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ahtrimble avatar image
ahtrimble asked

Bulk/Absorption/Float...and tail current

I hit a "super" frustration level...some advice and discussion would be helpful.

I am upgrading my system shortly. I am putting into place a second 5kw Quattro, second 150/70 MPPT, and adding a third LifePO4 220ah battery (will be a total of 630ah for the bank), everything is 48v...and all equipment is Victron except the batteries (2 x Elites, 1 x Trophy).

I am trying really hard to understand "best" settings for my LifePO4 battery bank. I will have 3 batteries, 630Ah (48v). I want to run my batteries 17% - 90% SOC to length their life cycle. So 53.2v will be my 100% SOC.

I am looking at setting my bulk charge voltage to 56v and absorption to 54v for 2 hrs and 0 tail current.

But...I can't figure out 3 things:

1) Are these setting optimum/best/appropriate?

2) What should be my "float" setting?

3) What the heck exactly is "tail current"?

I think I want absorption to 2 hrs and tail current set to 0 to allow cell balancing. But I don't actually understand what tail current is exactly to begin with to figure out if this is even correct thinking.

I live in very sunny AZ so I want my MPPTs to keep running even after my batteries hit my target of 90%SOC (my 100% SOC) so the MPPts can power my AC, etc. in the afternoon. But I am at a loss to really understand how I can accomplish my goals of not over-charging my batteries while maintaining my MPPTs production and not drawing my batteries down when full sun is present and loads are running high.

Any thoughts, ideas, suggestions...discussion? My head is about to explode and I just need some plain language help.

Thanks in advance!

(yeah, I've put in about 20 hrs of reading and still figure it out)

battery chargingLithium Battery
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2 Answers
snoobler avatar image
snoobler answered ·

Multiple questions across multiple topics leads to wasted time by all.

https://community.victronenergy.com/questions/122544/absorption-times-1.html



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ahtrimble avatar image ahtrimble commented ·
Sorry about that. I did a search and couldn't find any thread specific to that question/issue. I just figured if I had the question/issue that maybe others did as well. I was trying to draw attention to it. No ill intent meant.
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pwfarnell avatar image
pwfarnell answered ·

Tail current is the current at the end of charging. During bulk charging as much current as the charger(s) can provide goes into the batteries and the voltage increases until it reaches absorption voltage at which point the battery is fairly full. At this point the voltage is held constant and the charger throttles back, reducing the current, eventually falling to a low value, the tail current. However, it never reaches a tail current of zero, the battery will continue to overcharge, so you should never set the tail current to zero because it will not be reached, it should be something like 2-4% of your battery capacity, 12.6 to 25.2A.

When you go to float you could set a float voltage around 53.2V to keep the battery around 90% charged so no loads will be covered by solar. I am not completely familiar with trying to only get to 90% and hold it there from voltage alone, hence no suggestion for charging voltage. Perhaps someone will be along who knows more about trying to charge only to 90%.

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