This is strange.... (SF P90 on 2 RCR123a's)

[MacTech]

This is rather strange, I just purchased a SF G3, and I was playing "Lego" with the G3 and 6P, and I discovered that when I put the P90 in the 6P with two BatteryStation RCR123a's fresh off the charger (4.15V approx.) the light is *whiter* and looks brighter than when that very same LA is in the G3, in the G3, the LA has a vaguely "brownish" tint, even with fresh SF123a's.....

this makes no logical sense, when in the G3, the lamp is being driven by the full 9V load from three fresh primaries, when in the 6P and driven by the RCR123a's, it's only getting 8.3V, it's being *UNDER*driven, so *why* is the LA's color temp whiter and "brighter":thinking:

the G3 is brand new
the 6P is an old beater

so it can't be oxidation....

maybe the 6P's all metal construction has less resistance then the G3's metal "sleeve"

I could also swear that when the P90 is in the G3, i can see a slight, almost imperceptible dimming to yellow, almost unnoticeable, but I could swear it's happening, but when the same LA is in the 6P and driven by 2 RCR123's, I see no signs of dimming

when the Cree module is in the G3, it runs fine, no dimming or flickering

this makes absolutely no sense....

 

[jbosman1013]

It is being overdriven by the RCR123's because the voltage sags less with li-ions than primaries.

 

[Calamityville_Horror]

The 3V primaries sag significantly under load, so when the light is on the voltage is maybe more around 2.4 per cell, give or take. Rechargables maintain their 3.7V per cell pretty well, and would be slightly higher right off the charger, so that's 7.4V or more for two L-ions...compared to the 7.2V of 3 primaries. So, it should be slightly brighter as you observed. :thumbsup:

 

[KeyGrip]

I've seen this done before in discussion in the incan. section. Perhaps someone there will have an answer.

 

[jbosman1013]

somewhere here is a chart of what bulbs you can use with two 3.7v li-ions, you might be able to find it by using the search. Remember to BE CAREFUL those bulbs draw alot of amps.

 

[MacTech]

The RCR's i'm using are protected cells, I'd hope that would *reduce* the danger of LI-Ions in series (completely forgot about that little danger, as I mainly use these RCR's in my E1L-SR one cell) I know nothing can *eliminate* the danger, but I'd hazard a guess that recharging them at the first sign of yellowing would be safe...

so I'm overdriving the P90 (and reducing it's lifespan) then? darn, I may have to rethink this, but the light produced by the drive current from two RCR's is just so nice and pleasing....

after about 5 minutes or so of intermittent use, my RCR's *both* read 4.04V (down from 4.15V), seems like a good, stable current draw

however, the inherent risk of running a high-draw lamp on 2 RCR's needs serious consideration, do I really want to do this.....

 

[65535]

Well 2 things (maybe more) overdriving an Incandescent bulb produces a much nicer color band (higher K) and substantially more light, it does reduce life though. As others have said a lamp designed to run off 3 primary 1.3Ah (or so) lithium cells is really designed to run about 7 volts across the lamp leads. Where as your 2 lithium cells are popping out an amazing 7.5 or so volts.

For you I recommend LED's white light, and in your target lumen range and color range overdriving is not an issue.

 

[mdocod]

we do it all the time 2 li-ion in the place of 3 CR123s is the standard rechargeable conversion for li-ion and hundreds of us have done it.

Usually we run a pair of 17500 sized li-ion cells in something like a G3, longer runtime, flatter discharge. good stuff...

Don't worry about the bulb life too much there. It doesn't change much, after about 5 minutes of runtime on the RCR123s you'll see it dim down to a more familiar output level....

if you are interested in permanently using li-ions in incandescent configurations, check out the link in my sig line.