Hammerhead and high output cells vs low output

lizardland

Hi all,

two questions in one:

(1) is there any advantage in running high output cells? I don't have an analog secondary so don't need the higher output, I've got a Juergensen horseshoe board so not restricted to Winchester connectors

(2) can the Hammerhead be easily converted to run on low output cells? Is this doable myself or does it need to be returned to Kevin?

Cheers,

Stuart

O.C.Diver

Stuart,

Here is a partial answer. Not sure which wrist units you have, but the wrist units in most HH applications (HH, Optima, Revo, etc.) require 6+ millivolts in air to calibrate and I believe 40+ millivolts in 100% O2 to calibrate. The specs on an Tel. R22D have a factory minimum of 5? millivolts in air. As a result you can have a cell that is within factory spec but won't calibrate. AI equivalent has a minimum of 8 millivolts in air so the factory minimum is higher than the HH minimum. Not sure if these were the cells you were considering, but I believe the 6 millivolt applies to all HH handsets. As always, best to PM Kevin.

Ted

cys

Hi Stuart,

I'll take a stab at answering.

In my experiences with the R-10DS cells (which I guess are worth nought given the recent turn of events ) I don't see there being any advantage to high output cells.

I guess it'll run on either cell type without any need for modification. I transplanted my Delrin HH handset from my KISS where I used low output cells to my mk15 where I am using R-10DS cells without any mods to it.

Chris

Skipbreather

Read this.

Remember.

A good friend of mine DIED.

He died in part because he used R10D sensors w/ Hammerhead handset in direct contravention to the Hammerhead user manual, which CLEARLY states it is designed for 13 mv sensors.

Above ALL else, this site endeavors to keep CCR divers ALIVE.

Learn & help other CCR divers to live as well.

sannerman

My limited experience with HO cells is that they last longer then "normal" cells.
I put new cells in my MK15 when i bought it (2007-10) and have only changed one cell since, and my subjective feeling is that they are much more stable then normal cells. It´s weary seldom I need to adjust the PO2 setting when I calibrate.

/Z

lizardland

Hi,

sorry to hear about your friend but my HH unit is designed for high output cells. Kevin gave me the choice when he built it, I stuck with HO's because I already had new(ish) cells and didn't want to have to replace them. From the conversation with Kevin it's just the difference of a resistor on the board, I was just wondering if it's hackable myself or if I have to return it to the Grand Wizard :D himself.

Interesting. I'd been thinking for a while about getting my HH converted due to HO cells not being readily available here (unlike R22D's), the recent change in Teledyne's policy is making me wonder if now is the the time to do it.

Cheers,

Stuart

jradomski

Ted,
The last official specs for a R22d was 10mv -2.5 /+3mv meaning 7.5-13mv in air at SEA level

the HH requires 40mv at sea level meaning that if the HH measuring was dead on it would require a cell that measured 8.39mv in air.. but a cell with this value (in air with a linear cell) could still refuse to calibrate as the HH voltage is not a calibrated voltage measurement, and it might see the voltage as lower... You can clearly see this as the sec and promary usually have some variation in voltage measurement of the cells (not the po2, which IS calibrated)

The HH does not currently have an upper limit with regards to a call in o2.. Using a high output cell whose voltage is way down would trick the HH into thinking the cell is ok but isnt since the required mins would be met..

The HH without any divider network would still function properly and read proper po2 even on a high output cell up to a point..



The max cell voltage that can be measured is about 156mv (I'm not going to get into calculating this)

if a cell puts out 40mv in o2 (~8.4mv in air), then that cells max po2 would be 3.9 (in reality this is less because of setting the offset, but this is the theoritical max)

now lets take a cell with a nominal 20mv in air (95.4mv in o2), that max the max theoritical po2 1.64 (again probably less in practice!)

This is where a voltage divider is needed to adjust the scale as you would not want that a max available reading..

__________________
Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

Skipbreather

Hi Stuart-

You're correct, of course. HH Handsets designed for high output sensors do fine with them.

In my friend's case, he bought overhauled HH handsets meant for an Inspiration and patched them into a rig using R10Ds. The limitation Joe cited existed, and it at least appears a very high ppO2 condition developed. Kevin & I discussed the math and came up w/ a max readable ppO2 of about 1.15 to 1.20.

The take away here is that HH handsets are great, but must be used with the correct sensors for type.

Best,
Ken

deepwrecksc

I seem to have missed something here... what change? Are R10DS sensors no longer available for some reason??
Lee

cys

I'm sorry your friend died and I appreciate your contributions to this thread.

When I made the changes to my rig, I was in touch with Kevin. That said, modifying any rebreather is an experiment. Ultimately the implications and responsibility of the modifications fully reside with the person doing the modification. Never dive a rebreather where you have not observed all cells to be capable of outputting 1.6 ppO2. For my own part, I found one of my cells would not output a ppO2 of 1.6 2 weeks ago, and had stopped diving my mk15 until I got the situation sorted.