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mark1988 avatar image
mark1988 asked

MPPT for Non-Standard *51.2V* CATL LiFePO4 Battery Pack

Hi,

I'm interested in purchasing my first solar battery pack (together with a handful of used 500W panels) and since I can't quite afford Tesla's PowerWall, I decided to go with a Chinese PowerWall instead.

I'm ready to pull the trigger on this bad boy since it comes with CATL cells and 20 years warranty (spec attached). The only thing that concerns me is that it appears to be using a rather non standard 51.2V battery configuration?

I can see that Victron/SmartSolar MPPTs can be configured to deliver around 55-57V and so:

1) The charging voltage of this particular unit is 56V - would say the MPPT 150/45 work for my setup?

2) Is it worth messing about with a custom charging profile to begin with or should I be looking for something with a more standard config (e.g .48V)?


Any input would be hugely appreciated.


Thank you,

Mark


GSL ENERGY 51.2V 100Ah Wallmounted lifepo4 battery-16S CATL(下单之前确认回签的）.pdf

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gsl-energy-512v-100ah-wallmounted-lifepo4-battery.pdf (570.6 KiB)
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3 Answers
marekp avatar image
marekp answered ·

51.2V is very much standard voltage for 16 LFP cells.

1 LFP cell has 3.2V and 3.2 x 16 = 51.2

150/45 MPPT will work with it no problems.

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mark1988 avatar image
mark1988 answered ·

Hi and thanks for your answer.

I am a bit confused, maybe you can help me - yes, it's 16 cells x 3.2V but the recommended charge voltage for this unit is 56V and the 150/45 MPPT is rated at 48V (with the max adjustable charge being around 55V according to the product spec)? What am I missing here?

Sorry if this is a very basic question but I don't understand the difference in the voltages here and why it is ok to ignore it.

Cheers,
Mark

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

3,2V is the nominal voltage of LiFePO4 cells.
To charge a cell/battery the charging voltage have to be higher.
The absolute maximum for LiFePO4 cells is 4V but most manufactures recommend a lower voltage.
Victron recommends 14,2V for there 12,8V batteries that are 3,55V/cell.
Others say 14,4V (3,6V/cell) or 14,6V (3,8V/cell).
If the datasheet for your batteries says 56V (3,5V/cell) you should set the charger to that voltage.

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marekp avatar image marekp commented ·

Here are my settings for 16 LFP cells, inside my 150/35 MPPT charger. You have 150/45 but ranges for the voltage settings are the same as in 150/35 MPPT.

If I can set absorption voltage to 56.5V, you will be able to set it to 56V as your battery requires.

15035.jpg


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mark1988 avatar image
mark1988 answered ·

Hi, thanks again for your answers, they make perfect sense.

I guess what confused me was the 48V designation, if the unit is capable of delivering more than 48V why call it that? Does this setting actually do anything apart from perhaps defaulting volts / amps to certain values?

Also, since we're effectively saying that one needs to create one's own charging profile for batteries other than 12/24/48V to get the required voltage, are there any rules of thumb that I should follow here? I could simply use the 48V profile and scale it up all equally across all parameters by the same %age to get to the absorption voltage of 56V...? Happy to go with whatever approach makes more sense though!


Thank you,
Mark



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marekp avatar image marekp commented ·
12, 24, 36, 48V are only labels used for standard size batteries.

When you look at 12V battery, fully charged has more than 12V and is still called 12V battery.

Same applies to 48V battery. 48V it is only a label.

You will find batteries labeled 48V but some of them have 15 LFP cells inside and others 16 cells. All are called 48V battery. :)

Your battery manufacturer will tell you what voltages charger should use while charging them.


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