New to forum - DIY batteries discussion

[Mike90250]

Hi folks, new guy here. Maybe you can help me make a choice?

I am setting up a 3.2kw 48v array. Midnight Classic controller, AIM 6kw 120/240 IC. I am contemplating two battery options. 4 Renogy 12v 200ah AGMs, or a single SimpliPhi 48v 69ah battery. From what I understand, the pro's of LiFePO4 are a deeper discharge and more cycles. The AGMs cost half, and deliver more energy if I don't drain them past 50%.

What should I do here? Pay the price for the smaller capacity? Go with the AGM, and replace with LiFePO5 down the road when the costs may be better?

Go for a 48V golf cart battery bank (eight 6V 200ah batteries wired in series) About $800, rugged enough to last 1 abusive year, or 5 years well cared for.

[SunEagle]

I agree with Mike. 8 x 6V 200Ah batteries is the better plan.

But if you can't get them then the 4 x 12V 200Ah AGM would be better then going with the 48V 69Ah battery.

[TRA]

I agree with Mike. 8 x 6V 200Ah batteries is the better plan.

But if you can't get them then the 4 x 12V 200Ah AGM would be better then going with the 48V 69Ah battery.

Thank you both.

For simplicity sake, and time, going with the 4AGMs will be my best bet. I guess I can always buy a whole new array a few years down the road for the cost of one LiFePO4 battery now.

[PNjunction]

Headrc - there's no problem building a one-off project from any battery. I'm sure you can do it with your knowledge.

The reason we point out all the *other* issues is that most of the one-off projects are based around having a huge stash of used / unknown / mixed cells. If you can handle that, no problem. Most can't do that safely, or be hoodwinked into spending a load of cash on trash.

The same ethos applies to lead-acid projects before lithium became a "thing" for makers. We dissuaded those who wanted to start out a project something like this:

"My uncle has a warehouse of old / unused alarm-box agm batteries, and I want to wire up about 200 of those together for my off-grid bank."

Can it be done? Yes, but merely asking that question means one isn't qualified to do it! Know what I mean?

At the end of the day, the most important aspect aside from safety, is the question "Does the battery fit my application properly?", or is it merely a technical exercise? Two different aspects that often get confused.

And this is from an LFP proponent, but only if it makes sense in the overall scheme of things, and not just a tech exercise.

[jflorey2]

For simplicity sake, and time, going with the 4AGMs will be my best bet. I guess I can always buy a whole new array a few years down the road for the cost of one LiFePO4 battery now.

Yep. And odds are you will have to.

[TRA]

Yep. And odds are you will have to.

It's been eating at me for sure. I like the idea of longevity. The SimpliPhi is a pretty beefy battery, but I would need one at a minimum, two most likley, at almost $3K each. The Renogy AGMs, a bank of 4 runs just $1600. Will the cost of a LiFePO4 battery drop substantially in 3-5 years? I am going to guess "yes", But, i could be wrong.

Not being able to run smaller, more affordable LiFePO4 batteries in series is something that is a big problem too. Just finding a 48v unit was tough.

[jflorey2]

It's been eating at me for sure. I like the idea of longevity.

So do I. But keep in mind that you are probably going to destroy your first set of batteries. It's just what happens. Given that, I would go as cheaply as possible so the first lesson isn't too costly.

I would still recommend you consider FLA's. For $800 you could get 220ah worth of Trojan T105's - and it's hard to beat that as a set of "starter" batteries.

[PNjunction]

Will the cost of a LiFePO4 battery drop substantially in 3-5 years? I am going to guess "yes", But, i could be wrong.

Not happening - just the opposite in fact. Ten years or so ago, we all wished that to be true, but prices have not substantially come down. All the while lead prices going up.

As I noted in another thread, LFP is not a perpetual storage machine - like all batteries they age. So along with the price / performance ratio you think you'll get, another big question will be "will I never realize the 2000+ or so cycles during the LFP batteries' own chemical lifetime?"

Real world man. I dig LFP, but one really has to justify it from ALL aspects.

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[TRA]

Im going with a Midnight Classic charge controller. Do I need a different solution?

[Mike90250]

Im going with a Midnight Classic charge controller. Do I need a different solution?

being a Classic owner, as long as you understand the battery requirements and can program them into the controller (very easy with the Local App for windows) you should be fine.