Beacon Light

[sunny_nites]

Wow, been a while!

Really surprised at how well the batteries hold up on these little guys.

This one was made in February of of 2012 and is still proudly preforming keychain duty.

Hard to see the lights but my sculpture of early models is down from four working lights to two.

All the lights in the sculpture were built in November and December of 2011.

One thing I learned is that there has to be some kind of mechanical pressure to hold the wires to the battery. Tried may different methods but wire glue seemed to work the best for those flat style resin lights.

I've gotten away from making the encapsulated lights as I've learned that the batteries can vent. None that I have made have had a problem but I did move my sculpture out to the garage and I wouldn't recommend trying this yourself.

I've come up with a new model that I've been using for a while now. This one can even have the battery changed when it runs out.

Attached to my Thrunite T20

Has a mechanical holder for the wires as seen above.

I'm running this a little "hotter" than I would for a light that can't have the battery replaced. The light above is running around 8 micro amps on a fresh battery and should run for at least a year.

Hard to get a reference with the lights on to get the pictures but this light is vastly brighter than any tritium I have see, although it is admittedly much bulkier.

The cap is made of a stainless steel loop embedded in clear resin and surrounded by a semi rigid poly tube, that acts like an o-ring that helps make it water resistant. Not sure if I will go with some other mechanical method to secure the cap. Right not the cap is like a cork but is extremely tight and doesn't show any signs of coming out on its own.

 

[Bimmerboy]

What a cool thread! Some pretty funny comments too. :thumbsup:

Subscribed... I'd definintely like to try making some of these. Thanks, guys!

 

[alphazeta]

Q: does one use a decent/nice DMM to read the current? My sub $10 DMM gives me a current reading of zero on all settings.

I scrapped quickly one together with two L44 button cells(for a supposedly 3.10V) and a project leftover 2 ohm resistor + one generic 5mm LED. It is WAY too bright. I'll be surprised if it lasts the night.

BTW - needless to say -> cool thread!

BTW#2 - this light won't be living on my keychain but probably as a stationery light in some dark recess of my home. As space won't be a concern perhaps I should I should look toward building a find me kinda light by soldering a few D cells together?

 

[sunny_nites]

I haven't run across a meter that will measure super low currents either.

I'm purely going by calculations on the current outputs for the lights I have put together:

LED VD = 2.4
Desired drive current = 4 micro amps
Voltage of a fully charged lithium primary button cell = 3.2v

3.2-2.4/.000004 = 200K (went with a 180K, have to do some rounding to match what is available)

To figure runtime:
Current capacity of cell (CR927 in the newest version) = 30mah
Current draw of LED = 4 micro amps (or there abouts)

(((.03/.000004)/24)/365) = .865 of a year or around 7 or 8 months.

The above calculations assume all everything is static, which it will not be with a simple resistor. What will likely happen is the brightness of the LED will dim but keep running way past a year.

Good luck on your projects and thanks for the comments! These have been fun projects for sure.

 

[tylernt]

There is a device called "uCurrent" made by an Australian guy that goes by the handle of "EEVblog" and is sold by such retailers as AdaFruit.

 

[pyro1son]

love this idea and have tried all my leds but none light at such low current

 

[tylernt]

love this idea and have tried all my leds but none light at such low current

What voltage are you using and what color of LED? If the voltage is high enough, your LEDs should light even at very tiny current levels. But if the voltage is too low, then all the current in the world won't make them light.

 

[pyro1son]

Green LED @ 3.78 volts

 

[tylernt]

Green LED @ 3.78 volts

That's probably high enough. Each LED has a slightly different forward voltage, especially between manufacturers but even within a batch. 3.6V is thrown around as a "standard" but some LEDs are specified as high as 4.2V. But, even the ones specified at 4.2V will usually light at somewhat lower voltages, albeit with reduced brightness.

Is this a new battery and are you reading the voltage while it is attempting to light the LED? Voltage on a weak battery can drop significantly when a load is placed on it.

 

[pyro1son]

It's a fresh li-ion I'm testing with. The LEDs are rated to have a 2mA working current.

 

[tylernt]

It's a fresh li-ion I'm testing with. The LEDs are rated to have a 2mA working current.

Hm, I can't explain it then, unless maybe you've got a bad resistor. Sometimes the resistance will be higher than spec due to manufacturing defects.

 

[pyro1son]

I shall try some other resistors later

 

[sunny_nites]

I have tried Lots of different styles and manufacturers of LEDs and found that the tolerances, when you get into the micro amp range, varies wildly.

