Re: [MBZ] Using LEDs - was OT: Politics are angrier polls

[Curt Raymond via Mercedes]

I was trying to run 2x 3.xv LEDs off my 6v pack but the 6v is nominal, with the 
rechargable batteries I'm probably only getting 5.2v and my alkaline batteries 
are worn out and only reading 1v each so my problem was probably that I didn't 
have enough voltage to run them in parallel.
The problem for aiming is that I didn't really pay attention when I cut the 
piece of styrene the LEDs poke through so a couple of them just barely fit. The 
original system used a metal bar down the center as a stiffener and ground 
lead. I've got a couple LEDs leaning on the bar which makes them shoot off to 
the side. On one hand this reduces the overall brightness for reading, on the 
other hand it gives me a wider field of view so book placement is less 
important.I'm also debating adding another 10 LEDs to the array as well. Need 
to take it to camp and give it a shot before I make any decisions though.
3x 1.5v (or 1.2v in the case of rechargeable) cells like I'm using is pretty 
much the way all LED flashlights are today...

-Curt
 

  From: fmiser <fmi...@gmail.com>
 To: mercedes@okiebenz.com 
Cc: Curt Raymond <curtlud...@yahoo.com>
 Sent: Monday, January 11, 2016 2:49 PM
 Subject: Re: [MBZ] Using LEDs - was OT: Politics are angrier polls
   
> Curt wrote:
> 
> Looking around I found a bag of through hole LEDs I'd
> bought but never used. Dropping one cell from my battery
> pack gives me 3.6v using rechargeable batteries which I
> tested and appeared to be acceptable with my 35ma LEDs so I
> rewired the thing with those.

Again, the LEDs don't really care what the voltage is - so
long as they only have 35 ma passing through.  This is NOT
how most electrical devices work.

Using no resistor means you are depending on the source
impedance to limit the current.  It so happens that NiCd and
NiMh cells have a much lower internal resistance than
alkaline.  Therefore the LEDs will be brighter with
rechargeable than with primary cells - even though if they
are both the same voltage.

> I finished it last night and testing shows that it works
> pretty well for a reading light (its intended purpose)
> although it could stand a little work aiming the LEDs
> better.

Good!  If it works, the math is academic. *smiles*

With the through hole LEDs, it _is_ possible to aim
them.  If you don't want the focused spot, you may be able to
turn them into very wide angle.  I have filed the rounded top
off of many of them to get rid of the lens.  If you do that,
be careful to not take off so much you run into the wires
inside.

> I think you missed the point of my diode, I've got a single
> pole single throw 3 position switch. On low it activates
> one string of lights, on high it activates both.

You're right.  I missed that. *weak smile*

> Also in my experiments LEDs must be used in parallel
> which matches my understanding of how they work. Because
> they are one way valves the electrical pixies won't pass
> through like they would a normal valve. Certainly when I
> strung them up in series they wouldn't do anything... 

The problem with parallel LEDs has to do with the nature of a
diode.  Below the voltage threshold, no current flows.  Once
the threshold has been exceeded, the diode (LED) will flow
_huge_ amounts of current.  It is practically a switch.  To
survive, the current must be limited.  Either from the
batteries internal resistance or from a resistor etc.

The threshold voltage is a "typical" value.  Each device will
vary by a little bit.  If there are two 3.6 V LEDs, and one
is actually 3.599 and the other is 3.601, the voltage may
never reach 3.061 because the 5.599 diode has conducted all
the current the limiting resistor has allowed through.  If
you engineered the circuit expecting the diodes to share the
current, and one has "robbed" it all, it won't last very long.

That said, the 3.6 V white or blue LEDs seem to behave better
than the 0.7 V single color LEDs in a parallel circuit.

And using battery power without a separate current limiter
does warp the math a bit. 

To run them in series, remember to add the voltages, so three
3.6 V LEDs will have a threshold voltage of 10.8 V.



