Runtimes. Runtime Tests. Concerns, questions, observations.

[gadabout]

@LowLumen

Run time numbers are important to me for planning power outage lighting, for hiking or camping to estimate battery and charging needs. If you are outwith only an EDC with you and happen into a situation where you actually Need it; nice to know how long you have before it goes dim… …The other trick manufacturers pull is the ‘ANSI’ run time to 10% output (…where it drops to under 50% in the first 10 minutes) A run time/output test will show this and is good to know even for those who only care about Lumen. The only Fenix I have is an E21 (2AA) it draws 250ma on low and about 1A on high. I thought most Fenix drivers were efficient. This is a good one.

It's an interesting debate going here isn't it?

I agree with the above about being able to plan my battery requirements based on how many hours of lighting I expect to need. Sometimes I really do need this information, such as when trying to plan whether I'll get back from a night canoe training session without having to change cells (awkward in the boat). Other times it may just be my anal or OCD traits kicking in.

I don't place much stock in the 10% brightness readings either. This is how lenser has been able to quote such inflated runtimes - combining the 10% spec with tests done using alkaline cells! I'd hardly call a light that spends most of its runtime below 50% of its rated spec honest advertising.

[quote=LowLumen] Tailcap measures work well enough to estimate run times, and easier than waiting hours. Get yourself a meter, it's easy. [/quote]

I take some issue with the tailcap current measurements suggested however. Many drivers do not have linear current draw across all voltage levels. if using a boost driver on a single AA, when do you measure the current? Hot off the charger at 1.45V? Nearing depletion at 1.1V? Somewhere in between?

The issue is even more pronounced when working between 4.2V and 2.9V such as with a Li-Ion cell and a buck-boost driver.

Then, there is the question of how accurate, reliable, expensive is your multimeter? How much resistance is in the leads - do I use stock or do I need to make some fancy, heavy-gauge jobbies? How hard do I press on the cell?

Nah.... I like hard numbers obtained with a stopwatch and light meter (when anyone is dedicated enough to do this).

Perhaps calculating from a tailcap reading was what lead Fenix to their published runtime in the first place?

[LowLumen]

For linear regulators (7135) the tailcap draw will be constant and correlate well with run time. The buck/boost types are a bit harder to measure/estimate. For Eneloop I use the current draw at 1.2-1.25 volts. Most of the discharge curve is at this voltage so it averages well. For accuracy, I’m just looking for a ‘worst case’ number; I just want to know even with 80% charge I will get at least 4 or 5 or whatever hours.
If measuring multi-hour run time current levels, likely below 1 amp, the current measures even from my cheap meter are accurate.

I’m not arguing against doing run tests. It gives more useful information about output as well, and why not include current draw in the test as well. Just a shortcut to make a good estimate. …At least it should tell you when you need to be home to check the output.