Calling the electrically inclined

Howdy,
I was looking to purchase a YakAttck Vis carbon pro w/light.  It's powered by 3 AA batteries.

I've already made use of a 12v battery for my fish finder and things so I'd like to re-wire the light to use my existing power source.  Any one out there done this type of thing or think it would be possible.  I've seen some articles on similar things on the interweb but not this specifically.

Three AA batteries is only ~4.5 volts so you'll probably need to find a way to step your 12 v DC down to 4.5 V DC.  I'm not an electrician, but I'm guessing something like an old Walkman car power adaptor might be rigged for this purpose.  You'll have to pay attention to the voltage and amperage output of the adaptor and the specifications of the light.

Howdy,
I was looking to purchase a YakAttck Vis carbon pro w/light.  It's powered by 3 AA batteries.

I've already made use of a 12v battery for my fish finder and things so I'd like to re-wire the light to use my existing power source.  Any one out there done this type of thing or think it would be possible.  I've seen some articles on similar things on the interweb but not this specifically.

If you are going to use a 12V battery, you could save a lot of money by purchasing a boat light. Of course you would still need a flag.  Those are easy to come by. 

48" Pole Straight Pole All-Round Light $37.99


or a little more expensive:
Universal Fit Straight Pole Light, 42"L $54.99


I used a boat light I already had.  The bonus is that it can have a GoPro mounted on it since it is stiff enough. 
I attached mine to my crate.  I did not use the base they are designed to plug in to.  I just wired it to a battery pack.

You can find shorter or longer ones.

If you really want to use your Visipole light, here's what you would need to do:
You would connect your light in parallel with your sounder(i.e. red terminal of battery goes to the positive terminals of both the light and the sounder).  This gives you a 12 volt drop for both your sounder and your light.  As bsteves mentioned, 3 AA batteries is roughly 4.5 volts so you need to step down the voltage 7.5 volts(12-4.5).  I would say that you actually want a step down of about 8.5 to be conservative(and since AA batteries average about 1.2 volts during their discharge span).  So if you want a 8.5 volt step, you need to find out some specs from your light and see how much current it needs(probably in the order of tens of milliamps or less).  8.5 divided by the current is the resistance value needed.  Fry's is a good place to find resistors.  Look for higher watt values to be on the safe side and so you won't have to worry about heat dissipation.  Simply wire one end of the resistor to the positive lead coming from the battery, then wire the other end of the resistor to the lead running to the positive battery terminal of your light.  Then wire the negative terminal of your light to the negative end of the battery.  The problem you're going to be faced with now is how to make everything water tight and have a way to plug it into your battery.  West Marine has marine grade electrical plugs and these will do the trick for the connection.

This is getting me thinking.  I might get something like this wired up when I get some spare time.   

Cool, thanks guys.  Radio Shack here I come....

Just did a quick read on common LEDs.  White LEDs require about a 3.6 volt drop(the voltage drop varies depending on the color of the LED) and need about 30 milliamps.  This means you need a resistor of about 280 ohms to give you the drop you need.  Oh yeah, Radioshack has resistors too, good call.

If you really want to use your Visipole light, here's what you would need to do:
You would connect your light in parallel with your sounder(i.e. red terminal of battery goes to the positive terminals of both the light and the sounder).  This gives you a 12 volt drop for both your sounder and your light.  As bsteves mentioned, 3 AA batteries is roughly 4.5 volts so you need to step down the voltage 7.5 volts(12-4.5).  I would say that you actually want a step down of about 8.5 to be conservative(and since AA batteries average about 1.2 volts during their discharge span).  So if you want a 8.5 volt step, you need to find out some specs from your light and see how much current it needs(probably in the order of tens of milliamps or less).  8.5 divided by the current is the resistance value needed.  Fry's is a good place to find resistors.  Look for higher watt values to be on the safe side and so you won't have to worry about heat dissipation.  Simply wire one end of the resistor to the positive lead coming from the battery, then wire the other end of the resistor to the lead running to the positive battery terminal of your light.  Then wire the negative terminal of your light to the negative end of the battery.  The problem you're going to be faced with now is how to make everything water tight and have a way to plug it into your battery.  West Marine has marine grade electrical plugs and these will do the trick for the connection.

This is getting me thinking.  I might get something like this wired up when I get some spare time.   

Oh sure, wire it all properly-like with resistors and stuff.   What ever happened to Macguyvering you kayak fishing gear out of parts around the house?   

Oh sure, wire it all properly-like with resistors and stuff.   What ever happened to Macguyvering you kayak fishing gear out of parts around the house?   

When it comes to electrical stuff I decided against that after I went to school and learned what a shorted wire can do to polyethylene.   

Oh sure, wire it all properly-like with resistors and stuff.   What ever happened to Macguyvering you kayak fishing gear out of parts around the house?   

Wali moved to Florida.......

If you're on the Westside, check out Gizmo Guys on Cornelius Pass.  They'll even do the math for you if you're not sure what you need. 

Oh sure, wire it all properly-like with resistors and stuff.   What ever happened to Macguyvering you kayak fishing gear out of parts around the house?   

 
When it comes to electrical stuff I decided against that after I went to school and learned what a shorted wire can do to polyethylene.   

Yep, that is why you should always start with an in-line fuse at the battery terminal. If you use a resistor the voltage drop will be a function of the current drawn. A common problem is that there is an in-rush current at power on, this causes the voltage to drop too low and the LED to cuts off. Then the voltage rises and the light turns on draws too much current and cuts off. This could settle out or oscillate forever. This could happen slowly (flickering) or at a high enough frequency for you not to be able to see it, but which could create a lot of interference with your depth finder. A proper DC/DC converter with an in-line fuse is what I would recommend. Here is an example:

http://www.circuitdiagram.org/12v-4.5v-6v-9v-converter.html

This will give you the conversion that you want. You can blob the whole thing in epoxy to waterproof it once you verify with a voltmeter that it works. 

A second (Macguyvering) approach  would be to cannibalize a USB car charger. This will convert 12V to 5V. I would imagine that the extra .5V is unimportant (not hurtful).  However, I would not imagine this would hold up well in the wet/damp kayak environment. It is only included as a Macguyvering-type example.

You could cover the canibalized USB device in goop.

When I wired my transducer there were several places I was going to use electrical tape, and decided to cover them in marine goop instead.  Never had a problem with them, even after flushing to hull out multiple times.

Oh sure, wire it all properly-like with resistors and stuff.   What ever happened to Macguyvering you kayak fishing gear out of parts around the house?   

Wali moved to Florida.......

If you're on the Westside, check out Gizmo Guys on Cornelius Pass.  They'll even do the math for you if you're not sure what you need. 

What?  Who, these guys?  http://www.thegizmoguys.com/ 

Actually, I'll probably pay the real gizmo guys a visit for the materials.  Looks like they have what I'll need. http://www.surplusgizmos.com/

Liquid electrical tape is awesome stuff and found at most hardware stores. 

instead of wasting electricity by dropping voltage in a resistor, put a couple of more LEDs in series with your VisiCarbon. You could run two bow lights or a bow & stern light or whatever. 4V is a common voltage drop across high output LEDs. Amazon is a good place to shop for onesy and twosey quantities of LEDs. You can epoxy them into your hull. At work, we illuminate all kinds of parts by embedding LEDs in plastic.

Would it be difficult to change the Visipole light to have a 12 volt draw? Say an Led cluster for 12v or a single bulb of 12v. Maybe YakAttack has already addressed this?