inconsistant brightness levels with cree green led

[color_monkey]

I've done a fair few MR/H conversions, but I recently acquired two U.S 2.5's and have just finished adding sound to a stunt hilt I bought off Ebay. It seems the search function on this forum is a bit buggy because I couldn't find the answer I was looking for, or I'm not wording it correctly.

On to the issue in question...

My current setup
Cree 3watt green led no heatsink (came like that)
Ultrasound 2.5 board
2 3.7 volt trustfire lith ion cells on open circuit with kill key/recharge port
27mm 8 ohm mini speaker
mom tactile switch

The problem is that everytime I turn the saber on the brightness changes. Sometimes it's really bright and other really dull. I have checked all connections, and even made new connections. I still get this problem anyone out there got a clue? You never have to deal with things like this on MR conversions and I'm a bit lost.

Cheers

[Darth Xusia]

I assume you put the led on a heatsink.
Did you but those 2.5s on ebay?

[Jedi-Loreen]

You need a heat sink for your LED.

You're also giving your US board too much power, which will be causing your board to overheat.

Those 2 things could be the major part of the problem.

[color_monkey]

hey J-lo,
what do you mean too much power? I have 2 3.7 protected cells in series connected straight to the board which is only 7.4v approx. The U.S max voltage is 9v. I had to take this road with my power setup due to the small ID of the bottom of the hilt about 27.2mm or 1.07" which would not fit the tcss battery holders, in fact the back of the hilt just fits the U.S which I have mounted in a custom pvc sled.
-------------------
In answer to the other questions...
Yes I was an ebay purchase (a stock surplus from nova conceptions)
Yes I have since added a aluminum heat sink

Thankyou for quick reply

[Rhyen Skytracker]

The US 2.5 does not handle excess voltage too well. Anything over 1 volt over the LED forward voltage will cause the US 2.5 to get very, very hot. That is one reason the 3.7V Li-Ions are not a good battery solution for the US 2.5. One is not quite enough voltage and 2 are way too much voltage. I normally use 4 NiMH batteries with the US 2.5. I use the 2300 mAh AA size ones in a 2 x 2 configuration and mount the US 2.5 on top of them.

[color_monkey]

Rhyen Skytracker,

I tried that, but once you heat shrink the batteries it adds to the overall thickness of the pack and hence you can't get the battery pack in there. This is my first real custom saber and I have only had 11 attempts :D so whats a few more to get it right, and anyway my MHS parts will arrive soon so I may come back to it later when I have a better solution.

So just to clarify, I'm overfeeding the board and that is why the led's brightness is inconsistent.

Thanks I'll look for yet another way.:grin:
cheers

[Darth Xusia]

A luxV would help with the voltage issue, but those are getting harder to find.
EDIT: Look around and you can still find them.

[cardcollector]

Hey Darth Xussia...

You need to remove that website...:wink:

[Rhyen Skytracker]

Here is what some of the ones I made look like and they work fine with the sound card on top of them. http://saberconcepts.50.forumer.com/viewtopic.php?f=3&t=110
You have to be sure to get the thin heat shrink made for battery packs. The thick heatshrink takes up way too much room. Here are some pics with a 2x2 AA NiMH pack with a US 2.5 on top inside a hilt. The card is just laying on top of the battery pack now just so I could take the pics, but you still have plenty of room once the card is secured on the battery pack.

[Jedi-Loreen]

Hey Darth Xussia...

You need to remove that website...:wink:
Why?

Tim doesn't carry them anymore, and that website is one of the only places you could still hope to find one.

[cardcollector]

Well, I posted that website a few months ago to link the Lux I's to help someone with a PVC build, and a council member (I don't remember who) asked me to remove it because it sells items TCSS sells too.

If the rules have changed I apologize, I'll remove my posts if necesarry, I was just trying to help TCSS...

[Matt Thorn]

An obvious and simple solution would seem to be a 5V voltage regulator...or am I missing something?

[color_monkey]

Thanks guys,

The Lux V is a good option and I know a few places that still have heaps of stock.
The 5v regulator seems interesting Matt where can I get one of these that will fit into a saber?
anyways I got my MHS parts today so I'll be focusing on that for a while

I appreciate all the advice thank you

Cheers:D

[Matt Thorn]

Thanks guys,

The Lux V is a good option and I know a few places that still have heaps of stock.
The 5v regulator seems interesting Matt where can I get one of these that will fit into a saber?
anyways I got my MHS parts today so I'll be focusing on that for a while

I appreciate all the advice thank you

Cheers:D
Any "7805"-type linear regulator will do, but I find the ones in a TO-220, TO-220F, or TO-220FP package to be the easiest to work with. Where to buy it depends on where you live. If you have a favorite online electronic parts shop, just search for "7805 regulator" and you'll find one easily enough. Here's what the TO-220, TO-220F, and TO-220FP packages look like, respectively:
http://jp.mouser.com/images/stmicroelectronics/images/to-220.jpghttp://jp.mouser.com/images/njr/images/to220-3.jpghttp://jp.mouser.com/images/stmicroelectronics/images/to-220fpab.jpg
They are all just slightly more than 1" long and about 0.4" wide. You can trim the legs if you need to.

I wouldn't go with a Luxeon V. It's an awkward LED to work with, because it has a high forward voltage (6.84 Vf in the case of green), yet has a low maximum continuous current (700 mA). It's inefficient, and it doesn't make sense to buy a new (and already obsolete and discontinued) LED just to fit a higher voltage battery pack when it's so easy to control the voltage. You'll get a lot more run time between charges this way, and you shouldn't have a problem with heat.

[color_monkey]

Thanks Matt,
I'll look into that :)

cheers

[color_monkey]

Hey Matt,
Why can't I find what i'm looking for in this forum :(
anyway so I got the 5v to-220 regulators and I noticed when I got home that the wiring schematics were blank lol
How do I wire this thing up to my saber?