Re: [PSUBS-MAILIST] Batteries Bank

Based on the experience with my boat, I think AGM's are the way to go. If I built a new boat, I would use these. As a point of comparison, I can give you my experience with AGM batteries for a psub application.

I purchased 10 Lifeline Gp-2700T batteries about five years ago. These are 12V batteries rated at 100Ahr. They weigh 63lbs each. I operate my battery bank at 120 VDC. During the build phase of the boat, these were periodically top off with a dedicated 120 VDC battery charger that was setup for these particular batteries. Over the years, I have recharged these approximately 250 times. The initial cost of the batteries was $160 and the current cost is about $280 each. Over the five years, I have never, not one time smelled any off gassing during a charge cycle. I have never had any leaked battery fluid. I had to replace one of the batteries because I dropped it while removing it and riped a hole in the side. Even then, it still did not leak. Now that I am in an operational mode on the boat, I noticed that the battery life was not as long as when they were new. To analyze this, I built a poor mans battery tester which consisted of a 1200 Watt inverter that was connected to a bank of incandescent light bulbs with a light dimmer switch so that I could adjust load. I tested each of the 10 batteries against a 10 amp load and compared how long it took for them to drop below 11 volts. Compared to the data published by the manufacturer, these batteries tested between 40 and 70% of their initial capacity. The bottom line is it is time to replace the battery bank.

To me, one of the major arguments for using lithium batteries is they have a better power density (power to weight ratio). While this is important for a car, to me it is not as important for a psub as most of the time, we have to add ballast anyway to submerge. So using a less expensive battery that provides both power a ballast makes more sense to me. While they are inexpensive, conventional lead-acid car batteries leak acid and off gas while charging. As such, to me a good compromise is AGM.

Cliff

Cliff Redus
Redus Engineering
USA Office: 830-663-6445
USA mobile: 830-931-1280
cliffordredus@sbcglobal.com

From: Jon Wallace <jonw@psubs.org>
To: personal_submersibles@psubs.org
Sent: Sun, October 3, 2010 9:22:22 AM
Subject: Re: [PSUBS-MAILIST] Batteries Bank

The electrical requirements to fulfill the operating parameters of cars and subs are different enough I think, that the greater reserve capacity of Lithium is not enough to justify the added expense. It would be interesting to hear how many psubbers have found that lead/acid does not adequately serve their needs and would move to lithium if they could. Some time ago (in a different lead vs (?) battery discussion) Phil Nuytten advised that from his experience lead/acid provided the best "bang for the buck" for home-builders. The US Battery Rep that we had as a guest in July talked about all battery types and seemed to confirm that for all its supposed weaknesses, the good ole lead/acid battery was the way to go. That was my impression at least.

Jon

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