Hi, i am after a circuit that will light an LED if a fuse is blown, it needs to run at mains ( so +------|==3amp==|----[LOAD]------GND) with + and - being mains. the circuit here looked ideal: HERE except i cant help feeling it is not going to work.... if leds could be run of mains so easily, using one 100k resistor, it would be comon as hell. turbokeu has a circuit on his site here: http://www.turbokeu.com/myprojects/acled.htm for funning LEDs of mains and it is a lot more complex than the above! but not one for if a fuse was blown. Also the first site, on the second circuit for "Warning buzzer" the buzzer is shown connected directly over the 12v, so it would allways be on wouldent it? any ideas?
AFAICS the circuit's missing a high-voltage diode to block reverse voltage on the green led. The problem with resistor-only is it will produce a lot of heat (W = current2 x resistance), a series capacitor is better for dropping most of the extra volts as they produce imaginary heat, but they need 2-way flow as turbokeu's circuit. You could combine the two circuits, a single inverse diode will cover both leds.
Usually sold as Class Y2, X1 or X2, for continuous AC mains duty, and not expensive. 1N4004/5/6/7 are OK.
highest i can find is 275V AC http://www.rapidelectronics.co.uk/rkmain.asp?PAGEID=80008&CTL_CAT_CODE=31195 can find 300Vac but only in 22nf not 220nf ... since this is "Working Voltage" i wouldent of thought there would be a prob, unless the diodes rectify it...
Rapid do about 4 in 220nF all suitable for mains use. They only specify 250V AC but that's OK for any UK mains application, equivalent to 350V peak. 10-1342, 10-2680, 10-2778, 10-2494, all OK.
excellent, thanks alot! Will have to wait for enough stuff to order from them now... lol edit: found one 10-2778 in my stock... will try this out today!
Impedance of 220n+1k @50Hz is around 14.5k according to here so on 230V will give 16mA, resistor will produce I2R = 0.256W, so 0.5W is better. Or use 2 x 1/4W 470R in series, or 2 x 1/4W 2k in parallel. That 100k resistor in the first linked circuit, led current will be so low (2.3mA) it will probably survive the reverse voltage (for a few weeks). Still well dodgy.
all good and all working! Just need to get some more 220nf caps now! havent got enough on the books to order from rapid yet... looks like its going to have to wait...
it worked until i took the fuse out with the machine on (fuses doing there job) and there was a big flash and alot of buning smell... and the leds went black lol! decided to drop the idea...
Hi All, I came across this thread whilst I was looking for the same idea as bigal and wondered if I can ask a question. I know the thread was posted quite a while back so I'm hoping someone out there can help Whilst looking for a solution to my problem, I've seen two diagrams on the net (one of which is mentioned in the thread, the other one uses a zener diode which is in line with a 1n4007 on the Live line) For the life of me I can't get both diagrams to work reliably (one only lights a single colour and the other does nothing). What I'm ideally looking for, is a mains fuse indicator which will illuminate a green LED for mains ok which then turns red if the fuse blows. I know my way around a schematic and good with electrics but I'm not so good at my electronics so I'd appreciate any help, or even a reliable schematic to solve this problem. Many thanks.
