Roof top Solar panels ( charging issue)

[Sand-dog]

Hi guys, not sure where to post this question, general discussion I assume . My AGM battery 4 are 3 years old, when I put a multi tester across the top on a sunny day, Solar panels show charging 12.5 or more constantly on clear sunny day. It seems that my batteries aren’t receiving the full charge from the solar panels as they should which are 200 W total. 5 days later came to check and down to 4.5V. I have everything turned off …. If you review the photo below you’ll see one of the panels has laminating issues. I’m curious, is there a way to test each panel individually? the one or both may be too weak and 100 W isn’t enough for those four AGM’S

batteries

 

[Kevin D Pem]

Yes! Flexible panels go bad at an alarming rate. However we don't have enough information to diagnose the problem!

Here is what we need!!!

Full sun, what time of day?

Return trip,Full sun,same time of day.

Original voltage (not charging) with panels covered.

Last check voltage (not charging) panels covered.

Amp hours (battery capacity).

Hours of full sun? In the desert here in az I consider full sun from around 9:30 to about 4:30 about 7 hours of sun. Your system, that would be about 100 watts times 7hrs 700 watt hours or about 60 Amp hours. If you have 100 Amp hour batteries, that would be 200ah of usable power. So 4 days (if you're lucky) might bring the batteries up, but that doesn't take anything going wrong into the equation. You know like de-lamination on the panels. A bad cell in a battery. A bad connection.

Personally, I would disconnect the batteries and check them individually. 10 volts or less and you have lost a cell and that battery is toast,.edit: 12vdc is considered completely discharged

 

[Sand-dog]

Kevin - thank you so much I appreciate your help and insight. Here on the coast full Sun is about the same as AZ. Assuming we don’t have fog or clouds but the past week it’s been clear. The panels are 100w x 2 = 200 watts, I believe should be charging 13.6 V min, regardless of what the battery needs and the most that the controller is showing 12.5 output. I’m thinking after reading your review I have a bad S-rooftop panel, trying to figure out how to test it. I can disconnect each battery and test it, hate to do it. My guess is you’re right, it be nice to test the panel itself don’t know how too. Vehicle is parked 24 hours a day until our next trip. So No trip time, iOriginal voltage was around 12.8 V not under charge, last charge, panels not covered on roof when sun goes down, 4.5 V five days later. Kevin, I don’t know if this makes any sense.

 

[Kevin D Pem]

Kevin - thank you so much I appreciate your help and insight. Here on the coast full Sun is about the same as AZ. Assuming we don’t have fog or clouds but the past week it’s been clear. The panels are 100w x 2 = 200 watts, I believe should be charging 13.6 V min, regardless of what the battery needs and the most that the controller is showing 12.5 output. I’m thinking after reading your review I have a bad S-rooftop panel, trying to figure out how to test it. I can disconnect each battery and test it, hate to do it. My guess is you’re right, it be nice to test the panel itself don’t know how too. Vehicle is parked 24 hours a day until our next trip. So No trip time, iOriginal voltage was around 12.8 V not under charge, last charge, panels not covered on roof when sun goes down, 4.5 V five days later. Kevin, I don’t know if this makes any sense.

Did you disconnect anything? Like maybe reverse polarities?
Most often when those panels fail, they simply stop outputting power. Sounds more like a short. I think battery failure!!! The longer everything is connected the more expensive it will be to fix. 4.5 volts is a catastrophic battery failure! You may be able to take the battery out of the bank that's bad, unless it has already destroyed the family. CHECK THEM NOW!!! TIME IS YOUR ENEMY!!!

 

[Sand-dog]

Did you disconnect anything? Like maybe reverse polarities?
Most often when those panels fail, they simply stop outputting power. Sounds more like a short. I think battery failure!!! The longer everything is connected the more expensive it will be to fix. 4.5 volts is a catastrophic battery failure! You may be able to take the battery out of the bank that's bad, unless it has already destroyed the family. CHECK THEM NOW!!! TIME IS YOUR ENEMY!!!

I have not touch any of the batts, it is used MH, so prior owner could’ve messed with the bank. Will hopefully it’s only one battery within the bank. I can disconnect it and leave the others connected….fyi: did take about week to run down the AGM, damn they are not cheap. Thank you will let you know what I find.

