Does MPPT charge controller damages a battery ?

[Q-Dog]

Well, you could add more batteries. Doubling the batteries would cut the charge rate in half.

 

[Mohsin Ali]

Well, you could add more batteries. Doubling the batteries would cut the charge rate in half.

But alone Mppt will not help? It will give what it gets?

 

[Hedges]

12V x 145Ah = 1740 Wh

What charge rate is recommended, 0.12C?
0.12 x 1740W = 208W desired charge.

880W / 1740W = 0.50C, but likely output is 75% to 85% of 880W under direct sun (except during cool spring days.)

80A / 145Ah = 0.55C max capability

It does look like charge rate will be far too high for that battery.

Well, you could add more batteries. Doubling the batteries would cut the charge rate in half.

3x ~ 4x batteries would get to desired current under ideal illumination. But would fail to charge well with less sun.
Also add more panels so SCC can deliver its 80A most of the time.

Or get a smaller SCC.

But alone Mppt will not help? It will give what it gets?

Yes, unless it has a setting for reduced current.


What FLA? Is it a true deep cycle?
What is your usage, do you cycle it deeply and frequently?

AGM may be more forgiving of the charging conditions. I use SunXtender, also recently picked up Full River.
And then there is LiFePO4.

 

[Mohsin Ali]

Yes its a tall tubular deep cycle battery, battery usage is limited only during night time for running fans and lights, in the daytime it stays on float charging mode. I forgot to mention also I run fridge on that battery but during sunlight (9 to 5) . It draws 15 amp dc.

 

[Hedges]

Running the load while PV is producing is good.

How deep does the battery cycle at night? How much current does it get when recharging?
If current is limited because shallow discharge, and because sun off-angle in the morning brings battery up to absorption voltage before current from PV panels gets very high, you may not need to do anything.

But best care for the battery might be constant current at 0.12C (check the manual), so maybe a 20A SCC, overpaneled with SE facing panels, would do a better job.

I think sufficiently high charge current helps by stirring electrolyte.
Maybe an air pump to bubble electrolyte would be an alternative? But you have a relatively small battery, not a forklift battery.

Do you keep track of specific gravity and/or voltage of individual cells? When they diverge, should get an equalization cycle.

 

[Mohsin Ali]

How deep does the battery cycle at night?

About 11.6 volts

How much current does it get when recharging?

40 amps (15 amps load included)

 

[Hedges]

40A SCC - 15A load = 25A battery
25A / 145 Ah = 0.17C

Maybe a bit high (check the manual) but not by a large amount.

I'm not sure what SoC 11.6V works out to. It depends on whether "resting" or "under load".
If your SCC keeps track of Ah or Wh, and you can subtract what load took, that will give a better DoD figure. (but recharging has to put back something like 120% of what was used.)

You are probably OK for now, design a future larger system to work the way you want.

 

[Mohsin Ali]

40A SCC - 15A load = 25A battery
25A / 145 Ah = 0.17C

Maybe a bit high (check the manual) but not by a large amount.

I'm not sure what SoC 11.6V works out to. It depends on whether "resting" or "under load".
If your SCC keeps track of Ah or Wh, and you can subtract what load took, that will give a better DoD figure. (but recharging has to put back something like 120% of what was used.)

You are probably OK for now, design a future larger system to work the way you want.

But if I add more panels than charging current will also increase, is this the case?

 

[Hedges]

My suggestion is, if present system doesn't start charging until late morning, consider a second 20A SCC/PV system, overpaneled, which collects sun earlier in the day and does a steady 0.12C, getting battery to CV point before the 80A SCC really starts to deliver.

If the balance of DoD and PV panel orientation doesn't cooperate, then yes this would increase charge current instead of reducing it.

Are all your panels facing one direction?
Consider some strings SE, some SW. That will start earlier with 1/2 the panels, and peak will be lower. 880W isn't a lot of panels, might not be difficult.

Ideally for a big system, you have an SCC with shunt that hits target charge current. Mine does that because all current goes to inverter/charger; PV is AC coupled. Victron and Midnight have ways to do it DC coupled. A hybrid would do it, assuming it has a charge current adjustment, and might be the cheapest way to change yours (if you can find a 12V hybrid.)

With Lithium, you wouldn't need to limit charge current unless > 0.5C. Except if battery gets near freezing, then lower charge rate should be used.

 

[Supervstech]

But alone Mppt will not help? It will give what it gets?

Again...

Charge controllers do not push power.

They provide wattage to be drawn at a specific voltage level.

If the battery can only draw 10A, it will only draw 10A, it doesnt matter how many amps are available from solar.

If you have an 80A controller and a 10A battery, as long as the wiring is capable of 80A, and you have 80A of loads, the battsry will take 10A, and the loads will take the rest, if there arent wnough loads, the rest will just not be drawn.

 

[Mohsin Ali]

Again...

Charge controllers do not push power.

They provide wattage to be drawn at a specific voltage level.

If the battery can only draw 10A, it will only draw 10A, it doesnt matter how many amps are available from solar.

If you have an 80A controller and a 10A battery, as long as the wiring is capable of 80A, and you have 80A of loads, the battsry will take 10A, and the loads will take the rest, if there arent wnough loads, the rest will just not be drawn.

Thanks alot you explained it very well actually I was asking exactly what you explained.

 

[Mohsin Ali]

Thanks to all who helped me out there now I can summarize that
1) charging current totally depends on battery demand
2) SCC do not forcefully inject more current.

 

[Hedges]

So the question is ...
When your battery is at whatever SoC in the morning,
if SCC forces Absorption voltage (because with enough PV panels it has almost unlimited current capability of 80A,
How much current does the battery draw?

If CV/CC supply is current limited, it sets the charge current. If it can supply enough current to reach CV, the battery determines the current.

 

[Q-Dog]

Charging flooded lead acid batteries at too high an amperage can cause them to overheat, boil off electrolyte, possibly resulting in permanent damage.

 

[mikefitz]

Battery is Flooded Lead Acid, 12 volts 145 Ah , Solar panels are 880 watts combine and 80a SCC

My RV has a 180 amp alternator that charges the starter battery, so do I have a problem?
No I don't, the lead acid battery determines the charge current

 

[Hedges]

If you ever buy a replacement alternator, instructions will say, "Don't use alternator to charge a dead battery."

Normal starting load, DoD is minor and battery current quickly tapers off.

 

[Q-Dog]

My RV has a 180 amp alternator that charges the starter battery, so do I have a problem?
No I don't, the lead acid battery determines the charge current

Starter battery is designed to handle high amps. Deep cycle battery may not be.