Re: [PSUBS-MAILIST] Battery pods - connected or isolated from the cabin?

Alec,

I concur with your thesis that the open external battery pods on the K-350 were for ventilation of hydrogen and oxygen from conventional lead acid batteries. Sealed AGM's are designed so that no oxygen is off-gassed and hydrogen diffuses through the plastic case at a very small level (1-3% of a lead-acid battery). I have recharged my AGM batteries which are located inside the pressure hull of my boat probably 30 times without any detectable trace of hydrogen. If you are planning on using AGMs exclusively in the external battery pods, I vote for closed pods as the off-gassing issue has been mitigated with the newer technology and this removes possible leak paths into the pressure hull.

Cliff

----- Original Message ----
From: "Smyth, Alec" <Alec.Smyth@compuware.com>
To: personal_submersibles@psubs.org
Sent: Monday, February 11, 2008 9:50:33 PM
Subject: [PSUBS-MAILIST] Battery pods - connected or isolated from the cabin?

Hi all,

I'm building my battery pods and wondered if I could pick your brains.

On the K-350, I believe the battery pods are mounted on pipes that go through the pressure hull, thereby connecting the pods to the cabin. They can be isolated with screw-on caps. I presume Kittredge's reason was to allow forced ventilation during charging. Also, Busby explains that if you use hydrocaps in a sealed pod, the caps can consume the little O2 available in the pod during discharge (i.e., a dive), at which point they would cease to work and start releasing hydrogen that can quickly reach an explosive concentration. One approach to prevent this was to add O2 to the pods before diving.

Kittredge was no doubt designing for lead-acid batteries. But these days with AGM batteries, I'm wondering if the same issues are still of concern, or whether I can just make the pods truly isolated. I suspect the latter, because I'm not aware of the pods on modern submersibles being piped to the cabin. Perhaps I'd have to remove the pod endcap on land to charge the batteries. If so I'd be unable to charge afloat, but frankly I don't envision doing that, because I don't care for leaving the boat in the water for extended periods. Over days, condensation really starts collecting inside.

I can see several safety advantages in keeping these spaces truly isolated. Any opinions?

Thanks,

Alec

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