of the question - the absolute maximum standoff is ~36 volts if my
I've been going crazy with these warm white LED strip light thingees.
Given the manufacturing tolerances of
You could also use an LM3914 - it can
The beam angle is very wide - fully half the light on my kitchen sink
57V + 29.7V + 19.8V + 25.5V = 132VOn Jan 2, 7:39 pm, John Fields <jfie...@austininstruments.com> wrote:
On Mon, 2 Jan 2012 14:33:04 -0800 (PST), Chris Carlton
personalgrowth...@yahoo.com> wrote:
Thanks to every response. I don't feel nearly as insane as I did a few
short days ago.
I guess to be sensible, I'll start out simple (LEDs with correct/safe
resistors) and then also experiment with LED drivers, droppers and
regulators for possible energy savings over my 1st design. It's always
nice to have "improvements" in those areas to market if I get that
chance.
---
If what you're looking for is minimum power waste, then you should
implement series strings running at high voltages.
For example, if you ran the 30 mA strings you described earlier, you'd
have 18 LEDs dropping 3.8V each for a total drop of 68.4V, 18 LEDs
dropping 1.7V each for a total of 30.6V and 9 LEDs dropping 2.2V each
for a total of 19.8V.
Putting all of those 30mA LEDs in series would result in a total drop
of 68.4V + 30.6V + 19.8V ~ 119V, which is very close to nominal mains
voltage in the US, suggesting that you could full-wave rectify the
mains and run the LEDs without a current limiting resistor.
You'd need some kind of spike protection in order to protect the
string from transients, but we can address that later, if you're
interested.
---
My fixtures energy draw is pretty low now at less than 3.5w. Seems
great when I compare it to what it is replacing. However I can easily
see running 20-50 of these at once so it will add up.
Oh and I found some more LEDs with 30mA to replace the ones I have
that are 20mA so I would not have to mess with it and leave me cleaner
wiring in my series chains which are long because my LEDs are 3-4"
apart in most cases. Also I trying an experiment where I mixed the
20mA with some LEDs that are 40mA in a series. I averaged the mA based
on the number of each type LED. I did my resistor calculation based on
this average. So far it lights up! we'll see if it blows up!
---
If you run the 20mA LEDs at higher than 20mA, then their life will be
shortened.
---
Oh I was thinking of using laptop power supplies for this projects
future. They give 19V which makes for longer LED series strings and
they are dirt cheap ($5-10) to buy because of their popularity. What I
don't know is how reliable they are for power output??? Can I trust
them??? If I make the jump to drivers that guarantee my voltage this
may be the way to go! (LED power supplies are like $70.)
---
My suggestion is that you tailor your strings so that you can run them
directly off the mains using a full-wave bridge to drive the LEDs and
a small resistor and a Zener TVS to quell the spikes.
Would you like a schematic?
--
JF
Hey JF!!!
I may be a noobie but I was so sure that this is where I was heading.
(Resistors just seemed to be against everything I was trying to do. It
even seemed like adding another LED would be better than a resistor,
because that way all the power is being used to make light no matter
what. ???? wasn't sure if this was true.)
I found some more 30mA LEDs so they all match now, but was already
calculating things to run at reg mains. USA 110V because of the new
30mAs I have over my 110V @ 132V and wasn't sure what to do with the
extra 20V because a resistor was a billion ohms or something.
Yes I would LOVE a schematic!
Would you like a piece of my new company?Hell Yeah!! I love folks
who help get things done!
My new specs are...
3.8Fv 3.3Fv 2.2Fv 1.7Fv
30mA 30mA 30mA 30mA
15LEDs 9LEDs 9LEDs 15LEDs
-------------------------------
While it is theoretically possible to run a string of Leds into
it seems I also saw some regulators with like 10 Vout pins. But I got
Thanks JFOn Mon, 2 Jan 2012 18:02:49 -0800 (PST), Chris Carlton
personalgrowth...@yahoo.com> wrote:
On Jan 2, 7:39 pm, John Fields <jfie...@austininstruments.com> wrote:
On Mon, 2 Jan 2012 14:33:04 -0800 (PST), Chris Carlton
personalgrowth...@yahoo.com> wrote:
Thanks to every response. I don't feel nearly as insane as I did a few
short days ago.
