I'm planning to run a LED of mains power in a project. My idea is to use a series capasitor insted of a resistor. The circuit needs to fit in a very small space and i'm having prolems finding a capacitor rated for 230V AC that is small enugh. Does anyone have an idea of how a more regular capasitor would stand up to the mains voltage. I plan on putting in a small resistor in series in case the the capasitor should decide to die.
Maybe this is a mass-manufactured product where every cent counts.
I say, if you must use an LED, I suggest you ditch the capactor and use only a resistor like a neon does. Get the most efficient mA / millicandela LED available. So as to reduce the current down to 'neon current'.
Even with a very bright led I would have to disipate several watts, that is a lot of heat. How hot does neons get. Mybe I can cast it into something to make it look like a LED
Even with a very bright led I would have to disipate several watts, that is a lot of heat. How hot does neons get. Mybe I can cast it into something to make it look like a LED
The capacitor can be made half the size if you use a bipolar LED which lights when the power is applied in either direction, it also means you don't need another diode to protect the LED.
I need to fit it through a 13mm diameter hole. my plan was to use a 12mm diameter pcb. My plan is for a 0,33uF capasitor, a small signal diode and aprox. 470 ohm in series for safety. The capasitors I have been looking at are much larger than this.
The only capasitors with 250V AC rating (I would like 500V) I have been able to find are class X1, X2 and Y2 and they are enormous.
I think I can reduce the value of the capasitor to 0,22uF without much trouble.
I should probably also put about 1M ohm across the capasitor. I just did a test setup with a capasitor i pulled from an old computer monitor and got quite a jolt from the capasitor after it was unpluged.
I have used 47nF 1 kV capacitors with success. They are bigger than a 5 Watt resistor.
You need a 820 or 1 k.ohm 1 Watt resistor in series to limit the inrush current.
It yields in about 5 mA LED current which is fine for indicating purposes.
Most >5000 MCAD LED's are already quite bright with 1 or 2 mA current through it, you don't need 20 mA hence a oversized cap.
Go with neons whcih you can run at 680 µA and a 270 k ¼ Watt seies resistor for 240 Volts
The neon itself drops about 50 - 70 Volts.
And you can get blue and green neons as well now these days.
what about a 'phase controller' + resistor? SCR turns on after the line voltage (pos half cycle) is falling, when voltage drops below say 50 V, the SCR turns of for the remainder of the half cycle (about 10 % duty cycle or less). Adding a bit of silicon and a couple BJT's might be cheaper than a 1 kV capacitor. Don't forget an ordinary 250 VAC rated capacitor is going to be a bit too fragile, the fail mode is going to be a s/c. A 'X' rated cap (not a 'Y' rated) cap that's self-healing according to the data sheet, probably can't be relied on either.
what about a 'phase controller' + resistor? SCR turns on after the line voltage (pos half cycle) is falling, when voltage drops below say 50 V, the SCR turns of for the remainder of the half cycle (about 10 % duty cycle or less). Adding a bit of silicon and a couple BJT's might be cheaper than a 1 kV capacitor.
This sounds interesting, I did a quick google on SCRs, I'm guesing it would be something like the schematic i atached to this post. Maybe someone can help me a bit with this circuit.
I should probably also put about 1M ohm across the capasitor. I just did a test setup with a capasitor i pulled from an old computer monitor and got quite a jolt from the capasitor after it was unpluged.
Hello, in the image bellow you can find a circuit that I have runing for more than 2 years with no problem. This circuit is for 120 volt, but I have change the capacitor for 0.22uF @400v for 240 volt and the resitor is 1K 1w.
Hope this help you,
taz128 **broken link removed**
Nope, have used this set up for 20 + years with no problems.
If you have a good LED, you can use 2 x 33 k ohm resistors and reduce the current eve nore.
just test it out for yourself.
I use white LED pilot lights on time switches with a 1 Watt 100 k Ohm resistor and 1N4007 and they are still perfectly bright.
frimer, as you probably have worked out by now is that I like LED's a lot for indicator purposes, hence various threads on this forum.
Interesting I find that most people are obsessed to run LED's at 20 mA's.
No need for that with the new high efficiency LED's.
Most run perfect at a couple of mA's and for reliability use a resistive circuit, capacitors will work but a spike can still pop the LED.
Attached photo's I just took today from my white (13000 MCAD) led with a 100k Ohm 1 Watt resistor on 230 Volts and 1N914 in anti parrallel ( no 1N4007 used here ).
LED current 2.3 mA.
power dissipation in R 0.53 Watts.
If space allowes use 2 x 47 k ohm 1 Watt in series to spread any heat developed.
The red led (5000 MCAD) is controlled via a 39k ohm resistor and a 1N4007 diode
if you want to connect an LED straight to 230V, you may want to try this LED:
**broken link removed**
Unfortunately, being a 4-Watt LED, it must use a heat-sink , so no good for LED indicator purposes (unless you want a seriously sick bright indicator lamp )
The good thing of course, no extra components required whatsoever