(4) 33 volt 100 watt LED's wired in series, with a 25 amp 800 PIV stud mounted rectifier for 127 vac operation. Dang I wish this would work, it would save me a lot of money. Or then it might make the prettiest smoke signal :( Am I kidding myself that this project may produce lumens similar to 1,000 watts of metal halide. 240vac is not available to the site, and transmission wire ampacity is flaky.I did find 2.75 X 2.25" aluminum heatsinks for the smaller project. Ten ribs .125" in a .250" total thickness plate. Wondering what wattage LED this capacity of heatsink would support in a 35c ambient?It won't be long before we are in the .75 US kWh range and this stuff is important. Your help is invaluable. I save it and study it.

75 cents kWh, wow! If they allow net metering then a grid tie system would be a slam dunk with maybe three year payback.

Heatsinks tend to be rated using temp per watt for dissipation.I found a calculator that might be helpful but it doesn't give the square inches required per watt. They do list some info for dissipation of copper on a circuit board which could be a bit helpful..HEAT SINK CALCULATORMost likely if you do a search using "heat sink calculator" you most likely will trip across one that gives square inches of material required.On edit..Found a real nice calculator which looks like it should give you the info you need..ANOTHER HEATSINK CALCMore info on heatsink design..HEATSINK DESIGN

MEX wrote:"(4) 33 volt 100 watt LED's wired in series, with a 25 amp 800 PIV stud mounted rectifier for 127 vac operation. Dang I wish this would work, it would save me a lot of money. Or then it might make the prettiest smoke signal" Don't forget that the peak voltage is 1.4 times the RMS voltage. 127 x 1.4 = 178V! It will make a pretty smoke signal.

LScamper wrote:MEX wrote:"(4) 33 volt 100 watt LED's wired in series, with a 25 amp 800 PIV stud mounted rectifier for 127 vac operation. Dang I wish this would work, it would save me a lot of money. Or then it might make the prettiest smoke signal" Don't forget that the peak voltage is 1.4 times the RMS voltage. 127 x 1.4 = 178V! It will make a pretty smoke signal.Half Wave rectification without filter caps will result in HALF the voltage at 89V in theory but in practice generally you can count on about half of the AC RMS or about 60V-70V.Assuming those LEDS are designed from 32V to 36 V or 96V-108V for three in series which should be well high enough.However with the conditions of the electric service there I would be prudent to use a current limiting resistor (but that would require a very large one). I would recommend using a switching power supply (designed for such use) for each one which would protect the LEDs and provide a constant current source... Not a totally cheap solution but would be better in the long run...

Although (thinking outside the box..)For what Mex is trying to do, perhaps instead of going the high wattage LED route and having to blaze a DIY path into uncharted territories..Take a long look at high wattage CFLs...For instance you can get a 65W CFL HERE for about $11. This gives off about 4500 lumens.Then use a reflector to concentrate and direct the light a bit..Like THIS for $7Keeping in mind that the large wattage CFLs are about 12" in length and often will not fit into regular lamps but as long as you get the medium Edison base bulb it will fit any standard bulb socket. You do need to watch with these as they do come in larger base style and or may not have a built in ballast..I have a 85W CFL in my garage which puts out more light than a four foot long twin tube shop light..Need even more light, they make CFLs in even higher wattage levels like 105W and if I remember correctly 200W also.Where I work at, they replaced ALL the high bay HID lights a few years back with six tube four foot fluorecsent fixtures.We gained more light, less glare, better color rendition with a vast savings in power consumption and maintenance (paid a third party to rent a man lift and relamp the burned out HID bulbs every 3 months).A year and a half ago, I changed out a 175W mercury vapor outdoor light at my parents house to a 42W CFL outdoor light. The 42W CFL is considerably brighter than the old 175 mercury vapor light ever was...

