Where to obtain 32900 "F Size" LiFePo4 Cylindrical cells?

I'd like to try running my TK70 on 2 x 32900 "F Size" LiFePo4 Cylindrical cells, as the length and diameter is equal to 3 D cells.
But I cannot find anywhere to buy them in 1 or 2 item quantities.
Does anyone know a good place where one can buy such cells in lots of 1 or 2 for a reasonable price?

salivating on the outcome of this! lovecpf

I almost went through with a light using these cells, but decided they were too large.

In my pursuit, I did uncover a seller who would send them in smaller quantities.

If you are interested, you are welcome to email me, but please do not PM.

Here is my email:



Feel free to drop me a line and I'll pass on the relevant info.

The two F cells I ordered over a Month ago finally turned up in the mail today.

I haven't tried them out in the TK70 yet, I'm charging them up on the hobby charger first.

SWEET!!! this is going to be exciting. How many volts and mAH are they?? Have you had a chance to measure them to see if they really are 90mm long?

Thanks,
JD

Any updates samgab? This looks interesting

xed888 said:

Any updates samgab? This looks interesting

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Yes, I think 2 x 32900 "F" LiFePo4 cells are probably the ideal battery for the TK70.
It is very nicely balanced with the 3D sized battery tube, better than when it has the extender tube.
And better balanced no doubt than if it had the 2D sized tube for 2 x 32650's.
Also there is more capacity in F cells than equivalent LiFePo4 D sized cells.
And the voltage ranges of LiFePo4 works almost perfectly with the design voltage of the TK70.
Great success.
The only drawback is that I had a lot of trouble sourcing F LiFePo4 cells.
The person I bought my pair from, another user on CPF, said he was sending me the last two he had.
And of the two I received, 1 is fine, with the claimed capacity. The other only has 3Ah rather than 5Ah capacity.
It took about 2 Months for them to arrive, and they were the last two he had, so I'm not going to send the low capacity one back.
If it were a local supplier I would have. The problem there is not with F cells themselves, just in one of the units I received. But it still works fine in the TK70. I don't like having unbalanced cells making up a battery.
They can handle the current draw of the TK70 no problem.



B is the good cell, and A is the not-so-good cell. If I had 2 matched cells that performed as B does, it would be perfect.

The success is great to hear! Thank you for trying this samgab. Now we just need to find out where the general public can get these cells from.

JD

Hmm maybe we can do a group buy or something from a vendor that has to sell these in quantity. My main issue is don't have a hardcore hobby charger like you do so I wouldn't be able to know how my F cells would be performing. What charger do you have exactly? I'll look it up to see how much it costs.

Those are unprotected cells right? So wouldn't the TK70 essentially over discharge them? When does the TK70 step down from turbo to high? When there's 4 volts of juice remaining from the batteries? That's 2 volts for each F cell which I'm sure is WAY lower than the acceptable minimum charge.

Did you do a runtime test by chance?

CyberCT said:

Hmm maybe we can do a group buy or something from a vendor that has to sell these in quantity. My main issue is don't have a hardcore hobby charger like you do so I wouldn't be able to know how my F cells would be performing. What charger do you have exactly? I'll look it up to see how much it costs.

Those are unprotected cells right? So wouldn't the TK70 essentially over discharge them? When does the TK70 step down from turbo to high? When there's 4 volts of juice remaining from the batteries? That's 2 volts for each F cell which I'm sure is WAY lower than the acceptable minimum charge.

Did you do a runtime test by chance?

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I have a Turnigy Accucell 8150 which I bought second hand. But it can be bought new from a place like hobbyking for about $46 or an accucell 6 for about $24.
Those ones don't have a PC link but they will do the trick.
Or something like an IMAX B8 for about $40.
They're all pretty much the same, apart from minor spec differences.

This cell chemistry is designed to be discharged to 2V: http://bit.ly/wbx2Fs
It wouldn't be a problem if they were a good matched pair, but I have concerns with them being so badly mismatched, I won't be running any discharge tests on this pair.
But it seems to maintain turbo well, due to the higher stable voltage of these cells than NiMh.
The TK70 steps down from turbo to high at just a touch under 4V, it's about 3.8V, but at that stage the current draw is up to nearly 10A, so with hysteresis, it would equate to an OCV of >2V/cell.

