Resistor questions for Tri Cree B/B/W with NBv3

[SPACEMONKEY1]

Just calculating the resistors I need for my build. At first I had .5w 1.8 ohm resistors for the blues and 2w 1 ohm for the white LED, but after reading a bit it seems that 2w 1 ohm will work for the blues as well. Is this a correct assumption? The blues are listed at 3.1Vf @ 350 mA, but I'm assuming this is a conservative number? Tim has them listed at 3.47v @ 1000mA. So with Tim's numbers 2w 1 ohm would be perfect. I also have a 5mm blue accent LED, 3.3v @ 20mA, so the resistor should be 1/8w 22ohm. Does this sound right? One last question, I'm using the white LED as FoC, does it need a resistor? I've been researching for a while here and I've seen people saying it does not need one. Why is that? Probably gonna pick up a resistor for it today just in case. Thanks as always everyone for the help.

[NanoRex]

Since you want to drive the LED at 1000mA, you would use the forward voltage of the LED at 1000mA. So assuming you're using a 3.7V li-ion, your numbers are good. I would recommend popping a resistor on your FoC LED just to be safe.

[SPACEMONKEY1]

Yep I'm using a 3.7 li-ion. Figured better be safe than sorry with the white LED. Thanks NanoRex!! Picking up my wires and resistors today. Of course I still need to raid Home Depot for crystal chamber parts. So may be a few days before I start the actual build.

[NanoRex]

I've been working on my saber since October and I'm still in the parts collecting phase. A few days should be no problem :)

[SPACEMONKEY1]

Which parts are you looking for? I may be able to point you in the right direction for something. I was able to get the speaker off some model train website, 27mm and it actually fits snug in the V5 mount. I was able to find the battery, recharge port, heatsink, and led. Now my big obstacle is the chamber itself. I don't want to use the 3d printed one. Nothing against anyone using them, just want to come up with my own idea. So plumbing parts seems like the most optimal solution. I was just at home Depot and they have a ton of awesome connectors. Might be a lot of JB weld in this thing but I'm fine with that : )

[NanoRex]

I have most of my parts already. It's only taking forever because I need to get all sorts of specialized parts, and I have to wait for some to ship before I can order others. The last things I need right now are my customized hilt parts that Tim and I are working on, and I still need to 3D model my chassis parts and print them.

Good luck with the crystal chamber!

[SPACEMONKEY1]

I was thinking about modeling my own crystal chasis, I work at an animation studio so that's not a problem. Just really don't know where to start. Like how many holes it would need, tubes for wires, where everything would mount. Just too much but I could try something.

[NanoRex]

I'm actually not a huge fan of 3D printed crystal chambers. I prefer to use chassis parts from TCSS along with other parts that I find at the hardware store and fastener store, and on the internet.

If you do want to 3D print one, design the rest of your chassis first so you know where the threaded rods will be (so you know where you need holes through the chamber), then add holes or a channel to run wires through. G.O.T.H. 3Designs on Shapeways has some cool 3D crystal chambers that you could look at for inspiration.

[IkarosReve]

If it's 3.47v at 1000mA, wouldn't the resistor be 0.23ohms?

[NanoRex]

Actually I dunno what I was saying before, because a 0.5 ohm resistor should be fine for the blues (and probably your white as well), and will make them slightly brighter than using a 1 ohm resistor.

[SPACEMONKEY1]

Ok. So the larger the watts and ohm number of the resistor the less bright the led will be? That's where I was getting confused. Thought the 2w 1 ohm allowed more to the LED. So the original .5w 1.8ohm should be fine for all?

[NanoRex]

Ohms measure resistance. More resistance -> less current -> less brightness, so use the lowest amount of resistance that you can, provided that it's greater or equal to the amount you calculated.

Watts measure power. In the case of resistors, it's how much power the resistor can dissipate. Higher wattage -> can dissipate more power, and larger resistor. Using a higher wattage resistor won't affect the brightness of your LED at all, but it will take up more space in the hilt.

