Resistors in 2-mode P7 torches

[shuffles]

Howdy all,

I want to make my 5-mode MTE (DX 12060) a 2 mode by removing the driver and adding resistors to the tail switch. I'd like to be able to run at full power and at 75%. Currently, the medium mode is reported to be about 30%.

There's been some discussion in the past about what resistor values to use, and I'm currently thinking I would need about a 1 Ohm resistor to bring it to 75%.

It's also been suggested to use a 2 watt resistor for this application. A 2 watt resistor is huge, and I cannot believe that it would actually fit in the tail cap of this flashlight. :thinking:

What value and capacity resistors are included in the 2-mode lights from MTE, Aurora, Trustfire, etc?

Let's discuss.

Thanks!

 

[pepko]

I'm using 1ohm/2W for 3.5hours or 2ohm/2W for 6hours.

 

[pe2er]

What value and capacity resistors are included in the 2-mode lights from MTE, Aurora, Trustfire, etc?

6.8 Ohm in my MTE SSC P7. Current is ~400mA. Power dissipated in the resistor is 0.4A^2 * 6.8 Ohm = 1 Watt

 

[shuffles]

Thanks Pe2er! By your formula, I would guess that since I wanted 75%, that would work out to (2500MAh*.75)^2*1 Ohm = 3.515625 Watts, and that's not going to fit into the til cap.

 

[atropine1]

Don't know anything about electronics, but when you use resisters to lower the output of a light, is the power that doesn't make it to the light actually lost, as in it's absorbed by the resister and dissipated as heat?

Of it not, what is the efficiency when using resisters, it is close to 100%?

 

[pe2er]

Yes, using resistors, all excess energy is lost as heat in the resistor. Efficiency will not even approach 100%

If you want an efficient Dim mode, use a separate 1 Amp driver for the dimmed position.

 

[pepko]

efficiency with 6.8ohm resistor is not bad ... aurora P7 lasts about 14 hours on low mode (9% of max brightness) ...

http://translate.google.com/transla...ny/aurora-ak-p7-5-ssc-p7-c-2-mode&sl=cs&tl=en

 

[znomit]

efficiency with 6.8ohm resistor is not bad ... aurora P7 lasts about 14 hours on low mode (9% of max brightness) ...

Runtime has nothing to do with efficiency.
In fact with resistors the longer the runtime the worse the efficiency.
At the shortest runtime, zero resistance, direct drive off battery, efficiency is 100%

Once you start dissipating 10-20% of the power in the resistor you are better off using a driver(some drivera are better, 95%, some worse).

 

[shuffles]

OK Znomit. Can you point me to a driver that will give me two modes, 100% and 60-80% that will fit as a replacement to the existing one?