Where to get larger Lithium Ion?

[davep]

Hi there everyone. Thanks for the help I have recieved so far by the way. I really appreciate it.

I have decided that I will use only lithium ion rechargeables for my flashlight because there are too many advantages to them- (lightweight, high voltage, high capacity, fairly constant current). However they are so heavily restricted since they need protection circuitry in the batteries and the charger and can apparently blow up when charging above 4.3V.

There are tons of 18650's (18mm diameter, 65mm long) cylindrical cells available on ebay but I want to find larger diameter ones, up to D size. I have tried to contact a local saft distributor about their 4/5 D (34480) to see if I can get some but they say I need a protection circuit first. Moli (manufacturers) in Vancouver Canada close to me absolutely refused to let me buy their 26650's which they only sell to militaries. They wouldn't even give me the name of the packer who packages them and puts in protection circuits. Frustrating...

It seems like Li-ion is super restricted unless you get 18650's from sketchy ebay dudes.

Pila's would be good, but I need 10 watts which I highly doubt one pila would handle (~3Amps), or even 1 18650.

If anybody knows how to obtain larger than 18650's please let me know! Even if I can get just bare cells, the protection circuitry can be made. Thanks

The only way to make a small super high power rechargeable light is with these cells. Nimh won't cut it...

 

[CM]

Well, if you find out, let us know. Anything larger than 18650's are not consumer oriented and I think you're going to have a rather difficult time finding even assembled packs that house the larger cells. Saft makes 34xxx but they're geared for military/medical/specialty applications. Your best bet is to stick with consumer type cells and modify (or select) flashlights that can be modified to hold these type of cells. A pair of 18650's can now be had that can supply an excess of 4AH. I admit these are suboptimal for D size applications but that's as close as you'll get without resorting to specialty size cells.

CM

 

[PeLu]

It depends how restricted you are regarding the form factor, Li-Poli cells and batteries are easily available through the RC community. If you want to stick to cyclindrical cells, just take as many as you want in parallel.
When using 18650 cells, check first their maximum current, some of them are as low as 1.5C, but most of them should be good for 2C. A check for the voltage drop should be fine for a rough guess.

 

[davep]

I will try to get some 26650's somewhere. They are the perfect size for a small 1 cell 10 watt light. The 26650's take 5amps easily, this is only 1.5 C but they can be taken further I'm sure as this chemistry can do apparently 5C continuously too. Even though they are restricted, I will do whatever I can to get some. I'll then try to get a bunch if I have the chance. Unfortunately I don't think 2 Nimh C's would take a 5C drain that easily to get me 10 watts. But I did some looking around and found that the max drain of Nimh is anywhere from 1C to 30C with some decent stuff saying 3-4C. I wonder how fast Nimh's get destroyed when drained at 5C?!

 

[davep]

I'm going to be looking for Lithium polymer as well since they easily take a 5C drain and have more energy per size than lithium ion. This may be the ideal solution. However, I cannot find cylindrical versions at the moment. There are standard equipment for rc cars and airplanes. It would be perfect for my light too. The good thing is that they take a massive current drain so this opens up more doors now...

By the way, please offer suggestions, comments...!

 

[cy]

Just wanted to make sure you knew about the dangers of Li-ons possibly catching on fire and possibly exploding during the charging proccess.

There has been several threads warning of this. the RC airplace crowd has warnings all over. Shouldn't be too hard to find.

maybe that's why the mfg are so touchy about selling li-on batteries direct to consumers.

 

[Klaus]

Dave,

2 pcs of 2A 18650s in a Mag 2C host is an easy and cheap solution offering 2 x 2A @ 3.7V nominal and if you modify the setup to have the cells run in parallel you get plenty of amps to draw even at just a conservative 1C rate - you then put your three 3Watt LEDs in parallel in the Mag head using a Fraen Tri-Lense (need to mod the head a bit I think) and you have a nice setup I think. Or you design/buy a nice boost driver with the 3 LEDs in serial as you planned and can also use the cells in serial, or go with the cells in serial and use a buck driver with the 3 LEDs in parallel, plenty of options, but in general I think 2pcs of 3.7V 2A 18650 cells should be nicely driving your 3 3Watt TVOJ Leds for a wile, runtime estimate probably in the 1+ h area when driving the LEDs at 1A each ?

For a start it might even work out nicely with the 2 LiIons in parallel and the 3 LEDs in parallel too running straight off the cells in direct drive or slightly resistored as the LEDs are low Vf. Whatever circuit in between will certainly be more sophisticated though.

Just my 2 Euroc-cents and YMMV

If you DO FIND 26650s please let us know /ubbthreads/images/graemlins/buttrock.gif

Klaus

 

[PeLu]

When it is just for a high load application (and runtime is not that important), you could use 18650 Li-Poli cells which can give 12C continuolsy and 20C for 5 seconds. Lower capacity than 'normal' 18650 Li-Ion cells, but much higher power.

As cy mentioned above, it is the risk when you abuse the cells which makes the manufacturers reluctant.

[ QUOTE ]
davep said:
But I did some looking around and found that the max drain of Nimh is anywhere from 1C to 30C with some decent stuff saying 3-4C. I wonder how fast Nimh's get destroyed when drained at 5C?!

[/ QUOTE ]
It is not the chemistry alone. NiXX cells come in two (usual, there are actually more) electrode types: sponge and sinter. First one gives about one third more capacity, latter one has much better high load behaviour.
NiMH high load cells are mainly available in SubC form factor. The best ones can also be loaded for up to some 20C. Best to ask the RC community