[Gorth]

Actually if you read the manual, any led that only needs a small resistor (<.5ohm) you can change the drive to the led from the board to less than 1Amp, so you can max out the possible current going to you leds

[Gorth]

You could also put small resistors in parallel or larger resistors in series. For example for your blue led, having two .5ohm resistors in parallel would give you .25 ohm resistance which is much closer to the number you need

[darth_chasm]

Actually if you read the manual, any led that only needs a small resistor (<.5ohm) you can change the drive to the led from the board to less than 1Amp, so you can max out the possible current going to you leds

I've done both ways and can confidently say that using resistors is the more reliable method. We're talking about .5 watt resistors, they're not going to take up that much room if that's the concern. If anything, buy the resistors so you have them as a back up. They're a few bucks at most and you won't have to go back, place another order and pay another shipping charge.

[SPACEMONKEY1]

Thanks for all the info with this everyone!!! Gonna try and find a .5 ohm 1.8 or 2 w resistor for the blues. And a 1 ohm .5 watt for the white FoC LED.

[SPACEMONKEY1]

One last question. Nano, you said I could probably use the .5 ohm resistor on the white as well? My calculation is telling me that I need a .55 ohm resistor at .5 watts. Would I be pushing it if I put this one on the white with it being .05 over the needed ohm resistance?

[Generic Jedi]

As long as you use the white LED for FoC, the 0.5 ohm 3 watt resistor is fine.

[SPACEMONKEY1]

As long as you use the white LED for FoC, the 0.5 ohm 3 watt resistor is fine.

Generic, why would it need to be 3 watt and not .5 watts or even 1 watt?

[NanoRex]

Generic, why would it need to be 3 watt and not .5 watts or even 1 watt?

That would be fine.

[Generic Jedi]

I mentioned the 0.5 ohm 3 watt resistor because that's the one in the store. It's also the one I used, so I can verify that it works.

The ohms part of a resistor protects the LED from excess current, but dims the LED. A white Cree LED, powered by a 3.7 volt battery solution, needs a 0.55 ohm 0.55 watt resistor. The 0.5 ohm resister will slightly overdrive the LED, but it'll be fine as long as it's the FoC LED.

The watts part of a resistor is the rating for how much energy the resistor can dissipate. If the resistor is trying to dissipate more energy than it's rated for, it might fry. Fried resistor = fried LED. A 0.5 watt resistor may work fine, but I recommend using a higher wattage rating.

[SPACEMONKEY1]

I mentioned the 0.5 ohm 3 watt resistor because that's the one in the store. It's also the one I used, so I can verify that it works.

The ohms part of a resistor protects the LED from excess current, but dims the LED. A white Cree LED, powered by a 3.7 volt battery solution, needs a 0.55 ohm 0.55 watt resistor. The 0.5 ohm resister will slightly overdrive the LED, but it'll be fine as long as it's the FoC LED.

The watts part of a resistor is the rating for how much energy the resistor can dissipate. If the resistor is trying to dissipate more energy than it's rated for, it might fry. Fried resistor = fried LED. A 0.5 watt resistor may work fine, but I recommend using a higher wattage rating.

Generic, thanks for the help and info with this. Went ahead and ordered the .5 ohm 3 watt resistors for my LEDs. Should be good to go now. just have to find a crystal.

[jamiemp]

I am also getting a BBW TriCree from TCSS and using a 3.7V battery.
Here are the specs for BBW
-Blue Cree Part# XPEBBL-L1-0000-00301
45.7 Minimum Luminous Flux @ 350mA
Forward Voltage @1000mA = 3.47v
-White Cree Part# XPEBWT-L1-0000-00F51
266 Minimum Luminous Flux @ 1000mA
Forward Voltage @1000mA = 3.15v
Based on formula, I need a .23 ohm with .23w for the blues(ordered .47ohm 0.5w resistor) and .55ohm and .55w for the white(ordered 1ohm 2w resistor).
Would those work? I just chose those based off what was in stock on TCSS.

Any advice/help would be appreciated.
Thanks!

[Generic Jedi]

Those will work fine. The 0.5 ohm 3 watt resistor on the white LED will give you a slightly brighter FoC than the 1 ohm 2 watt resistor.

Make sure to put a resistor on each LED.

[jamiemp]

Those will work fine. The 0.5 ohm 3 watt resistor on the white LED will give you a slightly brighter FoC than the 1 ohm 2 watt resistor.

Make sure to put a resistor on each LED.

