Does anyone know the answer?
Sherri Lynn wrote:So, I have a question about max charge rate. We have a system set up with 17 sets of 4 each solar panels that are 12v, 5 amp. This should be a total of 4080 watts (if I am figuring this right). We have three battery banks set up at 48 volt (8 batteries per bank of L16E, 6V 360 amp hour batteries each bank). We are having trouble with the state of charge getting up to 85% and stopping. It wasn't doing this earlier, but we had something kick out the system and had to restart it, and it has been doing this since. Now the ME-ARC is set at an 80% charge rate, and we are thinking that given the amp hours being a total of 1080, that we should set the charge rate at 100%, but we were afraid to make a mistake, having read about overheating the batteries if you charge it too fast.
Does anyone know the answer?
You should measure the voltage of the circuit after the charge controller and before the batteries to see what the controller is doing when you hit that 85% mark. It may be possible that when the system tripped your controller defaulted back to a lower voltage setting? Other than that your controller may be going into the topping charge phase and is taking too long to complete the topping charge phase of the charging cycle in a reasonable amount of time, due to the Ah rating of the battery bank, and the limited amount of daylight.
A "12V" solar panel typically has 36 cells each putting out 0.55V. After the diode losses you will be getting a little over 18V, which your charge controller will step down to whatever it thinks is best for charging your 12V battery, typically just under 15V and then nearer 12V for trickle charge as the battery approaches full.
Its best to let your charge controller's circuitry work out how to charge your batteries. What is the reasoning behind trying to set a "charge rate" rather than allowing your charge controllers to set the charging voltage according to the detected charging circuit voltage?
SETUP: 05 Charge Rate - Used to set the maximum charge rate allowed
to charge the batteries during Bulk, Absorption, Float, and Equalize
charging. Selections are Max Charge = 0% up to Max Charge = 100%.
The Max Charge = 0% setting helps minimize charging while continuing
to allow pass-thru power. The rest of the selections are provided to
limit the charge rate to the battery bank, which helps prevent battery
overheating caused by charging at too high a charge rate.
The Max Charge selections are provided as a percentage of the inverter/
charger's maximum charging capability. Refer to label on the side of the
inverter or the operator's manual for the inverter/charger to determine its
maximum charge rate. Once you ﬁ nd this maximum charge rate, determine
the percentage needed to limit the charge rate to your battery-bank.
Example: If the maximum charge rate of your inverter/charger is 100
amps and you need to limit the charge rate to 50 amps, choose the
Max Charge = 50% selection (50 amps = 50% of 100
Default setting: Max Charge = 80%
But during the winter months we have shorter day and so we don't get as much hours of sunlight.
The angle of the sun ray are lower so we get less energy.
In the winter we are indoor more so we use more light, tv, computer, etc aka more electricity not going AC.
Maybe you have finally started to use the washer during the day, and so their is less energy available to be stored because you are using it as it is being produced.
Also possible that you have acquired some new electric using devices (gaming pc/circular saw).
Or you just have some family/friend staying for the winter using extra electricity.
Assuming it is fact a problem with the battery bank:
You might just have to equalize the batteries, or even test the specific gravity of each cell.
Do you know what made your system fail the 1st time, was something on the load side asking for too much power or was it a problem on the supply side, like a controller/electronic going bad, rats shorting wires sending a surge running thru the supply side making stuff unstable.
Your array at nameplate can do just under 80 amps if the controller will. At 1080ah storage you can charge at 200 amps! Remember, you need power in excess of consumption if you want to charge, so average amps to the battery will still be lower than c/5 minus efficiency.
I would service the battery (clean connections, top off electrolite and check specific gravity of the cells.), then fully charge and equalize then re-check electrolite levels and specific gravity.
Chances are, you just need equalization and a little more pv watts. Set your control to 100% or max amps and make sure you have enough absorb time (1hr per 100ah capacity) and be sure end amps is set low enough to allow full absorbtion.
If you have damaged cells, remove them and match good batteries in 2 strings of 8. You will have a battery that is more full, more often as long as your nightime and cloudy day loads can be optimised and you might not need more modules.
Next time you need a battery, if it will be lead acid, i would reccommend the 2 volt l16 in a single string of 24 1,100 ah cells that will take a serious beating over 3 parralell strings at a competitive cost.
Either way batteries that are more full, more often last longer.
Which leaves the questions i should have asked if i were to try to help.
What inverter?, And how many are there?
Is the battery flooded? (You did say Trojan 360ah l16, tells me likely flooded)
If the battery is flooded, is there abnormal or uneven electrolite loss when topping off.
Do you have a battery monitor installed?
What fault was displayed when the system protected itself?
What is your daily power consumption?
What is the pv production?
What is the AC source to the inverter?
Its been a while since your post, so i hope you have already resolved any issues.
Also you described a problem and didnt actually ask about the problem, you asked about charge rate and so this is un asked for and is for my curiosity.