Life and Death of a Cell

[Major Clanger]

Probably nothing of interest here to old hands but newer rb divers may get something out of it. Nevertheless, a real time example of the death of a cell, re-iterating the need to regularly current limit check cells and replace within recommended timescales. This cell was less than 19 months old from date of manufacture, had shown very little variation during linearity checks and always reacted quickly to pressure changes. Cells 2 and 3 had recently been changed.


Cell 1

Date Linearity check Lim check
13/2/13 10.8/50mV 1.6

26/3/13 10.8/50 1.6

17/4/13 10.4/49.2 1.7

25/4/13 10.6/49.7 1.6

11/5/13 10.6/49.7 1.6

20/5/13 10.6/50 1.6

30/5/13 10.6/49.5 (last time calibrated) 1.6

19/6/13 1.6

23/6/13 Dive 1 in shallow lake, cell showing signs of slightly lagging other two but could maintain set point of 1.3 , but dropped set point to 1.0 as a precaution. Dil flush lowered all readings as expected but cell 1 remained slightly lower. Dive 2 kept to shallow check dive, blasted 02 at it at 6m, limited to 1.35 and voted out by other two cells.


The conclusion here for this cell is that even though it has performed faultlessly for its life in the unit, it failed relatively pretty quickly even though the session before today gave the expected reading. Regular monitoring showed the only indication that something was changing when it became clear that cell 1 was starting to lag the other two by a set point reading regularly of 0.02 less during the dive, which was unusual behaviour compared to how it had performed. It couldhave been somethng else causing the lag, but in this case I suspected it was due to becoming limited. No new lessons learnt, just a reminder to remain familiar with cell behaviour, query any variation and test regularly.

[notdeadyet]

Yep, that pretty much matches my experience. Nice happy cells, then when they fail they fail fast.

[graham_hk]

I am not sure I understand your numbers ... 10.x in air and then ~50mV at 1.6 ?

[Major Clanger]

I am not sure I understand your numbers ... 10.x in air and then ~50mV at 1.6 ?

The mV outputs are the linearity check results during calibration and the 1.6 etc, the current limit check result in water. Format shown on here, not as I entered it in table form spaced out with headings.

HTH's

[Major Clanger]

Yep, that pretty much matches my experience. Nice happy cells, then when they fail they fail fast.

I think if I take away anything from the quick failure, it's to blip the O2 a bit more often during a dive when using older cells.

[WFO]

also worth a watch

https://www.youtube.com/watch?v=HlGM1wFVjAY

RF3.0, cells presentation Dr Arne Sieber

[Diving Pete]

How long did you have the cell actually in use... I thought they are surposed to be changed at max 18 months.

If yours lasted 19 months - thats a good un.. & to be fair you must have been expecting it to fail ....

I change mine normally between 12-18 months & because I run 4 cells I've never had to end a dive due to one failing yet...(since 2004)...:

[Major Clanger]

How long did you have the cell actually in use... I thought they are surposed to be changed at max 18 months.

If yours lasted 19 months - thats a good un.. & to be fair you must have been expecting it to fail ....

I change mine normally between 12-18 months & because I run 4 cells I've never had to end a dive due to one failing yet...(since 2004)...:

Kept it in a bit longer than usual as I was hoping to see its failure characteristics and had no heavy dives planned. I'm now looking to rotate each after 12 months use.

[JPTaylor]

I change mine normally between 12-18 months & because I run 4 cells I've never had to end a dive due to one failing yet...(since 2004)...:

Why would you end a dive if one failed?

You have three, if other 2 OK, press on..... well i do