New person needing help

[mrfuzzy4]

I want to help my friends wire up a table of theirs with some ultrabright leds, but I've swiftly learned that this is kinda out of my league, and don't know where to go.

they want to be able to plug it into a wall outlet, and have a switch. So far everything i thought i knew is wrong, but here's where I'm at.

120v outlet should be used at about 80%, so 100v or 17amps.
leds like DC, so i would need a rectifier of some sort and a capacitor to even out the current. wire all that to a switch, then to the leds in a circuit and i'm good!
something tells me that's not right. also, I have no idea how to hook up a rectifier, so i don't know quite what that entails.

the other option is to use cold cathodes. those use like .3amps, so if i just bought a power brick or something of the like, i could just spice it all together. i would need like 8 or so, so i would need a 3amp box? and use resistors? would it be easier to use a batter pack? how long would AAs hold up?
I think i'm over my head...

 

[ericgibbs]

I want to help my friends wire up a table of theirs with some ultrabright leds, but I've swiftly learned that this is kinda out of my league, and don't know where to go.

they want to be able to plug it into a wall outlet, and have a switch. So far everything i thought i knew is wrong, but here's where I'm at.

120v outlet should be used at about 80%, so 100v or 17amps.
leds like DC, so i would need a rectifier of some sort and a capacitor to even out the current. wire all that to a switch, then to the leds in a circuit and i'm good!
something tells me that's not right. also, I have no idea how to hook up a rectifier, so i don't know quite what that entails.

the other option is to use cold cathodes. those use like .3amps, so if i just bought a power brick or something of the like, i could just spice it all together. i would need like 8 or so, so i would need a 3amp box? and use resistors? would it be easier to use a batter pack? how long would AAs hold up?
I think i'm over my head...

hi,
It would be better if you told us: the type of LED and how many you want to use on the table...

 

[mrfuzzy4]

oh i'm sorry, thought i put that!
I was thinking ultra bright leds, ~3v a piece, and as many as possible, which is about ~31 to my calculations.

 

[ericgibbs]

oh i'm sorry, thought i put that!
I was thinking ultra bright leds, ~3v a piece, and as many as possible, which is about ~31 to my calculations.

What current rating are these ultra bright leds. ?

Throw us a bone.

 

[mrfuzzy4]

Unique Leds High Quality hard to find LED and LED products with fare shipping and everyday low pricing - LEDS :: 5mm LEDS :: 5mm Blue led 5860mcd

that's what i'm looking at.
i think the answer is .02amps?

figured it was bet to let you see it then me mis-report anything else.

and sorry, as i said i'm still really new at circuits and whatnot.

 

[mrfuzzy4]

**broken link removed**

that has info on the cold cathodes.

no ideas?

 

[ericgibbs]

hi,
So you have ~31 leds. with a Vfwd of ~3V at 20mA.

Say you used a 24V dc power supply.

Connect 7 leds in series, that approx 7 * 3V = 21V drop across the leds.
So you have to drop 24V -21V = 3Volts at 20mA [0.02A], this means a series resistor of 3V/0.02 = 150R.

Make 5 of these 7 led/150R strings....thats a total of 35 leds.

As each series string will require 20mA, thats 5 * 0.02 = 100mA [0.1A]

So the 24V dc power supply should have a current rating of at least 100mA, I would choose 250mA.!

Do you follow this.?

 

[mrfuzzy4]

makes sense, more or less, but is there a 120vac to 24vdc converter (not the right word i believe) for sale? That's the problem, i'm unsure as to how to convert it correctly to dc.

thank you for the help by the way!

 

[ericgibbs]

makes sense, more or less, but is there a 120vac to 24vdc converter (not the right word i believe) for sale? That's the problem, i'm unsure as to how to convert it correctly to dc.

thank you for the help by the way!

You say 120vac to 24vdc converter, that would make it 'dc', which is what you want.

Read the label on the power supply [convertor] make sure it says 24V dc

 

[mrfuzzy4]

no, i mean is there actually a converter, i assume we're talking about a typical plug you'd get with an electronic device like an external hard drive or printer, that will convert to 24vdc for sale? or do i have to make one

 

[audioguru]

The datasheet for the LEDs say that their max voltage is 3.6V. Then 7 in series need 25.2V and might not light with only 24V.

The LEDs have an extremely narrow viewing angle of only 10 degrees minimum. Then harly anybody will see them. Use LEDs with an angle of 30 degrees more.

 

[mrfuzzy4]

The goal is just to get them to illuminate a space, not necessarily be seen.

 

[audioguru]

LEDs with such a narrow angle will light small dots on the ceiling.
My Luxeon SuperFlux LEDs have an angle of 70 degrees and light the space in my hallway.

 

[mrfuzzy4]

how much, and are their stats the same as the ones i previously posted?

also, how would this work with cold cathodes?

 

[audioguru]

My Luxeon Superflux LEDs have 4 pins and their max current is more than double the max current of ordinary 5mm LEDs.

 

[mrfuzzy4]

but the question remains, how do i get a 24v, 1A power box?

 

[ericgibbs]

but the question remains, how do i get a 24v, 1A power box?

Is it going LED's or Cold Cathode lighting.

Did you check the label on that 120Vac/ 24Vdc convertor [psu] that you were considering, as I suggested,
also why are you talking of a 1amp supply.

If your LED's do have a Vfwd of 3.6V then connect only 6 in series, change the 150R to suit.

Its make you mind up time...

 

[mrfuzzy4]

Is it going LED's or Cold Cathode lighting.

Did you check the label on that 120Vac/ 24Vdc convertor [psu] that you were considering, as I suggested,
also why are you talking of a 1amp supply.

If your LED's do have a Vfwd of 3.6V then connect only 6 in series, change the 150R to suit.

Its make you mind up time...

ok i mis-read, you suggested .250A

and i was wondering how possible both were. I know less of the cold cathodes, so i was originally looking

I don't have a 120vac to 24vdc converter, i was going to purchase one online, i assume like a laptop charging cable and just cut the end and splice it together.

ok i mis-read, you suggested .250A

and i was wondering how possible both were. I know less of the cold cathodes, so i was originally looking

Off-the-Shelf and Custom 24 volt Power Supplies.

something along the lines of this maybe?

 

[ericgibbs]

From your link.
Off-the-Shelf and Custom 24 volt Power Supplies.

An overkill at 750mA, but it would do the job.

 

[mrfuzzy4]

here's info on the cold cathodes,
12 volts and about 0.3 amp

so could i do 4 rows of 2? and what resistors would i use?

thank you for the help btw. I understand that I'm not the clearest person because i'm not sure quite what i'm doing, so thank you for bearing with me.