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Batteries not living up to expectations


DoubleH

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Hi. Member for a while but this is my first post.

I got a small system going at the beginning of the year to power up lights, TV etc during outages. Axpert 5Kva invertor, 9 panels and 8 x 102ah deep cycle batteries for the 48v ask. 

My issue is that despite the relatively low load of between 500 and 700 watt, the batteries simply does not last - sometimes not even the 2,5h loadshedding slots in Pretoria. Although I have forgotten most of my matric science lessons, this bank should last longer than what it does. The invertor manual supports this thought.

I have charged all 8 batteries individually and they all read around the 12,8v mark when done. But as soon as it gets load the volts drop like a countdown timer!

Any experts out there than can assist me finding a solution to this?

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31 minutes ago, DoubleH said:

102ah deep cycle batteries for the 48v ask. 

You have 204 Ah in total, with 102 Ah batteries you can normally only take a maximum of 20% from them before you start damaging them, 20 % of 204 ah at 48 volt only gives you 3,2 hours when new. If you get less now, they might be damaged already.  

 

31 minutes ago, DoubleH said:

9 panels

What size?

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38 minutes ago, Jaco de Jongh said:

You have 204 Ah in total, with 102 Ah batteries you can normally only take a maximum of 20% from them before you start damaging them, 20 % of 204 ah at 48 volt only gives you 3,2 hours when new. If you get less now, they might be damaged already.  

 

What size?

270w. 3 arrays of 3.

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Batteries, Batteries, Batteries... Tut, Tut, Tut... I will put R1k on the block that your first problem is the batteries.

I hate the fact that no-one told me the maths about batteries before I did my first big solar install... Normal Lead Acid, even "Marine" or off the shelf "Heavy Duty" or whatever are not going to survive most solar installs. Unfortunately, Voltage does not equate to actual power delivered or actual power available. Think it simple, and think it "good' (my thesaurus really couldn't supply a better word for what I wanted to say).

Rough Math based on your info and equipment mentioned:
Load: 810w/h maximum -> delivered for 24 hours in the day -> 19.44KW used per day.
Solar: Your Solar array can deliver (I am assuming you have 250W panels or more) 9 x 250W = 2,250KW per hour max for max 8hr of daylight = 18kW per day
The above says you are already drawing more than what you are generating..

Battery logic says (based on the calculation you provided above) you are drawing a 810W load (19.440KW/day for 24 hours) , and only supplying a solar power (and battery backup) of (18KW/day as the only max draw from your solar kit for perfect sunlight). Now that 18KW/day I mentioned has to be stored somewhere first before it can be used... Ideally batteries... But your batteries can only store a single amount of max 8.1 KW and only 1/2 of that is usable... You only have a usable power of roughly 4KW in your batteries (This is almost a Lead battery standard that only max 1/2 is available to use without destroying)... Generally, you can't store 18KW of power into batteries that have a capacity of only 8KW and expect it to last, especially since you will almost always need to feed in more solar power to the batteries than what you need to draw...

I know all batteries are different, but he basic math clearly says that your storage power (AKA batteries) are the biggest issue.

Ok, think I have proven my point, and Jaco's... Batteries - The power you generate from all this free energy and solar power, it has to be stored somewhere before you can use it... And dammit batteries are expensive! - Welcome to the club! (Then we can look at fixing your load vs panel generation😀)

 

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