One cell slow to wake up. Your thoughts?

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Now just think the probleb, that is you life or aborted dive worth saving 50€/$, when you have already 9000$ machine. Cos of time and gas to divesite is probably already over that. If you already think there might be problem, just fix it and don't wait it happen.

Just to be clear, I'm trying to understand something about calibration issues and the response of cells that are within spec. I'm not trying to save money by diving with faulty gear - sorry if you got that impression. Even with a new cell, I will still have the same questions.

Have written to Shearwater, will keep you posted.
 
Sounds to me like the automated calibration procedure is kinda meh, and a dodgy cell is compounding the problem. Assuming you're actually using 100% O2 and not some concentrator garbage or the like.

Cell "wake up" is a thing when you first take it out of the package, because they're stored in sealed bags full of inert gas. I leave mine for an hour then put it in my mini cell checker with O2 to get a baseline reading before installing them. That's really the only time that it should exhibit that sort of behavior. If it's exhibiting this type of behavior outside of the package, you've definitely got a dodgy cell.

Run all 3 in the cell checker to see what's going on without any of the electronics involved. It certainly sounds like the calibration procedure just assumes that you'll get a good purge, so when you have some lower FO2 gas "contaminating" your purged loop, it jacks your results up. Like has been pointed out, your numbers are out of scope. If your numbers are good in the cell checker, but they're not in the unit, then you've got a unit problem. If they're bad in the cell checker, then they're not gonna get better in the unit no matter how solid the unit is.

Personally I don't like automated calibration routines because they make assumptions that may or may not be true. Garbage in, garbage out type of thing. My Pelagian is literally two pots in the handset that you use to adjust the displayed PO2, just like the Analox units. It's about as dead simple and accurate as you can get. The SF2 has a cap that screws on one of the hose ports and blows O2 straight across the cells. You don't hit confirm until the values stabilize, and you can see the mV vales during calibration, so you can make sure your numbers are where they're supposed to be. It doesn't do anything with the solenoid, doesn't require complete purging, etc. It's got an LP port on the top of the cap so it provides positive pressure, making "contamination" a non-issue. I dunno if the JJ will let you do this, but it's worth looking at.

If you can find a decent way of calibrating with just the head disconnected from the rest of the body you'll use less gas, and you'll be able to control the variables a little bit easier. If you can find a Tupperware bowl that's the right diameter, they make great "head only" bottom halves. Couple that with some sort of cap with an inlet that lets you blow O2 straight to the cells and bypasses any automatic solution, you're more likely to get as accurate a calibration as reasonably possible.

Either way, you know you need a new cell, but it's worth doing a bunch of fiddling to see how it's behaving in difference scenarios.
 
Sounds to me like the automated calibration procedure is kinda meh, and a dodgy cell is compounding the problem. Assuming you're actually using 100% O2 and not some concentrator garbage or the like.

Cell "wake up" is a thing when you first take it out of the package, because they're stored in sealed bags full of inert gas. I leave mine for an hour then put it in my mini cell checker with O2 to get a baseline reading before installing them. That's really the only time that it should exhibit that sort of behavior. If it's exhibiting this type of behavior outside of the package, you've definitely got a dodgy cell.

Run all 3 in the cell checker to see what's going on without any of the electronics involved. It certainly sounds like the calibration procedure just assumes that you'll get a good purge, so when you have some lower FO2 gas "contaminating" your purged loop, it jacks your results up. Like has been pointed out, your numbers are out of scope. If your numbers are good in the cell checker, but they're not in the unit, then you've got a unit problem. If they're bad in the cell checker, then they're not gonna get better in the unit no matter how solid the unit is.

