Join Date: Feb 2010
Location: Narragansett Bay
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Re: Realistic expectations for my house batteries
Welcome to the fight. Power management and tracking can be quite consuming, especially on a power hungry boat. Triple if your OCD about things like this.
A shunt and battery monitor are minimum ante into the game. You need to know how much draw you typically have, but you also need to know how much charge is going back in. Knowing how much charge is going back in may even be more important, because it's the only way to really know if you've properly topped up a flooded acid bank. You need to see how much acceptance amperage there is, not just count amps. Topping up increases longevity (is saves money) and maximizes capacity.
You are right, the rule of thumb is that one shouldn't use more than 50% of lead acid capacity, but capacity lowers as batteries age. It's hard to know what capacity really is after a few years. On the other hand, there is no law about that. It's simply considered the level that balances the number of useful charge cycles in the battery's lifetime against useable capacity. You can discharge to a lower State of Charge SOC, getting more useable capacity, but the batteries will die sooner. Vice versa, as well. Be light on their usage and they last longer, but of course, are less useful.
Balmar sells a Smartguage that is supposed to be able to determine SOC in a percentage, after it automatically "learns" you bank over a few cycles. I have one. It has allowed me to identify some real flaws in the OEM setup, which I've fixed. It also caused me to identify that I wasn't maintaining full charge, due to poor charge settings. I'm still not fully convinced it works, but I have to give it credit for causing me to debug. This will be my first season with both new wiring and charge settings, so I'll know over the next month or so, if I think it's SOC is accurate. Some swear by it.
Finally, 550 ah may not be enough for a power hungry boat. We only have 440ah and there is not way I can make it 24 hours with everything on...... ie cruising. I have to run the generator at some point. When I run this bank to it's demise, I'm upgrading to lithium. Twice the capacity in the same footprint and much more efficient charge profiles, without the need to top up to prevent decay.
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In the harsh marine environment, something is always in need of repair. Margaritas fix everything.
Last edited by Minnewaska; 04-08-2019 at 04:15 PM.