PLI not lighting

[Silver Serpent]

In parallel, voltage remains the same but current is shared. Your diagram looks like it should work. Calculate everything according to the 6v power supply.

[ZacMuleer]

Awesome! Thanks, SS.

Admittedly, I'm not sure how buckpucks actually work, so with it being removed, I'm still assuming (and hoping) that my LED will be just as bright.

Since I am making the resistor calculation at 1000mA, and the voltage is the same, is my main LED set to produce at 1000mA (and the PLI set at whatever it's current is from the resistor that I don't know the value of)? So rather than dimming the bulb, it just drains the battery quicker?

If that's right... Good thing I have a PLI.

[Silver Serpent]

Yes, but not significantly so.

Warning! Paper napkin math ahead! With a 10 segment PLI and each LED running approximately 20mA, you're only drawing a max of 200mA (at full battery charge) with the PLI. That's only 1/5 of what your main LED is using. The fewer LEDs illuminated on the PLI, the less power it'll be using. It works out to an average of 110mA draw over the lifetime of the batteries, assuming you drain them dry.

So, 10-15% less runtime, but you get a cool power gauge. It's not a bad tradeoff.

[ZacMuleer]

OK, So I've officially failed at my first attempt at rewiring the saber. THough, I got me some good learnin' in the process.

First lesson, don't touch hot solder. Yeah, seems obvious NOW. :-p

For real, though - I attempted to run the PLI in parallel with the main LED, this time without a buckpuck. I clipped the JST connector off my SPST latching switch and began to rewire as shown in the diagram before. Long story short, I ran into two problems: first, the PLI wouldn't light up when I turned the switch on and found there was a bad connection. I ensured a good connection and hit the switch... bwah-wah-wah... The PLI did not light, and the main LED was MUCH much dimmer. Heck, I could look into the LED without blinding myself. I'm not exactly sure what I was doing wrong, so I'm going back to the drawing board... literally.

I found a great little Java app that will allow you to build a circuit with all the inputs and data you need. Link here: http://www.falstad.com/circuit/ Now, I know just enough about electrical components to be dangerous - but not as enough to do anything useful, so this was a handy tool. I've attached a screenshot of my intended saber.

circuit.jpg

Now, the PLI LED (the lower icon) is a rough estimate. SS mentioned that the PLI lights at about 20mA per light (I got the version that lights up one at a time.) so I input a resistor that allowed for about a 20mA current over the PLI. So it is a guess. I am thinking about taking out the resistor that came with the PLI and using my own. Anyway, the calculation came out to 180 ohms resistance needed for the PLI. (I'd assume the lowest value wattage, at 1/4W.)

Now, the main LED. I used a Seoul P4 Blue - so the forward voltage is 3.25. I like how bright it is with the buckpuck pushing 1000 mA, so I used that as my baseline. Using the graphic above, in order to get 1A across that LED, I'd need a 2.8 ohm resistor. Now come some questions:

1) Could I put some resistors in series to create 2.8 ohm resistance? Like, would two 1.2 ohm resistors in series "make" a 2.4 ohm resistor?
2) Putting a 3.3 ohm resistor on there brings the current down to 800mA. Would that dim the LED THAT much? And if the higher resistance is bringing down the LED's current, how dangerous is it to essentially "overclock" the LED current, at say, 1.2A?
3) Is the problem ultimately that I am only using a SPST latching switch, and not a DPDT? I really like the plain button, and don't think I could fit a DPDT in the hilt, as it would go in too far.
4) Are my calculations completely off for the PLI, and what corrections would I need to make - both in the theoretical diagram, AND on the physical component? (Leave the resistor? Or use a resistor suited for a different power level? And would it go into the same slot on the back of the PLI, or can I solder it to the positive line that feeds into the PLI?)

THANKS IN ADVANCE!

Dan

[Silver Serpent]

Assuming you have the PLI from the store, there is a special resistor that you plug into it based on your battery voltage. Choose the one for a 6v power source. You won't need an extra resistor. My math earlier was just for figuring out a decrease in battery life, not for resistor calculations.

As for question 2: the Seoul P4 blues are very friendly when it comes to overdriving. 1.2A isn't going to cause any significant issues. Just be sure you're using a thermal tape pad to attach it to the heat sink. Heat is the enemy of LEDs when you're overdriving them. A 2.7 ohm resistor would work just fine, as would a 2.2ohm. I wouldn't go much lower than that.

Your wiring diagram (once you remove the resistor next to the PLI) *should* work fine. Check the batteries if it's not working well. Check your solder connections too. AAA alkalines don't last too long in a saber before they get weak. I've been there, and done that.

[ZacMuleer]

LOL - Thanks, again, as always, SS.

As much as I was hoping it was the batteries, when I removed the PLI (using the pre-packaged resistor for a 6V source) the LED went super bright again. So I thought it was something to do with the 3.3ohm resistor connected to the main LED. (Yet the PLI still didn't light.) I should just rewire and resolder, since I am still getting the hang of that. I hope it is a case of poor connections and low batteries. I am stoked to get a second opinion on my diagram, though. Tells me I'm not going totally crazy in making things up. lol

[ZacMuleer]

Ooh - does the wattage have anything to do with it? This 3.3 ohm, 5W resistor looks intense. What would the consequences be if I used a 3.3 ohm (or a 2.2ohm), 1/4W... or a 1W or whatever?

[Silver Serpent]

If you use a 1/4W or a 1W, there will be a puff of smoke, possibly a small fire, and you'll have to order a new resistor (possibly a new LED as well.)

[ZacMuleer]

Hahaha - duly noted! 5W it remains then.

[ZacMuleer]

Well, hole-lee crapola.

SS, I can't thank you enough! It works like a charm. Was definitely a case of crappy wiring. Great lesson to learn on my first saber. Now, it still looks like a rat's nest, but I got it closed up and PLI glows, and the blade is just as bright as it was before! SUCCESS!

(Admittedly, I'm cheating a little bit. I'm using the "4.8V" resistor on the PLI, because even with fresh new batteries, it was reading in the red with the 6V resistor. It's mostly for looks anyway - I'll end up switching the batteries if the blade looks dim regardless if it says green or not. but this is still a fantastic improvement over what it was before.)

Thanks for the help, all. Will post pictures as soon as all the tidbits are finished.