Cell replacement policy.

Mdemon

I bet 5p you work in IT.

prharris

It made sense to me, but then I used to

RichClark

Close... my field is related.

Damn, I'd never realised how my work and the people I work with effect your language and terminology.

Feel free to paypal the 5p to smug_git@notquiteanITjob.com

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Drmike

wasnt going to mention this (again) as i bring it up everytime this subject is mentioned but seeing as you opened the door...

I and a buddy years ago had all 3 cells in our units non linear temp compensation (that was the only conclusion we could come to

So this was a BATCH issue with all 3 cells. My buddy had a tox (mild)

pre and post dives cells calibrated fine and worked fine. start of dive they worked fine but as dive continued the ppo2 wouild drift even though displays still read 1.3 1.3 1.3

Deadly

Nobody wants to hear this - so Im sure they wont

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Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

dave t

I can hear you Mike and I agree that used to happen quite a lot, as far as I know it was one of the areas that AP worked with teledyne to improve. There used to be this old chestnut about the differebce between r22d's and r22buds I think that stemmed from the fact that teledyne changed the temp compensation circuit and it was done in the ones badged BUD first before it spread to the r22's, at least that is what I was told. This is another example of the comment I made about cells not being built for the job they do for us.

As a matter of interest I always buy my cells from AP why! because they test every single one before they sell it to the diver. They dont always catch them all but the do weed out most of the weak ones. not that there should ever be any weak ones in the first place, but thats another matter

Dave

Drmike

My concern is that this proves there can be batch issues. Batch issues that (as in this case) might NOT show up by diver testing seeing as the cells worked fine on surface and at 6m. My buddy was lucky I think I must have a fairly high tolerance of high PPO2s. Someone else (should this or another batch issue happen again) might not be so lucky

this is why i am most against changing all 3 at once - testing (in this case) wouldnt/didnt highight the fault.

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

Steve

I mentioned it a few times here and on Dive Oz.

Mike is spot on. When Craig C and I did the analysis of Fred's unit we found all 3 cells were between 2 and 3 years old and severely current limited. They obviously just passed calibration (35mV on the Meg) but when we saw them the max we could get was 3mV in air. We didn't bother with a 100% O2 test as it was quite obvious they were shot.

The other factor in Fred's case was hearing loss. The old bugger was half deaf and couldn't hear a solenoid firing. This info is from his wife.

The cells were from the same batch but they were old so I cant see what it has to do with anything in this case. This isn't meant to say that there arent batch issues though. I had a horror run with Teledyne cells from the D6 and H6 batches. Lots failed in a few weeks.

Great guy and he is sadly missed by many.

I was taught 15 years ago that you replace cells after a year. The only 3 exceptions were;

1. if they don't reach 35mV when in 100% O2 and at sea level,
2. if your displays wont show 1.6 when you have 100% O2 in the loop at 6m or,
3. if you flood a unit.

These things mean the cells go in the bin. Stick to that and all will be OK

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Dutchy

Would you please share your reason for doing this? I'd argue that you have the chance of being confronted with some defect in such batch. Having cells from different batched IMHO increases the risk of having a problem with an individual cell but have less consequences...but then again you may have a reason that outweighs my risk spread (mitigation) strategy reason.

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prharris

Sorry Dave,
I missed this the first time around.

I did a dive on Le Poulmic (max 18m (ish and all was fine) at the end of the dive on the safety stop, one of my buddies dropped a knife without noticing.

I have been doing a lot of OW teaching on OC recently and just duck-dived from 6m to 12m without thinking, and it was after this that the cell was over reading, so I wondered if I'd managed to get water on the face.
I discounted this though, as on the Kiss, any water seems to gather in the base of the scrubber, in my experience and so figured the the knife-saving manoeuvre would have just soaked the bottom of the s'lime.

Back home, I stripped the unit and found no evidence of damage and things seemed OK.

The cell re-calibrated in O2 and as I'd not had a failure before, I left it in for the next dive - again on Le Poulmic (Girlfriend's DM mapping project ).

This time the cell was all over the place from the start of the dive, and even after was reading high in air.

I have just put a new cell in (Shearwater Cell #1, or the right-hand most cell as you look down onto the scrubber head) and all 3 cells are calibrating in O2 OK, them coming down to 0.21 - 0.23 in air.
I know that this is not a good test as 0.21 - 1.00 is not the range that we operate in, but do not have any method of running up to 1.6 at home, still I live in Plymouth 1/4 mile from the sea

One extra thing that I did notice was that as I disconnected the cells 1 at a time to identify which position on the Shearwater corresponded to which cell, although the voltage when disconnected went to 0.0, it did drift up again even with no cell attached, as I've seen this on some meters, I put it down to op-amp operation with no load on the i/p, maybe I should have shorted the inputs to confirm this.

r
Paul

dave t

thanks for the info Paul