battery calculations
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Oddjob
Flashlight Enthusiast
You can do both. If you know how many mAh an LED is being driven at you can extrapolate a runtime. For example if you know a certain light level is 100 mAh and the battery provides 500 mAh then you will have roughly 5 hours of light at that level. This is not exact since the mAh on some RCR's are not always as advertised and primary cells do not always list their mAh. Other factors to consider are the regulation circuitry vs. direct drive and how much light you consider to be useful. Some members here do great runtime tests and graphs that are really helpful since they are based on the light actually being on vs. using equations. I'm no expert so I hope more knowledgeable members can chime in but that is my understaing of things.
TigerhawkT3
Flashlight Enthusiast
Just want to put in a reminder that current draw is measured in mA, not mAh. Thus, when you divide (for example) 500mAh by 100mA, you cancel out the mA unit and get 5h. 500mAh/100mAh would simply be 5, with no units, and that's not what we're aiming for here. That would be useful if we wanted to compare a 500mAh battery to a 100mAh one.
jerry i h
Enlightened
Sorry, my friend, but the answer is the latter. I trust no one and nothing for torches that are used in critical applications (work shift; camping/outdoor fun stuff). Put fresh batts in that sucker and start the stop watch. Only way to tell for sure. A calculation can give you a very rough ballpark estimate at best.
mdocod
Flashaholic
How long some flashlights will run, is really dependent on what you define as "still running." Some are regulated some are not, some drop out of regulation when the cells are nearly drained and give another few hours of low output. On alkaline cells, the total runtime when used in short bursts will be different than it would be in a continuous discharge.
Let me say this:
If you know what the independently tested capacity of a particular cell is, when used at a load similar to the flashlight in question, then you can extrapolate fairly accurate estimates of runtime. Using label capacity or manufactures suggested capacity on alkaline cells will not result in any sort of useful results for such an estimate. Runtime estimates are easier to do with cells that have flat discharge characteristics, like lithium and nickel chemistry.
If you have a specific flashlight and cell combination in question make it known, I'll try to run through an example of how you would go about estimating runtime with whatever flashlight is in question.
Eric
Let me say this:
If you know what the independently tested capacity of a particular cell is, when used at a load similar to the flashlight in question, then you can extrapolate fairly accurate estimates of runtime. Using label capacity or manufactures suggested capacity on alkaline cells will not result in any sort of useful results for such an estimate. Runtime estimates are easier to do with cells that have flat discharge characteristics, like lithium and nickel chemistry.
If you have a specific flashlight and cell combination in question make it known, I'll try to run through an example of how you would go about estimating runtime with whatever flashlight is in question.
Eric
Marduke
Flashaholic
The second method is always more reliable, but math can give you a good sanity check of the minimum expected.
You could try fiddling with this:
http://www.kenworster.com/ledcalc/
You could try fiddling with this:
http://www.kenworster.com/ledcalc/
