Hello everyone. My first post. I do apologize as I am sure this is duplicated somewhere. I have been struggling pretty good, think I am trying to learn to run before I crawl, I am in a bind though.

So my brother in law does security work, brought me a light bar, not an LED lightbar but an incandescent bulb bar. I think the dang thing is Chinese, numbers on bulbs are 222 / 100, the 222 has two lines over the numbers....i can't even find the watts on them. Connector type is two pins out the bottom of the bulb. I may try to switch these out with some smaller amp light if i can find one to fit.

I am controlling this bar with a dewalt 18v battery for a drill, works great. Measured amps, they come back at 12amp for the lights....wow.

so my big hurdle, as I am new to this.

This is my first attempt to drive a larger voltage/current circuit then the arduino can handle by itself.

I started reading about transistors last week. Followed a nice few videos on youtube where they used a 12v led strip, worked great...i did the same steps, FRIED my uno....lesson learned about using a resistor off the pin 13 before the transistor.

so my question. where I need help. Again, im am struggling, im sure i need to read lots and learn lots to understand this all myself.

I have various transistors. All kinds, NPN and PNP, i understand I need to use NPN (easier to start with). I have blown a few up, so I am not getting the math right.

1. How do I determine how much the amount of current coming from the arduino pin 13 to the base/gate of the transistor? I need to know this, so i can determine if the transistor will activate at all when the arduino blinks, right?

2. all of my transistors, including the TIP31 i just bought last night from radio shack all say they have enough max volts to handle the job, as im only using 18v.

3. I want to protect the arduino, so I know I need to put a resistor in between the pin and the transistor..How do i determine how big of a resistor to put in that spot? I have read everyone from 100ohm to 2000ohm.....I dont' want to guess, I want to know how to mathematically determine the correct amount.

4. This can wait a bit as well. My brother in law wants it to be able to do more then just "blink", wants to be able to select a switch or knob and make it chase, fade, blink, left to right, etc..
I understand that fade and blink and chase are all programs....so for the arduino to do those operations, it has to have the right program.
Is it possible to write each of those effects as say a subroutine? and then somehow connect say a switch or knob, and then based on that input (switch position or where knob is turned), it could change a value in the program, and it will know to look for the "blink subroutine" or the "fade subroutine" ?

My other option would be, as I get better with this, i Have heard of people connecting the arduino to a raspberry pi, and then the raspberry pi just reprograms the arduino for whatever it needs.

I appreciate any input and help.
Again, i do recognize greatly that I need to learn basics and start from ground up. Gonna be fun.

Snapetwo,

You might want to consider using a simple relay instead of a transistor. I think that would be a lot easier and probably safer.

You might want to consider using a simple relay instead of a transistor.

A "simple" relays to reliably switch 12Amps?

wants to be able to select a switch or knob and make it chase, fade, blink, left to right, etc...

You didn't mention that the lights in the bar were individually controllable. If they're not (only one pair of leads), unless you take it apart and re-wire each light separately, you're not going to be able to "chase or left to right, etc..." since it'll appear as only one "light" made up of several bulbs (in series or parallel).

Ty for the replies thus far.
My apologies, the lights are in fact individually wired, hence the effects I would like.

Re relay... My bad. I didn't realize the lights were all individually controlled.

What is the current draw for each individual light?

Well right now, with 1 light, connected to 18v, I'm pulling about 1.8amps.

one FET per lamp, no biggie.
you can control many lamps.
did you say how many lamps you have ?

Look at AOI514 or AOI510 from digikey, logic level drive, very low Rds, will not get hot with 1.8A current flow.

Thanks for the info. I tried looking up those numbers and didn't find them.

Here is a link to digikey.com for the 514 (note that the number is A oh eye 514 )
http://www.digikey.com/product-search/en?keywords=AOI514

That one is rated 30v 17A

NOTE: this is an old part and digikey has this line on the price page "Part Status: End of Life; Last Time Buy Date: 06-30-2016. Minimums may apply."