 

[Sand-dog]

Kevin one last Q - you were 100% spot on thank you. 3 AGM’s all three disconnected from one another and disconnected from solar & shore power. And after resting for 15 minutes the first two batteries settled at 12.85 V conservatively, the third battery settled at 8.92 V . I did find that my two in-house electric fans (maxxfan) were running on their own about 5 days. They just came on and in fact, I could not turn them off. I had to pull fuses, had issues with both fans in the past, ordered new PC board. And may have causes the drain and Not on shore P. QUESTION when plugged into shore power all three show around 14.4 V, but the third battery the bad battery gets pretty warm. I would rather replace it later as it’s $700. So am I asking for trouble I don’t really do much dry camping this time of year I just left it plugged into power.

Q-2, I would like to move the power connect for the 3 house batteries to the middle battery and not this end battery which is bad and will need replacing. Maybe it would draw better from being in the middle what do you think?

 

[Kevin D Pem]

You "need " to disconnect the bad battery!!! The bad battery will give the controller the idea the batteries need charging. In turn the controller will cook your good batteries. They will vent and dry out!! In short order none of you batteries will be any good.

With what you describe you will likely still have the power you need without replacing the bad battery.

While you're at it the charging wires should be connected so the current travels through both batteries.

 

[Sand-dog]

Thank you KEVIN makes total sense

 

[Rich W.]

I haven’t read all of this but measuring voltage is kind of dancing around the issue. In and of itself, it isn't a good measurement of anything.

 

[RVThereYet]

Rich,

Your comment about measuring voltage is not a good way to measuring anything surprised me.
Not an electrical engineer but what other method is used to determine a battery is bad?
Never heard of another method to check a battery. Even under a load test, it is voltage that tells the story.
Been in aviation for 54 years and voltage has been used on all the craft that I have flown.
Please enlighten me.

 

[Rich W.]

Rich,

Your comment about measuring voltage is not a good way to measuring anything surprised me.
Not an electrical engineer but what other method is used to determine a battery is bad?
Never heard of another method to check a battery. Even under a load test, it is voltage that tells the story.
Been in aviation for 54 years and voltage has been used on all the craft that I have flown.
Please enlighten me.

I was referring to testing battery health. If its all you have its better than nothing (12v batteries should be around 12.6v at rest) but it wont give you state of charge or capacity. When testing panels of course its fine. Having read all of this now, I agree with Kevin that removing the bad battery is paramount and ypu probably don’t need it anyway. Sorry for any confusion I caused.

 

[B52Bombardier1]

Hello,

Rich W is correct. A measurement of the battery voltage only reveals half of the power equation - volts x amps = watts or . . . power . . . the ability to do useful work. You need to take your batteries to a well equipped auto parts store for a "load test". Charge them up first to whatever you think is a full charge. Then go to the auto parts store to run the test that will show how many amps they can deliver within a short amount of time. This is usually a free test.

At three years old, I think you have at least one bad battery.

Rick

 

[forty_caliber]

Sounds like a bad cell to me as well. Are these lead acid chemistry? If you have to spend time and money on batteries, is it time to consider LiFeP0?

 

[LMHS]

... I would rather replace it later as it’s $700...

Wow. And my daughter thinks the two 6V 200AH SLA batteries that I'm ordering for her truck camper is expensive at $180 each. And this time we got free shipping! This new set of 6V 200AH SLA batteries are cheaper than what I bought last summer (currently $220 ea on Amazon) when I upgraded the single 12V battery that was on the used camper when it was bought in 2022. But then the cheap battery bank is on a cheap used truck camper, charged with two cheap (about $50-$60 on sale with coupons stacked with 20% employee discount) Harbor Freight 100W mono solar panels (I love that parking under a light fixture in the parking lots can keep the batteries "up" overnight with no loss even with the refrigerator running) with a cheap ($20) 30amp MPPT solar charge controller and the 2000Watt inverter is a cheap Harbor Freight inverter (it was a return that the buyer said didn't work - I think it was a "dispose" one that was tossed in the trash. I also have a 1500W inverter that I got the same way - works but not needed for now). The most important thing we run on the camper is the cheap Thomson 7.5cf refrigerator/freezer (on sale plus we used our "Sam's Cash" to get the price down to $70). And the cheap 700W microwave. And the cheap TV. And the cheap region free DVD player. We got a theme here! A cheap battery system so we can park in cheap/free places and parking lots. The camper has been plugged in one night so far this year and four or five nights total for last year. Threads like this make me think I have no business being on this forum. I'm either too poor or too cheap. Who knows, one day I might get serious and put what I have learned from my cheap system into a more acceptable/expensive system. But probably not.