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tkmbe avatar image
tkmbe asked

Inteligent battery charger now working. How should I set Battery low/high voltage level?

Hello


I've an Victron Smart Solar Charger 75/10 and 2x12V EVH12390 CSB Deep Cycle AGM Batteriees and and 48V DC Power Supply (as mentioned in other post) and it works great as Inteligent Battery charger!!!

I'm in doubt about setting values for the battery on/off levels and charge configuration.

From the net I've found the following values:

State of Charge Sealed or Flooded Lead Acid battery voltage Gel battery voltage AGM battery voltage
100% 12.70+ 12.85+ 12.80+
75% 12.40 12.65 12.60
50% 12.20 12.35 12.30
25% 12.00 12.00 12.00
0% 11.80 11.80 11.80

Deep Cycle
State of Charge 12 Volt battery Volts per Cell
100% 12.7 2.12
90% 12.5 2.08
80% 12.42 2.07
70% 12.32 2.05
60% 12.20 2.03
50% 12.06 2.01
40% 11.9 1.98
30% 11.75 1.96
20% 11.58 1.93
10% 11.31 1.89
0 10.5 1.75

Now my battery has the following specs:



So from the Battery Voltage and Charge time for Cycle Use I interpret that 70% charge level is at 1.9V which would be 11.4V
which from the table above gets 2.05V per cell i.e. 12.3V and this is a big difference...
Does I interpret something wrong?
(My load is only about 1-1.5A max at 24V)

Nevertheless connecting to solar charger after full charge with a normal charger my batteries have 26V i.e. 13V beginning test with 0.6A load after 1.5h still 25.73V i.e. 12.87V so I'm pretty confused about 100% values etc....

Any hints would be nice :-)


I want to discharge my battery about 40% max. to get good battery life or can I use 50% for Deep Cycle batteries without problems?
The application is from a tower with communication equipment...
I too want if the output cuts off because low battery, that it goes on after short period of loading the battery.
(if there was a power loss over long period and batteries were drained, I cannot wait hours to go online for my system)
What would be a good Load switch high voltage level?
If I load batteries with 10A/24V and there are 24V/39Ah at a level of 50% discharge (20Ah) I guess the batteries would be charged in 2h.
So if the table is right with 50% 2V I have 4% charge in ten minutes (120min 50%)
So cutt off 50% would be 24V and 24.4V on or should I set less than 24.4V?
As mentioned I want to go online not more than 15min after power comes on

Here my current configuration:


MPPT Controllersbattery charging
batteryspec1.png (211.2 KiB)
batteryspec2.png (120.3 KiB)
screenshot-20200215-201343.png (89.5 KiB)
screenshot-20200215-201343.png (89.5 KiB)
screenshot-20200215-200054.png (112.3 KiB)
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3 Answers
tkmbe avatar image
tkmbe answered ·

Was in wrong space...

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JohnC avatar image
JohnC answered ·

Hi @tkmbe

I admire your determination, but there's too many factors involved to make much sense out of all that theory.

From your initial tables, pick yourself a level you'd like to maintain. Let's say it's 12.30V. Then understand that it's a standing V, and adding a load or a charge will vary it instantly. Then determine, with no charge on, how much lower than 12.3V it will go with your normal load applied. Then set your cutout thereabouts.

This might be a bit 'mushy' in practice to do, but you'll work it out.

And oh, I think your 29.4V Absorb is too high. It will also be subject to temp comp, so may go even higher in practice. You'll gain nothing up there, except stressing your batts..

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tkmbe avatar image
tkmbe answered ·

John


Thanks for answer. What would be a better Absorb Voltage?

The Cycle Voltage of th bat is from 14.4V to 15V, so I tought 14.7 is fine.

Is it better to use 14.4V instead?

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JohnC avatar image JohnC ♦ commented ·

All personal opinion of course, but those appear to be sealed batts, and I wouldn't go above 14.4V myself.

The only real reason to do that would be to charge them faster in a short solar day. And even if you could detect a rise in Amps, the question then arises as to whether you're boiling off electrolyte, which you can't replace.

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rainerb avatar image rainerb commented ·

Hi,

I have a 24V system with Exide Sonnenschein A602 Solar batteries and the manufacturer recommends for cyclic solar use also 29,4V absorption voltage for max 2 hrs. per day. Can this be so wrong then?

Regards

Rainer

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JohnC avatar image JohnC ♦ rainerb commented ·

So wrong? Not necessarily, your gels are slightly different animals though, and may need a little more 'encouragement' to perform.

You've chosen to quote 29.4V from a 'switch regulator' curve. What's that mean, a pwm? The standard curve A is still 28.8V..

All very well for batt makers to produce lab figures, but the real world means they're usually installed in multiples. Special care needed then, imbalance an ever-present threat. I prefer to back off rather than push my luck.

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