Fx-ion Batteries and chargers

[pete_the_caver]

I have an FX-ion charger but now the Fx-ion battery has died.  Having dismantled the battery pack I have found it to be a single rather large PCB protected Li-ion cell and it appears that it is the cell that has failed rather than the PCB.

As I would like to keep using this charger due to its rather expensive nature, can anyone tell me whether i can replace the cell with another similar sized PCB protected Li-ion cell? or is the charger specifically designed for the original cell?  i.e are the charge currents too specific for different LI-ion cells?

cheers.

 

[pete_the_caver]

I now know having chatted to Kieth at Speleotecnics that the cell was 5.6V 5AH.  My "Interweb" searches can not find a replacement cell this size and Kieth wanting to cover himself wont say much (fare enough) so the question is: could I assemble a battery of similar size by arranging PCB protected cells in parallel and would this work with the Speleotecnics Li-ion charger?

I feel a rather annoyed that having invested in such an expensive charger that I'm now expected to bin it because the company that sold it has withdrawn it even though lithium batteries are clearly the way of the future.

 

[potholer]

Note that I'm not a lithium expert, and what I write here is from information absorbed, not direct experience.

I think that *generally*, as long as a Li-Ion cell is a roughly similar capacity to the original, it should be OK with the original charger.

To get the same capacity out of 18650 cells, you'd be looking at 2 or 3 in parallel, and though in theory 3 cells in parallel should behave pretty much like one larger cell, I couldn't be sure if there are any subtle differences.

A good place to ask for advice is probably on candlepowerforums, in the 'Flashlight Electronics - Battery Included' section. As with any forum, there are differing levels of experience and self-confidence there, but given a little time, you should probably be able to spot who knows what they're talking about. Also, on Lithium topics, if someone says something daft, someone else will probably be fairly keen to correct them.
If you used a decently decriptive post title (like "Is it safe to replace one 5Ah lithium cell with 2/3x 18650s?"), you'd probably attract enough attention to get useful replies.

Are you sure that's 5.6V?
Lithiums generally come in multiples of nominal 3.7V cells (which vary between about 4.2V fully charged, and ~3V when flat. It's hard to see how to get 5.6V from that.
3.6V would seem more likely, and the fact that the Li-Ion worked with the same bulbs/LEDs as the nominal 3.6V NiCd/NiMH packs would lend weight to that.

In any case, I was under the impression from a conversation I had ages ago (with someone who I'd trust) that the cells in at least some packs were SAFT cells, something like the ones described at:
http://www.saftbatteries.com/Produit_MP_cell_range_301_69/Language/en-US/Default.aspx
(Though it's quite possible that models/capacities of previous models were different to the current ones.)

Even if that is the case, whether it's easy/possible to buy those cells in one-off quantities is another matter.

 

[pete_the_caver]

Sorry... that 5.6V was a typo, it should have been 3.6V

cheers

 

[ChrisJC]

Ah, being 3.6V is good. That makes it the same voltage as a single cell. (so it's either a single cell or multiple cells in parallel)

Personally I would search around for a pre-made battery pack that will fit in the Headlite casing with the correct voltage. If you make your own pack by putting cells in parallel, I believe there are some issues with doing that, which is why I would advocate buying a ready-paralleled pack.

If the charger has a 2 pin connection, then that's easy. If it has 3, then the extra one is a temperature sensor, which makes achieving compatibility very different / difficult.

There have been a few threads on charging Li-Ion cells on Mine-explorer.co.uk.

Chris.

 

[Agrophobic]

If you want to parallel up smaller cells to make up the capacity, i wouldn't recommend individually protected cells unless you can charge them independently. I'd use unprotected cells in parrallel and then protect the pack with the old pcb. as long as the pack ends up with a similar capacity as the original cell you wont have any charging problems.
Laptop batteries are a good source of 18650 size cells but be VERY careful not to short them out while you're working on them.
Sadly cells and pcb's are hard to come by in this country and the cheap chinese ones on the net are nowhere near the capacity they claim so are easy to overcharge with the resulting "venting with flame" as exploding batteries are known.

 

[pete_the_caver]

Fab.  There are some good American model building sites i've been looking at. would these be a safer source of cells?

 

[Agrophobic]

Yeah, the states seems to be the best place for good quality cells and pcb's but shipping costs can be prohibative, shipping companies panic when you mention Li-Ion. can't remember why.

 

[Pete]

Having taken one apart it's 4 18650s in parallel giving 5.5Ah at 3.6V (on load) 4.2V when fully charged. You can buy replacement packs and indeed with the way batteries have moved on you can get almost the same capacity from 2 cells these days, the Varta lithium packs you can get from Farnell are a pretty close equivalent and they are sold pre shrink wrapped in 2p or 4p arrangements. Getting the cells out is an absolute swine though, Speleotechnics used potting compound/rubbery glue to hold the packs together which is really difficult to get apart. Although like you I felt somewhat cheated at the cost of the charger the equivalent now is less than ?30 and will cope with different combinations of cells and so more futureproof. Just make sure you get the polarity of the wires right if you replace the batteries, not so critical if you still cave using Halogens but if you use LEDs they just plain won't work!

 

[Agrophobic]

not so critical if you still cave using Halogens but if you use LEDs they just plain won't work!

Erm...... very critical. connect two cells together the wrong way round and they'll take your hand off. please be very carefull with li-ions guys. because of thier low internal resistance they can supply huge current. they then get hot and vent with flame. I'm not saying dont make your own packs, just be carefull.

 

[pete_the_caver]

Thanks all.

I know about all the Li-ion issues and have been building homebake caving lamps for over 20 years so I know all about polarity as well, but thanks for the concern; others without the knowledge may read this. 

The next thing I want to know about is DC-DC conversion, voltage doubling etc so i can build a lamp with one of the new 590 lm triple reble stars. Off the self current regulators need a 2 volt buffer above the Vf of the LED which would require in input a bit over 11V so I would like to bump up a low voltage ie one Li-ion (or several in parallel) or build a NiMH pack (my NiMH smart charger only works upto 8 cells and gets upset if they aren't well ballanced  and who wants this many cells on the back of your skid-lid)

All these new qustions are for a new topic so thanks again

Happy caving (hopefully more time caving than lamp fetling)

P.