Personally I don't like automated calibration routines because they make assumptions that may or may not be true. Garbage in, garbage out type of thing. My Pelagian is literally two pots in the handset that you use to adjust the displayed PO2, just like the Analox units. It's about as dead simple and accurate as you can get. The SF2 has a cap that screws on one of the hose ports and blows O2 straight across the cells. You don't hit confirm until the values stabilize, and you can see the mV vales during calibration, so you can make sure your numbers are where they're supposed to be. It doesn't do anything with the solenoid, doesn't require complete purging, etc. It's got an LP port on the top of the cap so it provides positive pressure, making "contamination" a non-issue. I dunno if the JJ will let you do this, but it's worth looking at.

If you can find a decent way of calibrating with just the head disconnected from the rest of the body you'll use less gas, and you'll be able to control the variables a little bit easier. If you can find a Tupperware bowl that's the right diameter, they make great "head only" bottom halves. Couple that with some sort of cap with an inlet that lets you blow O2 straight to the cells and bypasses any automatic solution, you're more likely to get as accurate a calibration as reasonably possible.

Either way, you know you need a new cell, but it's worth doing a bunch of fiddling to see how it's behaving in difference scenarios.

Thanks! Super helpful, as usual. This is what I wanted to read, more than just being told to replace the cell.

I also suspect that auto calibration is an issue. It counts down until the mV stabilizes, but of course stable output doesn't guarantee 100% O2 on the cell face, it just means no change in whatever they are exposed to. On the other hand, JJ and Shearwater are known for good engineering, so I'm hopeful that it may just be something that I'm doing wrong, but I'm not sure what.

Will try the cell checker this weekend, but since it's the mini-checker it relies on the head electronics, it's not a stand alone unit.
 
I'll probably attend your funeral.
 
Will try the cell checker this weekend, but since it's the mini-checker it relies on the head electronics, it's not a stand alone unit.

Get this with the volt meter ends so that you can check values with a multimeter instead of going through the head. Should be the same type of cable, just no SMB. If you've got a corroded cable in the head, you're never gonna be able to test anything accurately because you'll just be validating your bad data.

Mini Check Cable and Cell Checker Cables
 
Get this with the volt meter ends so that you can check values with a multimeter instead of going through the head. Should be the same type of cable, just no SMB. If you've got a corroded cable in the head, you're never gonna be able to test anything accurately because you'll just be validating your bad data.

Mini Check Cable and Cell Checker Cables

Ordered. Thanks again.
 
It’s been alluded to a little bit here, but I would also question the cell cable and connection. I’ve had all sorts of weird readings (before, during, and after dives) on my Inspo when the cables start to corrode. In your case, that’s fixed by replacing the cable rather than a trip back to the factory (jealous of that). I suppose you could switch cell positions or run the mini-check with the voltmeter or Fischer lead to rule out the connector in the head, but I don’t think you’ll be able to differentiate between a cell and cable problem with the cells the JJ uses.

Either way, as many people have said here, the ultimate solution is a new cell. Questioning your equipment during a dive is never fun.

Jim
 
Quick follow up.

The next weekend, cell 3 returned to its original air output (lower than 1 and 2 but more firmly within spec range - 9.7 mV). Haven't been diving since all this happened, probably done for the season.

Got the multimeter cables and a multimeter. Cell output is sightly higher on the meter (10.8/10.8/10.0) than on the JJ controller (10.5/10.5/9.7). No issues with changing the connectors around, it's just cell 3 reading below the other two, not the contacts.

Did the cell checker run with the JJ, since it's a lot quicker to have all three mV readings simultaneously than to have to plug and unplug banana jacks three times for each pressure level. Also, one of the best new features in the latest Shearwater firmware update is that the mV screen stays on until you change it, as opposed to switching back to the standard display after a few seconds. Running the linearity check was a LOT faster this time than when I did it last year with the old firmware, constantly chasing the mV screen!

Below is the linearity check - all looks good, even the one reading low. If anything, that one is closer to linear than the other two with higher output. Will probably do yearly service and change all of the cells before dive season starts up again.

Thanks again for all of the input!

Screen Shot 2019-12-01 at 3.32.24 PM.png
 
https://www.shearwater.com/products/perdix-ai/

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