SF 9P flashlight, how much longer run time over 6P with Malkoff's?

[RWT1405]

I am wondering how much longer run time a SF 9P (3 cell) will have over a SF 6P (2 cell) with a Malkoff M60, M60L, M60LL, etc.. Malkoff states an 8 hour full output on the M60LL in a 6P (2 cell), what might I expect from the same M60LL in a 9P (3 cell)? A "ballpark" idea of what I might expect in more run time (1 1/2 run time = 12 hours?; double run time = 16 hours?, etc.) would be helpful! Thanks in advance!

 

[RWT1405]

Thank you to everyone for their help on this.:candle:

 

[roymail]

Frankly, I just don't know or have any way to find out. I know that 3 cells has more capacity than 2 cells, so you should definitely get more runtime. With a 9P you may want to consider 2 x 17500's as an option.

Regardless, the Malkoff drop-ins provide excellent runtime. Personally, I think the M60L is a good compromise between output and runtime. And, using 9v primaries to drive it should be awesome.

Perhaps mdocod (Eric) could help you with your specific question. Just send him a PM.

 

[xcel730]

I'm no expert in this, and I am curious to know as well. But I'm pretty sure that 3 batteries running in serial has the same Mah as two batteries ... it's the voltage that increases. In other words, one CR123a has 3v, two CR123a in serial has 6v, and three CR123a in serial has 9v. On the other hand, if you run the batteries in parallel, the voltage remains the same, but the Mah increases. In our scenario one CR123a has 3v and 1500Mah, two CR123a in parallel has 3v and 3000Mah, and three CR123a in parallel is 3v and 4500Mah.

Regardless, running on 3 x CR123a should last longer ... maybe it has to do with the current draw (from Malkoff it says that running on 6V the current draw is 170ma) ... maybe if you run 3 x CR123a the current draw will be lower? :thinking:

I'm still trying to learn the electronic complexities

 

[mdocod]

I'm not 100% sure about the behavior of the malkoff drop-in...

but, I can make guesstimated guesses!.... (here goes...)

it's rated to run 90+ minutes on 2xCR123s.

On 3 CR123s I would expect around or at least 140+ minutes runtime.

On a regulated device like this, when you apply a higher input voltage, the device automatically reduces current draw to compensate, the result in runtime gains is coming from 2 aspects:
1. You are gaining 50% overall power available by adding a 3rd cell.
2. You are reducing the load on the cells while in operation, so they can deliver more of their available power to the module and not be wasted as heat within the cell.

As a rough estimate, you could say that when you run the M60 on 2 cells, each cell delivers about 3.4 watt/hours of "juice." When you bump it up to 3 cells, the reduced load means that each cell may deliver closer to 3.6 watt/hours of juice. (just examples, this is not specific to any cell I am thinking of)..

So... with the example above:
2 cells deliver 6.8 watt/hours of power.
3 cells deliver 10.8 watt/hours of power.

So not only are you gaining runtime going to the 3 cell configuration, you are squeezing more power out of each cell, which means you are saving $$$....

----------------------

but IMO, a pair of 17500s is the way to go if you plan on using it regularly

 

[RWT1405]

Thank you all for responding! This is the part of flashlights were I feel all new again. LOL! And thank you mdocod for your response as that is what I was thinking, but wasn't sure of how to "show" it. As always, the people here and their knowledge amazes me!