LED activation from 5v winding?

[daz]

I know this is a stupid question and i can probably figure it out myself, but just so i don't screw it up and ruin this switch i'm asking for advice on how to do this. I bought one of those square marshall style 4 pole lighted power switches because the bulb in mine went south. It said 20A @ 125v so i just figured it was a bulb only to later after i already ordered it see it's got an LED. So rather than toss it i thought why not use my unused 5v rectifier winding to power the LED. I'm assuming the 4 poles are not configured the same as in the ones with the bulb in them so one side should be the LED and the other the for switching 120v. If thats correct i can use the rectifier winding, but rather than experiment with diodes and resistors to get a proper DC voltage on it can someone describe just how i should wire it up from a 5v winding? I know it's pathetic to have to ask this but if i burn out the LED the switch is useless to me. Already left my amp on for hours once w/o realizing it so i gotta have that light working. Not to mention the fear of working on a live amp w/o realizing it's live !

EDIT: i just realized it says 12v LED. So i guess it's not gonna happen unless theres a way to do voltage doubling?

[R.G.]

All LEDs must be wired up with something to limit their current. They are a diode, and only make light when conducting in the forward direction. But they are also diodes (!) and do not limit their own current, so if the voltage forward on them gets above their turn on voltage, they conduct all the current they can, even if it burns them up.

Burn up for normal small LEDs happens at something above 20ma average or 100-200ma peak. Resistors make good current limiters, but must be sized to keep the current under the safe max, and from there to cut the current down so you don't get blinded.

Different colored LEDs have different forward voltages. Red is generally in the 1.2-1.5V range, increasing for orange, yellow, green, and blue, with green and blue being 3-4V. White ones are generally three LEDs in one package, or a UV LED exciting phosphors. So you have to know how much voltage goes across the LED to figure the resistor.

LEDs do not like to be broken over reversed. That happens at only a few volts, so in general , do not ever subject an LED to AC. If you simply must run it from AC, provide either a series diode to prevent reverse current, or an anti-parallel diode to conduct the other direction voltage nondestructively.

So an LED on 5Vac requires a resistor and at least one other normal diode to keep it from dying.

There is a way to do voltage doubling and tripling, and whatever. Google "voltage multiplier" or "Cockcroft-Walton".

[Leo_Gnardo]

i just realized it says 12v LED. So i guess it's not gonna happen unless theres a way to do voltage doubling?

First, you're not using the 5V winding to power a rectifier, right? Because then it would be floating at the rectified high voltage, 400, 500V or so. That would take this idea out of the running entirely.

Yes you could make a quick n dirty voltage doubler from an otherwise unused 5V winding and run a 12V LED from it. LED's themselves require about 1.8 to 3 volts to light up, 12V rating tells me there's a resistor in series with the LED. There's also polarity to consider, get it backwards and no light will come from your LED. Enough reverse voltage, and you will wreck the LED.

For the doubler, just have a blink at a schematic for McIntosh tube amp, Bogen used 'em too for high voltage. Copy that, and you can use a couple of low value caps say 47 uF 25V, with a pair of 1N4001 (or any higher voltage 1N400x rectifier).

Good luck with your project.

[g1]

Which switch and does it said 12V right on the switch?
The marshall style ones are designed to be powered by 120V, so 5V wouldn't run it.

[Pedro Vecino]

Marshall switches I know uses a neon and a 1/4w series resistor. Is not it a simpler way?
In older models the problem is usually a degraded welding. Less common is that the neon has been damaged but replacement is simple.

[daz]

Which switch and does it said 12V right on the switch?
The marshall style ones are designed to be powered by 120V, so 5V wouldn't run it.

Yes, It's a automotive switch. Says it's 12v in the ad. But the switch side is 120v/20A so i assume it's for use in either application but for auto they have the 12v LED on one side.

[daz]

Marshall switches I know uses a neon and a 1/4w series resistor. Is not it a simpler way?
In older models the problem is usually a degraded welding. Less common is that the neon has been damaged but replacement is simple.

