O2 cells

Garry Whyke

Hi all,

Just fitted a new cells (D6) purchased last summer.

Read 0.16 on start up. After 2 days recovered to 0.18. Still not up to 0.21 yet though.

Thinking this was duff just openned another new one. This read 0.14.

Anyone else experienced this?

Do they recover or have they had it?

Thanks

......... Garry

tflaris

I am a newbie to Rebreather diving but if I remember correctly I believe I have read somewhere to store them in an inert gas like nitrogen or helium. I have also read that even if stored in a sealed bag they will deteriorate within 12-18 months.

__________________
"Except for this one, I have come to the conclusion that all generalizations are false" -Jim Hayes

Tino de Rijk

what do you mean with "the old one read 0.16" or "new one read 0.14"..?
Reading the cells through the handsets (classic) or wrist display (vision) without calibrating the unit first is totally meaningless.
If you would put a voltmeter to it, you would see that each cell outputs a different voltage, somewhere in the range between 8mV and 11 mV (out of the top of my head; haven't got a manual at hand right now). So you see that is already a 30% or so margin! That is no fault, that is by (Teledyne) design: it is impossible to make them 100% the same each. That is exactly what the calibration process is all about: it matches each cell's indivual mV reading at 100% O2 to the value "100". That correction value is then stored to calculate the match of the cell's output to the percentage of oxygen it is exposed to - also at 21%.

So: after fitting cells, you should calibrate as designed, with 100% O2, and then you should be able to e.g. take the head off the scrubber, subject it to air, and you should read 0.20 or 0.21 from all three cells.
Any other procedure is useless, and tells you nothing about the cell quality. D6 means may 2006, so should still be well within the 12-18 monts safe use bracket.

ciao,

Tino.

calibration

Garry Whyke

Hi Tino,

Thanks for the comments.

The 0.16 & 0.14 was oxygen in air, and not mV reading.


.......... Garry

Nad

It depend, I don't know if every sensor is the same about deterioration but usually the life is done for air ambient (21% O2).
More the O2 present less the life.
At the present many sensor last 3/4 years, not if used with a rebreather.
I change mine after around 12 month but they still read 1.6 at 6 m.

Nad

__________________
The Impossible is often the Untried

Tino de Rijk

....yes, they MAY live for longer than the 12-18 months, even with a "reasonable" likelyhood, but do YOU want to be the crashtest-dummy to find out if your particular cell is 2.5, 3 or 4 years lasting?... And do you want to find that out halfway in a dive...?

The manufacturer's spec of 12-18 months should be read as: "a 99% (not a 100%!) change the cell will work as expected within this time span, and within the PO2 exposure range expected; so supplying a linear rising output in mV in the range of at least 0.20-1.70 bar)".

After that period, it will not suddenly die; it will first slowly, and later on rapidly decay, starting to not be able to reach specifically its high PO2 output voltages. So it will become essentially unpredictable in its working, especially at the higher PO2 a rebreather exposes it to (you might e.g. still be able to analyse a EAN32 mix with it, although even that I would not gamble on with a "spent" cell).

So you could be lucky with you having a good one, lasting 3 years, or unlucky, with having one that starts to fall fast after 19 months. The point is simply this: "luck", "chance", "gamble" and "unpredictable" have no place in Rebreather diving. They can & will likely kill you.
So, DON'T save money on pushing a cell's life. Stick to the recommended 12-18 months. The recommendation is not there for nothing....

ciao,

Tino.

pabusk

Just a minor point Tino,

Isn't D6, April 2006 instead of May 2006

(Just trying to get to that illusive custom text under my name )

Cheers,
Paul

Tino de Rijk

Yep, you're right, I miscounted my fingers......
for those that don't know about the datacode on the APD cells:
- D = 4th letter of alfabet = 4th month of year = april;
- 6 = 2006.

Simple.

ciao,

Tino.

Nad

This is why I wrote: "...not if used with a rebreather..."
I never wrote something about pushing a cell's life and I didn't read anything from someone else.
Here NO ONE IS PUSHING THE CELL'S LIFE! It's ok now?

Nad

__________________
The Impossible is often the Untried

PhilSiswick

No-one has really answered Garry's question - are his cells dead? Seems that way to me.

Which brings me onto a linked dilemna. It would appear that cells degrade similarly quickly in the Rebreather and the original packaging. Therefore, it's fairly likely that, when you open the packaging for your spare cell(s), it's going to be just as dead as the cell you want to replace.

So, is it worth opening the packaging, testing the cell and then putting it in a small box (where the residual O2 can be used up quickly, hopefully maximising the life), rather than leaving them in the unopened packaging?

From what I've read, that would mean you have cells that you knew worked when you received them (and can return if they don't, saving you money), rather than risking having spare cells that are dead. Seems to make sense to me - anyone care to throw rocks at my approach?

Cheers,

__________________
Phil (WSKD 0001)

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