Charge Controller Setting

[rk9989]

I have a question about the upper voltage disconnect on my charge controller. My system is as follows:

- 2 Interstate 6-Volt GC2 batteries connected in series (12 Volt System)
- 2 Renogy 50-Watt Panels connected in parallel
- WindyNation P30L PWM Charge Controller

The purpose of my system is to be able to survive short grid outages (less that a day) and to learn more about these technologies for the time when I can invest more $$$ in a larger system.

From what I can tell, my battery bank is fully charged at approx 12.7v. In the past I have used a plug-in battery charger to charge the batter bank and it has been working well. As I experiment with solar, I would like to get these charging off my two new panels. The first time I tried it, batteries were charged to something like 13.8v, higher than I have seen before, and making me worry if everything is alright. I see on the battery manufacturer's website that around 12.7v is fully charged. So the next time I tried charging from the panels I went into the charge controller to adjust the "Over Voltage Disconnect", which should disconnect the panels at the specified voltage. This charge controller won't let me set the value below 13.0v and when I did it stopped charging well before the batteries were fully charged. During my testing, my panels were delivering power at 18 volts and 5 amps.

Now my question is, how should I set the max voltage for the charge controller. I understand when it is charging that the voltage will need to be higher, and once the charge is disconnected the batteries should return to the appropriate full charge. Any advice on how I should set this?

Richard

[Sunking]

Your problem is not knowing much about batteries and chargers. Bulk and Absorb charge is 14.4 volts, Float is 13.2 to 13.6 volts depending on manufacture.

12.7 would be a battery rested for several hours disconnected from everything indicating a 100% SOC. On a controller after charge should be in FLOAT.

Read this it may help or totally confuse you.

Last thing 100 watts of panels using a PWM controller on 2 GC2 golf cart batteries is not near enough power to maintain those batteries. So keep using your AC charger assuming it is 25 amps.

A 100 wat panel with PWM only generates 5 amps, you need 20 to 25 for a pair of golf cart batteries wired in series. With PWM that takes at least 360 watts, or with MPPT 250 watts.

[rk9989]

Your problem is not knowing much about batteries and chargers. Bulk and Absorb charge is 14.4 volts, Float is 13.2 to 13.6 volts depending on manufacture.

12.7 would be a battery rested for several hours disconnected from everything indicating a 100% SOC. On a controller after charge should be in FLOAT.

Read this it may help or totally confuse you.

Last thing 100 watts of panels using a PWM controller on 2 GC2 golf cart batteries is not near enough power to maintain those batteries. So keep using your AC charger assuming it is 25 amps.

A 100 wat panel with PWM only generates 5 amps, you need 20 to 25 for a pair of golf cart batteries wired in series. With PWM that takes at least 360 watts, or with MPPT 250 watts.

Thank you for the prompt reply and for the good information. You are exactly right, I don't know much about batteries and chargers, but I am trying to learn on a small scale before making any big mistakes. One follow-up question. You mentioned needing a 20-25 amp charger for this size of battery bank. My AC charger can charge at a maximum of 12A. Will this damage the battery or simply require more time to charge fully?

Richard

[Sunking]

You mentioned needing a 20-25 amp charger for this size of battery bank. My AC charger can charge at a maximum of 12A. Will this damage the battery or simply require more time to charge fully?

Takes longer, can stratify the battery, and can cause premature failure from sulfation.

FLA batteries require a charger that can produce C/12 to C/8 charge currents. Where C = the battery Amp Hour rating and 8 and 12 are the hours required. So for Example a 225 AH Golf Cart battery needs a minimum of 225 AH / 12 H = 18.75 amps, and a maximum of 225 AH / 8 H = 28.125 amps. C/10 is perfect or 25 amps. So in practice you can go down to 15 or 16 amps, and up to 30 to 31 amps.

Stratification is where the heavier acid settles to the bottom of the jar floating the water on top. This occurs from either letting batteries set to long like in storage or from chargers with too low of a charge current. At C/12 to C/8 once the batteries near Gassing Voltage will cause the electrolyte to bubble and roll stirring things up.

In addition to Stratification from too low of a current can also prevent Lead Sulfate Crystals from dissolving fully. Lead Sulfate Crystals cause 95% of all Lead Acid battery failures, and every lead acid battery will fail. As soon as the battery is discharged from either a load or setting lead sulfate crystals begin to form on the plates and build up. The deeper you discharge them, the process accelerates. Once you go below 50% depth of discharge the crystals will harden and at that point there is no way to dissolve them. By applying at least a C/12 current will dissolve most of the soft crystals back into solution. Eventually the crystals will be thick enough there is nothing you can do and the battery fails to take or give a charge.

How soon that happens depends on a lot of factors but anywhere from 1 year on cheap abused batteries, and can last as long as 5 to 8 years on high end batteries given TLC.

Here is what you need to know before you dive in too deep. Anything you take off the grid and put on batteries, is going to cost you 5 to 10 times more than buying power from the Power Company in never ending battery replacement cost. It is EXPENSIVE so be careful what you ask for.

[thastinger]

Doesn't sound like you cycle this system everyday, sounds like it is emergency backup power to me. If so, you'll be ok just letting what you have "super trickle" charge the batteries but if you cycle them, you need more panel to charge them at the proper rate.

The battery manufacturer should have a website with VPC (volts per cell) charging specs to set into the CC for off-grid applications. If not, Trojan has theirs posted on their site so that might be a starting point for your CC settings.

[rk9989]

Doesn't sound like you cycle this system everyday, sounds like it is emergency backup power to me. If so, you'll be ok just letting what you have "super trickle" charge the batteries but if you cycle them, you need more panel to charge them at the proper rate.

The battery manufacturer should have a website with VPC (volts per cell) charging specs to set into the CC for off-grid applications. If not, Trojan has theirs posted on their site so that might be a starting point for your CC settings.

That's true. The purpose of the system was to provide short-term emergency power. My AC charger keeps it full and ready for when it is needed. My intent with the 100W of panels was to be able to restore some power to the batteries in the event of a longer-term emergency, well knowing that the panels would not be able to charge back the amount I would use in one day, but would provide something. I also just wanted to learn more, and that is working. Clearly I need more panels to make this operate well. Thanks for your help.

[thastinger]

Assuming the batteries were full when the power outage occured, they would be capable of providing more power than you may think if you adopt the proper mindset. You could charge flashlight batteries or run C-PAP machines with the proper adapters and equipment, and your panels would be able to provide about 20% battery capacity per day.
You're not talking about much power here as I'm sure you realize, but if you selected the proper LEDs and other items, you could have a few of the normal creature comforts in an emergency.