LED Question

Thread Starter

kanxrus

Joined Apr 28, 2009
8
I am new here, and really have not clue about electronics. However I am bored and would like to modify my drill.

I have a 18v cordless drill with a single LED light. The light turn's on and off with the trigger switch.

I would like to know if it's possible to add a capacitor on the hot wire that leads to the light, so when I release the trigger switch the capacitor stores enough power to leave the LED on for a few seconds?

Coming of the switch to the LED is 3.2 volts, and 25mA, according to my meter.

Thanks
 

mik3

Joined Feb 4, 2008
4,846
You will need a quite large capacitor to power a LED for a few seconds.

How many seconds will you like?

Where is the LED connected to?
 

Thread Starter

kanxrus

Joined Apr 28, 2009
8
two seconds. The LED runs into the trigger switch. The black and red wire in the picture.
 

mik3

Joined Feb 4, 2008
4,846
From the picture, the trigger switch is connected to the controller. There is no LED there.
 

Thread Starter

kanxrus

Joined Apr 28, 2009
8
the red and black wires run into a black cover with a small board in it. The LED is on the other side of the black cover.
 

mik3

Joined Feb 4, 2008
4,846
You can't just place a capacitor in parallel with the LED, you need to open the black box to see where the LED is connected to.
Also, if you connect a capacitor in parallel to the LED without knowing anything else you might destroy something in the box.

By the way, you will need a capacitor 0.5 F to power your LED for 2 secs.
 

mik3

Joined Feb 4, 2008
4,846
Does the small board above the push button which controls the speed of the motor contains a potentiometer or limit switch?
 

zero_coke

Joined Apr 22, 2009
294
You will need a switch to activate the capacitor after the drill's button has been let go...I think this is how it should be.
 

Thread Starter

kanxrus

Joined Apr 28, 2009
8
I have no idea. I'm going to assume this may be more complicated than it looks. I was hoping for a simple wire cut, and a little soldering.
 

mik3

Joined Feb 4, 2008
4,846
I have no idea. I'm going to assume this may be more complicated than it looks. I was hoping for a simple wire cut, and a little soldering.
You have to find what controls the Led first (possibly a transistor) and then find out how to modify it.
 

zero_coke

Joined Apr 22, 2009
294
Yeah like Mik3 said, you need to find what is controlling the LED to go on/off, and then modify it.

As of now, that "controller" is doing this:

When it receives signal from drill button that it is pressed, it tells LED to light up. When button is let go, it tells LED to turn off.

What you have to modify the "controller" to do is

When button is pressed, turn on LED and charge capacitor. When button is let go, use energy stored in capacitor to light up LED until all energy is used. If you get a 0.5 F capacitor it should be sufficient to light it up for about 2 seconds like Mik3 said.

I think it should be like this because it makes sense I don't know...maybe I'm thinking too programming than cicuit design lol.
 

Thread Starter

kanxrus

Joined Apr 28, 2009
8
I appreciate your guys input. This looks a little beyond my abbilities. Thanks again.
 

SgtWookie

Joined Jul 17, 2007
22,201
Not meaning to sound overly cynical, but it would be much easier to simply carry an auxiliary flashlight.

The problem is that the motor will also be across the LED's power supply. This will deplete the voltage from just about any capacitor of reasonable size and cost that you might contemplate using for the purpose.

However, you might be able to accomplish what you desire if you can find the current-limiting resistor for the LED, insert a low-Vf diode between the limiting resistor and the battery connection, and connect a large capacitor across the limiting resistor and the LED's ground.
 

Thread Starter

kanxrus

Joined Apr 28, 2009
8
I use this drill for putting screws in cabinet install jobs. This way you don't have to keep the trigger pulled the entire time to see in dark places. It's a great feature, and another drill manufature has the patent on a delayed LED light. There delay is about 10 seconds. I don't care for there tools, so I wanted to see if I could modify my Dewalt drill instead.
 

zero_coke

Joined Apr 22, 2009
294
I use this drill for putting screws in cabinet install jobs. This way you don't have to keep the trigger pulled the entire time to see in dark places. It's a great feature, and another drill manufature has the patent on a delayed LED light. There delay is about 10 seconds. I don't care for there tools, so I wanted to see if I could modify my Dewalt drill instead.
I think if you push the drill button half-way down without causing drillbit to turn the LED comes on. If I'm not wrong I've used a drill like this before...you would press the button lightly for the LED to come on so you can see where you are going to drill at, and then once you find the screw hole I guess then you can press all the way to get the motor to spin and hence the drillbit to spin.
 

Wendy

Joined Mar 24, 2008
21,848
It would be easier to use a transistor as a capacitance multiplier. It's an old concept, I'll see if I can draw it. You'll want to breadboard this before putting it in your drill to get it working...



Most of these parts are available from Radio Shack.
 

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