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New to LiFePo4 off grid - questions on setup

jtzako

New Member
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Nov 6, 2021
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I bought a house that came with an off-grid solar setup and have been working on updating it and have some questions on making sure I am using it correctly.
It had an older Outback FX60 charge controller so I upgraded to the FM80 (and the mate3s) and added an FNDC battery monitor. It had been working on flooded lead acid batteries that are getting a bit worn out.

With the new LiFePo4 batteries I got I seem to be having some difficulty getting them to charge correctly.
If I try and charge them (using absorb voltage setting) anywhere near what the mfg recommends (58.8v) I can watch it go a bit haywire when the voltage gets to around 57.5. I start seeing fluctuations in voltage and spikes going over 60V then the charging shuts down.

If I charge it to a lower number, such as 56V it doesnt do that, but I also seem to be getting far less useable power from them.
I also am not sure if I should be using float at all or exactly what my 'absorb' voltage should be set to.
Then there's the refloat/rebulk settings. Any idea what they should be set to? (I set them to 52v just so it'd be above the mfg recommended 51.2 V for 80% DoD)

I notice that my system is backing off on solar input and keeping the battery at around 54V which is the CC's Float value. Is that OK for the battery (not shortening the life) and still giving me a decently 'full' charge so they will last the night?



FM80 Charge Controller
2x Inverter VFX 3648
Mate3s
2x OBPS PS2DC Industrial Control Panel 3004905
Kohler Generator 14RESA (A/C - auto generator start)
OBPS Auto transformer PSX-240
15x Sharp ND-208U2 Solar Panels
2x HSKY 48v 103Ah Batteries (parallel)
 
The voltage irregularity is likely due to your cells or batteries being out of balance at the extreme upper end of charge. BMS(s) may be taking batteries offline to prevent overcharge, and that's why you see the charge controller shoot way high before it can clamp its output down.

Very familiar with the FM80.

Set absorption to 55.2 and float to 54.4. At 55.2V, you can get 98%+ charged. At 54.4V, you can get 95%+ charged; however, they will take longer than a "standard" charge to the prescribed 3.55-3.65V/cell.

Set re-bulk to 52.8V (3.3V/cell).

Set "absorb end amps" to 5% of your total Ah capacity, e.g., 206Ah battery is fully charged at absorption voltage and 10.3A charge current.

Set absorption time limits to 4 hours. This is due to the longer absorption time needed to fill at the reduced voltages. Typically, if you were charging to 3.55-3.65V/cell, you would set absorption to 1 hour or less.

Make sure equalization is disabled.

Make sure temperature compensation is disabled.

Make sure your batteries have built-in low temperature charge protection if they may ever see temperatures below freezing.
 
The voltage irregularity is likely due to your cells or batteries being out of balance at the extreme upper end of charge. BMS(s) may be taking batteries offline to prevent overcharge, and that's why you see the charge controller shoot way high before it can clamp its output down.

Very familiar with the FM80.

Set absorption to 55.2 and float to 54.4. At 55.2V, you can get 98%+ charged. At 54.4V, you can get 95%+ charged; however, they will take longer than a "standard" charge to the prescribed 3.55-3.65V/cell.

Set re-bulk to 52.8V (3.3V/cell).

Set "absorb end amps" to 5% of your total Ah capacity, e.g., 206Ah battery is fully charged at absorption voltage and 10.3A charge current.

Set absorption time limits to 4 hours. This is due to the longer absorption time needed to fill at the reduced voltages. Typically, if you were charging to 3.55-3.65V/cell, you would set absorption to 1 hour or less.

Make sure equalization is disabled.

Make sure temperature compensation is disabled.

Make sure your batteries have built-in low temperature charge protection if they may ever see temperatures below freezing.
Thanks for the info. I have an issue: The FM80 temperature settings do not have an "Off". I only have Wide or Limited and two sliders to set if I chose Limited. They wont see that cold of a temps. Typically the ambient temp where they are is around 60F.
 
The voltage irregularity is likely due to your cells or batteries being out of balance at the extreme upper end of charge. BMS(s) may be taking batteries offline to prevent overcharge, and that's why you see the charge controller shoot way high before it can clamp its output down.

Very familiar with the FM80.

Set absorption to 55.2 and float to 54.4. At 55.2V, you can get 98%+ charged. At 54.4V, you can get 95%+ charged; however, they will take longer than a "standard" charge to the prescribed 3.55-3.65V/cell.

