D cells and Malkoff Dropins?

thermal guy

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I started thinking of a project and need some help with battery capacity.
If a Malkoff M61 module will run for 1-2 hours off a 3400/18650 how would the runtime be if I ran them with D cell batteries a D cell is like 5000 mah but only 1.5 volts so not sure if they would be better or worse.
 

alpg88

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its a simple math, divide battery capacity by a draw (use Wh ratings) and you will get theoretical run time. you also have D cell capacity wrong. i posted correct info in your different thread, alkalines are not made to handle large loads, 1-1,5A is ideal, higher currents will decrease capacity, it is true for all cells not just alkaline. but alkalines are affected more than others except carbon zink
 

thermal guy

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Ok so help me out here cause all this is very confusing for me.IF I ran a Malkoff m61 that has a draw of 800ma.what would theoretical runtime be with a D cell vs a 18650 3400 mah?
 

alpg88

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Ok so help me out here cause all this is very confusing for me.IF I ran a Malkoff m61 that has a draw of 800ma.what would theoretical runtime be with a D cell vs a 18650 3400 mah?

sure.
1 D cell has 12-18ah capacity at 1,5v. m61 takes 800ma at 6v as per malkoff website, that means you need 4 cells in series. range of capacity is 12-18ah. depending on manufacturer, lets take 15ah for our purposes. 15000\800=18,75hours

2x18650 at 3,4ah devided by 800is 4,25 hours, that is on paper, in reality since voltage of 2 18650 is higher than 6v, it's 8,4v, actual draw may be lower, without knowing efficiency of driver, we can assume you will gain about an hour.
 

thermal guy

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Ok and forgive my ignorance here. If that's the case you would be able to run that module much longer on 4-D's then 2-18650 correct?
 

alpg88

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Ok and forgive my ignorance here. If that's the case you would be able to run that module much longer on 4-D's then 2-18650 correct?
yes. 3-4 times longer.

another thing reflector size, m61 has 26mm reflector, maglite has about 50mm reflector, you will get more throw with maglite drop in and mag lite reflector, especially if you use deep led maglite reflector. z battery sells those separetly for like $7 iirc
 
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thermal guy

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Ok see THATS why I was pushing for me to run a m61 in my mag.but as you say his mag drop ins might be as efficient so not sure
 

thermal guy

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yes. 3-4 times longer.

another thing reflector size, m61 has 26mm reflector, maglite has about 50mm reflecor, you will get more throw with maglite drop in and mag lite reflector, especially if you use deep led maglite reflector. z battery sells those separetly for like $7 iirc


Oh ya I know that I have have many Malkoff lights and drop ins. I was literally just seeing what my options were thanks.
 

thermal guy

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I'm going back to the HDS threads where at least I know what the hell im talking about lmao 😂
 

alpg88

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efficiency is not the same as draw. or runtime, also when i calculated run time i did not take driver efficiency into account, i do not know how many % it is.
on his website he says m61 runs 1,25 hous from 2 cr123. typical capacity of cr123 is 1,4ah if we multiply by 10 to get to 14ah (close to what d cells have) we'll get 12 hours, not 18 as i calculated without accounting for driver efficiancy.

his mag drop in lasts 6 hours on 3 cells and adds 2-3 hours for each additional cell. so 4 cells will give you 8-9 hours.

if run time (not efficacy) is your only concern go with m61.
 
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Kestrel

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A body-diameter, Mag/D (or /C) -thread compatible head to retain a Malkoff M61 (or M31) would be pretty cool. Would have to be a two-component solution so as to interface with the existing Mag socket(s), but would certainly add some flexibility to the platform - especially adding more battery types to the mix. And runtimes could be pretty epic as suggested. Just thinking out loud ...

Fivemega did a couple runs of the 2x & 3x C-cell, P60-compatible flashlight hosts back in the day. I had a couple and had fun running M30's in them for a while - would have kept them if I had been more 'prepper' minded ...
 
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thermal guy

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Alpg88 Seriously thanks for all your information you have given me.its much appreciated
 

xxo

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sure.
1 D cell has 12-18ah capacity at 1,5v. m61 takes 800ma at 6v as per malkoff website, that means you need 4 cells in series. range of capacity is 12-18ah. depending on manufacturer, lets take 15ah for our purposes. 15000\800=18,75hours

2x18650 at 3,4ah devided by 800is 4,25 hours, that is on paper, in reality since voltage of 2 18650 is higher than 6v, it's 8,4v, actual draw may be lower, without knowing efficiency of driver, we can assume you will gain about an hour.

I think I am missing something here. A Alkaline D at 800 mA is going to have about 9 Watt Hrs (and a little over 8 Amp hrs) vs a 3400 mAh 18650 with about 12.24 Watt hrs (3.6 x 3.4), If for example you use 3 alkaline D's to bring the Voltage up to about the same as the 18650, the 3 D's should have a total of about 27 Watt hrs. which should run about 2.2X (27/12.24) as long as the single 18650.
 

fivemega

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Fivemega did a couple runs of the 2x & 3x C-cell, P60-compatible flashlight hosts back in the day.
I think you are refering to this.
By adding proper size extension tube to
this possible to use 3-4 or X D cells.
Also possible to use 2 serial 26650 (7.4 V, 7000mAh).

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alpg88 said:
he says m61 runs 1,25 hous from 2 cr123. typical capacity of cr123 is 1,4ah if we multiply by 10 to get to 14ah (close to what d cells have) we'll get 12 hours, not 18 as i calculated without accounting for driver efficiancy.
If LED module is correctly regulated, tail current will vary on different battery voltage as long as applied battery voltage is within the range.

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xxo said:
I think I am missing something here. A Alkaline D at 800 mA is going to have about 9 Watt Hrs (and a little over 8 Amp hrs) vs a 3400 mAh 18650 with about 12.24 Watt hrs (3.6 x 3.4), If for example you use 3 alkaline D's to bring the Voltage up to about the same as the 18650, the 3 D's should have a total of about 27 Watt hrs. which should run about 2.2X (27/12.24) as long as the single 18650.
I think alpg88 was talking about 2 serial 18650 in post #4
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alpg88

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I think I am missing something here. A Alkaline D at 800 mA is going to have about 9 Watt Hrs (and a little over 8 Amp hrs) vs a 3400 mAh 18650 with about 12.24 Watt hrs (3.6 x 3.4), If for example you use 3 alkaline D's to bring the Voltage up to about the same as the 18650, the 3 D's should have a total of about 27 Watt hrs. which should run about 2.2X (27/12.24) as long as the single 18650.

not you, me. it's embarrassing, but i completely disregarded how much D cells lose capacity depending on the load, i knew they do but not as much, energizer claims d cell is 20ah at 25ma load,but only 10ah at 500ma. your numbers are correct, however i did mean 2 18650 in series, not parallel, he needs 6v min
 

thermal guy

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You should be embarrassed. How in the world did you miss that😂😂😂
 

thermal guy

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That of course was meant as a joke I literally have no idea what's what here. I'm going to go do a little research and studying and see if I can start to understand all this
 
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