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 Post subject: Led conversion help
PostPosted: Thu Aug 09, 2018 4:27 pm 
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Joined: Wed Jul 09, 2014 9:52 am
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Location: kelowna, BC, CA
After 2 tries at this and the LEDs exploding. I'm obliviously doing something wrong. I know enough to try it and do something I shouldn't either way.

Can someone correct my math so no more led explosions?

Is the smoother installed right?

I think I installed it right. The diode won't backfeed right so current only flows one direction?

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 Post subject: Re: Led conversion help
PostPosted: Thu Aug 09, 2018 5:07 pm 
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Joined: Thu Aug 03, 2006 4:43 pm
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Location: Ottawa, ON, CA
5 ohm's is way too low a value for your current limiting resistor....
I'd start with something closer to 500 ohms, and then adjust up or down from there depending on how bright you want it....


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 Post subject: Re: Led conversion help
PostPosted: Thu Aug 09, 2018 5:27 pm 
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Joined: Thu Jan 13, 2011 11:29 am
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Location: St.Catharines, ON, CA
I'm no guru but I think the diode and 2 LED's are in backwards.
I could be wrong.

G


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 Post subject: Re: Led conversion help
PostPosted: Thu Aug 09, 2018 6:05 pm 
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Location: Toronto, ON, CA
dcrooks wrote:
5 ohm's is way too low a value for your current limiting resistor....
I'd start with something closer to 500 ohms, and then adjust up or down from there depending on how bright you want it....


This. Figure out your LED current and voltage drop from the datasheet. Then Use Ohm's law to figure out the resistor's resistance and power value.

I bet you'd be looking anywhere from 150 to 400 Ohms or so.


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 Post subject: Re: Led conversion help
PostPosted: Thu Aug 09, 2018 6:09 pm 
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Location: saskatoon, SK, CA
Yup....push resistor up to 500 or 600ohm and flip a diode....
A/c circuit. Smoother not really necessary unless you can notice the flicker.

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 Post subject: Re: Led conversion help
PostPosted: Thu Aug 09, 2018 6:27 pm 
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Location: Toronto, ON, CA
KING OF AUDIO wrote:
After 2 tries at this and the LEDs exploding. I'm obliviously doing something wrong. I know enough to try it and do something I shouldn't either way.

Can someone correct my math so no more led explosions?

Is the smoother installed right?

I think I installed it right. The diode won't backfeed right so current only flows one direction?

Attachment:
20180809_172157.jpg

I agree with @dcrooks. Most LEDs draw mA, so the resistor needs to be much higher than what you're using.

To calculate the resister value, you need to subtract the voltage drop across the LED and rectifier diode from the Vin. Devide this by the current needed to drive the LED. So for example, 6.4v - 2.7 - .5 = 3.3v. Say each LED draws 20mA but there's 2 in parallel drawing 40mA. 3.3/.04 = 82.4ohms. 100ohms would be a better place to start. Power requirement for the resistor is V x A, or 3.3 x .04 = .13 or 130mW. A 1/4 watt resistor should be ok, but higher would last longer and stay cooler.

These calculations are based on assumptions... actual specs and measurements will be needed to dial it in.

-- 09 Aug 2018 22:27 --

zhenya01 wrote:
dcrooks wrote:
5 ohm's is way too low a value for your current limiting resistor....
I'd start with something closer to 500 ohms, and then adjust up or down from there depending on how bright you want it....


This. Figure out your LED current and voltage drop from the datasheet. Then Use Ohm's law to figure out the resistor's resistance and power value.

I bet you'd be looking anywhere from 150 to 400 Ohms or so.


What he said lol...

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 Post subject: Re: Led conversion help
PostPosted: Thu Aug 09, 2018 7:18 pm 
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Joined: Wed Jul 09, 2014 9:52 am
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Location: kelowna, BC, CA
Its looks like -6.4 but it was supposed to be + 6.4.
Is that why you asking me to flip the diode.
I'm having an issue right now and am checking my work. Now I'm questioning things. There are two supply lines coming out of that transformer both carry a positive voltage ones 6 ac and the other was 8 ac. I ran both ends of that transformer wire to a electrical outlet ground and both put out voltage. Which is the positive line? Transformer no good?

