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Vrla's & LiFePo


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Hi to all

I currently have Mecer 5kva hybrid, 4xnarada ndt190, 6x300w poli pv's for utility backup.

Current daily use according to my prepaid meter is 5kwh.

1) Wil it be possible/advisable to add a leoch lifepo 48100C parallel to the vrla's?

2) If possible how should the settings be done for off-grid setup.

According to article it might be beneficial.


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31 minutes ago, Greenmile said:

1) Wil it be possible/advisable to add a leoch lifepo 48100C parallel to the vrla's?

I thought about it for a bit. At first I thought it might be a good experiment, to see how they could compliment each other. Then I realised there is a big problem. By the time an LFP battery drops to 12V (if we assume 4 cells for the sake of argument), it's already at a fairly low state of charge (around 25%), whereas the lead acids are still somewhere above 50% SoC. Even at this point the LFP battery will likely continue to do most of the work, because the lead acid bank's internal resistance simply rises so much faster as it goes below 50%.

What is more, it will hinder proper absorption charging of the lead acids, because LFP will hog all the charge current all the way up to 96% SoC, and only then as its internal resistance starts to rise will the lead acids start to charge. Finally, to get a lead acid completely full, it has to be held at absorption levels for a long period and typically it will be float-charged the last 15% of the way. If you spend all morning recharging the LFP, you might not have enough hours left in the day to finish charging the lead-acid pack.

The paper is very interesting though. I think what you have to keep in mind is that the paper is written for "telecom reserve applications", where they are not cycle daily. It's similar to another paper I often link that got the same result: That in such applications dissimilar strings can have advantages.

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14 minutes ago, Greenmile said:

should I rather get rid of them

Depends on how much money you'd get if you sell them now, and whether you already bought the LFP battery (or are in a hurry because maybe you foresee the currency tanking... which is something that is always with us). I think the consensus around here is to cycle them and get some value from them, then scrap them whenever they die some 18 months or whatever later, but for me it seems pretty much a six vs half-a-dozen thing :-)

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I am not sure exactly how the inverter distributes energy.

Is it possible to setup the Mecer to only use excess solar during the day for utility.

When I change Utility to SBU setting it starts to use battery energy at noon.

I wish to keep the batteries always on float and still be able to cycle to 50% during municipal outage.

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