  
___
http://www.okiebenz.com

To search list archives http://www.okiebenz.com/archive/

To Unsubscribe or change delivery options go to:
http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com

Re: [MBZ] Using LEDs - was OT: Politics are angrier polls

[Curt Raymond via Mercedes]

You can buy LEDs with the resistor already integrated. In fact I think with 
some you can even buy a PWM switching power supply already integrated so you 
can run them at your chosen voltage. Thats what I'd intended to do but not what 
actually happened. 
The LEDs I ruined were surface mount package which wasn't as easy to solder as 
I'd hoped. Looking around I found a bag of through hole LEDs I'd bought but 
never used. Dropping one cell from my battery pack gives me 3.6v using 
rechargeable batteries which I tested and appeared to be acceptable with my 
35ma LEDs so I rewired the thing with those. I finished it last night and 
testing shows that it works pretty well for a reading light (its intended 
purpose) although it could stand a little work aiming the LEDs better.
I think you missed the point of my diode, I've got a single pole single throw 3 
position switch. On low it activates one string of lights, on high it activates 
both. The diode sits on the jumper from the high side so that it doesn't turn 
on when low is called for.
Also in my experiments LEDs must be used in parallel which matches my 
understanding of how they work. Because they are one way valves the electrical 
pixies won't pass through like they would a normal valve. Certainly when I 
strung them up in series they wouldn't do anything...
-Curt
 

  From: fmiser <fmi...@gmail.com>
 To: mercedes@okiebenz.com 
Cc: Curt Raymond <curtlud...@yahoo.com>
 Sent: Sunday, January 10, 2016 7:35 PM
 Subject: Re: [MBZ] Using LEDs - was OT: Politics are angrier polls
   
> Curt wrote:
> 
> Tonight while I was not watching television I learned how
> to wire in a diode. I'm rebuilding the light I use over my
> bed at camp converting it from fluorescent to LED.


> I'd wired the LEDs in 2 strings with a 3 position switch, I
> wanted one position to turn on one string and the other
> position to turn on both. I harvested a diode from an old
> computer power supply to make that work and I think it
> would work except I discovered that what I THOUGHT were 6v
> LEDs turned out to be 3.6v. You push 6v (ie 4 D cell
> batteries in series) into a 3.6v LED and it cooks off
> pretty quick, whoops! I'm curious how bright the LEDs will
> be at 3v, they were SUPER bright at 6.

LEDs don't work like that.  It is the _current_ (amps) that
matter.  The 3.6 V is not supply voltage - it is the voltage
drop across the diode when conducting.

And if you are supplying DC, you don't need a diode with it.

And it's usually not a good idea to wire LEDs in parallel.

So - do you know the current rating of those LEDS?  20 ma is
typical for "old fashioned" general purpose LEDS.  Newer,
brighter LEDs can be designed for a whole lot more.

The you subtract the LED voltage from the supply voltage (6
minus 3.6 equals 2.4) and then using ohm's law figure out
what size resistor you need to drop 2.4 V at the design
current.  So if those are 200 ma LEDs, and R=E/I, then
2.4/0.2 = 12 ohm.  Then we need to be sure you won't fry the
resistor.  Watts = current X voltage, so 2.4 X 0.2 = 0.48
Watt.  A half watt resistor would be big enough - just.  But
it's a good idea to always overrate wattage a bit.  I would
use a 1 W resistor.

With a 6 V supply, for each of the 3.6 V LEDs (if they are
rated for 200 ma), you would need a single one watt 12 ohm
resistor in series with it.

If that's not clear enough, let me know and I'll answer
questions or go into more detail.  *smiles*


  
___
http://www.okiebenz.com

To search list archives http://www.okiebenz.com/archive/

To Unsubscribe or change delivery options go to:
http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com

Re: [MBZ] Using LEDs - was OT: Politics are angrier polls

[Curt Raymond via Mercedes]

I was considering that before I ended up dropping my pack voltage.
I forgot to mention the specs on the light I built, 10x 35ma LEDs so about 
350ma, I'm using 2500mah AA rechargeables (Amazon basics, cheap and low self 
discharge) in D cell carriers, the case was originally designed for D cells but 
rechargeable D cells are expensive and the charger is expensive. The AAs should 
have power enough for 5 or 6 hours before the batteries sag too bad and they 
get dim. Thats more than I was getting before with the fluorescent bulbs and 
10,000mah D cells. I need to do some testing but I think this light will be a 
good way to use up D cells that aren't powerful enough to run the camp shower...
-Curt
 

  From: Dan Penoff via Mercedes <mercedes@okiebenz.com>
 To: Mercedes Discussion List <mercedes@okiebenz.com> 
Cc: Dan Penoff <d...@penoff.com>
 Sent: Monday, January 11, 2016 9:48 AM
 Subject: Re: [MBZ] Using LEDs - was OT: Politics are angrier polls
   
I got a bag of like 25 LEDs with dropping resistors for operation on 12VDC on 
Amazon for $8.00, I think.

