Forth Cell in the head

[Adrian Kelland]

Know nothing question here;

Is consensus 3 out of 3, or 2 out of 3? I would say 3/3 as 2 could be wrong, but what is really done? 3 wrong must be really unluck or poor maintenance?

Adrian

[Mdemon]

Originally Posted by NotDeadYet

For good cable glands try Rapid Electronics, I got some from them which are rated to 150m. Only about £1 each. If you f**k it up, Plumber's epoxy is good for sealing the hole up, I did this on my Ray scrubber.

Got a part number? Couldn't find them...

Is it these beasties? "Index nylon cable glands"

[MartinS]

Mark/Anyone else who's interested

This is the inf I have been sent re: your question.

On no account should this be done unless the unit is at least 12 months old. This would invalidate the guarantee and cause problems at the factory.

The drilling should only be done in a pillar drill with a pilot hole drilled first. This ensures a perfectly square hole. The spec can be found on the Fischer web site http://www.fischerconnectors.com

The plug is a 103 series sealed front projecting recepticle IP86 rated.

The cable from plug to cell is availablle from AP, and then you need to be a dab hand with the soldering iron!!!

The link cable has to be made up to spec with waterproof shielded cable 2 core and the designation for waterproof cable is HOF*RN the * is a number that denotes the size..Don’t quote me on this but I use 4 core microphone cable!!!

The cell connection through the cable is trial and error to get the polarity right, and the fischer plugs are a bitch to assemble.

The plug fitting into the head needs to be Tapped with a M14x1 tap. Then screwed in, locked with the locking nut, and then set in glue, I used, Locktite universal adhesive... BUT I did not tap the hole.

HTH
Martin

[Mark Chase]

Originally Posted by nigelH

Probably impedance matching. The cell wants to see 10K hence I think both the VR3 and the Turtle provide that. Actually the cell can run into less (very low internal impedance) so parallelling up another probably wouldn't make much odds but....
I fancied taking all three, through their own 100K resistors out to a socket I could put my own electronics into. I can't see the worth in adding a fourth cell to the equation - if things start going wrong I've lost my consensus so I don't know who to trust so I'm outa-dare asap.

nigelH

Fourth cell for me, is mainly for tracking PP02 for real dive decompression data on the VR3. It is obviously handy in the event of a total electronics failure on the YBOD but that’s not very likely unless you flood the head in which case it’s a total chocolate teapot having a fourth cell


ATB

Mark Chase

[NotDeadYet]

Originally Posted by Mdemon

Got a part number? Couldn't find them...

Is it these beasties? "Index nylon cable glands"

That's the one. It shouldn't really need a deep rated gland as the inside should be at ambient pressure, all you need is it to be gas/water tight, not pressure tight.

[Pierre Farrugia]

Hello all,

Are you talking about this http://www.therebreathersite.nl/fitt...ourth_cell.htm

Regards

Pierre Farrugia

[MartinS]

Pierre

I think that's exactly what is being discussed - well done that man!

Regards, and dive safe

Martin

[nigelH]

Originally Posted by Mark Chase

Fourth cell for me, is mainly for tracking PP02 for real dive decompression data on the VR3.

I have a problem with that.
I watch three cells that I calibrated and know the history of drift slowly apart over a long dive and then a fourth cell in a totally different thermal enviroment (the temperature compensation is at the back of the cell) is to be trusted to calculate the deco periods?
Nope. The voting logic controls the ppO2 very well so the schedule is based on that not some arbitary other cell.
Even fitting it inside the head doesn't do it for me as much as I like the idea of squeezing four cells round the outlet.

I know I'm in a minority here.

nigelH

[Brass Monkey]

Originally Posted by nigelH

I have a problem with that.
I watch three cells that I calibrated and know the history of drift slowly apart over a long dive and then a fourth cell in a totally different thermal enviroment (the temperature compensation is at the back of the cell) is to be trusted to calculate the deco periods?
Nope. The voting logic controls the ppO2 very well so the schedule is based on that not some arbitary other cell.
Even fitting it inside the head doesn't do it for me as much as I like the idea of squeezing four cells round the outlet.

I know I'm in a minority here.

nigelH

You may be in the minority Nigel but you have given me food for thought. I have been thinking of the fourth cell and squeezing it around the outlet. This is the first time I have heard anyone going against the fourth cell, your points have given me pause, now I'll wait to see how it all pans out before going down this road.


Dave.

[Rob Evans]

I've given the whole 4th cell thing a lot of thought over the last 3 years and really can't justify the aggravation. The Y-piece and its associated drift problems are more hassle than I want to deal with & if I'm going to go drilling holes in the lid it's got to be for a really bloody good reason. I did recently - HUD won, 4th cell not even in contention.