mppt 60amp enough

robocop

Hi

I have here a mppt 60 amp to charge 12    12v 250ah gel batteries.

inverter is 110vac . 3kw 

think mppt 60 a is not enough to charge during the day (tropic 6 hours of sun)

Or do I need a 120a to charge those  gel batteries 

appreciate your comments about this

Bob

BryceFreeman

You can estimate how long the charging will take with this equation:

Battery Qty*battery V*battery Ah / controller A*V

That is to say, 12*12.8V*250Ah / 60A*12.8V = 38400/768=50h

Considering the power loss during working, the actual timescale will be longer than the result.

So I think you can consider a bigger controller.

BB.

You need to look at the charging current specification in the GEL Battery's manual... Some are rated for a relatively low charging current of like 5% rate of charge... Others can accept higher current.

We also need to know if this is a 12/24/48 volt battery bank system... To take a guess:

12 batteries * 12 volts * 250 AH per battery = 36,000 WH battery bank
36,000 WH * 10% rate of charge = 3,600 Watts of charging power
3,600 Watts of charging power * 1/0.77 panel+controller deratings = 4,675 Watt array (nominal 10% rate of charge)

A 60 Amp MPPT charge controller can charge a battery bank at with a typical "over sized" PV array:

12 volt bank:
14.5 volts charging * 60 amps * 1/0.77 panel+controller derating = 1,130 Watt "Max cost effective" array

24 volt bank:
29.0 volts charging * 60 amps * 1/0.77 panel+controller derating = 2,260 Watt "Max cost effective" array

48 volt battery bank:
58.0 volts charging * 60 amps * 1/0.77 panel+controller derating = 4,519 Watt "Max cost effective" array

So to even get a 10% rate of charge into your 12 batteries, you would need have a 48 volt battery bank.
 
If you were are going for a 5% rate of charge, then a 24 volt battery bank with a ~2,260 Watt array would meet that requirement on a single 60 amp MPPT controller.

In any case--We do need more information--Such as how deeply you discharge your battery bank every day--Or daily loads, battery bank voltage, etc... to give a "better" answer.

GEL batteries are frequently not a very good option for solar power systems... They, typically, have a lower charge rate acceptance than flooded cell or AGM (for lead acid batteries). So you cannot discharge them very deeply because of limited hours per day to recharge.

Flooded cell and AGM batteries accept higher charging current (10%-20% or 25%)--So you can charge them more quickly when more deeply discharged. SOME GEL batteries can be damaged by higher charging current (gassing causes bubbles in GEL, which don't go away--Limiting electrolyte to plate contact area.

10% rate of charge is the typical suggested minimum rate of charge for an off grid system... Being in the tropics with lots of sun all year round--sometimes can get away with less than 10% rate of charge (again, guessing without knowing your loads).

-Bill

robocop

forgot to write 12 batt of 250ah in 3 battery bank  of 48v

BB.

Does your battery manual list a maximum rate of charge for your batteries?

What size solar array do you presently use?

Are you able to recharge the battery bank to 80-90%+ State of Charge at least a couple times a week (based on your loads and amount of available sun) with your present system--Or do you need more charging energy?

3x 250 AH strings = 750 AH total
60 amps / 750 AH = 0.08 = 8% rate of charge (assuming at least 4,519 Watt array in full sun)

-Bill

robocop

for information  . am using now 4pcs   500w  in 2s2p configuration

BB.

• 2,000 Watt array * 0.77 panel+controller derating * 1/58 volts charging = 26.6 Amps "typical best case" charging current
• 26.6 Amps / 750 AH battery bank = 0.035 = 3.5% rate of charge

That is a pretty low charge rate unless just "floating" the battery bank for storage (typically 1-2% minimum rate of charge for float storage).

In the end, your 60 amp MPPT charge controller is not the limiting element of your current system. Unless your actual daily Watt*Hour usage is very low, you really need more panels, and probably another charge controller...

Again, depending on your daily energy usage.

On average, most battery banks die from under charging/over discharging. More charging should give you longer battery bank life.

-Bill