Hello, my name is Chris and I have a project I have been working on. I am trying to make a electrofishing device that operates off of a 12 volt car battery. I understand that the gated pulse rate for the current is optimum at 25-50 pulses per second (A variable pulse knob would be great). And operating from 10-20 Amperes in the water.The pulse must be a capacitor discharge pulse. The whole idea is to emit an interrupted charge to the water with an insulated line appx 15 to 20 feet long attached to a small chain that will drag the lake bottom (positive side). The ground will only be submerged over the edge of the boat 6-12" under the water with a weight. The current operating at that pulse causes a phenomenon called galvanotaxis (muscle contractions causing the fish to surface but not harming fish. This is used by the Dept of Natural Resources to tag fish and count population. I want to use it to take a census of my pond fish. Please contact me with some type of circuitry that I will need I would greatly appreciate it. I hope this post helps others that carry the same interest. Here is where I am getting my idea from, so if you need more information, please look at this .pdf http://www.amazing1.com/download/FISH80IN.pdf

Regards,

Chris

Well, there are a few clues here. Based on the supplied data, the system normally puts out 25 pulses per second with an amplitude of 300 volts into a 500 ohm load. They say the maximum average power is 25 watts. Using the formula: average power = peak power x duty cycle, the pulses must be about 5ms long.

So, how would you build such a circuit? Here is one idea. Buy a 50 watt 12v to 120vac modified sine wave inverter. These will put out a 60Hz waveform with 160 volt peaks. Take that output and connect it to a voltage doubler circuit, which can source about 25 watts of power. This will yield about 300+ volts DC. Next, build a 5ms pulse generator circuit, with a variable 20Hz to 50Hz pulse rate. One or two 555 timers would work. Feed the output of that to a high voltage n-channel FET (IRF744) which is connected to the electrodes. Use a 40 watt incandescent light bulb as a current limiting device in series with the FET. You could tap into the 120vac signal to power the pulser circuit. It would not need much power, perhaps 12v at 3ma. Keep in mind that this circuit is dangerous. There are some high voltages involved.

Thanks David,

This helps out alot, but just a question, how is this high voltage going to pass through the timer and FET without burning them up, or is it even an issue. ME+ little electrical experience = dumb question sometimes

I'll see what I can do.

If it were me, I'd buy a 50Hz 240vac inverter and get into its guts to change the drive frequency from 50Hz to 12Hz. Then, the inverter would generate 330 volt pulses, lasting about 5ms at a rate of 24 pulses per second. But, you would need some test equipment to locate the right parts to change. The external drive idea might be easier for you. I'll try and post something yet today.

This is what I came up with.