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Trolling Black Box for Fishing

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alvinholt

New Member
I am trying to build a black box to induce a constant adjustable positive voltage on my downrigger between 0 and aprox 1.5 volts DC. The cathode being a sacrificial zinc trim tab on my outboard and the Anode being my stainless steel Downrigger. I am going to utilize my boat battery 12 VDC for source power. Question; Can I use a simple voltage divider IE: a 100K resistor and a 10K Pot or do I need to use an OpAmp or other regulator circuit :?: The current natural voltage is +.430 in fresh water. Advantages and Disadvantages, Any replys appreciated.
Reference: https://www.protroll.com/blkbox4.html
 

k7elp60

Active Member
Black box power supply

From your post I assume you want to replace the blackbox with a homade device. You will need more than just the pot and a resistor.
If I am right then it will take a few components and a power transistor,
as the current may vary depending on the salinity of the water. If you use your own digital volt meter it will be easy to accomplish. I would
be glad to post a schematic for you.
:D Ned
 

Roff

Well-Known Member
Hey, Alvin, I grew up in Bakersfield. I was just there about a month ago for North High's 50th anniversary party.
Anyway, I drew up a circuit for you. If you can't find the op amp, you can use an LM324, but it's a quad, so you'll have 3 unused sections instead of one. You can actually use any single-supply op amp which has a supply voltage rating of at least 15 volts and whose inputs will work down to the negative supply rail (ground, in this case).
You probably already have a cheap DVM to monitor the output.
If you have any questions, post them here and/or PM me.
 

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alvinholt

New Member
Trolling Ionizer

Thanks for the offer Ned, and Thank You for the diagram Ron.
I will try putting it togeather before I go out again I'll get back to the message board when I bench test it. It's always nice to have a little project to work on. :)
 

k7elp60

Active Member
This circuit should do the job. I initially discounted using the LM317T because of the output will not go below 1.25 volts. Then I decided with
a couple of diodes in series on the output would do the job, the diodes
drop approximately 0.7 volts. Course the voltage drop varies slightly
with current. Anyway the circuit should work fine.
:D Ned
P.S. The 250 ohm pot may be hard to find, but a 1K (common value)
will work, the voltage will go higher and the adjustment may be a little more critical
 

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Roff

Well-Known Member
I toyed with the idea of an unregulated circuit also (I know that the LM317 is a regulator, but the diodes, as was pointed out, are not), but I was concerned about not knowing how much the current fluctuated. It probably won't fluctuate much in a given body of water, with the downrigger(s) not moving relative to the boat, so this circuit is probably fine, and it certainly is simpler.
 
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