Question about Cells life

bazSXD

bazSXD

Member
Okay ... it may seem daft but does anybody know the answers to these few simple cell questions:

When does a cell's life start counting down ??? From date of being made or from the date of install/use in the unit ??? Based on Martin Parker's view its from the date on the cell. This makes retailing cells very hard, would you buy a two month plus old cell ??? Aren't they sealed in the air tight bag ??? Do they degrade even when not in O2 ???

Does the usage of the cell work on time in the unit or miles on the clock??Given the cell is always working but, say only does two dives a month (24 a year) does it die quicker or not??

The reason for these questions is that I can't find the answers in black and white anywhere. I have my views on this but I'm after the world wide view.

regards Baz
 
bazSXD said:
Okay ... it may seem daft but does anybody know the answers to these few simple cell questions:

When does a cell's life start counting down ??? From date of being made or from the date of install/use in the unit ??? Based on Martin Parker's view its from the date on the cell. This makes retailing cells very hard, would you buy a two month plus old cell ??? Aren't they sealed in the air tight bag ??? Do they degrade even when not in O2 ???

Does the usage of the cell work on time in the unit or miles on the clock??Given the cell is always working but, say only does two dives a month (24 a year) does it die quicker or not??

The reason for these questions is that I can't find the answers in black and white anywhere. I have my views on this but I'm after the world wide view.

regards Baz
Click to expand...

To quote a well known CCR manufacturer:

"If you store a new O2 cell in air, it will last about 12 months. If you store a new O2 cell in nitrogen, it will last about 365 days. If you store a new O2 cell in a sealed bag, it will last about 52 weeks!"

In all seriousness, new cells start to degrade the minute they are manufactured. That said, there are certain things that can be tried to slow the death of the cell. It is important that the cell is not stored in high PO2 as that will cause the cell to die more quickly.

As far as retailing cells go, this is a very tricky issue as I can attest to from personal experience. At Dive Addicts, we try not to have any cells sit on the shelf longer than 60 days as consumers get fussy about the manufacturer date (and rightfully so, I might add!). The "just in time" inventory principle becomes very important with a consumable that starts dying the first day it is on the shelf and I wish I had a reasonable solution for you with regards to how to work around this, but unfortunately I don't. The only thing that has worked for us is to order small batches frequently so that we don't get stuck with inventory gone bad.

Good luck!

Kind regards,
Randy
 
Hi Randy .... yep that's exactly what we do ... six cells at a time. This is a pain but as you say customers get a bit touchy about cells older than two months.

regards Baz
 
Most manufacturers sell their cells packed in a Mylar bag to try to slow the degradation of the cell. But this only slows it a bit.

This is also why new cells must "wake up" when you open them from the manufacturer.
 
From "The Practice of Oxygen Measurement For Divers" by John Lamb:

"The useful life of the cell depends upon the concentration of oxygen and temperature. If it is left inside the sealed gas barrier bag or original container at ambient temperature, its life expectancy should only deteriorate by 1/20 of its in-air life per year."
 
WFO said:
Does anyone still store them in inert gas or has that been proven ineffective?
Click to expand...
If they're sold in sealed bags with very little air, that air will soon become nitrogen as the O2 is consumed.

I've said elsewhere that I've tested JJ cells by connecting a voltmeter through the wall of the bag prior to opening it and found that there was little or no voltage at all. As soon as the bag was opened, the cells sprang into life.
 
Randy Thornton said:
To quote a well known CCR manufacturer:

"If you store a new O2 cell in air, it will last about 12 months. If you store a new O2 cell in nitrogen, it will last about 365 days. If you store a new O2 cell in a sealed bag, it will last about 52 weeks!"
Click to expand...



"Well known", but ... well.... <sigh>..... it's a casual comment that is over a decade old. Bottom line is that it's hardy a source that I would cite as a reference without people laughing at me. He wrote that with the benefit of a bit of informal observation and nothing else. I'd want a little more scientific answer than that, to be truthful.

Reading the cells thru the bag is an interesting data point, and one I always suspected was true. I dunno if anyone remembers the Pelican case I made years ago and documented that had a BC quick connect fitting on the side that allowed me to inert the interior with nitrogen for cell storage. It definately helped storage of cells. In the end I was just too lazy to use it though.

Guessing... cells sealed in the bag can be opened and put into service almost forever. That's from a very unscientific observational standpoint. In the "new age" of ISO and CE and all of that,... follow what the manufacturer of the cells suggests as best practice.

Cells are cheap. I can buy 3 cells for the average price of one divers fee to go on a dive boat for one day of wreck diving. I don't know why we don't change the damned things out every 6 months, to be perfectly honest.


Dave

.
 
Dave Sutton said:
"Well known", but ... well.... <sigh>..... it's a casual comment that is over a decade old. Bottom line is that it's hardy a source that I would cite as a reference without people laughing at me. He wrote that with the benefit of a bit of informal observation and nothing else. I'd want a little more scientific answer than that, to be truthful.
Click to expand...

Dave,

Thanks for pointing out the overly obvious! As both you and everyone else on the planet knows, this was meant as nothing more than a observation that regardless of what tactics we take to try and extend the life of cells, they have begun their eventual demise the minute they gave birth. Sure, you can try to be cute and eek every last breath out of a cell, but at what cost? IMHO, it is better to just rotate them out at a sensible interval, all the while testing and validating as you go to make sure that they are working as advertised.

