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Voltage settings for CALB LiFePo4
#1
Do these settings seems safe/sensible to you guys:

Absorption setpoint: 56.8 (3.55v/cell)
Absorption time: 0.1hr (minimum I can set on Outback)
Balance voltage 3.5v
Hi-volt cut-off: 3.75v
Outback FM60 Float voltage: 52.8v (3.3v/cell) (I can't disable float on the solar charge controller)
Bypass-extra mode set to auto-level @ 3.45v/cell

So far, 10 days in, everything working nicely and they are staying balanced. I'm never at home when the sun is up, but I check them every evening and the system looks good. LattePanda board is here so I can get remote monitoring working soon.
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4, 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset.

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#2
Hi, Speaking in terms of lead acid batteries, float voltage is the voltage to maintain after reach the maximum voltage of bulk charging, for lithium batteries you must set floating voltage equal or a little below bulk charging voltage, so that sounds weird to me that float voltage of 52.8v.

You lose 10% of capacity of lithium batteries every 0.7v you don't fully charge, to round people with li-ion batteries charge them to 4.1v instead of 4.2v, 3.55v of 3.65v in your case (absortion setpoint) seems Ok, a little more conservative..

I don't understand balance voltage of 3.5v, balance is the action to equalize the voltage of all cells in battery, so what does it means these 3.5v for you?.

The minimum voltage for CALB batteries is 2.5v, I can't see in your numbers nothing close to 2.5v or 2.5x16=40v as low-volt cut off, maybe 2.6 is ok, that way you make less than 80% of DOD on every cicle. CALB datasheet claims 2.6v-3.6 is 80% of DOD.

And I think your Hi-volt cut off should be 3.65 as manufacturer recommends.

Regards
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#3
In lead acid/other chemistry, typically you set float to be quite a way lower than bulk - in this case it is set so the cells are held at their resting voltage (considered to be 3.3v for LiFePo4, accordiing to my research) when full, yet the charge controller will pick up the load that comes and goes on the inverter side when the sun is shining bright and the batteries are full - no diversion load on this system yet.

Lo-voltage cutoff is set at 2.6v/cell as per standard batrium LiFePo4 settings.

I agree, balance voltage should be set at the absorption setpoint, and ideally the absorption timer should be adjusted dynamically based on information from the batrium, depending on how many cells are left to reach absorption setpoint. But as yet there is no integration between batrium and outback. I will change the balance voltage to the same as the absorption setpoint and leave the timer at 6 minutes. They seem to be holding balance well.

In batrium speak, balance voltage is the voltage at which a cell will start bypassing and is user adjustable.
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4, 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset.

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#4
With lithium, you set the float charge as close to top voltage as possible. You don't want the charger float charging lithium. It is bad for them. So set the float value as high as possible. If you can actually set the float "above" top voltage, even better. Means the float will never kick in.
Floating lead acid means it keeps a steady supply of "current" dumping into the cells. When lithium is fully charged, this can actually cause the bonds to break down internally. So in the end, even if you are cutting your top/bottom voltages a little shorter to extend cell cycle life, you'll be hurting the cycles more so by trickle charging.
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#5
I'm not familiar with batrium terms, so that's beacause I misundertood that mix of terms, yes, 3.5v is a good point to start balancing, with your cells I supose probably it won't happens, I mean at least in the beggining with all your brand new cells, from same manufacturer and same capacity they won't unbalance, other history is our packs made by houndreds of recovered and different cells, they tend to unbalance, at high discharge currents and when are not fully charged.

All BMS I know are based on top balancing, so a weak pack will last less time and will unbalance shortly, the other way when charging that same pack will reach to top voltage sooner. So yes, wait until packs reachs close to the top voltage to start balancing.

So, apart of commented before of setting float same to bulk charging, you have a good setting.

Regards
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#6
(06-13-2018, 07:35 PM)Korishan Wrote: With lithium, you set the float charge as close to top voltage as possible. You don't want the charger float charging lithium. It is bad for them. So set the float value as high as possible. If you can actually set the float "above" top voltage, even better. Means the float will never kick in.
Floating lead acid means it keeps a steady supply of "current" dumping into the cells. When lithium is fully charged, this can actually cause the bonds to break down internally. So in the end, even if you are cutting your top/bottom voltages a little shorter to extend cell cycle life, you'll be hurting the cycles more so by trickle charging.

Damn, guess I need to figure out a way to disable float on my outback fm60 then... I guess I would then set my rebulk voltage to something like 3.2v/cell so bulk would kick back in if required later in the day after a bit of discharge.
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4, 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset.

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#7
+1 the max voltage per cell for LiFePo4 should be 3.65V & over that really isn't good & that's already much higher than the "knee point" (see below). Seems even though manufacturers say this 3.65V is the full charge voltage, that's actually not good for the batteries for long term use.

With my LiFePo4 banks, I've tried to:
- learn the "knee" where the cell voltages start rising quickly, ie the cells are apparently full, I set that as the max charge voltage (Constant Voltage level). For mine this seems to be 3.41V/cell
- set the absorb time to ~1 hour at the above knee CV level. I use the absorb time to allow the charge "tail current" to drop away (apparently can't measure & automate with my gear so approximate instead :-) ).
- set the float voltage to 3.40/cell. At this voltage, the cells are not drawing any charge current, just sitting there even with house power in use & the MPPT's + panels supplying that.
- set the batrium system to balance at that same "absorb" voltage, this seems to even out & balance the cells nicely so far (~6 months in here).
- I've also set the batrium to auto balance if the cells are above 3.37V & 85% SoC

PS it's Victron MPPTs + inverter & Batrium BMS here
Running off solar, DIY & electronics fan :-)
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#8
I'll have a look at extending my absorption time and watch what happens. On the outback stuff, if you have the flexnet DC %soc tracker (we do) you can set that to terminate the charge on the mppt controller when the charge rate drops below a certain value, they call it return amps.

Good to see that my float voltage isn't miles away from yours.
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4, 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset.

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#9
I charge my cells to 3.5V and have Balancing to start at 3.5V. This ensures that As soon as I have excess the balancing kicks in for those cells going above.

Ie if any cell is off that cell will hit 3.5V+ before others > going into balance. Still plenty of room left to max that is 3.65 so no worries and no gain in capacity really going higher.
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