A hotwire that's practical...

[missionaryman]

This is about my 15th hotwire build and I'm starting to get over the whole 500000000 lumens for 10 seconds wow lights, I want something practical that's still bright.

The cheapest & easiest bright hotwire to build is the ROP so I chose it but I don't want fiddly battery carriers, expensive chargers or difficult charging set ups. I also want good run time so here's what I came up with:

2D host, KAI MOP reflector & glass lens, KAI 2D LiIon Protected pack + charger, pelican bulbs, Numstar 5 cell bulbs. About $100

*If you stop there you can only use the ROP low & the Numstar, the Kai pack wont light the ROP high no matter how many times you click*

NTC - but just one NTC however cuts your voltage down too low and you get a yellow beam so here's my solution:

4 NTC's in parallel = very little resistance and a beam almost indistinguishable from direct drive. Still white hot.

You could just use a 2C with extender & AW's C cells but they're fiddly to charge, you must charge them individually and I hate using extenders.

The 4 NTC's fit in the cap and there is a Perspex disc separating the battery from the modified spring.

So there you have it, not the brightest hotwire in the world but has three beam options:
750 Lumen, 1Hr
450 Lumen, 2Hr
200 Lumen, 5Hr
one piece battery pack that's easy to charge, excellent run time, robust, serviceable, small - ish & simple

I love it - thanks to Northern Lights for his help with the NTC's and advice on how to use them.

 

[Frank423]

Great idea :thumbsup:

May I ask you were you got these NTC's from?

 

[missionaryman]

Northern Lights sent them to me because I cant get them here in Australia - he and a few other CPF members who have dabbled with them will be able to tell you where to get them from

 

[Norm]

Where did you buy your reflector?
Norm

 

[Stereodude]

Where did you buy your reflector?
Norm

I'm guessing KaiDomain since it's a KD MOP reflector. I'm pretty sure it's this one.

 

[missionaryman]

yep that's the one

 

[2xTrinity]

Intersting find with the NTCs. With two of the Kaidomain D-Cells, I found the ROP high would not strike, so I decided to hook up an Ammeter in series and see if any current was being drawn. The resistance introduced by the meter was enough for the lamp to strike. ROP Hi when "cold" is therefore just barely on the edge of what the protection circuit will allow.

You could just use a 2C with extender & AW's C cells but they're fiddly to charge, you must charge them individually and I hate using extenders.

The extender is not necessary for 2C if you do the following:

Cut down and pre-compress the spring
Remove the switch retainer ring, reinstall the switch assembly "higher up"
Use dremel tool to remove excess materail from switch assembly.

I've got my 2C ROP running AW C-Cells, and room for a spare in the tailcap, with no extenders, and very little spring force on the battery.

Also, you can series charge the 2 AW C-Cells. I know many people do that with charging jacks built right into the light (I plan to implement this, and an LED to act as a battery voltage indicator at some time in the future). The only time individual charging would be necessary would be if you periodically check voltage and find the cells are getting out of balance. In the case of the Kai cells, I'm not sure If I'd trust the balancing circuit in the 2D pack without hte ability to tap the cells individually and look at the voltage for myself. I'd rather go for the loose kai cells (which would still work with a 2-cell charger), and use the method I described above to create a little extra room.

 

[Anglepoise]

missionaryman great post.

Can you let us know more about how you selected and tested to get 4 NTC's working together. I am presuming you used 4 so that the warm resistance was reduced to almost nothing , but you still had resistance when cold so no inst flash.

Any findings on your NTC use would be appreciated.

 

[missionaryman]

missionaryman great post.

Can you let us know more about how you selected and tested to get 4 NTC's working together. I am presuming you used 4 so that the warm resistance was reduced to almost nothing , but you still had resistance when cold so no inst flash.

Any findings on your NTC use would be appreciated.

I just typed up this huge detailed response and accidentally closed firefox, GTG to work now but I'll get back to you throughout the day.

 

[missionaryman]

So all i did was test each different NTC and compared to direct drive, they all had different soft start duration and resistance levels but when you parallel them you reduce the soft start effect and the overall resistance.

 

[toby_pra]

Nice and clean mod!:wave:

At last very good runtimes...

 

[Northern Lights]

Ametherm SL12 1R010 NTC we found to work best in hot wires. Here is one with a fuse in tail caps.

Because changing the amps that flow through the NTCs the resitance changes, especially when running below their rated maximum, the NTC do not appear to behave in a way consistant with applying Ohm's Law equations, like parallel equations. If you take the final measurements of the parallel stack and of the individuals in it too, you will find that the numbers do fit the equations but it is based on the resistance obtained from the amps running in each NTC. The bulb amps changes too when the voltage changes. The entire system is filled with unpredictable variables; experiments like Missionaryman's is the only way too find out if the hypothesis works.

 

[EvilLithiumMan]

Great mod, and I couldn't agree more with the practical approach. My favorite "lukewarmwire" is a MagCharger bulb, run at a regulated 7 volts. 50% brighter than the MC, in a 2D host and ligther by 14oz. - runs for 2 3/4 hours with the KD Li-Ion pack.

 

[Norm]

I'm guessing KaiDomain since it's a KD MOP reflector. I'm pretty sure it's this one.

I didn't see that.
I just wondered how it's holding up to the heat?
See my post here http://www.candlepowerforums.com/vb/showthread.php?t=194834
Norm