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RE: [PSUBS-MAILIST] Hydrogen Build-up



Batteries produce MOST of their hydrogen during charging, but they do produce hydrogen gas while discharging and even while just sitting doing nothing. With most batteries we run across every day like car batteries, this isn't enough to worry about, but with larger batteries like those used in Psubs, it is significant enough to be a concern. 
 
Also, hydrogen gas is a small enough molecule that even though a pod may be air and water tight, it might not be hydrogen tight. For example, most check valves will prevent air and water from moving back up a hose, but will not prevent hydrogen gas from moving passed. If you batteries are inside your sub, that is bad. If they are outside, that is good as they will self vent. 
 
Switches and motors can produce sparks that can ignite hydrogen, but so can static electrical charges. Make sure your pod and batteries are grounded to a good earth ground.  


From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Dan H.
Sent: Wednesday, April 12, 2006 5:30 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Hydrogen Build-up

Steve,
 
I'm not a battery expert and wasn't going to respond to this thread but since your life may hang in the balance, I'll respond. :-)
 
Most of the hydrogen produced from batteries is produced on charging.  Some is produced on discharging, but not much.  No matter whether charging or discharging, there is always hydrogen present at the top of each cell within the battery and it oozes out. 
 
It's best to keep the batteries away from anything that could possible ignite it, or in a safe place incase they do go off.  That's one advantage of having them in a separate pod.  The other advantage is the room it frees up in the hull.  The disadvantages are, some method of venting while charging has to be provided for and a battery in a pod isn't as easily gotten to for service.  Also there are weight factors and the expense of a separate pressure pod etc. etc.
 
There are Hydrocaps available which absorb the hydrogen, and convert it to water I believe, but they have their flaws too.  I don't know of a scrubber for a battery pod, but it sounds plausible. 
 
My batteries are in pods, and don't have Hydrocaps but I have pod vent caps I open while charging.  The vents vent into the hull so I can charge while in the water but I must leave the sub hatch opened.  While in use, the vents are capped off with heavy pipe caps.  The end of each battery pod on my sub are made so an explosion will blow the pod end off, and hopefully not impact the hull.
 
One thing I've noticed is, I don't get a whiff of hydrogen when I open my pod vents after use and before charging.  So I assume what I was told about most of the hydrogen being produced during charging, and not while in use, is true. 
 
Damn I'm long winded, but hey, if it could save a life, I'll talk!  ;-) 
 
Take care, Dan H.
 
 
----- Original Message -----
Sent: Wednesday, April 12, 2006 4:51 AM
Subject: [PSUBS-MAILIST] Hydrogen Build-up

G-day all

 

From the material I have been reading and what I remember Hydrogen gas is formed in lead acid batteries when charging and dischrgeing. My understanding is that if you ventilate the battery compartment  with the atmosphere when running on the surface and the air in the pressure hull when submerged this can stop a BIG BANG!

 

Can anyone suggest the amount of Hydrogen as a % of the Subs atmosphere is required for an explosion to occour? Is there such a thing as a Hydrogen Scrubber? Is hydrogen produced more readerly when charging or discharging the batteries.

 

By contributing to this string the life you save could be mine<J

 

Regards

 

Steve P


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