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diy solar

Mystery of the draining battery

MasterPivot

MasterPivot

New Member
Joined
Feb 17, 2023
Messages
3
Location
Kent, WA
Hi! I am fairly new to solar, and would really appreciate some help.

My issue is with a small solar power system I built in my shed with the intent to power small devices in the yard. At the moment, only the chicken coop door's motor and timer are hooked up, with an on-demand water pump set to be installed this spring.

The system is composed of a 20W solar panel connected to a 20amp PWM solar charge controller and 12v 9ah battery. Currently attached is a timer and a 12v motor.
More details on the parts if needed:


I had installed the system last year and it worked well until recently, when the chicken door appeared to stop working. After much investigation and testing, I was able to confirm that continuity was good and that the motor and timer were in working order. I then discovered that the battery was draining from its normal 14.4v during the peak of the day down to 10.6v overnight (SCC's Discharge Stop), despite having almost no discernable drain on it (just the timer).

I thought that the problem might be a faulty battery, seeing as its voltage had dropped below the amount needed to even run the motor. To test the system, I did the following tests:
  1. After charging the battery during the day to a decent amount (13.6v), I completely unhooked it and left it alone overnight. The battery did NOT drop in voltage.
  2. Then, I hooked the battery back up to just the SCC and disconnected everything else off of it. Again, the battery looked good overnight.
  3. Next, I reattached the solar panel to the SCC and battery. Overnight, the battery dropped to 10.6v! "Aha", I thought!
  4. Being thorough, I then removed the solar panel from the SCC and wired up the timer and motor again. The battery dropped to 10.6v! "WTF!"
  5. Finally, I removed all and attached the battery straight to the timer and motor. Again, a drop to 10.6v!

Is the battery just not holding a charge properly? And, why is the battery draining when BOTH the solar panel and SCC are connected to the battery overnight, but not when just the SCC is connected? Is the SCC faulty?
 
Charge up the battery and conduct a load test. If you have a known amperage load, like a 12v -1amp light, it is simple matter of running and seeing how long it goes before your battery voltage drops low.
 
I would not think the solar panel would be pulling anything, but the timer definitely pulls less than 0.01amps (it also has it own battery backup).

Since the battery is rated as 9ah, that should mean the battery should last at least 900hrs?
 
MasterPivot said:
Hi! I am fairly new to solar, and would really appreciate some help.

My issue is with a small solar power system I built in my shed with the intent to power small devices in the yard. At the moment, only the chicken coop door's motor and timer are hooked up, with an on-demand water pump set to be installed this spring.

The system is composed of a 20W solar panel connected to a 20amp PWM solar charge controller and 12v 9ah battery. Currently attached is a timer and a 12v motor.
More details on the parts if needed:


I had installed the system last year and it worked well until recently, when the chicken door appeared to stop working. After much investigation and testing, I was able to confirm that continuity was good and that the motor and timer were in working order. I then discovered that the battery was draining from its normal 14.4v during the peak of the day down to 10.6v overnight (SCC's Discharge Stop), despite having almost no discernable drain on it (just the timer).

I thought that the problem might be a faulty battery, seeing as its voltage had dropped below the amount needed to even run the motor. To test the system, I did the following tests:
  1. After charging the battery during the day to a decent amount (13.6v), I completely unhooked it and left it alone overnight. The battery did NOT drop in voltage.
  2. Then, I hooked the battery back up to just the SCC and disconnected everything else off of it. Again, the battery looked good overnight.
  3. Next, I reattached the solar panel to the SCC and battery. Overnight, the battery dropped to 10.6v! "Aha", I thought!
  4. Being thorough, I then removed the solar panel from the SCC and wired up the timer and motor again. The battery dropped to 10.6v! "WTF!"
  5. Finally, I removed all and attached the battery straight to the timer and motor. Again, a drop to 10.6v!

