Guru
Joined: 13/10/2014
Location: AustraliaPosts: 2199
| Posted: 01:21am 18 Dec 2023 |
I thought this might be of interest to someone, here is my LiFePO4 battery adventure (or was that miss adventure) as it could apply to other OTC 12V LiFePO4 batteries.
Over the past few years we’ve seen many horror stories of fake 12v, 24v and 48v LiFoPO4 batteries, dubious quality claims, overrated battery current, fake prismatic 3.2v cells going back years before that. I often wondered what was inside my 12v bank of batteries, which until recently, had been running just fine.
A bit of history: A few years back when everything was in short supply, I was looking for batteries for a 24V to 240V backup inverter emergency supply. I had a few second hand solar panels, and although I would have liked to have built my own battery from 3.2v cells, it was early days in the build and I had health issues, so I grabbed a few locally available 12v batteries “made in Australia” as in “the battery case was made here”. They were relatively low cost and yes, hindsight would have been good.
Interestingly, these same batteries are now almost 50% dearer.
I ended up making a High power 48V inverter based around Wiseguys design, a fabulous design BTW. I added a lot more panels and wired the battery banks to 48V, adding a few more of the same batteries. Each bank has 4 in series with Active balancers.
Each bank has its own solar charger and solar array, and banks can be charged independently of the running bank.
There is a separate high power Solar array and regulator / charger that connects to the Inverter input, downstream of the connected battery bank(s), basically, this stops the batteries cycling around a small voltage difference during normal running loads which are primarily handled by this Main solar regulator.
During fair to good solar conditions, the batteries are just a current sink for sudden transient loads. Of course at night they get to discharge to some degree - which is a good thing. Once charged, for most of the day the charge current into the Battery is zero and the batteries sit at a low charge float voltage.
Each bank can be switched in or out depending on the load requirements and cannot be parallel connected if the SOC if different (large current difference auto detected) between banks.
Each bank has separate monitoring of Current and Voltage and these values, including solar array status are auto logged and graphed in real time.
NOTE: I am not going to discuss or be preached to on the problems of series 12v LiFePO4, or the problems of Paralleling the same.
You can post, but I will ignore it – Why? Because I am completely aware of the pitfalls. I took steps to mitigate these problem and it appears that after few years running I have succeeded in doing that, no BMS failures, no over current charge/ discharge and no variations across batteries in any bank, until recently.
I noticing flickering of the LED lights when there had been almost none before – and random Inverter dropout due to low voltage detect trip when switching things like Laptop SMPS wall plugs -> typical random 280A Peak DC input surge which was nothing to the Inverter and batteries in the past.
I started to look a little closer at the problem and realized there were major issues with some of the batteries in the banks, well almost all in fact.
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