I was trying to create a half wave to turn ac to kinda dc to remove flicker. Too much math for one day.


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 Post subject: Re: Led conversion help
PostPosted: Fri Aug 10, 2018 3:04 am 
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Location: St.Catharines, ON, CA
KING OF AUDIO wrote:
Its looks like -6.4 but it was supposed to be + 6.4.
Is that why you asking me to flip the diode.
I'm having an issue right now and am checking my work. Now I'm questioning things. There are two supply lines coming out of that transformer both carry a positive voltage ones 6 ac and the other was 8 ac. I ran both ends of that transformer wire to a electrical outlet ground and both put out voltage. Which is the positive line? Transformer no good?

I was trying to create a half wave to turn ac to kinda dc to remove flicker. Too much math for one day.


Brain cramp.Seen the neg but AC so irrelevant.

G


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 Post subject: Re: Led conversion help
PostPosted: Fri Aug 10, 2018 3:20 am 
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Location: hawkesbury, ON, CA
when plug in wrong polarity. led will not work.


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 Post subject: Re: Led conversion help
PostPosted: Fri Aug 10, 2018 3:59 am 
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Location: Ottawa, ON, CA
A forward biased LED should have a voltage drop of about 2.2 Vdc across it.
The current should be able about 10 mA through a single LED.

Think your electrolytic cap is in backwards.
The large plate indicates the positive.


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 Post subject: Re: Led conversion help
PostPosted: Fri Aug 10, 2018 4:13 am 
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Location: Bouctouche, NB, CA
I would also place the resistor after the capacitor, not before. But yes, your resistor value is much too low.


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 Post subject: Re: Led conversion help
PostPosted: Fri Aug 10, 2018 7:11 am 
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Location: Medicine Hat's where E's at, AB, CA
KING OF AUDIO wrote:
Its looks like -6.4 but it was supposed to be + 6.4.
Is that why you asking me to flip the diode.
I'm having an issue right now and am checking my work. Now I'm questioning things. There are two supply lines coming out of that transformer both carry a positive voltage ones 6 ac and the other was 8 ac. I ran both ends of that transformer wire to a electrical outlet ground and both put out voltage. Which is the positive line? Transformer no good?

I was trying to create a half wave to turn ac to kinda dc to remove flicker. Too much math for one day.


The 6V secondary output of your transformer has no "positive" or "negative", it still is AC. Don't worry about which leg measures AC to a true ground, not important here. Transformer is OK.
Whichever leg of that secondary you tie the Neg side of your capacitor and the Cathode(s) of your LEDs to then becomes the Negative.
Your original schematic showed the diode in the correct position, just needed the resistor moved to "after" the capacitor, and its value bumped up to somewhere between 220 to 680 Ohms, somewhere around there.
6 volts AC half-wave rectified might give you quite a bit of LED flickering.
Another issue is that if this is an amplifier or receiver that you are modifying, the 6 VAC supply will tend to "sag" with the output of the unit when pushed a bit and the LED's output will be visibly affected.
I personally would have gone with a voltage-doubler circuit which offers greater room for filtering and steady output if the supply AC drops a bit.


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 Post subject: Re: Led conversion help
PostPosted: Fri Aug 10, 2018 7:25 am 
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Location: saskatoon, SK, CA
But given ac circuit should one of the leds not be flipped?

I woulda just replaced the bulb lol!

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 Post subject: Re: Led conversion help
PostPosted: Fri Aug 10, 2018 11:41 am 
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BinkyTheCat wrote:
But given ac circuit should one of the leds not be flipped?

I woulda just replaced the bulb lol!
You could do that....the LED is a diode after all. Eliminate the rectifier. Flicker won't be terribly noticeable so long as the LEDs are side by side.

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 Post subject: Re: Led conversion help
PostPosted: Fri Aug 10, 2018 12:01 pm 
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Yup. Some are more susceptible tho.

Friend had an led xmas tree....liked the way it twinkled.
I couldn't see it.

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