Luxeon V + DB700 vs DB1000 ?

[SiamLight]

I have Lux V Bin VY0VW. I will drive with 2*123A(Li-ion 4.20*2=8.4v). Does it work better with DB700 or DB1000?

 

[lmcmann]

One thing to think about (if I remember correctly, anyone feel free to correct me), is that the LuxVs are specd to run at 700ma. 1A is overdriving them by quite a bit, and will shorten the life down into the hundreds of hours before noticable degradation. You'll also have to get rid of all that extra heat. Another thing is that the DB's need a drop of at least 0.8 volts to be in regulation. That Vref is:
V.............7.35V - 7.83V
If you try and pull 1A off those R123 (those are rechargables, right?) It's going to quickly fall out of reg, and go into direct drive. Not that this is bad, just that you might want to add a third cell in there if you have room.

Eh, random thoughts from a mind missing caffeine.

Larry

 

[wptski]

Check this thread: JSB123 thread

I posted a few runtimes there and some battery plots from a CBA. My Lux-V DB750 draws .86A from 2xJSB123 and Lux-V DB917 draws .99A from 2xJSB123. I plan on using 2xPila168S with the two Lux-V DownBoys.

Setting the CBA to the current drawn on a DownBoy looks like a clone of a runtime!

 

[RussH]

If you are using only 2 cells, I'd be tempted to try it direct drive. From wptski's CBA produced chart it looks like they would quickly drop to the 3.6-3.7v (*2, or about 6.7v) range which closely corresponds with the normal Vf for a Lux5.

I believe there have been some posts about DD with the lithium CR123A non-rechargeable cells, which in my experience drop down to 2.8v -3.0v under near 1 amp loads. So you can put me down as agreeing with lmcmann except that a good heat sink like a hotlips would keep me from worrying about a 1 amp Lux5. My 1.5amp MR-X by Hotbeam (with hotlips heatsink) is still running strong after I don't know how many (40-50?) hours use.

 

[SiamLight]

Larry and RussH : Maybe it does not work optimum with DB, if DB need a drop 0.8v.
Vin-Vf ; 8.4-7.83=0.57v!
If I drive in DD with series resistor 0.8 ohm 1/2w, better or not?
Bill : Can you plots runtimes Lux V 2*JSB123 DD mode(with series resistor)?
Thanks for all suggestion
SiamLight

 

[Krit]

Hi Siamlight, I try to DD with li ion * 2 and put 1 watt resistor. It get very hot to resistor. I'm not sure resistor will burn or not because high current come out from liion cell.

 

[SiamLight]

Hi Krit, thanks for your comment.
I calculate the resistor like this:

I(operating current)=0.7A
Vs(source voltage)=8.40V
Vf(forward voltage)=7.83V
Vr(volt drop at resistor)=Vs-Vf, 8.40-7.83=0.57V
R(series resistor)=Vr/I, 0.57/0.7=0.81 ohm
Power Dissipated by Resistor=0.57*0.7=0.399W

The power at resistor only 399mW!
or something wrong!

 

[wptski]

[ QUOTE ]
SiamLight said:
Larry and RussH : Maybe it does not work optimum with DB, if DB need a drop 0.8v.
Vin-Vf ; 8.4-7.83=0.57v!
If I drive in DD with series resistor 0.8 ohm 1/2w, better or not?
Bill : Can you plots runtimes Lux V 2*JSB123 DD mode(with series resistor)?
Thanks for all suggestion
SiamLight

[/ QUOTE ]
Yes I can! Which one, 15, 22, 30 or 60 ohm? You mean with a DownBoy? I have a 5W DB750.

EDIT: Whoops! You do mean direct drive mode! Need more info on just exactly what you want

 

[Krit]

I'm not sure about exectly power from li lion cell. Especialy from china. I DD U** Bin with 2 li ion without resistor and the current come out around 1.6 amp. The power seem to be around 12 watt and get very hot. The light change color to yellow a little bit. I have to shut down operated.

So I try to series the resistor 2 ohm 1 watt to emitter. The R is very hot from 2 minute operate. I'm not sure the R will burn or not.

If Siamlight calculated exactly. I should try it again.

Be careful to use the high output of Li-ion cell.

 

[SiamLight]

Re: Luxeon V + 2*JSB123 DD mode

Hi Bill, I mean direct drive with series resistor 0.8 to 1 ohm 1/2W.
Thanks,
SiamLight

 

[wptski]

Re: Luxeon V + 2*JSB123 DD mode

SiamLight:

Here's a runtime plot from the CBA using a .8 ohm resistor on a 5W DB750 which went for 38 minutes. I did this first just to check(watch) the resistor temperature and you can look at the voltage drop. I can do a lux output runtime next.

I wonder what those two bumps in the plot are?

 

[SiamLight]

Re: Luxeon V + 2*JSB123 DD mode

Bill:
Thanks,
SiamLight