Fenix LD20 voltage regulation

[burpee]

I have a Fenix LD20 that seems to have quit regulating the current in turbo mode. When I first bought and tested the light it ran in turbo mode for about 75 minutes and then dimmed almost instantaneously.

I easily detected this obvious dimming and knew I needed to switch batteries.

Several weeks later I was using the light and noted that it just didn't seem as bright as when I began using it. I switched to "normal mode" - cycled through the low power modes and then twisted the head to get to turbo mode and discovered that indeed the batteries had drained and the light had been out of turbo mode for some time. (twisting the head should have brightened the beam back into turbo mode)

Two questions: Does your LD20 leave turbo mode abruptly - so much that you easily notice the battery drain?

How can get information about the easiest way to "meter" the flashlight so as to "see" the current levels change as the batteries drain? Should the circuit show a "turbo current cut off?"

I have the meter and test lead and clips, but want any tips how to "jump" into the light's circuit.

Thanks.

 

[John_Galt]

What batteries are you using?

 

[burpee]

I've seen this result in several different sets of NiMH. But the very first run time test was done with Alkaline. (when I saw abrupt regulation)

I held test leads against the end of the battery and case and my "cheapo" meter was displaying 3.2A in turbo. I managed to sort of clip the leads and wait for the batteries to drain and did see a rather quick roll off to 2.0A that took about 90 seconds. But then after that batteries continued to drain at around 1mA per minute.

These results were certainly nothing like the "drop off" I saw when I used Alkalines. Maybe I should try them again.

Did anyone post a chart of battery drain (current/time) for a Fenix LD20?

 

[burpee]

Well I guess some questions just can't be answered.

I would have thought some bench guy could give me a tip on how to fix leads on a LD20 rightly enough to be sure I passing all the current possible.

It would appear the light draws 7 watts in turbo and 3 watts in the "high" standard setting. It cycles at 75mA when on SOS, but again i can't be sure of my contacts, nor have I repeated any of these test with different batteries.

I wonder how much the these values vary using Alkaline batteries.

 

[John_Galt]

3.2 amps seems really, really high... It should be closer to 2A.

That's with either Lithium AA's or quality Ni-MH cells. Alkalines will not be able to provide this much current, and not for very long, either, due to their extremely high internal resistance. So, noticeably lower output and much shorter run times are par the course for alky's.

 

[Bullzeyebill]

If turbo is well over one amp to the LED, then I can see the 3.2A current draw with two NiMh's. Can take 2+ amps to run at 1 amp to the LED.

Bill

 

[Mr Happy]

But what John said. I highly doubt that alkaline batteries have sufficient power to run an LD20 at full brightness on turbo, or at least not for very long. These ultra-bright lights are really designed for NiMH.

 

[burpee]

If turbo is well over one amp to the LED, then I can see the 3.2A current draw with two NiMh's. Can take 2+ amps to run at 1 amp to the LED.

Yeah I don't know why my meter was reading that.

But like i said, I was having to "hold" the leads against the bottom of the battery. I could not find a way to make good connections to the head.

Well lets see, from measuring other lights I would think the light would draw about seven watts to produce 200 lumen. That would indeed be 2.8A at 2.5V. Assuming a higher terminal voltage 2.9V - still results in 2.4A.

How many watts do you think it should draw?

Again, I'm just asking, but this LD 20 only gets 60-70 minutes "turbo" run time in front of a fan at 80 degrees using Energizer 2650, LaCrosse house brand, radio shack etc......less than hour on 2000mA

If I had a way "firmly" fix leads to the head I could watch the thing "regulate" and subsequently run down. I've done that with many other lights and have see "beautiful" regulators that maintain wattage almost perfectly to within minutes of total cell discharge. No so with this LD20.