Lazy cells: how much is too much?

Abbo

I have a recalcitrant cell that spends most of the time being voted out when I'm diving. Much of the time it is low by as much as 0.2. This has been the situation for the past 6+ hours of diving. In air, at room temperature and pressure, it still gives an output of 11.9mV. The poor thing gets locked in the can between dives on a dive weekend, because I fear someone going "is that a rebreather" and touching my toys if I leave the electrics open to dry out. Clearly that doesn't help. Is now the time for a mercy killing, or is it likely to recover if I treat it more kindly?

Doorduijn, Niels

My approach is that if you need to think about your cells, then replace them.

Rgs,
Niels

Stephane

Hello,

I guess your cell is current limitated. Do a calibration and you'll see if it can reach a PpO2 of 1bar.
What you can do also is to do a cell check on pure O2 at 6m at the beginning of the dive. In fact, you should always do this!

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Stéphane
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nigelh

It's not lazy it's stuffed.

If it doesn't want to come to the party send it home and find somebody else that will join in.

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nigelh

Abbo

Nope, the cells aren't current limited: I always check.

The cell is reading low and slow, which is a feature of a wet sensor. Meg cells face up, which surely makes it easier for water to collect on them? What you're saying is that even a good drying out is unlikely to save this cell from a mercy killing. Fair enough, I suppose my life must be worth more than a sensor.

bendomatic

just from a different perspective....

are you sure it is the one that has something wrong with it? it's only getting voted out as its different to the other two. it's always possible that the other two are the ones misbehaving but because they're in company it appears that they're not faulty. while i would agree that its less probable its not impossible. i would check all cells.

also could it be a wiring fault - i'm not so familiar with that sort of thing though. i would try your other "good" cells in that spot and see if same problem.

rachel

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Mephisto26

Hey, is it Cell#2???

I would also keep the cell for the moment and simply change its position...

I personally always let the head dry and even take qtips to quickly wipe over the cell faces after every day diving...

cheers

almity1

Thanks Rachel, had trouble with a cell much the same as Abbo, did what you suggested, great to confirm things. I can safely say the issue is with the cell.

Abbo, had the same issue as you, made a decision to get a new cell. One is coming this week, this will teach me to keep a couple of spares.

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Gilles

At the start of bottom on any dive I'll use my offboard bailout to flush the loop and check what the cells are saying. I like to mix the offboard with PO2=1.4 in open water. To enable this, you need something like

http://www.rebreatherworld.com/bail-...tml#post136402

At the end of every dive, I flush O2 at 4-6m and check how the wet cells are doing. This is E2D with man-ad on ex_cl.

If there's a cell always getting voted out, then I won't do any exended range with it.

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Gilles
http://www.dirrebreather.com

Drmike

really? you do this when reaching the bottom on every dive? So you hit depth, turn off your O2, flush your loop several times with off board OC gas then when finished you have a loop PPO2 of 1.4...you then? ...flush with dil again to bring it back to setpoint/get correct loop gas?....and not forgetting to turn your o2 back on .....Id be concerned that ;

a) you need to be sure what He/N2 mix is in your loop from a deco perspective so you would need to do another good flush of dil to get rid of baik gas and get loop gas back to what it should be He/N2 %
b) your p1ssing away a LOT of gas on deep dives
c) time consuming
d) requires turning off of o2

Personaly I dont think its a very sensible protocal for above reasons plus it only verifies to 1.4 (cells may be limited to 1.4 which is not far off setpoint) its reliant on you doing 2 very good flushes (that isnt easy or fast when your on the loop and can use up a lot of dil at depth), and requires turning off your O2 and blowing some of your oc bail gas (again on a deep dive, more)

Just spiking ppo2 to 1.6 or higher momentarily on descent will give you a larger safety factor as it proves cells arent limited to a higher degree (1.6 or higher instead of 1.4) If you have done surface cal to 1.0 and proved on descent cells arent current limited to say 1.6 then you have plenty of assurance everything is cool imo

Cells shouldnt be getting wet - i notice the meg is as bad as the inspo in this respect.

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