# Solar battery charge (Math against perception)

1. ## Solar battery charge (Math against perception)

Hi, I have a question related to my solar installation and the “real” charge of my batteries.

1) My set of batteries
I have 3 bat. Of 800 Amps
Voltage : 12V
BCI : 65
CCA : 800A
CA : 1000A
CR 150 Min

2) My PV’s (Photovoltaic’s)
I have 4 panels (90x60 cm)
V : 17.5V
A : 2.86A
W : 50w (these are the constructor’s infos)
So 4 panels I get : 200W

If I follow the math. I get
My bats. : 12v x 800A = 9600Wh
with 4 bat. 9600Wh x 4 = 38400Wh
Charging time estimated : 38400Wh / 200W = 192Hours

I conclude that I need 192 Hours to fully charge my 4 batteries.
(Ok all values are theoretical and they can fluctuate… all right)

My question: My regulator (responsible for the battery charge) gives me a signal of “FULL” after +- 3 hours – when the day is sunny. Almost every day as I live in Mexico
??????

If I unplug from the net battery and check the voltage it gives me: 12.6v (so yes it seems to be full)
(Well, the right way would be probably to discharge that battery via a 5Amps consumer and see how long it takes to discharge)

What is your opinion about it? From one side 192 Hours of charge and +- 3 hours on the other… ???
My estimation is wrong ?

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2. ## Re: Solar battery charge (Math against perception)

you are assuming your batteries are completely discharged. Is that the actual case?

3. ## Re: Solar battery charge (Math against perception)

No I just don't understand the big difference between the math 192 hours and the fact that after 3 hours my regulator tells me that the full charge is done.

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4. ## Re: Solar battery charge (Math against perception)

If it was almost full before...

Actually I don't even understand your battery specification. Battery capacity is counted in Ah, not A.

5. ## Re: Solar battery charge (Math against perception)

Well I just reproduced the battery specifications (written on it by the constructor).
But I agree with you Ah, I used Ah in my calculations....

- - - Updated - - -

My batteries are "almost" empty in the evening , using light, television, electronics etc... My voltage inversor shows me that the battery level is at let's say 11.5 V. Still the next day after +- 3 hours they seems to be full.

Ok I should just say : Great the Mexican sun is working for me

But this is not the point.

I would like to know and understand why (?) is there such a huge gap between a theoretical 192 Hours of charge and my 3 hours. that's it.

6. ## Re: Solar battery charge (Math against perception)

800 amp is not the amp hour rating of your battery.

It is the CCA (as listed in your post), cold cranking amps (max available at 0 degrees F).

CR is the time in minutes for the battery to discharge to 10.5 volts at a specific rate, 20 amps or so.

It likely if your batteries are in good condition that your charge controller is working fine.

Here in an example. Note the AH rating is only 55 amp hours, but the CCA is 775 amps (in your post the CCA 800 amps).

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7. ## Re: Solar battery charge (Math against perception)

Originally Posted by MarcelM0
If I unplug from the net battery and check the voltage it gives me: 12.6v (so yes it seems to be full)
Battery charge is an area where a tenth of a volt could be important. Notice that 1/10 V is a one percent difference. Our meters are rarely even that accurate.

Can you adjust your controller for 12.7V as the final voltage? That could increase your performance. A lot depends on the charging algorithm, of course.
If it helps, then try 12.8. Etc.

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8. ## Re: Solar battery charge (Math against perception)

These are (size) BCI 65 batteries, reserve capacity 150 minutes so about 62Ah each. 4 of them is 250Ah total.
Your solar charge controller probably needs to know what size (Ah) the battery is.

I think 12.6V is low after a charge, should be 13-14V.

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