Garden Lights and Fountain Troubleshooting

dherscher
dherscher Registered Users Posts: 17 ✭✭
This year I replaced two AC outdoor lights with two 7W Sunthin 12 V LED bulbs running off a 12 V lead acid RV battery with 160 amphr capacity being charged by a 50W Renology solar panel and the 10 amp charge controller that came with it. They system also powers a 4.2 W fountain pump that runs around 10 hours a day. The pump is controlled by a timer that I hooked directly to the battery, not the controller. The lights are hooked to the controller and turn on for 3 hours after the sun goes down. Wire gauge is never less than 14 AWG and the longest run is about 60 feet so voltage drop shouldn't be a problem.

It has worked well for a couple of months but I am now having issues where if it is cloudy for one day the battery level gets low and the lights don't turn on at sunset. However, after only a couple of hours of direct sunlight the controller tells me the battery is fully charged again. This seems strange, at 160 amphr capacity I should be able to run this stuff for a few days without trouble and even if it is cloudy it shouldn't drain so fast or charge so quickly.

I'm wondering if the battery is going bad (it had previously been used in a boat) or the charge controller is having issues, or if having the fountain pump directly attached to the battery is causing trouble. Any insight would be great.

Thanks.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    2* 7 Watts * 3 hours = 42 Watt*hours per night for lights
    4.2 Watts * 10 hours per day = 42 Watts for pump
    =========================================
    84 WH per day
    • 84 WH * 1/0.61 DC system eff * 1/50 watt panel = 2.8 hours of sun per day minimum (do you get that much sun on your panel?)
    And based on a 5% to 13% rate of charge for a happy battery bank:
    • 160 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 151 Watt array minimum
    • 160 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 301 Watt array nominal
    • 160 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 392 Watt array cost effective maximum
    Ok, from the math, it looks like the solar panel is pretty close to not being large enough for the loads... And is well undersized for the size of Lead Acid battery bank.

    At this point, my first guess is that the battery is being "deficit charged" and was never being properly recharged back over 90% state of charge every few days.

    Your charging system needs to hold ~14.5 to 14.7 volts or so for at least a couple hours per day to get the battery bank charged--If the charging voltage is never getting high enough/for enough time--The battery is not being properly recharged.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dherscher
    dherscher Registered Users Posts: 17 ✭✭
    I'm pretty sure it is getting more than 2.8 hours of sun on average and it doesn't seem to have any trouble getting to the point where the controller claims it is fully charged. My concern is that it goes from fully charged to dead after only one day of clouds. Is that what you mean by "deficit charge"? The controller is saying it is charged when it really isn't?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Lead acid batteries really need 14.4 to 14.8 (or more) to fully/quickly charge during the limited hours of sun per day.

    If you don't have high enough peak charging current (large ah battery vs panel current), the batteries do not fully charge and the (I guess) the plate pores become coated with insulating lead sulfate crystals.

    Can make the battery capacity less (quick to charge and discharge).

    We really try to get people to use a minimum of 5% rate of charge because of these problems.
    Oversized battery banks are not really our friends here.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dherscher
    dherscher Registered Users Posts: 17 ✭✭
    Thanks for the help. Apparently I need to learn a bit more about about batteries. I read a few PV books and thought I had a handle on it but I guess not. Can you point me to a good resource on batteries? I could use more info on this 5% thing and the efficiencies you used in your math. Does your math mean that I should have a solar array 3 times the size?

    Is there anything that can be done at this point? I also have 145 AH batteries that I could use instead, I just figured bigger was better. I can also reduce the load some but I probably can't add any more panels.

    Is the fact that there is almost always a load on it during the day time that is not plugged into the controller a problem?

    Is there anyway to get rid of the lead sulfate?

    I'm trying to think of what else I did wrong and what else I can do to fix it...
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    The inefficiencies are a bit on the conservative/worst case side--But for a system that you intend to be "automated"--You need to over design to allow for those days of poor sun that happen unless you are going to manually adjust the run time on the loads.

    The 5% minimum rate of charge--If you have a load on the system during the day (fountain pump), that even reduces the peak charging current more (loads draw from the panel instead of allowing the battery to recharge).

    Many deep cycle lead acid battery mfg. recommend 5% or even 10% minimum rate of charge to mix the electrolyte and "unclog" the surface of the plates.