Is the battery just not holding a charge properly? And, why is the battery draining when BOTH the solar panel and SCC are connected to the battery overnight, but not when just the SCC is connected? Is the SCC faulty?
Click to expand...
The battery is AGM which is lead acid based. My cousin had the same problem with his chicken coop solar system, similar AGM battery.

First, any lead acid based battery will require absorption. This takes time, lengthy times to get to full charge. Over time, not getting to full charge combined with days of no sun, limited sun and winter days of short sun duration take a toll on a lead acid based battery. The sulfation begins and compounds the problem as the capacity of the battery is much lower and the power draw remains the same each day.

The battery may show full voltage if sulfated. It will however have reduced capacity and suffer voltage sag under a load.

How to correct it? You might try this method:


and be sure to watch part 2:


Or buy 2 new batteries and a charger like the Battery Minder which I use for my AGM's. Why 2 batteries? As these are lead acid based, you need some type of absorption charge and desulfation. In order to get that, you want to swap out the battery being used with one that has been fully charged and desulfated. Maybe swap them every few weeks. As for why to use the Battery Minder, you want a slow charge rate without high voltages as an AGM is recombinant and high charge rates with extended high voltages will cause the water to be released.

As for my cousin, he decided to purchase a LFP battery and keeps it above 0C for charging purposes. Don't have to worry about sulfation, just keeping it above 0C to charge it.
 
Wow! That is quite an interesting process. And one I would rather not have to go through :)

Looks like I may be going to a LFP battery. Any suggestions about how to keep the battery warm (above 32F/0C)? Where I am, I don't often get such low temps but it happens on occasion during late winter (late January-February), like several times this past winter.
 
MasterPivot said:
Wow! That is quite an interesting process. And one I would rather not have to go through :)

Looks like I may be going to a LFP battery. Any suggestions about how to keep the battery warm (above 32F/0C)? Where I am, I don't often get such low temps but it happens on occasion during late winter (late January-February), like several times this past winter.
Click to expand...
You'll have to DIY or pay through the nose. Low temp protection comes at a premium.
 
MasterPivot said:
Wow! That is quite an interesting process. And one I would rather not have to go through :)

Looks like I may be going to a LFP battery. Any suggestions about how to keep the battery warm (above 32F/0C)? Where I am, I don't often get such low temps but it happens on occasion during late winter (late January-February), like several times this past winter.
Click to expand...
Keep it in the chicken coop? You have a bunch of winged hot water bottles running around. It won't get below freezing in there.
 
If you can get a good year of operation from one of these 9ah batteries (~$25) you might just call it the price of doing business. I use this style in my UPS and in it the batteries are about 3 years between replacement.
 
MasterPivot said:
Wow! That is quite an interesting process. And one I would rather not have to go through :)

Looks like I may be going to a LFP battery. Any suggestions about how to keep the battery warm (above 32F/0C)? Where I am, I don't often get such low temps but it happens on occasion during late winter (late January-February), like several times this past winter.
Click to expand...
Insulated box with heating pad controlled by a thermostat. You can discharge below freezing, you don't want to charge. You will need a large enough array for running the heating pad and charging the battery and you can't go wrong with an oversize battery due to the short winter days and cloudy days. With LFP, you don't need absorption and it likes being between 20 to 80% SOC unlike lead acid.

You can purchase any of the premade cheap batteries like the Chins, Redodo and just have an insulated box to set it in with a heating pads if you don't want to DIY. Still, you will spend $300 for a 100Ah battery, plus the heating pads and making a box. If the 9Ah battery costs 10 bucks, you could buy a new battery each year for 30 years or a pair to swap out (might last 3 to 4 years) for $20 and need maybe 6 or 7 pair over 30 years. I think my cousin found a 30Ah LFP for $70, personally I would have spent the $300 as it could be used for other purposes if needed.
 
I have a pair of expensive Odyssey PC925 AGM batteries in my side-by-side. I was using a Battery Tender solar panel to keep them charged. It wasn't enough. The charge profile wasn't right. I had to recondition the AGM batteries to get them working better and I switched to a different charging method.
 
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