cool flashlight mod; and resistor question for you engineers/physicists out there

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V

vexingv

Golden Member
Aug 8, 2002
1,163
1
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i have some old mag solitaires and am planning to do this mod but couldnt figure out what resistance to use for the resistor.

1) the mn-21 battery suggested would supply 12V
2) the voltage draw of a led is about 4V at max
3) the current for the led would be around 20 mA

thus i would need about 400 ohms of resistance. but do i need to take into account internal resistance from the battery and led? and what are the internal resistances of those two components?

thanks
 
L

loup garou

Lifer
Feb 17, 2000
35,132
1
81
Why not just do what the guy added:
Just a small addition to the Maglite Solitaire Mod 2. One can easily open the MN21/23 battery to obtain eight LR932 button batteries. Just use 3 of these and no resistor is necessary; the internal resistance is about 9 ohms per battery. I used a short section of 3/8 inch aluminum rod as a spacer.
Click to expand...
 
T

TitanDiddly

Guest
Dec 8, 2003
12,696
1
0
Originally posted by: vexingv
i would have to use a longer spring, but wouldnt a 12V battery last longer?
Click to expand...

No. It would actually run down quicker, because some of the current from the battery is being eaten up by the resistor. This way, you can buy one battery, and it will last longer because you are using only some of the button cells at any one time. Do it.
 
A

ArJuN

Platinum Member
Aug 13, 2005
2,816
0
76
Use a resistor even it says not to. The LEDs will last longer. And in this case, I think 470ohm would do the job.
 
9

91TTZ

Lifer
Jan 31, 2005
14,374
1
0
Originally posted by: vexingv
i have some old mag solitaires and am planning to do this mod but couldnt figure out what resistance to use for the resistor.

1) the mn-21 battery suggested would supply 12V
2) the voltage draw of a led is about 4V at max
3) the current for the led would be around 20 mA

thus i would need about 400 ohms of resistance. but do i need to take into account internal resistance from the battery and led? and what are the internal resistances of those two components?

thanks
Click to expand...


Get a switching regulator and don't use a resistor or a linear regulator. With the resistor, depending on the voltage and LED type, about half of the battery's energy is being converted into heat by the resistor. The LED is only getting sloppy seconds.
 
M

Minjin

Platinum Member
Jan 18, 2003
2,208
1
81
Throw away the Solitaires and buy a Dorcy AAA LED. ~$5. You'll thank me later.

Mark
 
S

sharkeeper

Lifer
Jan 13, 2001
10,886
2
0
Mag solitaire is a funny name.

They should have a mag hearts and freecell version. I imagine the freecell version would be popular at the pens. :)
 
J

JW310

Golden Member
Oct 30, 1999
1,582
0
0
Originally posted by: 91TTZ
Originally posted by: vexingv
i have some old mag solitaires and am planning to do this mod but couldnt figure out what resistance to use for the resistor.

1) the mn-21 battery suggested would supply 12V
2) the voltage draw of a led is about 4V at max
3) the current for the led would be around 20 mA

thus i would need about 400 ohms of resistance. but do i need to take into account internal resistance from the battery and led? and what are the internal resistances of those two components?

thanks
Click to expand...


Get a switching regulator and don't use a resistor or a linear regulator. With the resistor, depending on the voltage and LED type, about half of the battery's energy is being converted into heat by the resistor. The LED is only getting sloppy seconds.
Click to expand...

Suggestions for a switching regulator that will fit into the case of a Maglite Solitaire flashlight? Sure, a switching regulator would be a more efficient way of dropping the voltage down, but is it really a feasable solution for this application?

JW
 
9

91TTZ

Lifer
Jan 31, 2005
14,374
1
0
Originally posted by: JW310
Originally posted by: 91TTZ
Originally posted by: vexingv
i have some old mag solitaires and am planning to do this mod but couldnt figure out what resistance to use for the resistor.

1) the mn-21 battery suggested would supply 12V
2) the voltage draw of a led is about 4V at max
3) the current for the led would be around 20 mA

thus i would need about 400 ohms of resistance. but do i need to take into account internal resistance from the battery and led? and what are the internal resistances of those two components?

thanks
Click to expand...


Get a switching regulator and don't use a resistor or a linear regulator. With the resistor, depending on the voltage and LED type, about half of the battery's energy is being converted into heat by the resistor. The LED is only getting sloppy seconds.
Click to expand...

Suggestions for a switching regulator that will fit into the case of a Maglite Solitaire flashlight? Sure, a switching regulator would be a more efficient way of dropping the voltage down, but is it really a feasable solution for this application?

JW
Click to expand...

Hmm, I just looked up pics of that model and it's smaller than I thought. I don't know if anyone sells switching regulators that small.

 
P

PurdueRy

Lifer
Nov 12, 2004
13,837
4
0
a diodes forware resistance is very small...it would hardly make a difference. This is why it is often assumed to be zero
 
A

Antisocial Virge

Diamond Member
Dec 13, 1999
6,578
0
0
Originally posted by: sharkeeper
Is that an Inova? $9?
Click to expand...

That's a cheap knock off. ANGRY POSEIDON BLUE LED warning applies.
Click to expand...

Cheap knock off is right. I'll spend $9 instead of $35 anyday for a mini flashlight. I use mine at work everyday and its never let me down.

ANGRY POSEIDON BLUE LED warning applies
Click to expand...

I have no idea what this means.
 
A

Antisocial Virge

Diamond Member
Dec 13, 1999
6,578
0
0
Originally posted by: AgaBoogaBoo
ANGRY POSEIDON BLUE LED warning applies
Click to expand...
I have no idea what this means.
Click to expand...
Just means that the LED's will have a blue tint to them, not a very pure white at all
Click to expand...

Ahh. Not any real amount I think, I've compared it to regular mini mags and its a very white light compared to the almost yellow of them.
 
V

vexingv

Golden Member
Aug 8, 2002
1,163
1
81
Originally posted by: PurdueRy
a diodes forware resistance is very small...it would hardly make a difference. This is why it is often assumed to be zero
Click to expand...

but that battery's is fairly high, 9 ohms each or 72 for all 8. i just dont want too much reistance since it'll just make the light dimmer and the device hotter.

that knockoff inova looks pretty nice, but its a bit to big for a keychain light, same w/ the dorcy (fat diameter). i;m modding the solitaire b/c its really small, i have one already, and i need to stop by radioshack for a dvi cable anyway so why not pick up an led.

i know about candlepower, but i dont want to register another forum account just for one post.

thanks for all the input
 
9

91TTZ

Lifer
Jan 31, 2005
14,374
1
0
Originally posted by: vexingv

but that battery's is fairly high, 9 ohms each or 72 for all 8. i just dont want too much reistance since it'll just make the light dimmer and the device hotter.
Click to expand...

More resistance won't make the device hotter, it'll make it cooler.

Think of it this way- if there was no connection from + to - you could say it has infinite resistance. No current will flow since the resistance is so high, and obviously it won't get hot. On the other hand if you had very litte resistance, such as if you shorted out the battery with a wire, it would get very hot and drain very quickly.

The more resistance, the less current flow. The less current flow, the less heat.
 
V

vexingv

Golden Member
Aug 8, 2002
1,163
1
81
Originally posted by: mercanucaribe
Why does the Mag Solitaire use a special battery? To rape your wallet? What's wrong with AAA?
Click to expand...

the solitaire does use AAA, but in order to use an led it requires something w/ more voltage, hence the mn21 which supplies 12V.
 
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