Just my $.02

Regards,
Randy
 
bazSXD said:
Hi Randy .... yep that's exactly what we do ... six cells at a time. This is a pain but as you say customers get a bit touchy about cells older than two months.

regards Baz
Click to expand...

Jesus Baz, the last cell you sold me was six months old. That was the one Jamie delivered to me. Lets do a swap at Oztek hey?
 
Yesterday i went diving.

The night before i did all the usual tests and had something odd hapening on cell two. Cell 1 and 3 were running 47mv and were still in calibration from the my last dive in December. Cell 2 was reading great at 43mv but sudenly flickerd off then on again.

I striped the head back down on my JJ and disconected the cells to clean them

Cell 2 had snaped the brass/ / gold internal core of the cell and it was stuck inside the conector of the cable. It was a major PITA to get out with a tooth pick


I have never had this hapen before but its a good example of why not to calibrate over a problem.

ATB

Mark
 
Well the two cells I purchased 2weeks are over 6 months old..
I opened them left them to wake up for a few days... And calibrated... One won't go above 48mv on cal and the other a healthy 55.

On o2 testing, my old cell ( a year old)gets voted out before the other two can catch up to it at 1.6... They are slow to respond...

I struggle gettin the first cell above 1.7...

If Martin Parker's comment that any cell that can't read to 2.0 should be monitored carefully and replaced, should I replace this one?
 
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nickb said:
If they're sold in sealed bags with very little air, that air will soon become nitrogen as the O2 is consumed.

I've said elsewhere that I've tested JJ cells by connecting a voltmeter through the wall of the bag prior to opening it and found that there was little or no voltage at all. As soon as the bag was opened, the cells sprang into life.
Click to expand...

Nick how do you measure this voltage through the wall of the bag without piercing it, or do you make a tiny hole? I would like to test this six month old new cell that I got from Baz but don't want to open the bag till I need it or return it to Baz unopened.
 
nickb said:
From "The Practice of Oxygen Measurement For Divers" by John Lamb:

"The useful life of the cell depends upon the concentration of oxygen and temperature. If it is left inside the sealed gas barrier bag or original container at ambient temperature, its life expectancy should only deteriorate by 1/20 of its in-air life per year."
Click to expand...

Yes I read that recently too and the Author is the owner of Vandergraf, who make the JJ cells if I am putting two and two together. The books publish date is 1999 but I doubt much has changed in that time. I would be interested in testing the voltage of my bagged up new 6 month old cell.

I just keep mine in their bags and put that bag into a sealed container to keep it safe from impacts in the spares kit.
 
divingtactics said:
Nick how do you measure this voltage through the wall of the bag without piercing it, or do you make a tiny hole? I would like to test this six month old new cell that I got from Baz but don't want to open the bag till I need it or return it to Baz unopened.
Click to expand...
Sorry mate, you're gonna need to put a small hole in the bag to do this. I'm not using 'The Force'.
 
nickb said:
From "The Practice of Oxygen Measurement For Divers" by John Lamb:

"The useful life of the cell depends upon the concentration of oxygen and temperature. If it is left inside the sealed gas barrier bag or original container at ambient temperature, its life expectancy should only deteriorate by 1/20 of its in-air life per year."
Click to expand...

Just googled it and bought it. This was the cheapest source:
Vandagraph Books
 
Dave Sutton said:
"Well known", but ... well.... <sigh>..... it's a casual comment that is over a decade old.

Cells are cheap. I can buy 3 cells for the average price of one divers fee to go on a dive boat for one day of wreck diving. I don't know why we don't change the damned things out every 6 months, to be perfectly honest.
Click to expand...

Randy Thornton said:
Dave,
Thanks for pointing out the overly obvious!

Sure, you can try to be cute and eek every last breath out of a cell, but at what cost? IMHO, it is better to just rotate them out at a sensible interval, all the while testing and validating as you go to make sure that they are working as advertised.
Click to expand...

With the sniping you two could almost be mistaken for disagreeing with each other.
 
^^ cells are about the cheapest part of diving...


This discussion got me interested in a few things though, so this afternoon I did a little experiment just for grins.

Have a trio of cells that are 20 months old here, so I put them into the Meg, did a very careful head-only calibration, and the tossed the entire head into my hyperbaric chamber. Ran it down to about 160 feet in air, watching the PP02 and millivolts on the handsets. Settled in at about 1.6 or so (that was the target) and then left it there an hour to see if the cells might weaken after a time. Bottom line is that "these" particular cells tracked both in Millivolts and PP02 perfectly, and held that output for an hour. I'm wondering if this sort of longer test might not have some value... just scratching my head here.

Having a chamber big enough to put the entire head into is a handy thing... but a cell checker would have done the same thing.


Dave

.
 
Dave Sutton said:
I'm wondering if this sort of longer test might not have some value... just scratching my head here.
Click to expand...
Probably not - the variability between cells is just too high I think. I came from the 'you only need 2 good cells and a brain' school of cell replacement, so would routinely use cells for 18 months plus. I also would only ever change one cell at a time, generally on the survival of the fittest program.
(whichever cell is slowest to 1.6 gets culled first).
Some cells seemed to die reasonably quickly, one cell did close to two years in my rebreather, then another 3 years in my O2 analyser before I gave the analyser away to someone.
The cells in my Prism now would be between 18 months and 3 years old (I haven't dived it for 14 months before anyone gets upset!). The only thing I'd be prepared to bet on about their health is that the first cell to die WON'T be the oldest one. I know they all currently read to 1.0, as I chacked them a few weeks ago.

Mike
 
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