Hooking up a full wave rectifier to non-rectified LED light strands

[Tom L.]

Does anyone have a wiring diagram on how to hook up a pre-made full wave rectifier (like at radio shack http://www.radioshack.com/product/index.jsp?productId=2062583#showFullReviews) to an existing non-wave LED christmas light set (Costco)? :?

Thanks, Tom L.

[Tom L.]

Thanks Jeff, this helps alot. Question: how many string of LED can I plug together per Rectifer? The rectifier can handle up to 8 amps.

Tom

[huskernut]

Hi all, Why add rectification? Brighter, less flicker? Just wondering

[Tom L.]

Jeff,

I found another location on the web about "Hacking LED Christmas lights" at http://www.dirtside.com/led/hacking.html. He has a similar setup as yours above but added a resister and capacitor, I assume to further smooth out any flickering.

I don't know if I need to go this far in my set up. I just want to remove the flicker and be able to FADE up and down the various LED lights with LOR without burning out any LED's.


Tom L.

[Tom L.]

Thank you for the heads up - NO CAPACITOR.

Q: If I hook up the rectifier, will I be able to dim the lights, up and down?

[Dennis Cherry]

Tom L. wrote

Q: If I hook up the rectifier, will I be able to dim the lights, up and down?

Adding a bridge rectifier is fine and dimming is also fine. Have done that for 3 years.

You might want to try reducing the max intensity from 100% to 75%, you will see the fades better.

My 2 cents worth.

[Steven]

Hooking up a capacitor to the DC side of the rectifier will reduce the flicker even more, but:

1. It will increase the duty cycle, which will cause the LEDs to run hotter, which will decrease their life; and
2. It will make dimming nearly useless.

Several of the full-wave LED strings I bought were wired such that the rectifier was immediately after the plug, meaning that the socket at the end had rectified voltage. Thus, I just plugged a have-wave string into the end of the full-wave string and now I had two full-wave strings.

It made the half-wave string brighter with less flicker, but I was worried the excess brightness would make it burn out. So I left it turned on in the garage for a few days with no failure. I figured when I had it outside on a controller it would run much cooler.

[Ponddude]

The information on that website really is for LED lights that are constantly on. As Jeff stated, fading the LEDs won't work well and eventually end in smoke. Why? Well a rectifier is really just a way of switching the currently from AC to DC. It can also be done with 4 diodes. In the normal course of events in a transformer the capacitor is used to smooth out the voltage. However, because of the amount of energy that the capacitor is storing the lights would never fade off...or at least not like you would want them too.

[JonB256]

Don't be too quick to dismiss the capacitor.

The design of many AC LED strings relies on the charging of the capacitor to get the voltage HIGH enough to get full brightness. Sometimes, though, they will use too large of a capacitor and it doesn't discharge fast enough as you try to dim, giving you slow to non-existent dimming.

I got some super cheap strings a year ago and, when plugged into the wall, they looked great. No flicker, good brightness. But when unplugged, they took about 20 seconds to fade out. Way too slow. When I popped open the "block" near the plug, it turned out to be a Half-Wave setup with a resistor and a large value capacitor. It made the voltage very high and flicker free, even better than a full wave. (some mentioned Duty-Cycle earlier, though technically it is the RC time constant)

Since I wanted to dim these strings, I experimented with different size capacitors. I removed the 100ufd and put in a 10ufd. Good guess on my part because now it gave me a very rapid "off" when uplugged and was almost as bright at 100%. I tried a few other values, but 10ufd was the best response time. I modified about 30 of them and used them in my Marty Fan.

The reason I mention this is that, if you power your strings from a Full Wave rectifier bridge but the string is designed as a Half-Wave with a capacitor, it may burn brighter and it will not dim the same way. (because the Duty Cycle with 60hz DC ripple is not the same as at 30hz DC ripple)

[Randy]

Tom,

In addition to Jeff's schematic for the diodes and the LEDs above, you'll need a resistor in series with LEDs to limit the current. You can take measurements on an existing string to get the right value of current for those lights, but it is usually in the 13-16 mA range.

I use a 5 watt variable resistor (potentiometer) to figure the exact value of the resistor while measuring the current. I also just purchased a resistor substitution box to help in that area as well.

In fact, I'm planning to work out on the garage today and build up some small light count LED strings to use in an animated figure. It's possible to do what you want with a little bit of effort.

Let us know if you have more questions...

Randy