I guess to be sensible, I'll start out simple (LEDs with correct/safe
resistors) and then also experiment with LED drivers, droppers and
regulators for possible energy savings over my 1st design. It's always
nice to have "improvements" in those areas to market if I get that
chance.
---
If what you're looking for is minimum power waste, then you should
implement series strings running at high voltages.
For example, if you ran the 30 mA strings you described earlier, you'd
have 18 LEDs dropping 3.8V each for a total drop of 68.4V, 18 LEDs
dropping 1.7V each for a total of 30.6V and 9 LEDs dropping 2.2V each
for a total of 19.8V.
Putting all of those 30mA LEDs in series would result in a total drop
of 68.4V + 30.6V + 19.8V ~ 119V, which is very close to nominal mains
voltage in the US, suggesting that you could full-wave rectify the
mains and run the LEDs without a current limiting resistor.
You'd need some kind of spike protection in order to protect the
string from transients, but we can address that later, if you're
interested.
---
My fixtures energy draw is pretty low now at less than 3.5w. Seems
great when I compare it to what it is replacing. However I can easily
see running 20-50 of these at once so it will add up.
Oh and I found some more LEDs with 30mA to replace the ones I have
that are 20mA so I would not have to mess with it and leave me cleaner
wiring in my series chains which are long because my LEDs are 3-4"
apart in most cases. Also I trying an experiment where I mixed the
20mA with some LEDs that are 40mA in a series. I averaged the mA based
on the number of each type LED. I did my resistor calculation based on
this average. So far it lights up! we'll see if it blows up!
---
If you run the 20mA LEDs at higher than 20mA, then their life will be
shortened.
---
Oh I was thinking of using laptop power supplies for this projects
future. They give 19V which makes for longer LED series strings and
they are dirt cheap ($5-10) to buy because of their popularity. What I
don't know is how reliable they are for power output??? Can I trust
them??? If I make the jump to drivers that guarantee my voltage this
may be the way to go! (LED power supplies are like $70.)
---
My suggestion is that you tailor your strings so that you can run them
directly off the mains using a full-wave bridge to drive the LEDs and
a small resistor and a Zener TVS to quell the spikes.
Would you like a schematic?
--
JF
Hey JF!!!
I may be a noobie but I was so sure that this is where I was heading.
(Resistors just seemed to be against everything I was trying to do. It
even seemed like adding another LED would be better than a resistor,
because that way all the power is being used to make light no matter
what. ???? wasn't sure if this was true.)
I found some more 30mA LEDs so they all match now, but was already
calculating things to run at reg mains. USA 110V because of the new
30mAs I have over my 110V @ 132V and wasn't sure what to do with the
extra 20V because a resistor was a billion ohms or something.
Yes I would LOVE a schematic!
Would you like a piece of my new company?
who help get things done!
My new specs are...
3.8Fv 3.3Fv 2.2Fv 1.7Fv
30mA 30mA 30mA 30mA
15LEDs 9LEDs 9LEDs 15LEDs
-------------------------------
57V + 29.7V + 19.8V + 25.5V = 132V
US mains are 120VRMS nominal, +/- 10%, which means that the input to
your string could be anywhere between 108 and 132 volts.
It seems like since your string drops 132V with 30mA through it all
would be well since the maximum mains voltage would be 132 and all
that would happen if the mains voltage dropped would be that the
string would dim a little.
In truth though, there is some tolerance to the LEDs' Vf, and that
needs to be taken into consideration.
Do you have links to the LEDs' data sheets?
BTW, as others have posted, working with mains voltages is dangerous
even if you know what you're doing, and if you don't you could easily
kill yourself or someone else or burn someone's house or place of
business down.