Yes, and i looked for a bulb at the 2 elec surplus stores i went to (i've opened these switches up before) when they didn't have the switch, but they didn't have the proper bub either. Then i found the entire switch on ebay for a buck so it was a no brainer till after i bought it i saw "12v LED"

[olddawg]

Yes, and i looked for a bulb at the 2 elec surplus stores i went to (i've opened these switches up before) when they didn't have the switch, but they didn't have the proper bub either. Then i found the entire switch on ebay for a buck so it was a no brainer till after i bought it i saw "12v LED"

First off you are going to need to put a bridge rectifier and a cap on the 5v AC supply to get DC out of it. See if you can take the new switch apart and solder a resistor in parallel with the current limiting resistor To work with a lower voltage. OR... If you have the original switch apart... Just get a $1 ultra bright LED.. Stick it in in it and use the correct limiting resistor to that DC supply.

[daz]

First off you are going to need to put a bridge rectifier and a cap on the 5v AC supply to get DC out of it. See if you can take the new switch apart and solder a resistor in parallel with the current limiting resistor To work with a lower voltage. OR... If you have the original switch apart... Just get a $1 ultra bright LED.. Stick it in in it and use the correct limiting resistor to that DC supply.

I pretty much figured i'd need a bridge rectifier since that winding has no center tap, but heres another question for ya....being it's made for 12v, wouldn't that mean the LED inside already has a resistor and wouldn't i just need to open it up and reduce it's value ? Assuming it's a regular LED that is. I suppose it could be a special one that runs off 12v, no? Or do they even make LEDs that can run off of higher voltages than normal ones?

I might be missing something, (surprising eh?) but i found some voltage doubling circuits that are real simple and don't use a bridge rectifier to take A/c and produce double the voltage in DC. But again, i'm probably just missing something. here's an example... http://www.hobbyprojects.com/the_dio...e_doubler.html

[olddawg]

I pretty much figured i'd need a bridge rectifier since that winding has no center tap, but heres another question for ya....being it's made for 12v, wouldn't that mean the LED inside already has a resistor and wouldn't i just need to open it up and reduce it's value ? Assuming it's a regular LED that is. I suppose it could be a special one that runs off 12v, no? Or do they even make LEDs that can run off of higher voltages than normal ones?

I might be missing something, (surprising eh?) but i found some voltage doubling circuits that are real simple and don't use a bridge rectifier to take A/c and produce double the voltage in DC. But again, i'm probably just missing something. here's an example... Voltage Doubler Tutorial and Circuits - Voltage Doublers Diode - Voltage of Diodes - Electronic Hobby Projects

That's exactly what I said to do above ^^^^

[daz]

I see that now. Should read slower i guess. (assuming you mean the part about a parallel R) But what about that page i linked. They aren't showing a bridge rectifier but they are showing voltage doubling and DC from an ac source. Whats that about?

[Enzo]

The original switches used neon lamps inside. The same high voltage rated switch body was used in the switches for automotive, but they then added a 12v LED.

meanwhile, Why are we building all this circuitry and power supply just so we can avoid buying the proper switch? I know it is fun to fix stuff, but in the trade, I know of no one who opens switches and replaces neon lamps, because the labor cost is WAY more than a new switch. Lamp fails, new switch. That is usually how the world works. I still have square Marshall style rockers in stock. Same switch PV used on CS800s and such.

[daz]

The original switches used neon lamps inside. The same high voltage rated switch body was used in the switches for automotive, but they then added a 12v LED.

meanwhile, Why are we building all this circuitry and power supply just so we can avoid buying the proper switch? I know it is fun to fix stuff, but in the trade, I know of no one who opens switches and replaces neon lamps, because the labor cost is WAY more than a new switch. Lamp fails, new switch. That is usually how the world works. I still have square Marshall style rockers in stock. Same switch PV used on CS800s and such.

Because i already had ordered them b4 i saw it was LED. I just saw 120v/20A and jumped on it. I tried to cancel but they said it already shipped. So i just figured 1)-i already own it and 2)-i've had these neon ones go out now and then so i just figure a LED will probably outlast the switch itself. So i'd prefer it if i can use it.

[loudthud]

So this is a DPST switch with four terminals on the back? How are you going to switch 120VAC and separate the connections for the 12V lamp?

[daz]

I figured since it was 120v capable that the sides were seperate like 2 spst switches, one for the LED one for power. According the enzo thats not the case tho. He's saying they're the same switch as the marshall style but with a LED instead of neon. So if he's right i can't. I'll have to wait till i get it and make sure. It does make sense they'd use the same switch for auto tho and just change to LED, so hels probably right.