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jerrykco avatar image
jerrykco asked

Correct setup for two 12V 400Ah LiFePo4 Batteries in Parallel

I need help setting up my new Victron Equipment for charging. I want to be able to charge from solar and shore power. So at the bottom of this email are my two simple questions.

Victron Equipment:

  1. MultiPlus 12V, 3000VA, 120A
  2. MPPT 150/70-Tr SmartSolar charge controller
  3. MPPT 150/70-Tr SmartSolar charge controller
  4. Orion 12/12-30 DC-DC charger
  5. Cerbo GX
  6. LYNX Distributer
  7. SmartShunt 500A/50mV

Solar Panel Specs: I have two sets of two panels in series each panel is 410W

The solar panel specs are:

four 410Wh Solar Panels - two 410Wh on the RV roof plus two 410Wh deployable on ground (1640W total) (they are ~ 68" x 45")

Each Panels Specs
In Series


Maximum Power (Pmax) 410W

820

Watts

Maximum Power Voltage (Vmp) 31.35

62

Volts

Maximum Power Current (Imp) 13.08

26.16

Amps

Open-circuit Voltage (Voc) 37.12

74.24

Voc

Short-circuit Current (Isc) 13.96

Module Efficiency STC (%) 20.97


I have two new 12V 400Ah LiFePo4 Batteries I will be using in parallel (after I charge each up equally to full voltage individually) in My RV. The Battery Charging parameters from the manufacturer are:

Bulk | Absorption: For your Bulk | Absorption stage the ideal voltage is between 14.2V & 14.6. For full charge and balance the absorption mode should be set to last for at least 20 minutes per battery for multiple batteries in parallel.

Float: LiFePo4 batteries do not need a float stage for charging but a float voltage 13.4V and 13.8V can be used when connected to shore power.

Equalization: Equalization is not recommended for these batteries. Most chargers will allow you to shut this feature off or use a setting that does not use equalization. If you cannot turn off this mode then you will need to adjust the equalization voltage <14.6V.

Temperature Compensation: Temperature compensation is i]not needed for these batteries and in some cases may trigger the built in BMS to go into protect mode. For this reason, we recommend that the temperature compensation be shut off or set to 0.

Built in BMS Basic Features are:

High Voltage: >14.6V. If the individual cell voltage exceeds 3.2V during charging the BMS will prevent a charge current from continuing. Discharge is always allowed under this condition.

Low Voltage: <8.8V. If an individual cell falls below 2.2V during discharge, the BMS will prevent further discharge. Charge current is always allowed under this condition.

High Temperature: >65C. The BMS will prevent both Charging and Discharging during this condition.

High Current: The BMS allows a constant current of 100A (+/- 5%), 260A (+/- 10%) for 5 Seconds.

Passive Balancing: A passive balancing process is activated by the BMS at the top of each charge cycle when the battery voltage exceeds 14.6V ensuring that all cells remain at same SOC.

I have the Victron Equipment on a bench and all wired up to the Solar and Batteries. Just need to configure it. I can use the Android app now too.

Questions:

1) What is the proper setup configuration to charge the batteries from the MPPT's?

2) What is the proper setup configuration to charge the batteries from the MultiPlus from Shore Power?

Thanks for any and all help.

battery charging
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11 Answers
kevgermany avatar image
kevgermany answered ·

You've doubled PV charge current as well as PV voltage. Only voltage changes in series.

In the MPPTs set battery voltage to 12V, it should auto detect, but best check, battery preset to smart lithium. The other parameters will be ok. But reduce absorption to 30 minutes. Equalisation voltage should be 14.2. no automatic equalisation.

Set multiplus charge to the same values, absorption 14.2, float 13.5 (same as MPPTs). Reduce absorption time as well. Set lithium battery type. Set temp compensation to 0. Automatic equalisation off.



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jerrykco avatar image
jerrykco answered ·

Yes and thank you kevgermany!

That was a an error. At first I thought I was going to Series each set of two PV Panels (two on the roof and two ground deployed) then parallel combine them. But that was to much for a single MPPT. And I forgot to update the table. Good catch ;-)

I'll give it a try today!


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jerrykco avatar image
jerrykco answered ·

Hi again kevgermany,

I assume you meant turn on Expert mode (I'm not) and set the absorption time to 30m down from 2hours. Which I did. Charging one battery now.

Thanks again!

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jerrykco avatar image
jerrykco answered ·

Hi kevgermany,

I set the parameters you suggested for the MPPT and the MultiPlus.

However the MPPT only charges to 13.8V while the Multiplus charges the batteries up to 14.3V

What did I do wrong?