---
With that in mind, you might want to proceed like this: (View with a
fixed-pitch font)
First, set up three strings like this:
3.8Fv 3.3Fv 2.2Fv 1.7Fv
---[5LEDs>]---[3LEDs>]---[3LEDs>]---[5LEDs>]---
Each string will then drop about 44V, so if you connect them up in
parallel, like this:
+--[STRING1>]--+
| |
+--[STRING2>]--+
+----+ | |
MAINS>-----P||S---|~ +|--+--[STRING3>]--+
R||E | | |
MAINS>-----I||C---|~ -|-----------------+
+----+
you'll have 44V across and 30 mA through each string for a total of
90mA.
You'll drop about 1.5V across the bridge, so the transformer will have
to put out about 46V with a 90mA load, which is 4.14VA
Hammond makes a transformer, a 164F48, which has a 115V primary and
two 24V secondaries rated for 125mA that can be connected in series to
get 48V and Mouser has 3 of them in stock for USD 8.68 QTY 1.
Hammond rates their output voltages with 115V in, so instead of 48V,
with 120V in it'll be about 50V out.
With the 10% variation in US mains voltage, we'll have:
MAINS Vin Vout
-------------------
LOW 108 45
NOM 120 50
HIGH 132 55
On top of that, small transformers like this typically regulate at
about 30% from no load to full load, so for this one that would be 48V
out with a 125 mA load and 62.4V with no load, which is about
115mV/mA.
Then, since we'll only be presenting a 90mA load, that'll be a
decrease of 30mA from full load, so we can expect the output voltage
to rise to about 49V for low mains, 54V for nominal, and 59V for high
mains.
So now, since we only want 44V across the strings and we want to
protect against the high mains, we'll have to drop the extra 15V with
resistors, like this:
+--[R]--[STRING1>]--+
| |
+--[R]--[STRING2>]--+
+----+ | |
MAINS>-----P||S---|~ +|--+--[R]--[STRING3>]--+
R||E | | |
MAINS>-----I||C---|~ -|----------------------+
+----+
Since we want to drop 15V across each resistor and the current through
each one will be 30mA, Ohm's law says:
E 15V
R = --- = ------- ~ 500 ohms
I 0.03A
510 ohms is a standard 5% value and recalculating the current into the
string gives:
E 15V
I = --- = ------ ~ 29mA
R 510R
Then, the power it'll dissipate will be:
P = I˛R = 0.029A˛ * 510 ~ 429 milliwatts,
so a good choice would be a 510 ohm +/- 5%, 1/2 watt carbon film
resistor.
Now there's only one thing left to do, and that's to protect the LEDs
from spikes. We can do that by placing a 68V 1500W transzorb
http://www.onsemi.com/pub_link/Collateral/1.5SMC6.8AT3-D.PDF
across the output of the bridge, like this:
+--[R]--[STRING1>]--+
| |
+--[R]--[STRING2>]--+
+----+ | |
MAINS>-----+ +---|~ +|--+--[R]--[STRING3>]--+
P||S | | |K |
R||E | |[TVS] |
I||C | | |1.5SMC68AT3 |
MAINS>-----+ +---|~ -|--+-------------------+
+----+
Just for grins, at low line the output of the bridge is going to be
49V, so with a string dropping 44V there'll be 5V across the resistor,
so it'll only allow:
E 5V
I = --- = ------ = 9.8mA
R 510R
into the string.
At nominal mains, there'll be 54V coming out of the bridge, so that
translates to about 19.6mA into each string.
Anyway, that's basically how to do it passively at a safe voltage and
how to protect the LEDs.
It can be done actively so that the illumination from the LEDs remains
essentially constant over the +/- 10% range of mains voltage
variation, but it gets more wasteful of power and more expensive.
--
JF
An LM317 has a maximum rating of ~37 volts difference between
---
Yep. You seem to be hinting at selling