Can you use an accucell 6? I thought it had two choices for Li batteries, lilo - 3.6v charges to 4.1v and li-po 3.7v charges to 4.2v.
Are these ~3.6v fully charged? *edit* yes they are...

And upon further inspection of the manual it seems it also has a li-fe setting - 3.3v charges to 3.6v so, ignore me, carry on

could you get regular lithion "F" cells?

These LiFe 32900 cells have 5,000mAh capacity. Don't LiPo 32650 cells have 5,000mAh capacity as well? Wouldnt the 2x32650 cells with a dummy weigh less and have the same runtime? Is there an advantage to running the 32900s? I know that LiFe cells have less voltage than LiPo, but do LiFe cells generally have less capacity as well?

Thanks,
JD

Are these not the same: http://www.batteryspace.com/lifepo432900pfsizecell32v45ah90arate144wh.aspx ?

They also have 42120 (M size) cells.

I just realized that i should have probably rephrased my question from above. What i meant to ask is saftey the primary reason for running the 32900 LiFe cells over the 32650 LiPo cells? I have seen 32650 LiPo in 4,500mAh that puts those batteries at 33.3wh (3.7v*4500mAh*2). These LiFe 32900 at 5,000mAh would be 32wh (3.2v*5000mAh*2). If we take the math at face value the runtime would be about the same. The 32900 would weigh more but you gain the safety aspect. Am i correct on this? I wish both of those 32900 cells were giving you the 5,000mAh capacity. I would like to see what the runtime in turbo would have really been with those LiFe cells.

JD

Samgab, please respond to JudasD on his question above. I'm curious as well.

Also, if we were to figure out some group buy with a vendor, we should expect the cells to be matched correctly, yes? I wonder why your cells are so mismatched.

I am disappointed though on the capacity of these cells. I was expecting at least 1.2 hours of runtime because of the increased size.

@CyberCT: Currently i am running Tenergy Centura D Cells 8,000mAh. This comes out to 38.4wh (1.2v*8000mAh*4) and i only get about 45 minutes runtime on turbo. The two cell variations of 2x32650 LiPo and 2x32900 LiFe would probably get high 30min range. I would think that the 2x32600 LiFe would end up being low 30min range. It's fun to act like loss doesnt exist when working on paper

JD

I have the Fenix TK40, TK41, and TK45 which all run on 8 x AA cells. I have the TK35 which runs on 18650s. I'll use the TK41 vs the TK35 in runtimes as my example, since both are driving the XML LED to it's near max. I understand the eneloops are 2000 mah and my AW 18650 is 2900 mah so the 18650s have a slight advantage. In my TK35 my light runs for about an hour 40 minutes before it steps down from turbo. In my TK41 the light steps down from turbo to high at about 1 hour 32 minutes. With my Imedion 2400 mah cells the TK41 steps down from turbo to high at about 1 hour 43 minutes. So the 8 Imedions vs the 2 18650s yields nearly the same runtime. So seeing how the F cells are large cells, fatter than 18650s for sure, I thought they would beat the NIMH cells (4 Imedion D cells run for about an hour in the TK70) in runtime but it doesn't seem so? I thought I read in the TK70 thread that my exact AW cells last for 43 minutes on turbo in the TK70 and they are slimmer (hence less capacity) than 32900 size batteries.

The 8(AA)x2400mAh batteries yields 23,040wh. The 8x2000mAh yields 19,200wh. The 2(18650)x2900mAh yields 21,460wh. This puts your Imedions and the 18650s very close with the Imedions having about 7% more. Again this is without figuring in any loss, but you do see this in reality as the runtimes are very close.
I would have to go back and look at the TK70 thread. I dont remember seeing a test with 18650s on a TK70. That would be kinda neat.

JD

Hmm could I use an adapter to charge these F cells on my Pila IBC charger which is my 18650 charger? I just want to know which non-NIMH batteries I could use in the 3D tube without the 4D extension.