How long would it take my 20W solar panel to recharge my 12V 9Ah Lifepo4 battery?

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samuil asked May 14, '22

How long would it take my 20W solar panel to recharge my 12V 9Ah Lifepo4 battery?

Hello,

I would like to know if my Victron 20W solar panel be suitable to power my Invicta Lithium 12V 9Ah Lifepo4 Battery.

Victron solar panel specifications:

Lifepo4 battery specifications:

Power manager (MPPT):

I would also like to interface the solar panel and battery using my Victron SmartSolar MPPT 75/10 solar charge controller.

The reason why I ask is to get an understanding of:

1. Compatibility between all three components, &

2. An approximate or average on long would it take to charge up the battery, if the battery was in a depleted state (at a cut off voltage of say 10.5v).

Your help would be much appreciated. Thank you.

Lithium Battery Solar Panel victron products

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Answer 1 · 2022-05-14T05:58:31Z

kevgermany answered · May 14, 2022 at 05:58 AM

It will work.

These figures very approximate.

Charge time is dependant on how full the battery is and how much light there is.

Let's assume battery is at 20% depth of charge. So 1.8Ah remaining. Thus needs 7.2Ah of charge.

Panel will allow the mppt to output 20/14A =1.4A

So with full sun and a battery as low as you should take it, time to charge is 7.2/1.4=5.2h.

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samuil commented · May 14, 2022 at 06:26 AM

Thank you very much Kev!

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samuil commented · May 14, 2022 at 08:01 AM

Hi @kevgermany

I have one more question for you (hoping you know the answer, otherwise I can of course start a new thread.

In the Victron app for the MPPT it has the following options in the two screenshots below.

Question 1: Should I be changing max charge current to 9A to suit the battery?

Question 2: How do I adjust the low voltage disconnect and re-connect? If possible.

Question 3: What are your thoughts on temperature compensation? From my understanding the battery has a in-built BMS, should I let that control these variables or should I enable it in the Victron app?

Thanks again for your help!

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Alexandra ♦ samuil commented · May 14, 2022 at 02:25 PM

@Samuil

The recommended charge current is 5A for long life. Although it can take the 9A.

The 20W of panel can only produce 20W of power at 25°C.

You will not see the 9A of charging with one panel. Maybe 2A.

The Invicta does not have communication with the mppt so cannot control the charging, only disconnect or switch off if something is wrong. So your bulk and float voltages need to be correct.

With lithium temparature compensation is not needed, however low temp cut off is if you live in colder climates. This also can be taken care of by the bms.

Are you using the mppt load out to run a load?

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samuil Alexandra ♦ commented · May 15, 2022 at 05:17 AM

Hi Alexandra,

Thank you for your help, understood.

Question 1: How can I set the correct bulk and float voltages in the MPPT? I would have thought changing the MPPT to LifePo4 would have automatically set these correctly?

Question 2: Also how would I know what the correct bulk and float voltages are?

I am indeed using the MPPT load out to run the load.

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Alexandra ♦ samuil commented · May 15, 2022 at 06:04 AM

@Samuil

There are two voltages in the datasheet. Max charge voltage, you can use that, i dont know how sensitive the bms is though, if there is tripping then go 0.2v lower than that.

Then there is a standby spec you could probably use that for float.

Then the load out there are several options available to you. You can use user def. algorithm 1 or 2 under the load output menu to set specific battery voltages there.

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kevgermany ♦♦ samuil commented · May 15, 2022 at 07:04 AM

Just in case it's not clear, set absorption to 14.6V, float to 13.8.

Bulk voltage is not set. This is because the bulk phase has a lower, but changing voltage than the absorption phase.

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