Rechargeable AA NiMh Performance in lights?

[gcarter]

How much practical difference does the drop from 1.5V to 1.2V make when using these batteries in dive lights? Experiences?

TIA

 

[lucca brassi]

depends on consumption current

ops ( wrong understood )- have think on time droping between 1,5-1,2 V

 

[herman]

In actual practice, very little. What is more important is the light output over the life/charge of the battery. While there is some difference in the initial light output between a NiMh and alkaline battery there is more to the story...as usual. What you have to take into consideration is the discharge curve of the 2 batteries. While the alk battery does start off at 1.5v it quickly drops to around 1.25V but then continues on a long slow voltage drop until it's dead. On the other hand, NiMhs start at 1.25v but basically stays at that same voltage until they are almost discharged then drop rapidly. What this means in light output is the alk will be brighter than the NiMh for a few minutes but will soon fade below it's output and continue to get dimmer and dimmer until it's useless. The NiMh will start out slightly less bright than the alk but will soon be brighter and stay about constant brightness until it's near discharge when it will quickly get dim. Which you prefer is a matter of choice. Tech divers don't like NiMhs due to the somewhat unpredictable point at which it drops voltage/light. They prefer the more predictable but constantly dropping output of the alks. I on the other hand prefer the NiMhs due to the more constant light and the fact that they are rechargeable. If my light goes out, I just grab a back up or hang with my buddy but I am not deep into a cave or wreck. Pretty much all of the above light output goes out the window if you are using LEDs, they are a totally different animal.

 

[miketsp]

In fact it depends on whether or not the light incorporates a regulator circuit or not. I don't remember ever seeing an incandescent light with a regulator whereas all my LED lights do have regulators. So my LED lights produce an identical light output with all types of battery until you get onto the final section of the discharge curve when the battery voltage is insufficient to maintain the desired current.

 

[Progen]

I just got myself an UK SL3 eLED light. Was thinking of using Lithium rechargeable C cells with it. Will there be any problems in the real world since it was rated for alkalines?

 

[buddhasummer]

I just got myself an UK SL3 eLED light. Was thinking of using Lithium rechargeable C cells with it. Will there be any problems in the real world since it was rated for alkalines?

I could be wrong but I don't think all lights that run on alkalines can necessarily run on lithiums, can you check with UK Lights directly?

 

[Progen]

I could be wrong but I don't think all lights that run on alkalines can necessarily run on lithiums, can you check with UK Lights directly?

Yeah, that was what some sites said and it'd be freakin' frustrating to put in rechargeables, get amazed at the brightness for a while before ending up with a hot blown light.

 

[muzikbiz22]

I use rechargeable NiMh 3000 mAh C cells in my UK light. One of the best investments I ever made ! They're great, charge lasts forever, consistent output during use. All my strobes have Eneloops. Rechargeable's make life easier.

buddhasummer might be correct in, that Lithiums can be a little dicey.

 

[Progen]

From their website but not referring specifically to the SL3.

"Electrically speaking, it is OK to to use Lithium AA cells, such as the Energizer L91 Li/FeS2, in these products. The problem is that Lithium batteries are not rated for use in the hazardous locations for which the lights were tested. Only Alkaline AA cells by Duracell, Energizer and Rayovac are rated."

 

[spoolin01]

NiMH typically have higher usable capacity, so I think you'll appreciate them in either incandescent or LED application. NiMH will literally 'last longer'. As herman noted, under load there's little difference in usable voltage, and combined with capacity that gives a slight edge to NiMH in incandescent lights. In my experience, I see that difference at around the first hour with the 4 and 6 C-cell lights, when the alkalines are already dimming. With most LED lights, as miketsp explained, output is fairly constant even while voltage is dropping, within some limits. So the sloping alkaline discharge curve isn't as relevant, and the match between number of batteries and the LED driver specs determines how long the two battery types will perform similarly. The Cree LED drop-in module produces the same output in the UK SL4 and SL6 lights, but the 6 cell will go longer before starting to dim. An SL6 and the Cree module with alkalines might do every bit as well as with NiMH, over even more than one dive. Use to exhaustion should still favor NiMH, though I haven't done that comparison directly. Even with the occasional flood and loss of batteries, I find it less expensive to use NiMH batteries.