coin cell batteries:NEED ADVICE, please

[ti-force]

Okay, this isn't for a flashlight, but it involves batteries and I know you guys are very very knowledgeable about these things. So here goes, this is for a rifle scope that has an illuminated reticle that's designed for low light hunting, but the dot is so bright that it takes away from the target your trying to aquire in low light conditions.

The battery the scope uses is a cr2032 3v. If the voltage was dropped down to 1.5v wouldn't the dot be dimmer? If so, since 1.5v cr2032's don't exist, what do you guys recommend? I've looked at rechargeable 2032's, maybe that would work. But some how I need to get the voltage down to 1.5v and I'm not sure how to do that. Could I deplete the battery to that voltage some how?

Thanks in advance.

 

[Marduke]

A alkaline button cell and a homemade spacer to make up the diameter difference may work. You could also use 1xCR2016, and a homemade resistor disk in the extra thickness space.

 

[ti-force]

A alkaline button cell and a homemade spacer to make up the diameter difference may work. You could also use 1xCR2016, and a homemade resistor disk in the extra thickness space.

Thanks for the quick response and great ideas!!

About the alkaline, I think I read somewhere about one leaking and damaging the scope. Do you think that was caused from the recoil of the rifle?

Could you sort of explain the resistor disk?? Sorry, I'm truely Unenlightened.

Thanks

 

[Marduke]

A resistor disk would be just two plates and a small resistor connecting the two, and a bit of filler to keep everything together.

 

[ti-force]

How much would this decrease the voltage?

Where can I find the material to make such a device?

 

[Marduke]

How much would this decrease the voltage?

Where can I find the material to make such a device?

The value of resistor you choose would determine the voltage decrease. You can play with different values until you find just the right one.

Most hobby stores would carry them, as well as Radio Shack.

 

[ti-force]

Okay, thanks. When I have more time, I'll do some searching on here to try and find more info on how to build one of these.

 

[Phaserburn]

There is an easier solution. Get a coin cell light that uses a single led. Run it on a single 2032 cell for an hour to get some of the voltage down. Try it then. If it's still too bright, repeat. Once you get it where you want, you have a system to recreate additional cells.

Lights like this go for around $1. White led models use 2x2016 cells, but you can replace them with one 2032.

 

[ti-force]

There is an easier solution. Get a coin cell light that uses a single led. Run it on a single 2032 cell for an hour to get some of the voltage down. Try it then. If it's still too bright, repeat. Once you get it where you want, you have a system to recreate additional cells.

Lights like this go for around $1. White led models use 2x2016 cells, but you can replace them with one 2032.

That's a great idea. Is their any way to get an accurate volt reading from one of those cells, so I'll know what voltage the battery needs to be at when I find the desired brightness? Or should I just time the runtime?

Thanks

 

[Phaserburn]

You can by a multimeter to test voltage, but continuing to be low-tech, I'd just keep track of how long I've let the cell "bleed" voltage while being left on. If you want to be industrious, you can get a few lights, and run the first for an hour, the second for two and the third for three and compare all at once. You'd still have the 2016 cells they came with to convert back if you wanted to.

2032 cells have a very long, long runtime in a single led setup like this because the current draw is very low. Depending on where you want the cell to be for your scope, you may need to do a 2-4-6 hour test, etc. Try it out and see.

 

[ti-force]

Is there an incandescent light available that runs on cr2032's? If not, I've seen 2032 holders, could I wire one of those up to a cheap aa incan light?

Thanks for all your help.

 

[ti-force]

Could I buy some l.e.d.'s and make my own device for the soul purpose of draing these batteries? Maybe wire 2 or 3 l.e.d.'s to run on 1 2032 so it would "bleed" the voltage quicker. Or would that drain the battery too fast to be a safe option?

 

[R@ndom]

An incan powered by coin cells would die a fast and painfully orange death. My dad used to sell a incan light on eBay powered by 3 alkaline coin cells. It was pathetic even compared to a solitaire. But that was before LED's came along.

 

[Phaserburn]

I would stick with the led lights; you don't want to crush the voltage, only lower it.

 

[zipplet]

If you are desperate you can bend the legs of a 5mm super green LED such that they bend outward near the LED, then inward near the opposite end. It'll clip nicely onto the cell

 

[ti-force]

Hooking a super bright green led up to the battery via bending prong method sounds like the route I'd like to take. Especially when you consider the fact that I can buy 100 of them for $6.00. The only question I have is, in the specs for the led, it says forward voltage is 3 to 3.2. Will this be a problem when the battery drops below 3v? Please excuse my ignorance, I'm still an unenlightened NOOB.

Thanks

 

[ti-force]

What is forward voltage? I've done some searching but can't really come up with much. The reason I ask, is because the led emitters I'm looking at have a forward voltage of 3v to 3.2v. If I attach one of these emitters to a 2032 battery (3volt) and the battery voltage drops below 3 volts, will the emitter still be driven by the battery? My main goal here is to drop the battery voltage down from 3v to 1.5v or less.

Here are the specs for the emitter:

Emitted Colour : Green
Size (mm) : 5mm
Lens Colour : Water Clear
Peak Wave Length (nm) : 535-537
Forward Voltage (V) : 3 ~ 3.2
Reverse Current (uA) : <=30
Luminous Intensity Typ Iv (mcd) : 15000 to 18000
Life Rating : 100,000 Hours
Viewing Angle : 35 Degree
Absolute Maximum Ratings (Ta=25C)
Max Power Dissipation : 80mw
Max Continuous Forward Current : 20mA
Max Peak Forward Current : 75mA
Reverse Voltage : 5~6V
Lead Soldering Temperature : 240C (<5Sec)
Operating Temperature Range : -25C ~ +85C
Preservative Temperature Range : -30C ~ +100C



Thanks

 

[zipplet]

Forward voltage is the voltage at which the LED starts conducting current. Below this the LED should not light. It's a range (as stated) due to manufacturing tolerances.

 

[ti-force]

Oh, okay. So I need to find an emitter with a forward voltage of less than 3volts for my needs?

 

[zipplet]

The funny thing is, I've seen white LEDs with a supposedly forward voltage of 3V+ run on a single coin cell quite well... I don't know what's going on here. Someone chime in?

I recommend a plain super green LED with a lower vF if you can find one