R CR2 Cell "Situations" - anyone ?

I have a small CR2 powered flashlight that was originally designed for either primary or R CR2 size cells. (2 in series)

I have primarily used the AW RCR2 cells as they are the only fully protected versions that I could find, and of course, these are not available anymore, which makes me consider using un protected RCR2s.

Normally, I would not consider this, but the interesting thing is that there are a number of flashlights out there (such as Orb) which use these cells and drain them at quite high rates - yet - remarkably - I have not seen any reports of serious incidents. Of course high drain rates can cause limited cycle life, but that is not a big deal for me. I am mostly concerned about safety.

Any comments / suggestions / experiences with unprotected R CR2 cells ?

Thanks

HarryN

The Orb Raw NS uses a similiar cell (but not a CR2) - it's an unprotected cell and I think the main reason you don't see any incidents is due to the owners taking great care of the battery (after all the Raw NS is kinda special).

As long as the battery is not physically abused, overdischarged, overcharged or charged too quickly I don't see a problem. Single cell lights in this case are much safer. The simple design of the Raw NS actually makes it harder to cause a problem such as a short but you can easily overdischarge the cell so care is needed - check voltage before charging.

Unfortunately you say your light uses 2 cells so this makes things much more difficult due to the possibility of reverse charging. Does it have a low battery indicator/cutoff?

Edit: Ofcourse discharging them too quickly can also be an issue but I believe a 2C discharge is considered fairly safe?

Hi Zipplet - Thanks for the answer.

The original Orb Raw did use a R CR2 size cell, but you are right, the new NS version cell is a bit smaller still.

The light I am using is based on 2 cells in series, but I am thinking about re-designing it to put them in parallel with some reverse protection to prevent "back charging".

It is good that the users are careful, but that is not really sufficient unless the cells themselves are "more safe" than an un protected R 123. I guess that is really the question - is the smaller cell size of the 15mm size R cells really that much safer than a 17mm size cell ? Does 1/2 the power capacity somehow de rate things enough to make venting events very unlikely ?

Over discharging can sometimes be stopped with the right electronics, but not if I retain the ability to use both R and Primary cells.

From what I've read I'd say cell size is less of a factor as to if there will be an event or not - but if there is an event the smaller cell will vent less/explode less violently simply as it contains less material.

There are some battery gurus around here that should be able to chime in

Don't do it. Safety first!

Hello Harry,

If you are careful, you can get by with unprotected cells, but it is safer to use protected ones.

In general, you can expect smaller consequences with smaller cells should you ever get to the rapidly venting with flame conditions. Not too many lights use the CR2 size cell, so there isn't a lot of data on them. I have only tested the primary cells, so I don't know what to expect from the rechargeable ones.

With proper instructions to those who purchase and use the light, I think you would be OK.

Tom

Thanks for the replies. I have no desire to use unprotected R CR2 cells, it is just a simple matter that they are not available anymore AFAIK.

Perhaps the safest advice would be to ask users to replace them every 5 or 10 cycles. They are cheap enough now for this to not be a real economic issue. With cells at $ 4.00 / each, 2 cells = $ 8. 10 cycles is just $ 0.80 / cycle, so not really an issue if you are dropping a few hundered $ for a custom light.

I wonder if anyone would actually do this though, regardles of the price ?

Good to see you back on the "boards" so to speak Harry!


Karl

I don't think you need to go as far as asking users to replace the cells after a few uses. Tell users to switch off if they notice it dimming noticeably - the li-ion discharge curve should make it very noticeable and it does with my Lummi lights. Admittedly the Lummi lights are direct driven but it would probably make the regulator drop out of regulation too.

Maybe also ask your users to measure the cells with a DMM before recharging them and discard if the voltage is too low.

I know this is an old thread, however this was the highest ranking one which came up on google. I have some experience with them as I was also dissappointed when AW stopped making the protected RCR2 cells otherwise I would have bought them and used them.

I have the DX budget CR2 cells and one reviewer claimed that these were in fact LIFEPO4 cells instead of std li-ion 3.7v cells.

I tested the "hot off the charger" voltage and this was 3.45V settling to 3.3v after 10 / 15 mins without load. This led me to believe that they were lifepo4 chemistry just as the reviewer had claimed.

I run them in a WF-606A (P4 emitter) and the measurements I could take showed they were rated at 200mAh just like another reviewer had stated.

On the above torch, it is very noticeable when the power has dropped at which point I take them out immediately and swap in a freshly charged cell.

Checking the voltage with a DMM it comes in at around 2.1v when taken out.

The only issue is when you are not sure and still run it which is the dangerous point when the initial light level is high, but drops rapidly after a few seconds when the voltage drops. For users who only use the light for a few seconds at a time, you have to discipline yourself to monitor your usage or swap out for a new cell if you are not sure.

That is my experience, and one that is from < 10 cycles. I will post an update after 100 cycles so you have at least one review on these cells before you take the plunge.

The other point is that I have an RC charger that can specifically handle LIEFPO4 cells. The only concern I had was that the cutoff was set to 3.7 and not 3.6 as the literature on the net suggests, however the cells have been working fine whilst I have been using them. The charger also shows the amount put back in and this has always been around the 187 / 203mAh mark.

I hope this helps you somewhat.

Hi Pummy,

Thank you very much for looking into this and contributing to this thread. I am very interested to see what comes out of your testing.

I had put a lot of time and money into designing that 2 x CR2 light, and it is indeed a great loss to not have fully protected R CR2s around. I am still running mine on some old AW cells, but that won't be so much longer - then I am stuck with fully priced primary CR2s, which will work, but it's kind of pricey.

Take care,

Harry

Hi HarryN

As luck would have it I am now without a CR2 torch for a few weeks as a good friend wanted a small CR2 torch and in an effort to bring out the flashaholic in him, gave him my 606.

I have not continued the testing any further but I had an idea about why you could not put in a seperate PCB in that would fit. I have no frame of reference as to what is required or even if something that size if possible to obtain, not to mention the cut off voltages being adjustable to the LIFEPO4 chemistry.

Worst case I presume that you could use a 14500 protection PCB and reshrink once the PCB has been fitted?

Just an idea I had and thought you could at least consider that since a 14500 protection tab should be quite easily available.

I will pinch my other 606 off my father as I have some Q5's coming my way. I am fortunate enough to have the old 606 which drove a P4 hard, meaning I should be able to erk just a little more output out of the little monster. When that comes back I can continue my usage of the CR2 cells.

HarryN said:

I had put a lot of time and money into designing that 2 x CR2 light, and it is indeed a great loss to not have fully protected R CR2s around. I am still running mine on some old AW cells, but that won't be so much longer - then I am stuck with fully priced primary CR2s, which will work, but it's kind of pricey.

Click to expand...

Would it be possible to use a battery carrier that has built in protection circuitry for each of the raw RCR2 cells?

LumenHound said:

Would it be possible to use a battery carrier that has built in protection circuitry for each of the raw RCR2 cells?

Click to expand...

Hi - thanks for the comments. CR2 lights present a special challenge IMHO, because you give up a lot of energy storage for a size reduction (compared to the 123 size) and the price of running it goes up. The only reason to do this is to make the light substantially smaller than a 123 based design, which drives design constraints and frankly, design simplicity.

Since I already had the mechanical design of the light finished, a proto in hand, and a production run of PCB blanks (not populated) made for the light ($$s ). I really like this light, but frankly little interest in a major redesign effort. I am still toying with the idea of just selling off my proto as a "one of a kind", but have not reached that point yet.

I am still holding out hope for R CR2s, as operating a light from primary CR2 cells is impractical.