1686692566081.jpg


1686692566081.jpg (393.3 KiB)
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kevgermany avatar image
kevgermany answered ·

Where are you seeing/measuring this voltage?

Please post a shot of the mppt from Victron connect.


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jerrykco avatar image
jerrykco answered ·

kevgermany,

Since the batteries were brand new and shipped not fully charged and because I want to use them in parallel and because I wanted to learn as much as I can before installing them in my RV, I first wired up everything on my bench.victron-benchtop-setup.jpg

First I charged each battery with Solar PV's and the MPPT.

I was a little confused by the MPPT setup but thinking I set them up following your guidance I put out the PV Solar Panels and charged one battery at a time. But I only saw a maximum of 13.8V and it went into Absorption.

Next I wanted to test shore power and used the Multiplus connected to 110V AC. It charged the two batteries (one at a time) up to to 14.4V then went into absorption.

Anyway, to set it up again I will need to use a heat gun to bleed off energy and then put my ground deploy PV Panels out to run the test again.

Before I start to bleed of energy here is the image from this morning from Victron Connect to the MPPTvictron-connect-mppt.jpg

Let me know if you want something else before I start.


victron-benchtop-setup.jpg (1.4 MiB)
victron-connect-mppt.jpg (32.1 KiB)
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jerrykco avatar image
jerrykco answered ·

@kevgermany,OK I stand corrected. I bled energy from the battery, then hooked up the solar to the MPPT. And it behaved as it should. Switched to Absorption at 14.2V. Thinking back I must have tried it before I set the MPPT Values as you suggested including the battery type of Lithium.

My bad.

Questions:

1. Can I set the Absorption to 14.4V in the MPPT? It that wise?

2. In the Multiplus I set Absorption to 14.4V. Should I lower the Absorption voltage to 14.2V? for both the Multiplus and the MPPT's?

3. I noticed that when I was bleeding energy using the heat gun that the Mulktiplus shut off when the voltage dropped to 13.2V which is both the DC input low restart and the DC input low pre-alarm. The DC input low-shutdown is 11V. Shouldn't these three settings be different?

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kevgermany avatar image
kevgermany answered ·

We all do this sometimes.

1&2 MPPT and multiplus should have same settings, so yes. But probably better to stick to the low end of the manufacturer specs for LiFePO4.

3 Tune these as needed. The restart is to allow proper battery recovery, set too low you're going to get frequent shutdowns. Your BMS will prevent damage from excessive discharge. But better to treat that as an emergency backup. Also bear in mind that the voltage drop off with discharge is quite shallow compared to AGM. But a heavy load can cause temporary lower voltages. So the warning level needs to be lower than drop under load, but higher than shutdown. I think you'll enjoy tweaking this. Gives a great sense of satisfaction when you get it right.


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jerrykco avatar image
jerrykco answered ·

@kevgermany,

Yesterday I charged for a long time on Solar using the MPPT. I noticed that at first as reported above it was on Bulk and charged to 14.2V. Then i switched to absorption and I watched the Watts / Amps decrease over time. and then finally float. I also used the heat gun and dropped the voltage of the battery several times. But On Float it stayed at 13.5V and never went back to Bulk. That doesn't seem right, does it?

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kevgermany avatar image kevgermany ♦♦ commented ·
There's a rebulk offset setting. You can reduce this, probably by quite a lot. It will only switch out of float if voltage drops by that amount. Can take a while with super efficient lithium batteries. No manual here at the moment, so can't be more specific..
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jerrykco avatar image
jerrykco answered ·

Hi @kevgermany,

Not sure but I think I figured out that the issue is using a low float voltage in the setup for the MPPT.

The battery Manual states:

"Float: LiFePo4 batteries do not need a float stage for charging but a float voltage 13.4V and 13.8V can be used when connected to shore power."

When I initially set it up I put the 13.5V in for float in the MPPT. I have now changed that so they are the same (14.2V) for both Absorption and Float from the MPPT. I left the Multiplus at 13.8V for float While on Shore power. However that brings up the issue of having shore power and solar charging at the same time. Is there an issue if Float is 14.2V in the MPPT and Float is set to 13.8V in the MultiPlus and both are powered at the same time?

BTW the REBULK OFFSET Setting in the MPPT was 0.10V. I left it as is.

Your thoughts?

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kevgermany avatar image
kevgermany answered ·

Float. Many chargers can't disable float. Ideally with LiFePO4 no float. But no issue. Just keep flot/absorption at the low end of the spec shherange.

Having MPPT with higher settings at float will effectively turn off the multiplus charging, so good move.to save power.

Can reduce rebulk offset. Makes the charge cycle restart more quickly


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