Conversion possible.............or is it even wothwhile?

[Tejasandre]

Just got my $10 led for my mag in today. Maybe I'll get to try it tomorrow

 

[Chris C]

Why, exactly, would I only use one 18650 battery when there is room for more? Would that bump the voltage up too high? 3 D-cell batteries = 4.5v and one 18650 battery = 3.7v. Wouldn't using the 18650 be lower voltage and less light from the LED? Sorry if I sound ignorant.........that's okay, because I am when it comes to all of this stuff.

 

[Lynx_Arc]

Why, exactly, would I only use one 18650 battery when there is room for more? Would that bump the voltage up too high? 3 D-cell batteries = 4.5v and one 18650 battery = 3.7v. Wouldn't using the 18650 be lower voltage and less light from the LED? Sorry if I sound ignorant.........that's okay, because I am when it comes to all of this stuff.

Alkalines have a lot higher internal resistance than lithium ion cells such that under heavy current loads they can actually sag lower than lithium ion batteries do. 18650s off the charger are actually about 4.2v under a load that will drop them to 3.7v will likely drop the D cells similarly if not even more. If you shop around you probably won't find any 3D cell lights that can match the runtime and output of a single 18650 light can. An 18650 can be recharged and each time you drain 3 alkaline D cells that costs about $3 or more after about 9 D cells you can pay for a high quality 18650 that will give you hundreds of cycles for fractions of a cent to recharge it each time.
If you go to Duracells website you can find graphs that equate at a 2A current draw a coppertop D cell will drop to 1.2v in about 10 minutes and 1.0v in about 1 hour so your 3D light running about 8 watts to an LED will drop very fast in 2 hours down to 0.8v so for practical purposes you will get about 1000mah of power out of them at that load while a 2000mah 18650 would close to double that runtime and a 3400mah 18650 would almost quadruple or more that runtime while maintaining it brighter.
Simply put alkaline batteries are for light loads if you want to run high output LED lights you need rechargeables at or at least lithium primaries.
BTW if your LED and electonics are pretty efficient you could get perhaps 150 lumens/watt so 2A at 3.6v is about 7 watts or about 1000 lumens roughly of quickly declining light... perhaps 1500 lumens from the start dropping quickly to 1000 and to zero in 2 hours if the driver is regulated but likely the output would be a lot longer but at greatly reduced output. If you are running at a 500ma load you should get about 5 hours of runtime to 1.2v. 18650s typically strive to maintain 3.6v or greater till depleted and can handle loads up to 20-30A continuous for some cells a 2A load for an 18650 is no sweat while 2A on a D cell is a huge current load.

 

[Chicken Drumstick]

Why, exactly, would I only use one 18650 battery when there is room for more? Would that bump the voltage up too high? 3 D-cell batteries = 4.5v and one 18650 battery = 3.7v. Wouldn't using the 18650 be lower voltage and less light from the LED? Sorry if I sound ignorant.........that's okay, because I am when it comes to all of this stuff.

Li-ion has a resting voltage of 4.2v and under load the D cells voltage will drop considerably. So you would likely get better performance from a single 18650.

You could run more than one 18650, but you would need to do this in parallel, not series. Else the voltage would exceed 4.2v, but fitting them in might not be very easy in this config.

Personally I see little to no point in using an 18650 in a 3D. It would just seem to be a large tube for a small battery. Plus you can't exactly buy adapters easily.

I would use AA's instead. Specifically Sanyo Eneloop NiMh. You can get adapters to convert an AA to fit a D cell. These are cheap and readily available.

 

[Chris C]

Thanks to you both. It's obvious I need an education on this stuff and you've helped a lot. I do understand parallel vs series. I'm perfectly capable of making an adapter for the 18650 to fit the 3 D cell Maglite. And while it might take some "pondering", I have no doubt I could make an adapter that would allow for two 18650 batteries in parallel. Anyone on the forum you know of who has done that?

Yes, I realize three adapters for the D cell would only cost $21 plus shipping. The next decision would be whether to invest in rechargeable Eneloops and a charger or go with Ultimate Lithiums. Lithium route is cheaper initially, but doesn't make sense over the long haul. Something I don't know how to figure is how long 9 AA Ultimate Lithiums would last in the Maglite.

Oh, and I pulled an led light out of my camera bag last night to check it and the Alka-leaks had trashed it. As soon as I use up all the Copper-tops I have, I'll never use them again.

 

[Lynx_Arc]

One can estimate how long batteries will last in a maglight by knowing the current draw and what the battery can put out at that rate. An Energizer lithium primary AA battery has a pretty flat discharge curve under decent to heavy loads unlike alkaleaks they tend to hold up more like lithium ion based batteries. I believe a AA lithium has about 3000-3200mah capacity so 3 in series would match an 18650 of similar capacity while 9 should last similarly to 3 18650s. In theory you would have more power than 18650s could manage because you may not be able to squeeze 3 of them in the tube as they are a little longer than D cells. One advantage of 18650s is you could invest in a charging circuit and holders and wire them in there only have to unscrew the cap and plug in micro USB cord to charge them without taking them out of the holders.

 

[xxo]

Running AA Eneloops in AA to D adapters is probably the simplest way to go rechargeable in a D cell Mag. 1 AA to D adapters are OK, but run time is short. 3 AA to D parallel adapters increase run time but the adapters are cheap in both cost and construction – I've had a few that were DOA and if you use them a lot they will likely wear out, best to order some spares. The problem with the 3 AA adapters is that you end up with 9 cells to charge for a 3 D cell light and it can be a bit tedious removing and replacing all of those cells in the adapters.

Full size/full capacity 8-10,000 mAh NiMH D cells (I've had good luck with Soshines) are a good option, but they are heavy, expensive and require special chargers. Down sides are good chargers are hard to find and you will probably need 2 chargers to charge 3-4 cells at a time, as most only charge 2 at a time even if they have 4 bays. Also these cells are not as low self discharge as eneloops and will be need to be charged every 6 -12 mo, even if you haven't used them.

Protected 18650, 21700 or 26650 Li-ions are my favorite option after I started making my own 3D printed adapters – these are nice and light weight, you only have 1 or 2 cells to charge at a time and you usually don't need special chargers.

 

[bykfixer]

It really depends on how long you will use the light. Such as if it is to light the den during power outs and needs to run a few hours, or is it simply a light to use while putting out the trash or walking a dog and doubles as a hammer if needed to thwart a bobcat.
How bright are you figuring it needs to be also plays a role. If you want around stock output one of those fuel sipping Nite Ize LED light bulb replacement modules and some eneloops in a set of D adapters is nice and simple. You can buy eneloops with adapters or a set with a charger (or both) and keep 3 extras already charged knowing they'll be good for around 1/2 fuel left (at least) after a year.

I have a few 2D Maglites with D adapters and a Nite Ize module setting around like candle sticks. Lens down keeps the dust off that and just turn it on, flip it upside down tail down and let the light reflecting off the ceiling do its thing.

 

[Tejasandre]

I put a $9.99 led from that auction site. Still running the D'S that have been in there for years. Here's the results https://www.flickr.com/photos/43624831@N05/shares/74f29P