In my experience:
Blue and green LEDs work the best, at very low currents, in general. Red, amber, white, etc take much more current to produce visible light.
This was contrary to the way I thought it would be: SMD blue and green LEDs don't work at very low currents, as well as 5mm and 3mm LEDs do.
Inverted cone LEDs by far work the best at producing visible light at extremely low currents.
When you get into the nano amp range, the ability of an LED to provide any light will vary depending on the individual LED itself. IE, some LEDs from the same manufacturer will work at nano amp range, some wont and the ones that do work will put out different levels of light.
Around 800 nano amps appears to be the cutoff for any LED that I have worked with.

pyro1son, your LEDs may be putting out light but it might be too dim to see, especially if they aren't inverted cone types. Maybe try it in a really dark room or gradually decrease the value of your resistor until you start to get visible light. Once you know it is working, you can put a DC meter across the pins of the LED and measure the voltage drop to get their exact value.

 

[pyro1son]

Thanks for the info. Very informative! I shall give that a go.

 

[Dr.Jones]

If you want to measure the current, use the resistor as shunt, i. e. measure the voltage U of the resistor with resistance R and calculate I=U/R.

 

[alphazeta]

If you want to measure the current, use the resistor as shunt, i. e. measure the voltage U of the resistor with resistance R and calculate I=U/R.

Great tip! Thanks!

I haven't run across a meter that will measure super low currents either.

I'm purely going by calculations on the current outputs for the lights I have put together:

LED VD = 2.4
Desired drive current = 4 micro amps
Voltage of a fully charged lithium primary button cell = 3.2v

3.2-2.4/.000004 = 200K (went with a 180K, have to do some rounding to match what is available)

To figure runtime:
Current capacity of cell (CR927 in the newest version) = 30mah
Current draw of LED = 4 micro amps (or there abouts)

(((.03/.000004)/24)/365) = .865 of a year or around 7 or 8 months.

The above calculations assume all everything is static, which it will not be with a simple resistor. What will likely happen is the brightness of the LED will dim but keep running way past a year.

Good luck on your projects and thanks for the comments! These have been fun projects for sure.

Very useful 411. Thx!

 

[danjcla]

Which polymer to use?

Good thing as you can't fix it once the polymer has cured!

Sorry for the newbie question, but which polymer did you use? Later in this thread someone mentions "devcon", but they make a whole lot of products. I found an epoxy resin called "Alumilite Amazing Clear Cast", 16oz for $16. But it seems to have a niche target market; I'm guessing / hope that something more industrial would be cheaper than $1 per ounce, even in small quantities.

Also, awesome thread. Comes in high for a lot of google searches.

 

[DrafterDan]

Re: Which polymer to use?

Wow, not the longest 'wayback machine' post that has been resurrected, but this one is about 3.5 years old.

I don't recall if S_N ever mentioned which resin he used, however I bet it was along the lines of those 2-part epoxy tubes that are available at any hardware store. I've used them several times, they do cure nice and clear. Just go slow to avoid bubbles!
~D

 

[sunny_nites]

Re: Which polymer to use?

I really did a double take when I saw an update to this post!

Hard to believe but I have beacons going on 4 years old that are still working and even have a couple of beacons in that sculpture from page one that are still putting out light.

I tried a couple of different versions of epoxy but Alumilite seemed to be the best. I wouldn't recommend the two part Devocon type epoxies for several of reasons; they are very thick, very bubbly and will yellow over time or with much exposure to sunlight. Even the Alumilite can be tricky to get all the bubbles out. A vacuum chamber is recommended and would probably work the best but I used a pressure pot and it seemed to work pretty well and was vastly cheaper.

Now with that being said, I would recommend that you not encapsulate any type of battery because they can vent and it's hard to say what might happen to one encased in resin.

A better idea would be to use a small, single LED keychain light and build your beacon in it. That way the battery is not confined in anyway. Something along the lines of this re-purposed X-Light Micro housing:

You would want to use some mechanical means of holding the terminals of the circuit to the battery, the leads for the LED are way to weak. The above example uses the spring clip from the donor circuit and holds the battery in quite nicely. And with that whomping 180mah capacity CR2032 battery providing power, this beacon should run for years and years.

Good luck and thanks so much for the trip down memory lane!

 

[kaichu dento]

Re: Which polymer to use?

Norland 61 is probably the best epoxy for this. UV curing no-mix optical grade epoxy which it seems everyone on CPF was stocking up for trit installs. I've still got a bit stashed away but haven't paid any attention to trits in a while.