# Audio transformers?

1. Sep 17, 2010

### Evil Genius

Well the next step in my coilgun is a decent power source i every camera circuit that i use is burned up so i thought that i use a transformer well a audio transformer as the voltage multiplier but i cant seem to wire it right it actually doesn't charge the capacitors so i was wondering if it is possible for someone to help me i already did some searching around but all i could fine where main transformers.

2. Sep 18, 2010

### Bob S

What circuit schematic are you using now? If for example, you are trying to charge twenty 120-uF capacitors in parallel to 300 volts, the total stored energy is ~5.4 joules, so you will need a dc-dc converter that will run on a 12-volt battery and run @1 amp input for 1 sec (12 joules), or @100 mA for 10 sec to charge the caps. Ideal dc-dc converters made for this purpose are in the automotive CD (capacitor discharge) ignition circuits, such as the old (now discontinued) "Mark Ten B" kits made by Delta (or equivalent).

[added] here is a possible dc dc converter circuit for 12 volts to 300 volts.

http://www.eleccircuit.com/dc-power-supply-300v-from-battery-12v/ [Broken]

The transformer appears to be a standard 60 Hz 120 V to 12 V CT (center-tapped) transformer.

Bob S

Last edited by a moderator: May 4, 2017
3. Sep 20, 2010

### Bob S

Here in thumbnail is a LTspice simulation of the circuit suggested in the previous post. The voltage output into the transformer is a 24-volt square wave at ~150 Hz. If a standard 60-Hz 120V to 12V (10:1 turns ratio) transformer is used, the 24-volt square wave represents about 2.2 times more volt-seconds at 60 Hz and would saturate the transformer core, so the LTspice circuit is running at ~150 Hz. This would increase the lamination losses (which scale as ω2) by a factor of ~6.3, so a standard 120V to 12V transformer is probably not appropriate.

The transformer in the simulation has a 1:10 pri-sec turn ratio with a center-tapped primary. The rectified dc output is about 360 volts into 10,000 ohms (36 milliamps).

More appropriate transformers would be a 120V-to-24V CT 60-Hz transformer (which would reduce the dc output to ~180V), or an audio output transformer with thinner laminations. In either case, a spice simulation and/or bench test is recommended.

[added] The waveform in the second thumbnail represents the first 250 ms of the Vac (unrectified) output.

(Request to moderator- Pls move to the EE forum. Thanks)

Bob S

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Last edited: Sep 20, 2010