inconsistant brightness levels with cree green led

**color_monkey** · 04-24-2010, 08:43 PM

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** · 04-24-2010, 09:20 PM

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

**Jedi-Loreen** · 04-24-2010, 09:22 PM

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** · 04-24-2010, 11:03 PM

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** · 04-24-2010, 11:41 PM

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** · 04-25-2010, 01:11 AM

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

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.

cheers

**Darth Xusia** · 04-25-2010, 06:15 AM

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** · 04-25-2010, 10:41 AM

Hey Darth Xussia...

You need to remove that website...

**Rhyen Skytracker** · 04-25-2010, 10:57 AM

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/....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.