Lighthead conversion

J

johnandtricia

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Apr 30, 2006
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Ok I am going to try converting a lighthead for a camera we have at work it is a sewer cam but thats not important anyhow, right now we use 4 small halogen bulbs and of course they get hot and after time heat up the camera and cause problems plus halogen and sewer water dont mix. (sometime you get a leak). Now high intensity LEDS my be the answer. First question will a LED work on DC current? I will have to check the volts and amps but the amps for the camera vary from .65 to 1.50 the volts for the camera are 155 to 160. I will gladly give more info as it comes avail.
 
no one knows if leds run on dc current at least give me that much please also what is a good site to use to figure out what resistors are neded and such.
 
LED's require anywhere from 2.5-3.5v DC forward voltage. Resistors are used to keep down current...

I don't understand the english in your post enough to help anymore...
 
ok what is a go website to go to where I can find out info about how many resistors are needed and how to wire it up or wiring suggestions
 
If I understand right... you probably want white light to light up a sewer line. So get eight white 3.5 volt LEDs and connect them in series with a resistor so they use 20 mA each (I have a five LED flashlight that is fairly bright).

For your stated 160 volts input (why so high?) here is the math for calculating a resistor (R) for eight 3.5 volt LEDs at 20 mA:

R= (160-(8*3.5))/.020 = 6600 ohms.

A standard (cheap) resistor is 6800 ohms... so use that.

Since you are using a very high voltage source, you must use a fairly high power rated (P) resistor. Here is the math for that:
P= (160-8*3.5)*(160-8*3.5)/6800 = 2.56 watts.

You could use a standard 3 watt resistor; but I would use a 5 or 10 watt resistor that will run cooler (more is better here).

Wiring diagram:
+160V..6800ohms..+LED-..+LED-..+LED-..+LED-..+LED-..+LED-..+LED-..+LED-..Ground

You could use more or less LEDs or a different voltage but the math is the same.
 
Resistor calculators:
Metku
LED Center

Those will figure it out for you, but you are talking about some major voltage there! Be careful with that... According to those, you can run a series of like 41 bright white LEDs on that voltage!
 
MasterOfTheHat said:
Resistor calculators:
Metku
LED Center

Those will figure it out for you, but you are talking about some major voltage there! Be careful with that... According to those, you can run a series of like 41 bright white LEDs on that voltage!
Click to expand...

Tagged for info.
 
First of all thanks for all the responses I did some futher checking and got some better info. First to answer the question of why so much voltage the voltage is to run the camera and a tracked crawler which is teathered to the truck via 2000 ft of armoured cable. However our tech miss informed me of the voltage comming to the lighthead it is nnot 160 volts as originally stated it is only 12 volts. Right now we use 4 halogen bulbs which create alot of heat and do a number on the cameras. The lighthead is rectangular with hole in each corner where the bulbs plug in (sorry no pics) I am trying to convert this to save money on bulbs and wear on the camera. Now with that said I went to a sight to figure out what is needed and if I use 4 leds with a drop of 3.3 volts and 20 mA they will need to wired in paralell using a resistor of 120 Ohm and power rating of 1.16 volts. the voltage fluctuates from 11 to 13 volts so that should cover it please check my math and make sure it is correct. Worst case I blow up a $25,000 camera. Thanks again everyone
 
4 LEDs will not give you anywhere near the amount of light the halogens gave you. You'll need more like four clusters of LEDs. If you're dealing with 12V, you can do several strings like this:
12V--Resistor--LED--LED--LED--GND
Do you know how much power each of the halogens draws? That will give us a better idea of how much current we can afford to be drawing...
 
I totally agree with Mohonri. I've done turn signals and running lights for my motorcycle with LEDs. The voltage fluctuation there is between 9v and 14.8v. Because of the large fluctuation, I used series strings of two and three LEDs. With a smaller fluctuation like you have, you should probably uses strings of three LEDs. I like to aim for a target of 20ma per string, although most people seem to go for 30ma. The efficiency of LEDs is not linear, you have diminishing returns after a certain point, usually 20ma. Plus it helps keep the heat down.

Make strings of 3 LEDs and a resistor. Probably something between 100 and 150 ohms would be good. The resistor will dissipate about 1/10 of a watt, so a standard 1/4 watt resistor should be fine. Put as many of these strings of LEDs in parallel as you can and pack them as tightly as you can - LEDs just aren't as bright as traditional bulbs. I had to use between 12 and 18 high brigtness LEDs to replace a single automotive bulb.
 
Fenris_Ulf said:
Put as many of these strings of LEDs in parallel as you can and pack them as tightly as you can - LEDs just aren't as bright as traditional bulbs. I had to use between 12 and 18 high brigtness LEDs to replace a single automotive bulb.
Click to expand...
Another advantage of very bright LEDs is that their light is more directional--less of it is wasted out the sides as with traditional incandescent lamps.
 
Mohonri said:
4 LEDs will not give you anywhere near the amount of light the halogens gave you. You'll need more like four clusters of LEDs. If you're dealing with 12V, you can do several strings like this:
12V--Resistor--LED--LED--LED--GND
Do you know how much power each of the halogens draws? That will give us a better idea of how much current we can afford to be drawing...
Click to expand...

I've done a similar job adding a camera to a theodolite for a directional drilling rig. Two strings of three leds will provide enough light. The more leds you can fit in the better, of course, because cameras like light. The original halogens will be around 20 watts.
 
If the original halogens were each 20W, that's about 1.7A apiece. Off a 12V source, you can generally get about 100 LEDs per Amp of current (using 3 LEDs per string, and 20mA per string, with a 50% safety margin). So 4x1.7=6.8 Amps. That's a lot of LEDs you could power. A whole lot. The luminous efficiency (lumens per watt) of LEDs is actually about the same as incandescents or halogens, but again, LEDs can be better focussed.

As far as protection from sewer water goes, if you are using normal LEDs, you can just pot them in resin and forget about it. They'll never burn out in your lifetime unless you seriously overdrive them.
 
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