Cell dating question
- Thread starter rddvet
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Hey dude..
Cells are cheap. Sure, the "don't use after" date may partially be a CYA thing, but there may be something that the manufacturer knows about how they make the cells that I don't, so I'd rather follow their recommendation.
I've definitely seen some weird things with cells. I had one AI cell that worked great up until 90 minutes, then would read basically 25mv low (~0.5PO2) for 30 minutes, then would wake back up at the two hour mark. It was repeatable every single dive, I let it ride for 5 or 6 dives while waiting for a replacement to come in the mail -- and that was a new cell that had this weirdness.
Because of some of those experiences, I'm a firm believer in rotating the cells in such a way that each cell is from a different lot number. Think about how frequently there's a recall on a particular lot of tainted food due to a processing problem, now imagine a batch of O2 cells that had a flaw in the manufacturing process -- they could all potentially "fail" in the same way. I don't want all three of my cells to be from the same batch for this reason.
Cells are cheap. Sure, the "don't use after" date may partially be a CYA thing, but there may be something that the manufacturer knows about how they make the cells that I don't, so I'd rather follow their recommendation.
I've definitely seen some weird things with cells. I had one AI cell that worked great up until 90 minutes, then would read basically 25mv low (~0.5PO2) for 30 minutes, then would wake back up at the two hour mark. It was repeatable every single dive, I let it ride for 5 or 6 dives while waiting for a replacement to come in the mail -- and that was a new cell that had this weirdness.
Because of some of those experiences, I'm a firm believer in rotating the cells in such a way that each cell is from a different lot number. Think about how frequently there's a recall on a particular lot of tainted food due to a processing problem, now imagine a batch of O2 cells that had a flaw in the manufacturing process -- they could all potentially "fail" in the same way. I don't want all three of my cells to be from the same batch for this reason.
Thanks, that experience was what I was looking for. I was hoping you may be one of the people that answered. We had a long discussion with our first instructor on cells, rotating, and different lots, and it was one of the things on our list to discuss with you in January as well. He was on the side of not rotating as he felt the bad lots was a carry over from issues in years past, and wasn't really a concern nowadays, especially with the higher turnover of cells from places like DGX. I can't remember which cell manufacturer it was that had some bad lot issues. He also said his viewpoint is slightly controvesial and was based on his personal experience, so what we eventually chose to do was up to us to decide. I've discussed it with a few people I trust and have gotten around a 50/50 breakdown on rotate vs not rotating. I appreciate hearing your personal experience. It'll still be on our list to talk about a little further in January.
The goofy cell I had was from AI and it was in the summer of 2018. Granted, it was an SF2 cell (this was while I was waiting for my Fathom to be made), but it was still made by AI.
My Fathom head currently has a cell with a May 2020 (from Charlie), a cell with a Jun 2020 (from Charlie), and a DGX branded JJ cell (also made by AI) with a Aug 2020 expiration date.
My Fathom head currently has a cell with a May 2020 (from Charlie), a cell with a Jun 2020 (from Charlie), and a DGX branded JJ cell (also made by AI) with a Aug 2020 expiration date.
BTW, I have photos of the SPG, just sent them through FB messenger. You can put the gauge under inner tube bands to help hold it tight.
Thanks. Are the cells' expiration date based on 1 year from when you put them in or is it based on the manufacturer's "don't use after date? I'll look for the photos. I threw a button gauge on the regs because I had a couple lying around. I'll see how I like that and then will try the real spg.
Tassi Devil Diver
Contributor
Have a read of http://www.revo-rebreathers.com/wp-...ygen-Sensors-part-II_the-complete-picture.pdf and http://www.revo-rebreathers.com/wp-content/uploads/2016/02/Understanding_oxygen_sensors.pdf
Lots of great info about cells in those docs
Lots of great info about cells in those docs
The JJ manual is very explicit now, it says maximum 12 months in use and maximum 15 months age. So keep it in the unopened bag for six months and you only get nine months use.
With stuff like this the failure rate will follow some curve. You want to specify the lifetime so people stop using them before a high chance of failure. Also there has to be a limit on how long the testing goes on. There will be some that last twice as long, but that doesn’t make using a given one beyond spec safe.
https://www.amazon.com/Oxygen-Measurement-Divers-John-Lamb-ebook/dp/B01LST45AW
This book is quite easy to read and discusses most oxygen cell failure modes and some reasons behind the expiration dates. Written by the founder of Vandagraph.
This book is quite easy to read and discusses most oxygen cell failure modes and some reasons behind the expiration dates. Written by the founder of Vandagraph.
^this
Cell failure isn't always a predictable, linear thing based solely on dates. You can have weird cell responses within the use-by date range, but the manufacturer specifies a date to draw a line through the bell curve, minimizing the chance of a significant failure during use.
Think about the term "CYA" - often used as a pejorative. What would they be covering for, if there was zero risk of using a cell after it's use-by date? So the manufacturer must have some reason for setting that date. If they really just wanted to totally "cover" themselves, they could use a South Park style disclaimer.
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