Dan

Sent from my iPad

> On Jan 11, 2016, at 9:22 AM, Curt Raymond via Mercedes 
> <mercedes@okiebenz.com> wrote:
> 
> You can buy LEDs with the resistor already integrated. In fact I think with 
> some you can even buy a PWM switching power supply already integrated so you 
> can run them at your chosen voltage. Thats what I'd intended to do but not 
> what actually happened. 
> The LEDs I ruined were surface mount package which wasn't as easy to solder 
> as I'd hoped. Looking around I found a bag of through hole LEDs I'd bought 
> but never used. Dropping one cell from my battery pack gives me 3.6v using 
> rechargeable batteries which I tested and appeared to be acceptable with my 
> 35ma LEDs so I rewired the thing with those. I finished it last night and 
> testing shows that it works pretty well for a reading light (its intended 
> purpose) although it could stand a little work aiming the LEDs better.
> I think you missed the point of my diode, I've got a single pole single throw 
> 3 position switch. On low it activates one string of lights, on high it 
> activates both. The diode sits on the jumper from the high side so that it 
> doesn't turn on when low is called for.
> Also in my experiments LEDs must be used in parallel which matches my 
> understanding of how they work. Because they are one way valves the 
> electrical pixies won't pass through like they would a normal valve. 
> Certainly when I strung them up in series they wouldn't do anything...
> -Curt
> 

___
http://www.okiebenz.com

To search list archives http://www.okiebenz.com/archive/

To Unsubscribe or change delivery options go to:
http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com



   
___
http://www.okiebenz.com

To search list archives http://www.okiebenz.com/archive/

To Unsubscribe or change delivery options go to:
http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com

Re: [MBZ] Using LEDs - was OT: Politics are angrier polls

[Dan Penoff via Mercedes]

I got a bag of like 25 LEDs with dropping resistors for operation on 12VDC on 
Amazon for $8.00, I think.

Dan

Sent from my iPad

> On Jan 11, 2016, at 9:22 AM, Curt Raymond via Mercedes 
>  wrote:
> 
> You can buy LEDs with the resistor already integrated. In fact I think with 
> some you can even buy a PWM switching power supply already integrated so you 
> can run them at your chosen voltage. Thats what I'd intended to do but not 
> what actually happened. 
> The LEDs I ruined were surface mount package which wasn't as easy to solder 
> as I'd hoped. Looking around I found a bag of through hole LEDs I'd bought 
> but never used. Dropping one cell from my battery pack gives me 3.6v using 
> rechargeable batteries which I tested and appeared to be acceptable with my 
> 35ma LEDs so I rewired the thing with those. I finished it last night and 
> testing shows that it works pretty well for a reading light (its intended 
> purpose) although it could stand a little work aiming the LEDs better.
> I think you missed the point of my diode, I've got a single pole single throw 
> 3 position switch. On low it activates one string of lights, on high it 
> activates both. The diode sits on the jumper from the high side so that it 
> doesn't turn on when low is called for.
> Also in my experiments LEDs must be used in parallel which matches my 
> understanding of how they work. Because they are one way valves the 
> electrical pixies won't pass through like they would a normal valve. 
> Certainly when I strung them up in series they wouldn't do anything...
> -Curt
> 

___
http://www.okiebenz.com

To search list archives http://www.okiebenz.com/archive/

To Unsubscribe or change delivery options go to:
http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com

Re: [MBZ] Using LEDs - was OT: Politics are angrier polls

[fmiser via Mercedes]

> Curt wrote:
> 
> Looking around I found a bag of through hole LEDs I'd
> bought but never used. Dropping one cell from my battery
> pack gives me 3.6v using rechargeable batteries which I
> tested and appeared to be acceptable with my 35ma LEDs so I
> rewired the thing with those.

Again, the LEDs don't really care what the voltage is - so
long as they only have 35 ma passing through.  This is NOT
how most electrical devices work.