    I like to recommend a 5% minimum rate of charge because, with the limited amount of hours of sun in a day (especially winter), if you have a battery that is both discharged (say to 50% state of charge), and still have daily loads--That could take a few days of full sun to fully recharge the battery bank. At less than 5% rate of charge, many times the "average daily charge" of the battery slowly drifts down until the loads take the battery dead (and damage the battery).

    There are two forms of lead sulfate (non-battery engineer explanation)--One is a fluffy gray material, which is what forms when the battery discharges. A second hard black crystal is what the fluffy gray lead sulfate turns into over time if the battery is not cycling (starts to happen in hours/day). Once the black hard crystals form, there is no way of returning that back into the fluffy material.

    Some believe that a "desulfator" can do that. Others sell chemicals that may extend battery life--But usually those do not help much (if at all). Otherwise, a heavy charging current + cycling of the battery can help shed the black crystals to the bottom of the battery--But that is about it.

    Automated solar power with a lead acid battery bank is a pain. Either you have to over design (larger solar array than needed), add electronics to start a genset/notify you of charging problems, or you have to check the system every few days and see that all is OK. Otherwise, you run the risk of a short battery life and loss of power when it is really needed. Using motion detector type LED lights can help. You can get a meter that shows if it has been too many days since last full charge, etc...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dherscher
    dherscher Registered Users Posts: 17 ✭✭
    So if I used a 145 AH battery instead and reduced the load would that work better? Or do I really need to about double the system size? I guess I'm not really understanding what the rate of charge is, 5% of what? The charging current compared to the battery capacity?

    If I have a load on during the day is there any way to deal with the reduced charging current? I can easily check the battery on a daily basis and do check it frequently. Now that I know a bit more about destroying batteries I can better avoid it in the future.

    I also have the pump connected directly to the battery and not the controller. Is that an issue?

    The good news is that I only need this system to run from May to September so short winter days aren't an issue.

    Thank you so much for your help!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    dherscher wrote: »
    So if I used a 145 AH battery instead and reduced the load would that work better? Or do I really need to about double the system size? I guess I'm not really understanding what the rate of charge is, 5% of what? The charging current compared to the battery capacity?

    Yes, larger battery banks take higher charging current (and have their own self discharge to worry about too). We use the C20 Hour Capacity Rating of the Battery (a 100 AH battery discharged at 5 amps * 20 hours from 100% to dead = 100 AH capacity) and 5% to 13% rate of charge. I.e., 100 AH battery:
    • 100 AH * 5% = 5 amp charge
    • 100 AH * 10% = 10 amp charge
    • 100 AH * 13% = 13 amp charge
    If I have a load on during the day is there any way to deal with the reduced charging current? I can easily check the battery on a daily basis and do check it frequently. Now that I know a bit more about destroying batteries I can better avoid it in the future.

    What can be done is turn off the loads until Noon~1pm--At that point, the battery should be in "absorb" and taking less than its maximum charging current... At that time, you can turn on your "opportunity" loads and use the "extra current" from the solar panels and not affect the battery charging situation.
    I also have the pump connected directly to the battery and not the controller. Is that an issue?

    For normal operation--No, it is not a problem. If (for example) you can set your LVD to 11.5 (to 12.0 volts), you can have the controller turn off the pump on days where the battery is not getting fully charged. That would be nicer than letting the pump take the battery dead (very hard on lead acid batteries).
    The good news is that I only need this system to run from May to September so short winter days aren't an issue.

    Yep--Hours of sun per day, loads, and size of solar array are all playing together here.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dherscher
    dherscher Registered Users Posts: 17 ✭✭
    In an attempt to make this work better I have replaced the 160 AH battery with a 140 AH and ordered a separate solar water pump for the fountain. Until it arrives I have the fountain pump off from 10-1 and so far the battery has been staying charged. Does this seem like a workable solution?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    What are you going to do with the solar array, even a 5% array minimum would be better than what you have now (unless I missed something):
    • 140 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 132 Watt minimum rate of charge recommended
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dherscher
    dherscher Registered Users Posts: 17 ✭✭
    I'm just going to leave the array to charge the battery to power the lights only. Now that I know how I was destroying my last battery I'll also keep an eye on it to make sure it the battery is getting charged every day. So far (10 days) the battery has reached full charge by 1:00 p.m. If we have a spell of cloudy days I'll decrease the amount of time the lights are on at night or leave them off until the battery gets charged.

    I know it's not a 5% rate of charge but I'm hoping that it will still work if I keep watch.