new cell issue

[idiot fish]

Hi List,

Although the official word (from the manufacturer) isn't in yet - Thought it best to inform everyone that there may be a new way these things can kill us.

Brand new unit - new cells, first few dives were short shallow shore dives to familiarise myself before venturing deeper or longer.

After a few weeks (say 20 dives) I slowly started venturing longer and deeper. This is when the problem started to show.


At the start of the dive, calibration fine, able to hold reading of 1.0 for more than the 45mins dry linearity test. Descending to 6m, stop and check PO2 after O2 flush, PO2 reads 1.6 - no problem.

Off I go, 35 mins later I see the PO2 is rising on cell 3, when it reaches 1.45 set point was 1.3) I stop and do a dil flush, this shows that cell 3 is the correct one and cell 1 and cell 2 are wrong (as in feeding me with too high PO2)


I selected a lower setpoint and turned the dive monitoring the handsets.

After checking everything and carefully drying the cells etc etc and 'carefully' taking the unit down probably another 10 dives - each time the same.


Cells 1 and 2 were actually loosing output gradually throughout the dive. At the beginning - no problem, but they would drop almost linearly through the dives.


I have since changed the 2 offending cells for new ones and its perfect all three match and there is no time dependant drop.

So what we appear to have is new type of cell error that results in a loss of output with time (over a 30-40 min period) the same cells if left resting on a dive boat between dives start off the next dive working fine?!

After talking to the manufacturer they admit that it could be the temperature compensation board that is causing the problem - as in the dive time lengthens the hotter it gets. It may not we correcting for the temperature correctly.


The manufacturer have the cells now and are investigating. So the word isn't official yet - but I thought best to be safe and ask everyone not to assume just because the cells are ok at the start of a dive that they will not loose linearity during the dive.

I now do a number of dil flushes during a prolonged dive at regular intervals.


What do you suppose would have happened to me if cell three had been from the same batch? Chances are I wouldn't be here now as I would have had no

By the way - this is another very good reason to mix and match your cells age from different batches.


Safe diving

 

[madmole]

Not new at all, a well documented failure mode called current limiting exacerbated by the fact that the Inspiration drives the cells too hard (6 times the spec current for the cells)

Thats why they are fine at the begining of a dive and decay slowly with time. This has been noted by nearly every VR3 owner out their who see's the PO2 creep up slowly while the dive progresses. Its all to do with ion exchange in the electrolyte

Give em half hour between dives in air and they will all drop back in sync and look fine again

This is why the 6m 1.6 bar flush is so important at the END of the dive

Its also one of the main reasons I've gone to the Hammerhead (Current drain is 1/10th the Inspirations). Its also why you should change cells at 12 month intervals and not the 18 the manufacturer specs (and certainly not use them till they fail like some do!!!)

Full explanation and details in the cells section of my site

 

[idiot fish]

Hi Mole,


What is mentioned (and was taught about on the course) was 'current limiting', but that was described as a reducing ability to reach a high po2, which manifests itself over an extended period of time (months). What I experienced was an ability to reach a high PO2 but then a reduction during the period of the dive.

Nowhere in my training or in the manual does it mention that the cells can drop during a dive, and be fine again for the next calibration/dry linearity test.

The manual and training does talk about a linearity check (dry test at 1.0 bar) but both the manual and the training do not inform that this test is ONLY relevant if you are diving at lower set points that 1.0bar.

What is needed is to inform people that they should do a linearity test (45 mins at setpoint) at a higher po2 than the set point they will use.

Stopping at 6m on the way down wont help - as like mine - that would not show any problem. Checking at 6m at the end of the dive will show if there is a reduction during the dive, but that may be too late by then! !
:wacko:

 

[idiot fish]

My buddy recently had an undeserved O2 hit. Same reason - faulty cells


Predive checks his cells past every published test prior to the dive (and after) including linearity and current limiting tests. He could get a display reading of 1.6 at 6m prior to the dive.


Then on a wreck dive with some penetration my buddy had an O2 hit. Luckily he had it at 38m and we were out of the wreck and it was a mild one.

His cells like mine were all new as is his unit. Like my problem before he had same case of cells dropping during the dive (but tested ok prior to dive at 6m, po2 1.6 and not current limited

In his case all three of his cells were duff so unlike my incident he had no warning before his hit. His displays showed 1.3 right up to his hit. He flushed the unit will dil, recovered and we ascended without further incident.

After the dive his cells were all reading ok again and able to reach 1.6 at 6m.

He never noticed the dropping before as this was a longer dive and like mine before the cells are dropping after around 30mins of bottom time.

I wonder if there is a bad batch out there manufactured around March 2003. (C3)

I would recommend during any dive occasionally and momentarily manually pushing the po2 above set point to check sensors are not dropping before we get another fatality.

 

[madmole]

What were the symptoms on the dive?

Were the cells tested on the way back up?
Was a diluent flush done to verify the cells readings?

A good reason for not having 3 cells of all the same age fitted and for having a 4th cell (ie VR3) as a sanity check

 

[idiot fish]

He had an electric shock wave going down from his head to his feet and decribed the whole sensation as being very weird.

His sensors behaved the same as mine had:- a dill flush at the time showed that his readings were lower than they should have been.

After a surface interval sensors were fine again.

I now always wear a FFM and dont think Id ever feel comfortable diving CCR without one.

 

[BigJetDriver]

idiot fish once bubbled...
He had an electric shock wave going down from his head to his feet and decribed the whole sensation as being very weird.

I now always wear a FFM and dont think Id ever feel comfortable diving CCR without one.

Too close for comfort in both cases! Diver Mole is, of course, right when he says: "A good reason for not having 3 cells of all the same age fitted and for having a 4th cell (ie VR3) as a sanity check."

P.S.---I do like my Widolf FFM. The comfort factor, both physical and mental, is amazing!