Garden Lights and Fountain Troubleshooting

2* 7 Watts * 3 hours = 42 Watt*hours per night for lights
4.2 Watts * 10 hours per day = 42 Watts for pump
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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

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

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

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

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