Perfect! THanks!

[Nirraven]

I am going to wire the exact same build.

I am confused by the resistor calculators (http://www.led.linear1.org/1led.wiz). The calculator says i need a 1 ohm 2 watt resistor for the blue and the white?
What is the best resistor for this setup if i could get nearly all ohm's i want. For the blue's a 0.27 ohm and for the white a 0.6 ohm?
How much would be the brithness difference between a 1 ohm resistor or a 0.27 ohm resistor for the blues?

[Generic Jedi]

The resistor calculators give higher values than needed. You get more protection, but the LED will be slightly dimmer.

EDIT: You guys should really ask your questions in your own threads...

[Nirraven]

EDIT: You guys should really ask your questions in your own threads...
You mean my post? I was completly ONTOPIC.

It would be ridiculous if we all make a own thread with the same questions. I really don't understand your point.

[NanoRex]

It's already ridiculous. What you guys should really do is read the many many threads out there that ask the exact same question so there is no need to thread jack.

[Nirraven]

I searched and didn't found a acurate answer for my questions. Maybe my searching skills are bad.
So decided to post an answer in a thread with the exact same build i have? Whats wrong with that?

You could also just linked me the answer or give me an answer instead of this useless post.
If you know if there is a noticable brightness difference if you are using a ~0.23 ohm resistor to a 1 ohm resistor just give an answer please.

I also found out that the NB can change the voltage in the settings and the blue LED's are nearly the same voltage then a single li-ion battery. So i could just skip the resistor for the blue maybe.

I am new to building lightsabers and i only wanted to get some anwers instead of 2 useless posts. I know it sucks if there are the same anwers again and again but i couldnt found answers for all my questions at the moment. So i may ask something?

[Silver Serpent]

http://forums.thecustomsabershop.com/showthread.php?17109-Tutorial-FJK-s-quot-Down-and-Dirty-quot-guide-to-Ohm-s-Law

After you've calculated the proper ohm value, round up to the next standard resistor. Or round down if it's really close and don't mind overdriving the LED. ALWAYS round up with wattage, never down.

Is there a noticeable difference between a 0.23 and a 1 ohm resistor? Depends on your eyes. If you have two identical sabers next to each other, one with the 0.23 and one with the 1 ohm, you *might* be able to tell the difference. It won't be much.

Don't skip the resistor with a NB build. You'll have issues with errant swing sounds and otherwise erratic behavior. It'll work fine at first, but get irritating as the battery drains.

[darth_chasm]

The problem with "thread hijacking" (posting questions in another person's thread) is that you have muddied the original poster's thread with your own questions and back and forth with other members, as evidenced here. Suppose the OP wants to keep this thread open and clean for other questions related to their build or to expand on their original questioning. Now they have to sift through your questions, other's questions, explanations of etiquette and a bunch of banter unrelated to their original post.

Creating your own threads makes it much easier for everyone, including yourself, to follow.

[Nirraven]

http://forums.thecustomsabershop.com/showthread.php?17109-Tutorial-FJK-s-quot-Down-and-Dirty-quot-guide-to-Ohm-s-Law

After you've calculated the proper ohm value, round up to the next standard resistor. Or round down if it's really close and don't mind overdriving the LED. ALWAYS round up with wattage, never down.

Is there a noticeable difference between a 0.23 and a 1 ohm resistor? Depends on your eyes. If you have two identical sabers next to each other, one with the 0.23 and one with the 1 ohm, you *might* be able to tell the difference. It won't be much.

Don't skip the resistor with a NB build. You'll have issues with errant swing sounds and otherwise erratic behavior. It'll work fine at first, but get irritating as the battery drains.Thanks for the very acurate answer.


The problem with "thread hijacking" (posting questions in another person's thread) is that you have muddied the original poster's thread with your own questions and back and forth with other members, as evidenced here. Suppose the OP wants to keep this thread open and clean for other questions related to their build or to expand on their original questioning. Now they have to sift through your questions, other's questions, explanations of etiquette and a bunch of banter unrelated to their original post.

Creating your own threads makes it much easier for everyone, including yourself, to follow.I still think that i didn't hijacked the thread because i was ontopic.

[Forgetful Jedi Knight]

Enough with the bickering.