Ok guys, I need some help...

[harebawl]

I am building a 5w light using a 6 cell "c" m@glite. The 5 watt emitter I have is a "t" vF. I am thinking I need to run a resistor because of the low vF, but also I would like to "limit" the current to around 1000ma. I will be using alk. batts.

Now, do I need a 5 watt resistor? or does it need to be larger than that? Also, how many ohms am I looking at, I just want to get in the ballpark because this size resistor is starting to get a little large, and I need to get something ordered. I was thinking it would have to be around 2 ohms...?

 

[3rd_shift]

[ QUOTE ]
harebawl said:
I am building a 5w light using a 6 cell "c" m@glite. The 5 watt emitter I have is a "t" vF. I am thinking I need to run a resistor because of the low vF, but also I would like to "limit" the current to around 1000ma. I will be using alk. batts.

Now, do I need a 5 watt resistor? or does it need to be larger than that? Also, how many ohms am I looking at, I just want to get in the ballpark because this size resistor is starting to get a little large, and I need to get something ordered. I was thinking it would have to be around 2 ohms...?

[/ QUOTE ]

2 ohms looks ok.
A 5 cell direct driven may be the easier, more efficient way to go, since you don't have a lot of room in a c cell host for the electronic gear to be mounted.
I currently have a 5D cell direct driving a 5 watt emitter on a Hotlips with some wicked Nimh D cells with no problems.

Yours will cook to the tune of 2 amps in a 6 cell with no added resistance for a short while until.... /ubbthreads/images/graemlins/mecry.gif /ubbthreads/images/graemlins/crackup.gif

 

[HarryN]

The T bin Vf is nominal 6.4 - 6.8V, perhaps slightly higher for 1amp. 6 cells x 1.5 V = 9 V before they start to sag.

9 V - 6.5 V = 2.5 V drop from resistor. Voltage sag, etc and 2 ohs are right on. 1 - 2 amp x 2.5 V = 5 watts max. Most of the time it will be less than this by 50 %.

You might just be in luck. My order for custom made, aerospace grade, 2 ohm resistors just came in late last week. The part is 1206 size (nominal 3mm long x 1.6mm wide) in a surface mount format. Power handling capability is - much higher than 5 watts - due to the substrate used in the resistor.

You will still need to get rid of the heat - so some kind of heat sinking to the flashlight wall will be needed, regardless of the resistor used.

Since you bought that Lux V from me in the first place, let me know if you can use this resistor and I will drop one in the mail. You can be a beta tester and write up a comment on how it worked out. /ubbthreads/images/graemlins/smile.gif

Good luck - HarryN

 

[harebawl]

Thanks Harry! I think I can give it a try....I can epoxy it to the heat sink, or to the side of the mag body after I pull the bulb mount post out....And I'll let you know how I make out....I hope to be doing this over X-mas week...

Do you think it would get too hot for epoxy mounting????

 

[HarryN]

I think thermal epoxy should be fine, regular epoxy might be ok - I would avoid thermal grease. I have toyed with mounting them on the pad of a star, but that would just add to the heat challenge of the star heat dissipation. Still might be ok since it will likely voltage sag within a few minutes dramatically reducing the total power.

I will send two - one to use, one to loose - they are small.

 

[harebawl]

Thanks Harry.....Wow I looked back at your post and boy, those are small compared to what I was looking at having to cram in my light!

Thanks again!!

 

[HarryN]

Hi George - The resistors are en route via US mail. Should be there for Xmas time no problem.

You will notice that the lead from the Lux V is nominally 1.5mm wide, and this resistor is nominally 1.6mm wide. It makes for some interesting ideas on resistor placement on the star.

For maximum performance, it is ideal to remove heat as fast as possible from the Lux V star, so this would say to mount the resistor remote from the Lux V - on the wall for example. It is very tempting to mount the resistor right on the star itself given its size - something I personally would try if pushed for space.

We are all looking forward to some pics. /ubbthreads/images/graemlins/smile.gif