Filter Capacitors Question: For the Hardcore Electronics Geeks!

So basically I have a bank of 10 10W LEDs I put together based on the schematics of LED Christmas lights. This guy's site below has the equivalent schematic near the bottom of the page. (copying didn't seem right)

www.discovercircuits.com/H-Corner/AC-Powered

From what I've researched, X2 class filter capacitors are most suitable for this purpose, and .47uF is what is used for 120VAC. Naturally, they must be rated to twice voltage handled (+240VAC). What I didn't quite understand, yet, was capacitive reactance.

When I finished the circuit I expected one of two things... Huge bright light or flash and smoke. Neither happened. The LEDs were super dim. Basically, these schematics are based on 5mm LEDs. :crackup:

From what it seems, X2 class filter capacitors are hard to find above 10uF, and I need about 180uF or slightly less. So here's the question for the geeks out there: What makes X2 filter capacitors so special? Can I get away with another type? (safely, of course)

I know there's always a better way, but this is more kicks and giggles and laboratory stuff. I bought 20 of these arrays on DBay for 18 bucks, so I'm not out some huge investment. The odd bit of the matter is that I've already mounted the LED arrays on a custom-built-of-scrap enclosure with active cooling. I'd hate to gut it completely, being as how well it all went together.

Finally WARNING: Noobs don't try this! Mains voltage is very dangerous and you need to have the proper electrical safeties installed. Rest assured I do!

Here's a pic so you understand my problem:


Maybe more if I can find out what other capacitors will work! :eg:

Oil capacitors, of a proper voltage rating of course, would work. But 180uF @ 240+ volts won't be...compact.

Two electrolytics in series will work with AC: ----|(----)|---- and amount to half the capacitance of one cap alone, so you'd need two 200V+ 360µF. Of course, this means each cap will see some reverse current. It should be relatively safe if you add a reverse-protection diode to each cap. A cap that is 100% safe in this configuration will cost more than a proper LED power supply, so you'd either want to ditch this project or try the electrolytics. Use at your own risk.

The capacitors are low loss voltage droppers using the capacitor reactance rather than a resistor that dissipates the excess voltage. It is not a filter capacitor.

What type of LEDs are you planning to power? How much voltage and current? If you plan to power a bank of high power LEDs (hinted by the active cooling) then a proper switching constant current driver is necessary.

If you still insist of using a reactive dropper (which is not a good idea anyway) Back to back electrolytics will blow up due to the continuous AC operation. You will need oil filled motor run capacitors as these are much safer and are self healing when an internal arc occurs.

djQUAN said:

If you still insist of using a reactive dropper (which is not a good idea anyway) Back to back electrolytics will blow up due to the continuous AC operation. You will need oil filled motor run capacitors as these are much safer and are self healing when an internal arc occurs.

Click to expand...

Cyparagon said:

A cap that is 100% safe in this configuration will cost more than a proper LED power supply, so you'd either want to ditch this project or try the electrolytics. Use at your own risk.

Click to expand...

Thanks for the replies everyone. I thought it would be a bit on the bleak side, but when it comes to electronics I've found it's best to see what people have used in applications, rather than sort through the 100s of thousands of capacitors at Newark!

I'll probably take this one back to the drawing board... I thought 100W of light on 2 components was a bit on the fantastic side!

Quan, to answer your question I've got 10x 10W Warm White LEDs. They have a max current rating of 1050mA, run on 12V, and probably give off a really bright light. The project will definitely require a rewiring of the LEDs themselves, along with another type of current regulation and supply.

The LEDs are mounted on a plate of 1/8" aluminum, with a very large, low-profile heat sink glued to the back. 3x 120mm fans do the active cooling, powered by a 9 volt power supply. That supply is the majority of the components, seen at the left of the bank. The case used to be a pair of hard drive hot-swap caddies, mutilated for the cause!

looking around, you can use two of these.
IP67 Waterproof Aluminum Alloy External 72W Constant Current LED Driver - Silver (100~240V) - Free Shipping - DealExtreme

one driver can power a 3S2P array, the other wired to a 2S2P string.

Or you could use only 9 LEDs and use the 100W 3000mA drivers with a 3S3P LED array.

I'd highly recommend against those direct mains driven "power supplies" except for very low current, highly insulated products, like LED nightlights etc. A big LED array like that with a huge metal heatsink on it, running direct on mains is just asking for trouble. Just buy a proper LED driver