ratio of 500/9=55.

The transformer should be constructed so that it works efficiently at the frequency you intend to switch it at. It just so happens that audio transformers are typically used at frequencies from ~50 to about 20,000 Hz. Is that what you want to switch at?

Audio transformers are rated for impedance matching. It just so happens that the turns ratio can be computed from the impedance ratio. The voltage step-up (or down) is proportional to the turns ratio. The turns ratio is the square-root of the impedance ratio, or conversely, the impedance ratio is the square of the turns ratio.

If you need a 55:1 turns ratio, that would be a 3086:1 impedance ratio. For example, an audio output transformer which is rated at 12000Ω input and 4Ω output could be turned around and driven backwards to get a 55:1 step-up. However, I have never seen a 12000Ω:4Ω audio transformer, so it is moot.

You might find one that is 500Ω:3.2Ω, so that would only be √(500/3.2) = 12.5:1 which would only make 112V out of 9.

You could use a capacitive-diode voltage multiplier on the secondary side to step up the voltage further.

A photo-flash transformer may be more suitable.

btw-I recommend you use the taser on yourself!

spitso

Member
Attached is the schematic i will be using. It is a combination of schematics i found from
Stun Gun, Electronic Dazer, High Voltage
and
http://www.geocities.com/capecanaveral/lab/5322/coildrv.htm
Frequency can be adjusted to change taser characteristics.
But i would like this to be light and handheld so a normal transformer might be too bulky/heavy, thats why i would like to use a minature audio transformer.

any recomendations on a transformer
i can get these following transformers easily, will any of these be helpful?
Primary/secondary 1k ct/8 ohms- Ferrite core- 350mW rating
Primary/secondary 500 ct/8 ohms- Iron core- 450mW rating

Also what do you think about replacing the 2n3055 with an irf540

thankyou very much for help.

Attachments

• Combined schematics.GIF
8.4 KB · Views: 8,910

MikeMl

Well-Known Member
I see that the 555 astable frequency and duty cycle can be adjusted over wide ranges. What freq do you want to run at?

The fet should work. You want a fet with low gate capacitance. Leave out the 100Ω

I'd go for the 1kΩ:8Ω That is a 11.2:1 turns ratio. Ferrite is usually lower loss at high audio freq.

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spitso

Member
ok thank-you for that

in concerns of frequency ive got no idea, um i supposed id just adjust it untill i get best possible arcing on the output then ill replace variable with fixed (or might incorporate a pot for different arcing).

Only problem i have now is knowing the transformer limit of current on primary because no specs are given, only secondary output specs of 350mW are given.

blueroomelectronics

Well-Known Member
Arcing how far are you hoping a spark will jump in your design?

mneary

New Member
That design should produce a spark at least 500 microns long.

audioguru

Well-Known Member
You will be feeding high power into a low power transformer. It will be instantly destroyed.

spitso

Member
would like the acring be around 2cm long, something that can be easily visible.
But most of the work will be done by the voltage multiplier's.

colin55

Well-Known Member
You can buy a taser for less than $50.00. We used to build them but the Chinese version is less than the cost of manufacture. The most difficult part is the output coil (transformer). It needs to be "Pi" wound or potted. It's a simple 2kHz oscillator driving a spark gap that dumps into the primary of a 80 turn coil. The secondary produces about 3 volts per turn. The oscillator transformer can be taken from a$2.00 camera from a photo shop but the HV transformer needs to be hand-wound.

spitso

Member
cant buy tazers in australia....but still rather make one so learn how it operates.

Frosty_47

New Member
Just use a Flyback Transformer from CRT monitor.

Keep in mind that it's output can reach 27KV

That is more than enough to fry your neighbor's dog/cat/baby

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spitso

Member
did try that but it blow up the ic.
aswell those things arnt small so wont make my final product compact\handheld.

colin55

Well-Known Member
I have already explained the principle of a stun gun. You are wasting your time with all the other arrangements. You need to pump 1,500 volts into an 80turn primary and have about 3,000 turns on the secondary to get 50,000v out.

stevez

Active Member
I've got to think that at some point the voltage would exceed some breakdown point within the transformer if it was not made for that purpose. Sure, you can push some things and they just happen to work but at some point the transformer will fail.

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