Battery

Prepare for those inconvenient power outages, or for the trending living-off-the-grid

thunderstorm lightening coastal town
We sell a fabulous battery – Firefly’s 2v/4v model, which has all the advantages of their popular Group 31, but in a different format. Here's where I intend to use them in a future project.

With the increasing frequency of heavy storms and threats of power outages, I’ve been reviewing the emergency battery back-up system I have set up in my basement. This currently consists of 8x 185 amp/hr AGM batteries with an Inverter-Charger, plus a mains/generator Transfer Switch with generator plug-in access. There is also a Transfer Box that has six mains/inverter transfer switches with associated breakers and balancing meters which supply six circuits: the fridge, kitchen outlets, sump pump, basement outlets, front room outlets, and the oil-fired furnace.

girls jumping togetherContinuing on the theme of the previous blog, regarding wiring individual batteries in parallel to make a higher capacity bank, now we can look at the best way to wire them up.

I included a teaser graphic in that last blog that showed two batteries wired in parallel and with the two main cables, one positive and one negative, both connected to one battery. I expected a flurry of comments on this, but to my surprise received only one. Mr. D said that the configuration shown would result in uneven current draw from each battery, resulting in greatly reduced cycle-life of the first battery in line. Is that so?

And if so, what is the best configuration? What are the alternatives?

Yipee! Time to put on the testing hat once again.

battery charge checkingI saw some communications in a trade journal the other day discussing the common practice of wiring batteries in parallel to increase capacity. Specifically, one writer was warning of the possibility of a cell shorting in one of the batteries, resulting in the other batteries all discharging at a high rate of current into the short circuited cell leading to an apocalyptic event below decks. Is he/she correct? Well, yes and no.

Yes, this is very much a possibility, but is dependent on battery type. An old timer, like yours truly, will probably adhere to the notion that the likelihood of a shorted cell is real, but that’s because our heads are still stuck in “the good old days”, and we are not being practical.

Let’s think about this. How can a cell, one of six in a 12 volt lead acid battery, become short circuited?

pink floyd darkside of the moon 1200x600
Early pioneers of marine lithium battery systems used individual cells in a rectangular format, and some still do. These types of cells are referred to as “prismatic”, which by definition means having the form of a prism, which is hardly a representative description unless you imagine two prisms joined together to make a rectangle. A more accurate description would be: “a right rectangular prism”, as opposed to a “wrong” or a “left” rectangular prism, one supposes. But I digress …

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