Big Project LED's | Good Sam Community

29 Replies

Harvard
Explorer
Jan 28, 2014
LScamper wrote:
"do you have a engineering link, wiki's are NOT always correct"

http://www.learnabout-electronics.org/ac_theory/ac_waves02.php

http://arcarc.xmission.com/PDF_Electronics/Alternating%20Current%20-%20Part%202.pdf
LScamper
Explorer
Jan 28, 2014
"do you have a engineering link, wiki's are NOT always correct"

http://www.learnabout-electronics.org/ac_theory/ac_waves02.php

http://arcarc.xmission.com/PDF_Electronics/Alternating%20Current%20-%20Part%202.pdf
Harvard
Explorer
Jan 28, 2014
Here are a couple of screen dumps from a Velleman Digital Storage Scope. The input to the DSO is 60 Hz from the Signal Generator and the voltage has been scaled down 100:1 so I don't kill myself.

1.20 VAC RMS 60 Hz

2.40 VAC RMS 60 Hz
Harvard
Explorer
Jan 28, 2014
MrWizard wrote:
The Peak to Peak would be 240 VAC RMS x 2.828 = 680 Volts Peak to Peak

see this is the part i disagree with 2.82 NO
1.41 yes

i will read the wiki
do you have a engineering link, wiki's are NOT always correct

Keep in mind, when referring to 240 VAC RMS (ie L1 to L2) there are NO voltage readings using the center tap (Neutral) as a reference, only L1 to L2.
MrWizard
Moderator
Jan 28, 2014
The Peak to Peak would be 240 VAC RMS x 2.828 = 680 Volts Peak to Peak

see this is the part i disagree with 2.82 NO
1.41 yes

i will read the wiki
do you have a engineering link, wiki's are NOT always correct
Harvey51
Explorer
Jan 28, 2014
Another explanation of the 336 V peak to peak here:
http://wiki.answers.com/Q/What_is_the_conversion_for_rms_voltage_to_peak_to_peak_voltage#page4

I think you need to look at a sine wave graph with the RMS level indicated to get the idea. RMS is a very odd thing, hard to understand in detail though it's meaning as the voltage that provides the same power as an equal DC voltage is quite straightforward.
Harvard
Explorer
Jan 28, 2014
MrWizard wrote:
and so it IS
but the upper~lower limit of a 120v wave form is 170 spread not 336v spread

by your math one half of the wave form is 120v
there fore a 230v circuit would be over 672 peak to peak

by my math and understanding its the whole sine wave

60v each side of the direction change is RMS and the peak on each side of the direction change 85+ give or take depending on load factors

if I'm wrong point me to the right electrical info page with the correct info

What if the voltage were 240 VAC RMS?

In my interpertation:

The Peak voltage would be 240 VAC RMS x 1.414 = 340 Volts Peak
The Peak to Peak would be 240 VAC RMS x 2.828 = 680 Volts Peak to Peak
MrWizard
Moderator
Jan 27, 2014
and so it IS
but the upper~lower limit of a 120v wave form is 170 spread not 336v spread

by your math one half of the wave form is 120v
there fore a 230v circuit would be over 672 peak to peak

by my math and understanding its the whole sine wave

60v each side of the direction change is RMS and the peak on each side of the direction change 85+ give or take depending on load factors

if I'm wrong point me to the right electrical info page with the correct info
Harvard
Explorer
Jan 27, 2014
MrWizard wrote:
Where do you get the 2.82 from

Ever measure a120v source
It's 60v each half of the sine wave Not 120v
It's 120v rms of the complete sine wave, peak to peak is the whole sine wave Not one half

It's 1.4x of the complete sine wave there is No 2.82 , No 340v

Your using voltage Doubleler math

Simple half wave rectification does not produce voltage doubling

Sorry, I missinterperted your use of the term "peak to peak". In my experience it was, I thought, a term used to express the upper (+) and lower (-) limit of an AC waveform.
MrWizard
Moderator
Jan 27, 2014
Where do you get the 2.82 from

Ever measure a120v source
It's 60v each half of the sine wave Not 120v
It's 120v rms of the complete sine wave, peak to peak is the whole sine wave Not one half

It's 1.4x of the complete sine wave there is No 2.82 , No 340v

Your using voltage Doubleler math

Simple half wave rectification does not produce voltage doubling

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Big Project LED's

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