juke
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Post by juke on Dec 8, 2013 11:53:21 GMT
I just bought a string of 100 LED coloured lights for a small secondary tree. They are too bright and I'm wondering if it's feasible to dim them a bit.
The wall wart states 31V 4VA and a DC symbol. I know I can dim a single LED but would it be possible to reduce a string of 100?
I tried a Google search but didn't come up with anything helpful.
Syd
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solderdude
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Post by solderdude on Dec 8, 2013 16:17:22 GMT
If it is that low a voltage you can give it a try. Chances are there will be brightness differences across the whole chain.
Can't recommend any value as I have no idea what current will be drawn.
I don't think experimenting will harm anything. I do hope the wallwart is electrically isolated from mains but reckon it will be.
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juke
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Post by juke on Dec 8, 2013 16:41:48 GMT
If it is that low a voltage you can give it a try. Chances are there will be brightness differences across the whole chain. Can't recommend any value as I have no idea what current will be drawn. I don't think experimenting will harm anything. I do hope the wallwart is electrically isolated from mains but reckon it will be. I've had a look at the fine print on the leaflet that came with them. Each LED is 3v 0.03W. The wallwart is a tiny black thing, just big enough to grip to remove it from the wall socket but I have no idea otherwise. If that allows you to estimate a starting point resistor it would be great but not a worry if not, I'll just experiment, thanks Frans. Syd
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solderdude
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Post by solderdude on Dec 8, 2013 19:52:48 GMT
a white LED has a voltage of around 3V and 10mA is a 'normal' current for such an LED. It is possible that there simply are 10 rows of 10 LED's in series thus 100mA at 30V = 3W. a 4W converter thus seems logical. LEDs usually are current fed but just like you can power a red LED from a single 1.5V battery it is possible to power a white LED from 2 x 1.5V batteries. It is not easy to say/predict what the LED voltage will be at a somewhat lower current so will just have to wing it with values between 10 Ohm and 100 Ohm most likely. Wattage can be small, 1W will do.
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juke
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Post by juke on Dec 8, 2013 23:15:16 GMT
That's great Frans, I wouldn't have had a clue where to start. I have a fair selection around and between these values, maybe not so many at 1W but that can soon be remedied.
Syd
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