One cell slow to wake up. Your thoughts?

[doctormike]

I don't understand why cells that are exposed to air need to "wake up". Unless you are storing them in an anoxic environment the cells will already be "awake"

Except that cell #3 seems to be doing that. 10.6 / 10.6 / 9.0 in air on the build, then 10.6 / 10.6 / 10.6 when I pulled the head after the first dive.

 

[MegDiver792]

My cells when new measure 10.7 in air, and 50mv at 1.0.

 

[doctormike]

My cells when new measure 10.7 in air, and 50mv at 1.0.

So both of our cells are in spec, but yours are more linear than mine.

Not sure what to tell you. Maybe it's a JJ thing. But two years of diving and three different sets of cells, and I'm still getting that range of percentage off linearity.

Any thoughts about the original problem?

 

[MegDiver792]

Its a not a jj thing, its a cell thing. JJs read a cell same as any other rebreather on the planet. Your cell goes 9-40mv, thats 31mv to 1.0 PPO. My cells new are 10.7 - 50mv, thats 40MV. Thats almost 25% less range you have alone from .21 - 1.0. Your cell reads 40mv at 1.0, mine read 50, thats 20% less than a new cell.

Theres no such thing as cell "wake up", but there is such a thing as cell failure. One of the big symptoms for me is low output at 1.0, coupled with yours acting up, screams a cell issue.

Have you spiked that cell to 1.6 during a dive and verified its not voltage limited? (or current limited, depending on your religion)?

 

[doctormike]

Its a not a jj thing, its a cell thing. JJs read a cell same as any other rebreather on the planet.

No, calibration depends on how you test it, and that absolutely does vary from unit to unit. The JJ does calibration with an automated sequence that flushes the head with O2 with an open loop. Other units rely on manual operator flushes with three full gas exchanges. You can "tell" your rebreather that it is now at PO2 of 1.0, so whatever mV it is getting, it should assume that equals a PO2 of 1.0 in the loop. But you have no way of knowing how accurate that is. Rebreathers that depend on a manual flush or calibration kit or whatever may have different actual PO2 on the cell face.

Your cell goes 9-40mv, thats 31mv to 1.0 PPO. My cells new are 10.7 - 50mv, thats 40MV. Thats almost 25% less range you have alone from .21 - 1.0. Your cell reads 40mv at 1.0, mine read 50, thats 20% less than a new cell.

I'm not sure what the significance of that derived metric is, but it sounds like you are saying that the 9-13 manufacturer spec shouldn't be used? I mean, if that's what you are saying, that's fine, but there is no point in having a spec range if you are going to say that anything at the low end is out of spec.

Theres no such thing as cell "wake up",

So how do you explain what I am seeing with cell #3? Seriously, I'm not being snarky, I'm trying to learn.

Have you spiked that cell to 1.6 during a dive and verified its not voltage limited?

Yes, of course...

 

[MegDiver792]

I've already told you multiple times, if you cant get it, you cant get it. PPO is PPO, cell voltage is cell voltage. Good luck.

 

[doctormike]

I've already told you multiple times, if you cant get it, you cant get it. PPO is PPO, cell voltage is cell voltage. Good luck.

Thanks

 

[rjack321]

I would toss #3.
40mv in O2 is way too low. 43mv is minimum spec for my cells that start in the 9-13 range. 93% of expected means its linearity is shot, get a new one.
9/0.209 = 43mV expected
40/43 = 0.93 % of expected

there's no such thing as needing a dive to wake up, it is out of spec and should be retired

 

[doctormike]

I would toss #3.
40mv in O2 is way too low. 43mv is minimum spec for my cells that start in the 9-13 range. 93% of expected means its linearity is shot, get a new one.
(9/0.209 = 43) 40/43 = 0.93

Sounds reasonable.

But still wondering what's up with the recovery phenomenon (I won't use the term "waking up" any more, since that seems to be considered a myth).

I'm also curious about that % off linearity guideline. I have about 35 sets of 3 cell calibration data, three different batches over 2 years. The vast majority of them come in 92%-96% of expected. What do you use as a maximum deviation from linearity?

 

[rjack321]

Sounds reasonable.

But still wondering what's up with the recovery phenomenon (I won't use the term "waking up" any more, since that seems to be considered a myth).

I'm also curious about that % off linearity guideline. I have about 35 sets of 3 cell calibration data, three different batches over 2 years. The vast majority of them come in 92%-96% of expected. What do you use as a maximum deviation from linearity?

I was taught 3% deviation from expected at 1.0

Which is going to get bigger once you get to ppO2 1.2-1.3

Your 8% deviation at 1.0 will be 20% larger at 1.2 (0.096 or almost 10%) A 10% deviation means your 1.2 is really 1.3. That is too much.

PS your cell quality is awful. You need a better supplier