Homebrewed Electricity > Storage

Replacing my gel batteries

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DamonHD:
It doesn't seem nearly long enough ago since I bought my ~400Ah of 12V gel batteries for my off-grid system.

http://www.earth.org.uk/expanding-off-grid-PV-system.html

A year ago I wondered if I'd killed them a year ago, and I'm still wondering.  Anyhow it might be time to bite the bullet and replace them.

Given that loads are low (from less than 1W average for my core server load, to ~16W when taking networking gear off-grid to maybe 60W peak when powering my laptop occasionally) any sort of battery would supply the discharge current.  The primary aim is to keep my server off-grid through winter, and take other loads off too as above where possible.

I have a nice Morningstar SS-MPPT-15L charge controller for the primary array, and a cheap Chinese PWM controller in parallel for a small amount of 'extra' PV.

Question: AGM or gel for the replacements?  I know the gel should have the longer service life, but I wonder if chucking up to 15A+ peak charging current at it is what is finally killing it off, and if AGM would be more resilient?



Rgds

Damon

 

Simen:
Go for a 12V LiFePO4 bank. :)

You could manage with half the Ah, without sacrifice lifetime vs. LA-batteries...

DamonHD:
Thank you.

I'm not against LFP at all, as you see, and I'll eventually do that alongside many more kWh grid-tied for my house I hope, but for now there doesn't seem to be a good choice of solar LFP controllers*.  In fact, many of the BMSes seem to be totally proprietary and opaque.

Eg something that is MPPT and will work with my 60-cell PV panels and won't blow up with excess available input power!

But please show me that I'm wrong: I'd be happy to take that route.

Rgds

Damon

Simen:
I agree; there are not many (if any) solar-controllers there that really supports LFP - but most lfp-batteries would do ok with standard controllers set to 14.4V CV, as a proper controller would keep the voltage at 14.4V until the battery draws only a few amps. The BMS in the lfp-battery should manage the balancing just fine, but might struggle a bit if the cells are badly out of balance. A simple solution would be to connect a CV source for some hours, once a month, to let the bms fine-balance the cells.

I've run a 12V, 110Ah lfp battery in my caravan for a couple of years now, connected to a 15A MPPT controller and 160W of panels, and i checked the balance of the cells a month ago, and they were spot on. There is a constant load of 7Ah/day, year round (a smart-home controller and an AP) - and higher when i use the caravan. :)

DamonHD:
No more opinions?

In my situation is there any significant difference between gel and AGM?

Rgds

Damon

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