Set re-bulk to 52.8V (3.3V/cell).

Set "absorb end amps" to 5% of your total Ah capacity, e.g., 206Ah battery is fully charged at absorption voltage and 10.3A charge current.

Set absorption time limits to 4 hours. This is due to the longer absorption time needed to fill at the reduced voltages. Typically, if you were charging to 3.55-3.65V/cell, you would set absorption to 1 hour or less.

Make sure equalization is disabled.

Make sure temperature compensation is disabled.

Make sure your batteries have built-in low temperature charge protection if they may ever see temperatures below freezing.
One more question. I see on the OpticsRE page that the SOC is at 59%. I'm still getting sun and it seems to have been holding 'float' (54.4V) all day. Any idea why SoC is that low and has actually gone down a bit? My load has been very light today (under .4kwh) and I've had lots of sun so it has been producing more than the load the entire time. I notice the CC is not using the full solar, it seems to be keeping just enough to maintain the 54.4 V even though much more is available.

If it matters, the SoC is probably coming from the FlexNet DC. Unfortunately I only have one shunt and it is on the negative battery/inverter connection.
 
Like any battery monitor, OpticsRE likely needs to be recalibrated periodically by a full charge based on the absorption voltage and the absorption end amps value as an Amp-hr counter will get progressively less accurate over time. If you're not regularly charging to true 100% SoC, it's not going to be accurate.

It is critical that ALL charging and loads pass through the shunt being used by the battery monitor. If not, it will never be accurate.
 
Like any battery monitor, OpticsRE likely needs to be recalibrated periodically by a full charge based on the absorption voltage and the absorption end amps value as an Amp-hr counter will get progressively less accurate over time. If you're not regularly charging to true 100% SoC, it's not going to be accurate.

It is critical that ALL charging and loads pass through the shunt being used by the battery monitor. If not, it will never be accurate.
Today is the first day the batteries (and flexnet dc) were installed. Right now the only shunt sensor is connected to the DC side negative so. One side of that terminal is all negative side connections, the other side of the shunt goes to the inverters.

There isnt another sensor over on the AC side so I wonder if it doesnt know about charging that comes from the Generator. Ultimately the charge has to come back from the inverters to the battery through that shunt so I would have thought it would know
 
Like any battery monitor, OpticsRE likely needs to be recalibrated periodically by a full charge based on the absorption voltage and the absorption end amps value as an Amp-hr counter will get progressively less accurate over time. If you're not regularly charging to true 100% SoC, it's not going to be accurate.

It is critical that ALL charging and loads pass through the shunt being used by the battery monitor. If not, it will never be accurate.
Now that I'm looking at this more, I suspect it may not be picking up any of the solar charging. I'm assuming the FNDC only picks up what goes across the shunt. It would pick up the charge from the generator since that goes from the Inverter side over to the battery side.

However, it looks like ALL of the negative terminals except for the Inverters are on the same side of the shunt as the battery. I think I'll have to see if I can redo the wiring so the CC and Inverters are on one side and the battery on the other.
 
Generator-inverter-shunt-battery should still go through the battery monitor.

Inaccuracy is likely due to never charging to "full" as defined by the battery monitor. You may need to look these numbers up and reprogram them to your needs. I have no familiarity with your system, but this video describes the process for a victron shunt, and the concept is similar:

 
Generator-inverter-shunt-battery should still go through the battery monitor.

Inaccuracy is likely due to never charging to "full" as defined by the battery monitor. You may need to look these numbers up and reprogram them to your needs. I have no familiarity with your system, but this video describes the process for a victron shunt, and the concept is similar:

It did pick up the charge from the generator. After the generator ran last night to get the first full charge on these new batteries it did show SoC as 100%. It just appears it is not picking up the charge from the solar due to the way they had it wired.

Basically it goes AC Generator -> Inverter negative <-> Shunt side A <-> Shunt Side B <-> negative battery/CC/etc

I think the inverters should be on shunt side B and the battery on side A by itself so the FNDC can pick up all charge going to/from the battery.
 
You are correct. I missed that part. You're not getting SCC counted since it's on the battery side of the shunt. You may need to manually reset the monitor to 100% when you're confident it's there.
 
You are correct. I missed that part. You're not getting SCC counted since it's on the battery side of the shunt. You may need to manually reset the monitor to 100% when you're confident it's there.
I got the wiring sorted out and now the FNDC is picking up the charge correctly. Thanks again for the help.
 
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