Lithium Batteries Buyer's Guide—Part 3, Current (Amps) ...

If you are wondering if I suddenly became an illustrator or used AI to generate this, go with your instincts. It’s a long way from what a real human illustrator would be capable of, and I had to fix a bunch of mistakes, made by AI, in PhotoShop, using AI, and some remain, but it’s still a fun illustration.
If you are wondering if I suddenly became an illustrator or used AI to generate this, go with your instincts. It’s a long way from what a real human illustrator would be capable of, and I had to fix a bunch of mistakes, made by AI, in PhotoShop, using AI, and some remain, but it’s still a fun illustration. If you are wondering if I suddenly became an illustrator or used AI to generate this, go with your instincts. It’s a long way from what a real human illustrator would be capable of, and I had to fix a bunch of mistakes, made by AI, in PhotoShop, using AI, and some remain, but it’s still a fun illustration.

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Wow, figuring out how to put a lithium battery-based system together that will be functional for an offshore boat (not a camper van) and not break the bank, is even more complicated than I thought when I started this.

The good news is that we are getting a handle on it. So far we have covered:

Wait, it gets better. I’m confident that I can end this series with a reasonably simple checklist of buying criteria, although we will have to wade through at least two more in-depth chapters first, so I can link each checklist item to an explanation.

We need real understanding, not:

1. Cruiser looks at YouTube.
2. Cruiser installs unseamanlike system.
3. Cruiser maybe gets by, but knows it could have been better.

And the best news is that, at least as far as I can see at this point, doing it right won’t cost much more than doing it half-assed. Cost is about the DIY, or not, decision and/or bank size, more than the do it right or do it half-assed decision—analysis coming soon.

With all that out of the way, let’s dig into how much peak current (amps) we need our system to be able to supply. Oh, no one ever mentions that on YouTube?…Exactly…

With competitive price and timely delivery, OMMO sincerely hope to be your supplier and partner.

Additional resources:
How to Ace an Energy Management Interview

The Amps We Need

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First, let’s cover the minimum current capability that any BMS should have for us to consider it.

We all know that lithium batteries can supply huge amounts of current, and accept prodigious charging rates—think a Tesla with amazing acceleration that can be recharged in less than an hour—but that does not mean that the BMSs and batteries we will be considering can do that.

In fact, many (perhaps most) boat lithium battery-based systems can actually supply less peak current (amps) than a good lead-acid battery.

What gives?

It’s all about the Battery Management System we choose and how robust the internal wiring of the battery is. Let’s deal with the BMS first.

Deep cycle battery capacity by amp hours is measured at a 20 hours to discharged, and 100 hours to discharged which is the capacity usually on the battery label meaning it supplied 1 amp for 100 hours before it was considered fully discharged. The total amp hours is reduced as the draw rate is increased over that 1 amp rating. No load resting voltage of a lead acid battery is 11.8 fully discharged and 12.7 fully charged. Inverters have an operating range typically between 12.0 and 14.5 volts. Below the min voltage will trigger the low voltage protection and cease operation. To supply the enough current to an inverter at a voltage within the operating range of the inverter to power 1200 watts will take multiple batteries configured in a bank, so that under the draw of roughly 100-110 amps the voltage drop does not fall below the operating range. Deep cycle batteries should not be cycled below 50% capacity repeatedly, as it shortens lifespan considerably. True deep cycle batteries which you wont find at sams or costco can be cycled a bit deeper. A bank of four group 29 batteries rated 110 amp hours a piece wired in parallel for 440 amp hours could supply 220 amp hours at 50% cycle. No load voltage of the bank at 50% is 12.2 volts. A large current draw will have the voltage sagging below that, which would trigger low voltage shutdown in the inverter if your pulling heavy with it. So at 1200 watt load you could expect to hit the low voltage protection before reaching 50% of discharge. So you likely would get 1 to 1.5 hours runtime on those 4 batteries running an inverter powering 1200 watts load. On just one battery, its a matter of minutes before it trips.

 

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