Fenix P1 2-stage mod

[edit 28th July] Attention: This mod was just a proto and is not recommended, because it can be VERY dangerous. If the resistor used is too low (under 25 Ohms for a 1/4 Watt resistor) it gets very hot and can burn the lithium cell. Also the resistor can get loose and shorten the cell, what would be very dangerous too, especially with the fully closed P1 (has no exit for pressure!). (THX to jugeh)
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I've just wrapped one end of a small conventional resistor around the brass knob, so that the other end is 1 Millimeter over the knob.

Modus 1:
Soft turn-on: low modus, because the "+" of the battrey goes over the resistor.

Modus 2:
stronger turn-on: the lead of resistor touches the brass knob itself, so full-mode.

The Low Modus should be very low, because of the resistor not getting too hot!

I think, with a smd-resistor and a spring it can even better done.


Jens

Use imageshack.us to host the picture. Just load it onto imageshack, then scroll to the bottom of the page after the picture is loaded and copy the url of the picture.

Have you tried how many compressions the resistor will take before the wire gives and stays compressed?

The P1 can really use a 2-stage. Its so bright that its not suitable for close-up tasks in a dark environment IMO. Its still one of my current favorites.

cheers

picture:

jsr said:

Use imageshack.us to host the picture. Just load it onto imageshack, then scroll to the bottom of the page after the picture is loaded and copy the url of the picture.


done.

Have you tried how many compressions the resistor will take before the wire gives and stays compressed?

Click to expand...

no. just a proto! as mentioned, this can be done much more perfect with smd-resistor and spring. "They" (Fenix) could do this with little modification on circuit.


Jens

Nice simple mod. Simple enough you could rebend it if it got squished.

I'm working on a leaf spring drop in like you mention. More on that after I finish a similar current project.

What ohm resistor did you use and how is the low light level like? I don't have my resistor color band chart with me at work.

Very nice, and there is seemingly no "risk-factor" :goodjob:

Edit: Ehh, perhaps I stand corrected.

Blindasabat said:

What ohm resistor did you use and how is the low light level like?

Click to expand...

I just tried it with a 5ohm resistor and it worked like a charm. Low was usefully low, maybe 20% as bright as high.

Thanks for a great and simple mod win67.

Blindasabat said:

What ohm resistor did you use and how is the low light level like? I don't have my resistor color band chart with me at work.

Click to expand...

looks like 26 or 27? I think... confirmation?

A bit off topic... but where can a brotha get some resistors these days? :shrug:

phatalbert said:

A bit off topic... but where can a brotha get some resistors these days?

Click to expand...

Radio Shack has a somewhat meager selection these days. All I can find in the range to use with flashlights are 10 ohm 0.25W and 0.5W.
Newarkinone.com and Digikey have good selections.

maverick215 said:

looks like 26 or 27? I think... confirmation?

Click to expand...

yes, that could be. color code is red-green-green-gold-brown
it is very dim, enough for reading, but much dimmer than arc aaa-p.

tried also 10 ohms but the resistor went very hot.

BTW: my fenix p1 runs 60 min with an nearly new AW protected li-ion (specified 750 mAh) and 80 minutes with an 1-year-old much used unprotected li-ion (specified 650 mAh). the light was cooled in ice-cubed water. maybe some low Vf )).

Jens

win67 said:

tried also 10 ohms but the resistor went very hot.

Click to expand...

I played with the 5 ohm resitor mod for a while last night, and after a couple of minutes the torch got just as hot as if it had been running unmodified. I don't like the idea of a really hot resistor next to a RCR123...

Awesome mod! I've got a P1 on the way from Fenix-Store, so I'll be able to try it soon. By the way, does the P1 come with a cell, or will I have to buy some Titaniums?

I just looked on digikey and newarkinone, and I was floored by the enormous selection. Could anyone post a more specific URL? I just want a resistor like the one in the OP (but maybe with different resistance). Where might I find one of those?

Cool idea. But the risk of shorting out the Lithium or Li-Ion battery scares me a little. Be careful guys!

TigerhawkT3 said:

By the way, does the P1 come with a cell, or will I have to buy some Titaniums?

Click to expand...

No, it only comes with an empty indention in the packaging where a 123 cell should go.

I'm not too knowledgable about electrical matters, so please excuse the noob question. Would the modded high stage be slightly dimmer than the unmodded output because of the resistor present in the circuit? In other words, would some power "drain out" through the resisting path rather than flow directly to the head? Or, conversely, will the power take the path of least "resistance" and skip the resistor entirely?

I'm happy to here that all of you (and the P1) who tried this with a resistor smaller than 20 Ohms have survived!!!

At 5 Ohms your resistor has to "eat" about 0.68 Watts, at 10 Ohms about 0.45 Watts. So you are going to fry the resistor and the battery (which is in direct contact with the resistor)! 20 Ohm resistors of this size are at the very edge with 0.26 Watt.
Please make always some messurements of current and voltage and then calculate the needed values before you start these tests because short-circuiting and cooking of lithium-batteries is extremly dangerous!!!

See also: https://www.candlepowerforums.com/threads/124042

jugeh

Now I'm even more confused about resistors. Gadgetnerd said that a 5-ohm resistor worked like a charm, and then win67 said that a 10-ohm resistor ran very hot. Wouldn't a 20-ohm resistor be even worse? It seems to me that more resistance would put more strain on a resistor, and not the other way around. Doesn't a resistor absorb, in a way, the power from a cell? Wouldn't more ohms mean more power that the resistor has to deal with and dissipate?