Using no resistor means you are depending on the source
impedance to limit the current.  It so happens that NiCd and
NiMh cells have a much lower internal resistance than
alkaline.  Therefore the LEDs will be brighter with
rechargeable than with primary cells - even though if they
are both the same voltage.

> I finished it last night and testing shows that it works
> pretty well for a reading light (its intended purpose)
> although it could stand a little work aiming the LEDs
> better.

Good!  If it works, the math is academic. *smiles*

With the through hole LEDs, it _is_ possible to aim
them.  If you don't want the focused spot, you may be able to
turn them into very wide angle.  I have filed the rounded top
off of many of them to get rid of the lens.  If you do that,
be careful to not take off so much you run into the wires
inside.

> I think you missed the point of my diode, I've got a single
> pole single throw 3 position switch. On low it activates
> one string of lights, on high it activates both.

You're right.  I missed that. *weak smile*

> Also in my experiments LEDs must be used in parallel
> which matches my understanding of how they work. Because
> they are one way valves the electrical pixies won't pass
> through like they would a normal valve. Certainly when I
> strung them up in series they wouldn't do anything... 

The problem with parallel LEDs has to do with the nature of a
diode.  Below the voltage threshold, no current flows.  Once
the threshold has been exceeded, the diode (LED) will flow
_huge_ amounts of current.  It is practically a switch.  To
survive, the current must be limited.  Either from the
batteries internal resistance or from a resistor etc.

The threshold voltage is a "typical" value.  Each device will
vary by a little bit.  If there are two 3.6 V LEDs, and one
is actually 3.599 and the other is 3.601, the voltage may
never reach 3.061 because the 5.599 diode has conducted all
the current the limiting resistor has allowed through.  If
you engineered the circuit expecting the diodes to share the
current, and one has "robbed" it all, it won't last very long.

That said, the 3.6 V white or blue LEDs seem to behave better
than the 0.7 V single color LEDs in a parallel circuit.

And using battery power without a separate current limiter
does warp the math a bit. 

To run them in series, remember to add the voltages, so three
3.6 V LEDs will have a threshold voltage of 10.8 V.


___
http://www.okiebenz.com

To search list archives http://www.okiebenz.com/archive/

To Unsubscribe or change delivery options go to:
http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com

Re: [MBZ] Using LEDs - was OT: Politics are angrier polls

[fmiser via Mercedes]

> Curt wrote:
> 
> Tonight while I was not watching television I learned how
> to wire in a diode. I'm rebuilding the light I use over my
> bed at camp converting it from fluorescent to LED.


> I'd wired the LEDs in 2 strings with a 3 position switch, I
> wanted one position to turn on one string and the other
> position to turn on both. I harvested a diode from an old
> computer power supply to make that work and I think it
> would work except I discovered that what I THOUGHT were 6v
> LEDs turned out to be 3.6v. You push 6v (ie 4 D cell
> batteries in series) into a 3.6v LED and it cooks off
> pretty quick, whoops! I'm curious how bright the LEDs will
> be at 3v, they were SUPER bright at 6.

LEDs don't work like that.  It is the _current_ (amps) that
matter.  The 3.6 V is not supply voltage - it is the voltage
drop across the diode when conducting.

And if you are supplying DC, you don't need a diode with it.

And it's usually not a good idea to wire LEDs in parallel.

So - do you know the current rating of those LEDS?  20 ma is
typical for "old fashioned" general purpose LEDS.  Newer,
brighter LEDs can be designed for a whole lot more.

The you subtract the LED voltage from the supply voltage (6
minus 3.6 equals 2.4) and then using ohm's law figure out
what size resistor you need to drop 2.4 V at the design
current.   So if those are 200 ma LEDs, and R=E/I, then
2.4/0.2 = 12 ohm.  Then we need to be sure you won't fry the
resistor.  Watts = current X voltage, so 2.4 X 0.2 = 0.48
Watt.  A half watt resistor would be big enough - just.  But
it's a good idea to always overrate wattage a bit.  I would
use a 1 W resistor.

With a 6 V supply, for each of the 3.6 V LEDs (if they are
rated for 200 ma), you would need a single one watt 12 ohm
resistor in series with it.

If that's not clear enough, let me know and I'll answer
questions or go into more detail.  *smiles*

___
http://www.okiebenz.com

To search list archives http://www.okiebenz.com/archive/

To Unsubscribe or change delivery options go to:
http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com