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One cell slow to wake up. Your thoughts?

Discussion in 'Rebreather Diving' started by doctormike, Nov 5, 2019.

  1. doctormike

    doctormike ScubaBoard Supporter Staff Member ScubaBoard Supporter

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    So you think that it's the cells? I'm really at a loss here.

    These are JJ Vandagraph cells, straight from the US JJ distributor in two cases (two different US distributors over the years). At one point I used AI cells from DiveGear Express, but they were very wonky and I replaced them. So this is why I was wondering how accurate the auto-calibrate system is in terms of getting a good 1.0 flush over the cells, since other units don't rely on that. Could it be that your stricter deviation requirements require a better calibration sequence?

    Any suggestions? This is not a one off. I have a lot of data over the years.

    Thanks for the help...
     
  2. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

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    92% of expected is way out of line to me. Mine are usually 98-99% of expected until they get >9months old then it drops to 96-97%.

    Do you have a Narked cell checker? I wonder if your loop is <99% O2 so your not reaching expected because expected is actually incorrect (i.e. if your loop is 96% O2 then getting 95% of expected "100%" mV is reasonable)
     
    JohnnyC, MegDiver792 and FreeFlyFreak like this.
  3. doctormike

    doctormike ScubaBoard Supporter Staff Member ScubaBoard Supporter

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    yeah, that was my point about the calibration sequence.... maybe will post in the JJ FB group.
     
  4. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

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    Corrosion on your wiring or contacts will also mess with your voltages. You need to check the cells independent of the RB if 95% of expected is "normal" for you.
     
    MegDiver792 likes this.
  5. doctormike

    doctormike ScubaBoard Supporter Staff Member ScubaBoard Supporter

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    the unit is very clean and this has been from the beginning, but that’s a good point. Will try the cell checker (although I have the mini checker which uses the rebreather head)
     
  6. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

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    Its a start, at least you'll be positive about the gas on the cell faces.
    I flush my mini checker at least 8 times, air seems to hide in the crevices
     
  7. wedivebc

    wedivebc CCR Instructor ScubaBoard Supporter

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    You likely have a bad cell or there is a bad connections. Waking up a cell is not a thing, unless it had been deprived of any oxygen for a period of time which even then the effect is minimal.
     
    cathal and rjack321 like this.
  8. wedivebc

    wedivebc CCR Instructor ScubaBoard Supporter

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    you need to discuss mv not PO2 since the calibration factor can also be called into question. A leak in the loop allowing air intrusion can throw off a calibration.
     
  9. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

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    I think there's air in there.

    My point was that an 8% mV deviation from expected mV at calibration leads to a 0.1 ppO2 error.
     
  10. cathal

    cathal Nassau Grouper

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    To the OP,
    While online debate about cell behaviour characteristics can be a worthwhile pastime, for long term sustainable safe rebreather operations keep things as simple as possible, in line with a couple of contributors to this thread if there’s a doubt about the cell and it’s under warranty then just replace it. No amount of online discussion will fix the cell or eradicate the doubt for you as it’s a mission critical component. You have a 3 cell unit, you need each cell to be operating correctly, one of them isn’t, replace it.
     
    rjack321 likes this.

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