Running an LED off a 120v wall outlet

[raultiger]

Hey everybody,

This is my first post so I hope this isn't a stupid question, but here it goes.

I have I fairly high quality microscope, but the entire light system isn't working. I am looking to upgrade it to an LED light source with a switch and potentiometer in the circuit for dimming and turning it on and off. The problem is that I'm not really sure how to convert the 120 volt ac power into something that the LED can use.
Does anyone know how to do this?

Thanks

 

[BobK]

You start with a wall wart that lowers the voltage to something like 5V, then read this:

https://www.electronicspoint.com/got-question-driving-leds-another-work-progress-t228474.html

Bob

 

[Iron Will]

Hey there,
don't worry it doesn't sound ridiculous.

I think that wall outlet is much too powerful; the energy has to go somewhere.
Using massive resistors is very inconvenient.
After all an LED requires tiny amounts of e-current.

Why don't you just add an auxiliary circuit with a battery pack that directly powers the LED?

 

[Miguel Lopez]

I'm agree with Iron Will. A 9V battery could power the LED for several months, maybe a year.

 

[raultiger]

Thanks Iron will and Miguel Lopez!

I think I will try that. Just one more question. What kind of resistors would I need to make a 9v work with LED (most likely 5 volt). Also, any suggestions for kind of LED? It just needs to be white and fairly bright

Thanks

 

[Iron Will]

You're welcome

How many LEDs you intend to use?

if you purchase the LED they should come with their characteristics.
you can use this: http://led.linear1.org/1led.wiz to calculate the resistor required; click on the question mark next to the box where you enter the value for some useful information. For example, Whhite LEDs forward voltage of 3.3V.

I generally go for 20-30mA to each LED, gives good luminosity.

cheers.

 

[raultiger]

I had intended to use just one bright LED. I think that if I got a fairly high power led it would work well. Maybe one isn't enough?

 

[KJ6EAD]

If the existing lighting system has housings, mounting and optics that are good such as a ring light, it would be best to retain them and just build an LED light source to fit.

 

[Iron Will]

I am not too familiar with microscopes. Haven't used one in a while, but shouldn't the lamp be very bright? I guess it varies?

It's just if you use more than one LED, you will need more than one Resistor. Perhaps go for a 2x2 led Matrix?

Honestly, you should see how many can fit and what the brightness you need is. There are LEDs 1cm in diameter. I guess just one of those would be best.

 

[CocaCola]

It's just if you use more than one LED, you will need more than one Resistor.

Like LEDs can be run in series with a single resistor...

 

[Iron Will]

What's wrong with that?

 

[raultiger]

The existing light system is not working for some reason. I'm not quite sure why, but I know its not the bulb that is broken because I have tried to replace that already. And iron will, your probably right. It needs to be bright. I was thinking that there are some LEDs that are bright enough but I'm not sure. I can always look around for one that's bright enough or just go with the matrix approach.
I also just though of another problem... Im not sure how to mount this LED. Do they make mounts so that the LED could be replaced if needed? Im planning on selling this microscope so I would want the next owner to be able to chance the led if needed

Oh and k6ead, the original system doesn't seem very good... it uses some special kind of light bulb and it only has a mount for that specific kind.

 

[CocaCola]

What's wrong with that?

Was this in reply to me? If so can you elaborate?

 

[CocaCola]

I was thinking that there are some LEDs that are bright enough but I'm not sure. I can always look around for one that's bright enough or just go with the matrix approach.

Application will dictate this, LEDs are unlike bulbs in that they produce a focused area of light, even your common 3mm and 5mm LEDs can be painful to look at directly but they don't produce a huge amount of light and looking at them a few degrees left or right they drop off considerably...

Im not sure how to mount this LED. Do they make mounts so that the LED could be replaced if needed? Im planning on selling this microscope so I would want the next owner to be able to chance the led if needed

Yes, they make sockets and mounts that facilitate easy replacement of LEDs, or you can also use many common 'plugs' and just plug the LED in to the female end...

Like this, for example...

 

[BobK]

I'm agree with Iron Will. A 9V battery could power the LED for several months, maybe a year.

Uh, no. He is talking about a high-power LED. These typically start at 350ma and go up from there. A 9V cannot operate it for 2 hours. In fact, even at 5ma, a 9V battery could operator for only a few days.

Bob

 

[CocaCola]

Uh, no. He is talking about a high-power LED. These typically start at 350ma and go up from there.

Is this in a different thread because I fail to see it mentioned here?

 

[raultiger]

Thanks CocaCola that kind of socket would be perfect.
And as far as the application, the light is positioned parallel to the ground, the reflected straight up through a lense with then goes through an apperture, and is projected to the underside of the microscope slide. I dont think that the low viewing angle would be that much of a problem because it is straight on, not at an angle.

As far as the battery, a 9v wouldn't work for sure?

 

[CocaCola]

As far as the battery, a 9v wouldn't work for sure?

It will work but like all battery supplies your run time will be dependent upon the drain... If you are going to use this for hours upon hours and days upon days I would highly recommend you get a wall wart or alternative power converter that plugs in to the mains...

 

[raultiger]

Yeah im thinking that the wall wart would be the way to go. Changing batteries every two days wouldn't be fun... What kind of wall wart would i need? like how many volts would it need to cut the power down to?
thanks again

 

[BobK]

I had intended to use just one bright LED. I think that if I got a fairly high power led it would work well. Maybe one isn't enough?

Here.

Bob