APD cells

[Stephen McMullan]

The 3 new APD cells passed a dry dive in a Narked@90 cell checker with flying colours. They pretty much matched each other and my 21month old reliable Teledynes to within 0.01bar pp02 up to 2 bar. I'll test them in the wet tomorrow prob down to 63m ~ 2.5hr runtime all going well. One thing I did notice was that they seem quite loose fitting into the cell holder compared to the other brands including the Teledynes. Anyone noticed that?

[tonyf]

Hi Stephen

I think they are a better fit and tighten up at end of thread.

On the cell check, I think the mv is the one to watch out for.  When using the vision for cell the checker I dont think you see milivolts??  All three of my cells showed fine as a po2 reading to 2bar. The mv on one cell dropped to 7.  Even then I checked using mv. pressure , humidity and temp they were all good. I returned to AP for testing and all cell were replaced and fair play in one week.

Hands up I only saw the mv drop as I had a shearwater connected.  I would still be using the cells if not.  So maybe time to pull out the little fitting AP supply and check more often.

Hope the diving goes well for the weekend

Tony

[Stephen McMullan]

Hi Tony,

Yeah I could use the little doodah and voltmeter all right. However I normally spot cell millivolt outputs dropping over time by keeping an eye on the vision handset readings during calibration. As I'm sure you know the readings are related to the millivolt output of the cells just before the calibration factors are set. I can normally spot cell outputs declining over time like this.

Also I test whether a cell declines in the shorter term by putting in the pot, calibrating against 100% and then bringing the pressure up to 1.3-1.4 bar and letting it sit for 30mins+. If the cell checker gauge is reading 1.3-1.4bar and the vision handset is displaying less than this then the cell output is decreasing.

As I say I'm sure you know this but thats how I do it for info. Any other tips welcome.

S

[tonyf]

Hi Stephen

All good tests to spot voltage drop over time,  The new mv range is 9-12 and in fairness I think one if not all my cells were below this or on the edge from new.  So for me I will now log exact mv from new. Really should have been doing this anyway.  Although all seems fine when using unit, if my cells are below spec within a year I want new ones   too bloody expensive



Roll on the weekend

[Andy]

Just got a message that my cells are ready and waiting for me.  Hopefully have them in time for next weekend when I'll test them (one at a time).  My cell 3 is running slow behind the others so I'll pop that out and stick in a new one and see how it reacts and lines up with the two good cells.

Andy

[soheil]

So no excuse not to dive the curasoa next weekend Andy !

[Andy]

So no excuse not to dive the curasoa next weekend Andy !

Rez,

I've a far better excuse not to dive that wreck - the depth terrifies me .  We might try for the Amazon though!

Andy

[baza]

A sat phone would also help VHF coverage 55miles offshore can't be relied on.

[Peter McCamley]

http://www.globaltelesat.co.uk/satphone/Satellite_Phone_Terminal_Rentals.html?gclid=COG5_rP9t6sCFeomtAod5CxqeA

[Andy]

New Cells 

[soheil]

Here we come curasoa , Andy I take care of sat phone but my  lift bag isn't big enough to lift the Bell of  curasoa , see if  Baza got one for the job?

[Stephen McMullan]

Current limited cell :-

[baza]

Nice example... Good to see you diving with that cell all weekend..

[Stephen McMullan]

The problem only showed up on the Sunday dive. Its a nasty one i.e. the max output of the cell corresponds to 1.6 p02 (***)

I'm diving CCR five years now with just over 250dives/hours completed. Not that long ago a cell warning like that at the start of the dive and I'd probably cut the dive short and figured out what was going on back on dry land. Definitely would have been the right thing to do if there was any doubt in my mind what was going on. As it was I was happy to continue the dive. I determined that cell 3 was kaput but cells 1 and 2 were working perfectly from the following:

- doing a cell check at 38m by switching to low setpoint and doing a couple of good dil flushes and noting the cell outputs and reaction rates. The Vision controller tells you what the cell outputs *should* be i.e. there is a menu option on the handset to display that. The objective was to make sure that I had at least two good cells reading accurately. If not then I would have abandoned the dive, possibly even open circuit given the shallow depth just to be sure.

- spiking the p02 up to 1.6+ to determine that I had at least two cells which were capable of accurately reading above the 1.3 setpoint. If not then I would have abandoned the dive, possibly even open circuit given the shallow depth just to be sure.

- last sanity check at 6m on deco doing a couple of good 02 flushes to again determine that I had at least two cells giving me the correct p02 during the dive and my decompression schedule was correct. A failure at this point and I would have extended the deco schedule using pure 02 rebreather.

(***) Note that when I tested the bad cell (3) in the narked@90 pot it was able to output the equivalent of 1.6 p02 max as shown in the picture. In the water this was not the case and I guess that was due to the ambient temperature i.e. 9-10degC. The cell warnings started occuring as soon as I reached the seabed and the temperature of the gas in the loop started to cool. The max output of the bad cell was more like 1.25bar and if another cell (bad) happened to agree with it then I would have been fed pure 02!!!

I reckon ambient temperature is why a lot of cells calibrate fine on the surface and then misbehave on the dive and then after the dive check out fine!!!

[tonyf]

Hey Stephen, I agree with the temperature but would say its and increase in moisture and temp that cause the problem not decrease.  When you test in the pot at room temp ( shed temp) this is lower as when in the water you have the heat from your lungs and the heating up of the lime.  The cells are just above the scrubber in the Inspo as you know.  Your rate of breathing also will have an effect on the heat of the scrubber.

I could be wrong  

See ya soon

Tony