[PSUBS-MAILIST] Power sources

Fri Jun 2 09:07:56 EDT 2023

 My experience is that most Psubbers continue to use AGM but are exploring the possibility of switching to LiFePO4.  I know a while back Hank Pronk posted that he had switched to LiFePO4 for the E3000.
For the R400 which is currently being fabricated, I have switched to LiFePO4.  specifically, https://vestwoods.store/products/vestwoods-smart-12v-100ah-lifepo4-lithium-rechargeable-battery-bluetooth-monitoring-app-soc-data-4500-cycles-1-28kwh-100a-bms-low-temp-cut-off-ip65-replacement-for-rv-solar-marine-golf-cart.  I will use 12 of these modules.
While most psubs need a lot of lead ballast to submerge, having a lighter battery (also higher energy density) does not help in that you would just have to add more lead ballast to compensate for the loss of AGM battery weight.  One of the reasons I switched for the R400 was increased CB-CG spread over AGM which makes a small boat more stable.  In other words, I still have to add ballast, but I can place the ballast lower in the boat due to higher density of lead.  This battery has a lot of nice features including a group 27 form factor, 40% of weight of same capacity group 27 AGM battery. Also, the prices have really come down on these LiFePO4 batteries with lots of different suppliers, most out of China.  For the R400, I am configuring each battery pod as 3S2P at a nominal voltage of 36V.  While LiFePO4 have a much better safety record on fires due to their battery chemistry and smart chargers that keep you from overcharging, if I do get a fire in one of the pods, it's self-contained.  Also, the pods cap would just unseat to vent pressure.  I have three of these in my shop and I am playing with them.  So far so good.  One of the nice features on this battery is that it set up for Bluetooth Low Energy (BLE).  I am currently trying to hack the battery so that I can get my PLC to talk to each battery in the bank and get details such as SOC, voltage, temperature etc.  They do provide an iPhone/Android app that lets you interrogate each battery.  
So LiFePO4 for psubs is an experiment for me.  I will let you know how it works out when I get the boat operational.  I also would be interested in others experience with lithium batteries.
Cliff

    On Thursday, June 1, 2023 at 09:30:23 PM CDT, John Bussard via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Reading Busby and his discussion on the pros and cons of the battery types available at time of publication:

Is there sufficient data as folks move forward in new sub designs re: newer battery types- Specifically Li ion?  
I’m guessing that given the safety hazards there aren’t sufficient advantages to using- lead acid batteries seem to serve the majority of desired profiles.

Is this something that’s changing, or do folks expect to continue using old school batteries?  

Thanks for thoughts and history,
John
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